NC State Extension Publications

CONTENTS

Abstract

Introduction

Materials and Methods

Experiment 1

Experiment 2

General Procedures

Results and Discussion

Summary

References

Appendix Tables


The research reported in this publication was funded by the North Carolina Agricultural Research Service (NCARS) and by the United States Department of Agriculture, Agricultural Research Service (USDA-ARS), as part of a joint forage-animal research program. Mention of trade names, proprietary products, or specific equipment does not constitute a guarantee or warranty by either NCARS or USDA-ARS and does not imply its approval to the exclusion of other products that may be suitable.

Photo of a steer grazing.

Examining the canopy on-offer.

NC Agricultural Research Service and USDA-ARS.

Photo of a steer grazing and masticate being collected.

Diet selection process and masticate collection.

NC Agricultural Research Service and USDA-ARS.

Photo showing masticated boli of collected diet.

Masticated boli of collected diet.

NC Agricultural Research Service and USDA-ARS.

Photo showing masticate in a bag ready to be frozen.

Masticate mixed and subsample placed in plastic bag in preparation for quick freezing.

NC Agricultural Research Service and USDA-ARS.

Photo showing the freezing process.

Masticate subsample secured in metal tray prior to quick freezing.

NC Agricultural Research Service and USDA-ARS.

Photo showing the freezing process.

Masticate being quick frozen in liquid nitrogen.

NC Agricultural Research Service and USDA-ARS.

Photo showing different sized sieves.

Sieve-size series for estimation of large, medium, and small particle-size classes.

NC Agricultural Research Service and USDA-ARS.

Abstract

A warm-season grass is an important component of a productive pasture system in the upper South. To achieve the desired animal response, producers must select a productive perennial grass that will provide a diet of adequate nutritive value. In this bulletin, we summarize the results from two experiments that examined the characteristics of diets selected by grazing steers when offered different warm-season grasses at several canopy heights. In Experiment 1, we examined diets from six forages (five species and two cultivars of one species), and in Experiment 2, we examined four cultivars of the same species. Both the morphology (leaf, stem, and dead proportions) and canopy height at grazing were instrumental in both experiments in altering the nutritive value of the diet selected by steers. These attributes and the particle breakdown during ingestion (mastication) will likely influence dry matter intake and subsequent animal daily performance.

Introduction

Food bars or smorgasbords where large arrays of food types are available have been popular for humans because we pick-and-choose according to our likings. Ruminant animals also prefer certain plant components when offered a standing pasture canopy. Ruminants offered an excess of forage will consume (select) the immature, green leafy portion of the canopy first, followed by the mature leafy and less mature stemmy portions, with the more mature and dead tissue selected last. In this case, the canopy becomes a mini-smorgasbord. Selectivity resides to a large extent, however, on the magnitude and morphology of the pasture mass offered and can be altered by the animal’s ease of prehending the more desirable canopy fractions. For example, prehension can become complicated by the complexity of the canopy structure and the time required in seizing a desired bite.

Forages that freely exhibit large leaves without interference from the canopy’s stemmy matrix can be readily defoliated. Steers grazing such canopies can obtain their daily dry matter requirement in five to six hours. In contrast, forages with smaller leaves that are not easily selected, or a canopy that is mostly stems, may require steers to graze upwards of 10 to 12 hours. Steers not satiated by this time, however, generally discontinue grazing. This results in a reduction in daily dry matter intake of a diet with lesser nutritive value. Consequently, a steer’s daily performance is reduced.

We conducted two experiments, both having common objectives: (1) determining the diet selected by steers when offered perennial warm-season grasses differing in morphology and nutritive value and (2) determining the diet selected by steers when each forage type was offered at differing herbage mass.

Materials and Methods

We evaluated well-established stands of all forages in Experiment 1 and Experiment 2. Both experiments were conducted on a Cecil clay loam soil at the NC State University Reedy Creek Road Field Laboratory. The experimental stands of the various forages were established and maintained using conventional methods.

Experiment 1

Six perennial warm-season grasses were established in pure stands: bermudagrass (Cynodon dactylon [L.] Pers.), Caucasian bluestem (Bothriochloa bladhii [Retz.] S.T. Blake), Coastal panicgrass (Panicum amarum var. amarulum [A. Hitch. & Chase] P.G. Palmer), a selection of Eastern gamagrass germplasm (Tripsacum dactyloides [L.] L.), and a lowland and an upland cultivar (cv) of switchgrass (Panicum virgatum L.). All forages were subjected to three defoliation intensities, except eastern gamagrass, which was subjected to two defoliation intensities. This resulted in the following 17 treatments that were imposed and evaluated.


Seventeen treatments evaluated in Experiment 1.
Forage Targeted canopy height at defoliation

1. Bermudagrass (BG)
(cv: Hybrid 44)

Short: 4 inches grazed to 2
Medium: 6 inches grazed to 2
Tall: 8 inches grazed to 2

2. Caucasian bluestem (BS)
(cv: none stated)

Short: 6 inches grazed to 3
Medium: 9 inches grazed to 3
Tall: 12 inches grazed to 3

3. Coastal panicgrass (PG)
(cv: Atlantic)

Short: 10 inches grazed to 4
Medium: 18 inches grazed to 4
Tall: 26 inches grazed to 4

4. Eastern gamagrass (GG)
(selection: NC-1)

Medium: 13 inches grazed to 6
Tall: 26 inches grazed to 6

5. Lowland switchgrass (SGL)
(cv: Alamo)

Short: 10 inches grazed to 4
Medium: 18 inches grazed to 4
Tall: 26 inches grazed to 4

6. Upland switchgrass (SGU)
(cv: Trailblazer)

Short: 10 inches grazed to 4
Medium: 18 inches grazed to 4
Tall: 26 inches grazed to 4


Three land areas were established, each representing a replicate. The six grasses were planted in each replicate in equal blocks, with each block measuring 28 feet by 84 feet. The blocks of each grass within each replicate were then randomly assigned the three heights of defoliation (Short, Medium, Tall), with each defoliation treatment plot then measuring 28 feet by 28 feet. The noted exception was the block of gamagrass in each replicate, which was assigned two defoliation treatments (Medium and Tall), with each plot measuring 28 feet by 42 feet. This resulted in 17 treatments in a randomized complete-block design with three replicates.

We conducted the experiment for three years. Each year the experimental area was burned in late February and the plots clipped to remove all fall carryover growth. All plots were fertilized according to soil test results. Nitrogen, as ammonium nitrate, was applied at 80 lb/acre of actual nitrogen in late March, late May, late June, and late July. This rate was used consistently on all plots to remove nitrogen as a potential variable.

Because the overall data were unbalanced (initially only two defoliation heights for eastern gamagrass, slow recovery, and stand loss of some forages during the trial), we grouped the data into five balanced data sets. These data sets were then statistically analyzed according to the design. The results are presented separately for each of the five data sets. The treatment sums of squares were partitioned into Forage and defoliation Height main effects with the five degrees of freedom for the Forage sums of squares further partitioned into a set of orthogonal contrasts. These consisted of (1) bermudagrass vs. the other forages, (2) the finer-stemmed forages (Caucasian bluestem and panicgrass) vs. the coarser-stemmed forages (gamagrass and switchgrasses), (3) the two finer-stemmed forages (Caucasian bluestem and panicgrass) compared (Caucasian bluestem vs. panicgrass), (4) the leafier, more lax gamagrass vs. the upright switchgrasses (Alamo and Trailblazer), and (5) a comparison of the lowland switchgrass (Alamo) with the upland switchgrass (Trailblazer).

Experiment 2

In previous animal evaluations with differing types (upland and lowland) of switchgrass (Panicum virgatum L.), researchers noted differences in animal responses (Burns et el., 2009). In this experiment, we examined the degree of animal selectivity that may occur among cultivars of the same species. We compared four cultivars, one upland cultivar (Cave-in-Rock) and three lowland cultivars, each established in pure stands. Two of the lowland cultivars (BoMaster and Performer) were initially selected germplasm and have subsequently been released as cultivars (Burns et al., 2008a, 2008b). The eight treatments that were imposed and evaluated were as follows:


Eight treatments evaluated in Experiment 2.
Switchgrass cultivar Targeted canopy height at defoliation
1. Cave-in-Rock (CIR) Short: 16 inches grazed to 4
Tall: 22 inches grazed to 4
2. Alamo (ALA) Short: 16 inches grazed to 4
Tall: 22 inches grazed to 4
3. BoMaster (BOM) Short: 16 inches grazed to 4
Tall: 22 inches grazed to 4
4. Performer (PER) Short: 16 inches grazed to 4
Tall: 22 inches grazed to 4

Four land areas were established, each representing a replicate. The four grasses were planted in each replicate in equal blocks, with each block measuring 28 feet by 84 feet. The blocks of each grass within the replicate were then randomly assigned the two heights of defoliation, with each defoliation treatment plot measuring 28 feet by 42 feet. This resulted in eight treatments in a randomized complete-block design with four replicates.

We conducted Experiment 2 for two years. Each year the experimental areas were burned in late February and the blocks clipped to remove all fall carryover growth. All plots were fertilized according to soil test results and nitrogen, as ammonium nitrate, was applied at 100 lb/acre of actual nitrogen the last week of March or first week of April and again the first week of June. This rate was used consistently on all plots to remove nitrogen as a potential variable. Rainfall in Year 1 was very favorable, whereas in Year 2 rainfall was lacking.
In addition to herbage mass estimates (see “General Procedures” below) obtained before defoliation, estimates were also taken of the residual herbage mass remaining at the end of the growing season. Stand counts, as a percent occupancy of the land area, were also determined at that time. To assess any carryover influences of defoliation on the productivity and survival of these switchgrass cultivars, we took a yield harvest and a stand count in May of Year 3.

The data were analyzed statistically according to the design with the cultivar main effect sums of squares partitioned into an orthogonal set of three comparisons consisting of (1) Cave-in-Rock vs. others (upland cultivar vs. lowland cultivars), (2) among lowland cultivars of Alamo (an established cultivar) vs. two newly released cultivars (BoMaster + Performer), and (3) between the two newly released lowland cultivars BoMaster (selected for improved yield and against nutritive values losses) vs. Performer (selected for improved nutritive value and against yield losses).

General Procedures

Treatments were maintained in each experiment at their targeted canopy height by multiple defoliations during the season. This was accomplished using steers weighing from 600 to 1,100 lb, depending on year and defoliation time. General defoliations occurred as needed based on the forage species and the targeted height for defoliation. Intensive experimental samplings, however, were limited to two times each year, once during mid May to early June and a second time during late June to early July. This provided forages that were produced under more moderate spring growing conditions compared with forage produced under stressful summer growing conditions. This was achieved in Experiment 1 and only in the first year of Experiment 2. Because of dry weather conditions in Year 2 of Experiment 2, only one evaluation (June) was conducted.

Before defoliation of each plot, we obtained 15 height (extended and bulk) measurements from each plot and averaged for the treatment. For the general defoliations, three steers were allocated to each plot and permitted to graze until the appropriate stubble height was attained. In cases where defoliation occurred slowly or incompletely after several hours of grazing, additional steers were then added that day or the following day for a brief time to complete defoliation. Following defoliation, animal waste was manually removed, if needed, from each plot to avoid potential influences on steer preference.

At each detailed experimental grazing to evaluate the diet selected by steers, as opposed to the general grazings, a slightly different procedure was followed. Canopy heights were first measured as noted above for the general defoliations. Then, prior to each of the two yearly detailed evaluations, three random quadrants were taken from each plot. The forage was first measured at each site for both normal canopy and bulk canopy heights, and then cut to the appropriate stubble height and weighed. The three samples were composited within each plot, thoroughly mixed, and one subsample was obtained and transported to the field laboratory and refrigerated until separated into leaf, stem, head, and dead fractions. Another subsample was obtained and oven-dried at 170° F and used for dry matter determination. A third subsample was quick frozen in liquid nitrogen in the field, freeze-dried, ground to pass through a 1 mm screen, and stored in a freezer (-16° F) for later laboratory analysis.

Once forage sampling was completed, steers fitted with an esophageal fistula and held overnight in confinement with free access to water were given free access to a plot and their masticate collected. This was accomplished by removing the cannula and collecting the extrusa via a plastic-lined net. The first several boluses were discarded, and masticate collection followed during the next 20 to 30 minutes. The resulting masticate samples, including saliva, were immediately thoroughly mixed, placed in plastic bags, flattened and placed on a metal rack, and submerged in liquid nitrogen and thereafter transferred to a freezer (-16° F) until freeze-dried. Following masticate collection, three steers were allocated to each plot, and the subsequent defoliation procedures followed those of the general defoliations noted above.

Following freeze-drying, duplicate 15 g samples were separated by dry sieving using eight screens (5.60, 4.00, 2.80, 1.70, 1.00, 0.50, 0.25, and 0.125 mm) in a Fritsch Vibrator system, resulting in nine particle sizes (including the particles that passed through the 0.125 mm sieve). The particle sizes of the duplicate samples were used to determine mean and median particle sizes, and the nine particle sizes were reduced to three particle-size classes: large (>1.7 mm), medium (<1.7 > 0.5 mm), and small (< 0.5 mm). The duplicate subsamples were subsequently combined, and a whole-masticate calculated. The samples of the three particle-size classes were ground through a Udy mill to pass a 1.0 mm screen and held in a freezer (-16° F) for laboratory analysis.

All canopy and masticate samples were analyzed using near infrared reflectance spectroscopy (NIRS) technology for ash, in vitro true organic matter disappearance (ITOD), total nitrogen times 6.25 to estimate crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) , cellulose (CELL), and lignin determinations. The CP and all fiber estimates were corrected for ash concentration.

Results and Discussion

In both experiments we examined the characteristics of the diet selected by steers when given access to forage on-offer at differing herbage mass. In Experiment 1 we compared different forage species with very different morphologies, whereas in Experiment 2 we compared forages of the same species with very similar morphologies. The results from these contrasting experiments will be addressed individually.

Experiment 1

A greater number of defoliations, as expected, occurred for the Short treatment, averaging 11 during the season for both bermudagrass and the lowland switchgrass cultivars (Table 1). The frequency noted for switchgrass was not expected, although it is very well-adapted to the upper South environment. The Tall treatment had the least defoliations, averaging greatest at 6.7 defoliations for bermudagrass and least at 5.0 for both Caucasian bluestem and the upland switchgrass.


Table 1. Defoliations that occurred by height (Ht) for each forage each year.
Treatment Year1
Forage Ht2 1 2 3 Mean
Bermudagrass S 9 13 11 11.0
M 7 11 9 9.0
T 5 8 7 6.7
Bluestem S 9 9 7 8.3
M 6 7 6 6.3
T 5 5 5 5.0
Panicgrass S 10 9 -3 9.5
M 8 8 - 8.0
T 5 7 6 6.0
Gamagrass S NE4 NE NE -
M 3 9 7 6.3
T 4 6 6 5.3
Switchgrass
(Lowland)
S 10 13 10 11.0
M 8 9 8 8.3
T 5 7 6 6.0
Switchgrass
(Upland)
S 7 8 - 7.5
M 6 7 - 6.5
T 4 6 5 5.0
1 Defoliations were initiated May 6 in Year 1, April 15 in Year 2, and April 20 in Year 3.
2 S = Short, M = Medium, and T = Tall (see materials and methods, Experiment 1, for target heights).
3 Stand deterioration by Year 3 prevented evaluation.
4 NE = not evaluated.

Characteristics of the forages evaluated (presented in data sets 1 through 5) differed, as expected, in canopy height. This occurred when expressed as either extended height or as bulk height and consistent with the differing growth habit (upright vs. more decumbent) among the forages (Tables 2 and 3). As expected, the differences noted either between or among forage heights (depending on the data set) at time of defoliation were generally significant, as was the forage by forage-height interaction (F × Ht). On the other hand, herbage mass values among forages were generally similar before and after defoliation, with little differences in the quantity removed by grazing (Tables 2 and 3). As expected, the herbage mass differences noted either between or among forage height treatments (depending on data set) at defoliation were generally significant, but the F × Ht interaction was not. By design, the morphology (proportion of leaf, stem, dead, and head) among the forages differed appreciably (Tables 4, 5, and 6). The extremes were bermudagrass and gamagrass. Bermudagrass, a fine-leafed forage, generally had, numerically, the least proportion of leaf (40% – 44%) and a consistent presence of heads (5.7% – 8.5%), whereas gamagrass had the greatest proportion of leaf (72.3% – 73.7%) and essentially no heads (<1.0%). Because of its fine-leafed characteristics, bermudagrass is often presented and viewed as a very leafy forage. Unlike gamagrass, however, the morphology of bermudagrass is such that the selective consumption of the leafy portion without consuming stem is somewhat restrictive and may account, in part, for only moderate daily steer performance generally obtained when grazing bermudagrass (Burns and Fisher, 2013). Bluestem and panicgrass, being intermediate between bermudagrass and gamagrass, were generally similar in leaf and stem proportions before defoliation and have been shown previously to give from similar to greater steer performance than bermudagrass (Burns et al., 2012). Further, whether of the lowland or upland type, the switchgrass cultivars had similar morphology before defoliation.



Table 2. Extended height (ExHt), bulk height (BkHt), and herbage mass (HM) before and after grazing and forage grazed (FG), data sets 1, 2, and 3 (dry matter basis).
Treatment Set 1 Set 2 Set 3
Before After Before After Before After
ExHt BkHt HM BkHt HM FG ExHt BkHt HM BkHt HM FG ExHt BkHt HM BkHt HM FG
inches -- lb/acre -- inches -- lb/acre -- -- inches -- lb/acre inches -- lb/acre -- -- inches -- lb/acre inches -- lb/acre --
Forage:
Bermudagrass (BG) 14.51 6.11 47171 3.31 22241 24931 13.42 5.52 44192 3.32 23772 20422 11.93 4.83 39243 3.03 20743 18493
Bluestem (BS) 22.7 6.4 4049 3.6 1696 2354 19.9 5.7 3539 3.4 1652 1886 17.6 5.1 3041 3.2 1466 1575
Panicgrass (PG) 30.1 10.9 4035 7.9 2114 1869 -- -- -- -- -- -- -- -- -- -- -- --
Gamagrass (GG) 33.1 12.2 4955 8.8 3143 1811 26.9 10.3 3726 7.3 2363 1363 -- -- -- -- -- --
Switchgrass (SGL) 31.1 11.4 4682 8.2 2184 2498 27.1 9.8 3882 7.3 2135 1747 23.2 8.3 3197 6.3 1834 1363
Switchgrass (SGU) 29.4 11.3 3970 7.3 1955 2015 -- -- -- -- -- -- -- -- -- -- -- --
Height:
Short -- -- -- -- -- -- -- -- -- -- -- -- 12.46 4.26 22696 3.26 12656 10046
Medium -- -- -- -- -- -- 18.35 6.65 31825 4.75 19525 12305 17.5 6.1 3410 4.3 2075 1335
Tall 26.84 9.74 44014 6.54 22194 21734 25.3 9.0 4601 6.0 2312 2289 22.7 8.0 4483 5.1 2034 2448
Significance (P):
Forage (F): <0.01 <0.01 0.83 <0.01 0.07 0.91 <0.01 <0.01 0.71 <0.01 0.40 0.74 <0.01 <0.01 0.25 <0.01 0.49 0.31
BG vs. Others <0.01 <0.01 0.62 <0.01 0.99 0.56 <0.01 <0.01 0.31 <0.01 0.40 0.49 <0.01 0.01 0.12 0.01 0.35 0.19
(BS + PG) vs. (GG + SG) <0.01 <0.01 0.44 <0.01 0.08 0.99 -- -- -- -- -- -- -- -- -- -- -- --
BS vs. PG <0.01 <0.01 0.99 <0.01 0.33 0.57 -- -- -- -- -- -- -- -- -- -- -- --
GG vs. (SGL + SGU) 0.05 0.25 0.46 0.07 0.01 0.55 -- -- -- -- -- -- -- -- -- -- -- --
SGL vs. SGU 0.38 0.85 0.47 0.17 0.58 0.57 -- -- -- -- -- -- -- -- -- -- -- --
Height (Ht): <0.01 <0.01 <0.01 <0.01 0.08 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
Linear -- -- -- -- -- -- -- -- -- -- -- -- <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
Lack of Fit -- -- -- -- -- -- -- -- -- -- -- -- 0.83 0.95 0.82 0.52 0.02 0.05
F x Ht -- -- -- -- -- -- <0.01 <0.01 0.28 <0.01 0.03 0.85 <0.01 0.01 0.14 0.01 0.67 0.49
1 Each value is the average of multiple estimates and the mean of three years and three replicates (n = 9).
2 Each value is the average of multiple estimates and the mean of two heights, three years, and three replicates (n = 18).
3 Each value is the average of multiple estimates and the mean of three heights, three years, and three replicates (n = 27).
4 Each value is the average of multiple estimates and the mean of six forages, three years, and three replicates (n = 54).
5 Each value is the average of multiple estimates and the mean of four forages, three years, and three replicates (n = 36).
6 Each value is the average of multiple estimates and the mean of three forages, three years, and three replicates (n = 27).

Table 3. Extended height (ExHt), bulk height (BkHt), and herbage mass (HM) before and after grazing and forage grazed (FG), data sets 4 and 5 (dry matter basis).
Treatment Set 4 Set 5
Before After Before After
ExHt BkHt HM BkHt HM FG ExHt BkHt HM BkHt HM FG
inches -- lb/acre -- inches -- lb/acre -- inches -- lb/acre -- inches -- lb/acre --
Forage:
Bermudagrass (BG) 13.11 5.01 39921 2.91 17731 22191 11.62 4.52 35242 2.72 15512 19742
Bluestem (BS) 19.4 5.5 3609 3.7 1783 1826 12.0 4.9 3037 3.3 1534 1503
Panicgrass (PG) 25.9 9.1 3190 7.0 1537 1653 21.6 7.6 2564 5.8 1279 1285
Gamagrass (GG) 25.0 10.1 2831 7.3 2038 792 -- -- -- -- -- --
Switchgrass (SGL) 26.8 9.2 3921 6.9 1921 2000 23.2 7.9 3286 6.1 1749 1536
Switchgrass (SGU) 25.9 9.0 3387 5.9 1703 1684 21.9 7.3 2723 4.9 1311 1412
Height:
Short -- -- -- -- -- -- 12.84 4.24 18414 3.34 967 8734
Medium 18.93 6.63 28133 4.73 1681 11323 19.0 6.3 2947 4.5 1715 1232
Tall 26.4 9.3 4163 6.4 1904 2259 25.4 8.8 4293 5.9 1772 2521
Significance (P):
Forage (F): <0.01 0.01 0.37 <0.01 0.37 0.17 <0.01 0.01 0.27 <0.01 0.43 0.53
BG vs. Others <0.01 <0.01 0.21 <0.01 0.89 0.12 <0.01 0.01 0.12 <0.01 0.70 0.15
(BS +PG) vs. (GG + SG) 0.01 0.01 0.96 0.01 0.15 0.43 0.01 0.04 0.51 0.03 0.52 0.78
BS vs. PG <0.01 <0.01 0.47 <0.01 0.29 0.71 0.01 0.01 0.30 0.01 0.36 0.60
GG vs. (SGL + SGU) 0.29 0.27 0.14 0.08 0.27 0.04 -- -- -- -- -- --
SGL vs. SGU 0.51 0.81 0.37 0.12 0.35 0.50 0.31 0.37 0.23 0.04 0.15 0.76
Height (Ht): <0.01 <0.01 <0.01 <0.01 0.10 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
Linear -- -- -- -- -- -- <0.01 <0.01 <0.01 <0.01 <0.01 <0.01
Lack of Fit -- -- -- -- -- -- 0.93 0.55 0.52 0.80 0.01 0.01
F x Ht 0.02 0.16 0.50 0.04 0.08 0.43 <0.01 0.06 0.66 0.05 0.28 0.61
1 Each value is the average of multiple estimates and the mean of two heights, two years, and three replicates (n = 12).
2 Each value is the average of multiple estimates and the mean of three heights, two years, and three replicates (n = 18).
3 Each value is the average of multiple estimates and the mean of six forages, two years, and three replicates (n = 36).
4 Each value is the average of multiple estimates and the mean of five forages, two years, and three replicates (n = 30).

Table 4. Proportions of leaf, stem, dead, and head tissues of herbage mass before and after grazing, data sets 1 and 2 (dry matter basis).
Treatment Set 1 Set 2
Leaf Stem Dead Head Leaf Stem Dead Head
Before After Before After Before After Before After Before After Before After Before After Before After
----------------------------------------------- % of whole-plant dry matter -----------------------------------------------
Forage:
Bermudagrass (BG) 40.01 22.51 45.01 58.11 8.81 17.51 7.61 0.61 41.12 25.12 44.82 57.62 8.12 15.92 7.52 0.082
Bluestem (BS) 48.7 27.4 43.8 52.7 5.8 20.9 1.1 0.3 52.2 29.0 40.6 50.3 7.2 21.1 0.9 0.3
Panicgrass (PG) 52.0 24.2 43.2 64.8 4.6 11.2 2.4 -- -- -- -- -- -- -- -- --
Gamagrass (GG) 73.7 55.8 18.8 30.9 7.3 13.3 0.9 0.2 72.8 52.9 19.7 33.6 7.4 13.5 0.5 0.3
Switchgrass (SGL) 49.0 24.9 45.9 68.9 5.2 8.8 -- 0.4 48.0 26.3 45.6 63.6 6.4 11.4 -- --
Switchgrass (SGU) 49.2 22.8 43.6 71.2 5.4 10.9 3.6 1.1 -- -- -- -- -- -- -- --
Height:
Short -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Medium -- -- -- -- -- -- -- -- 53.74 34.04 37.04 49.94 7.84 15.94 2.74 --4
Tall 52.13 29.63 40.13 57.83 6.23 13.83 2.63 -- 52.8 32.7 38.4 52.7 6.8 15.1 3.2 0.3
Significance (P):
Forage (F): <0.01 <0.01 <0.01 <0.01 0.73 0.03 0.21 0.77 <0.01 <0.01 <0.01 <0.01 0.94 0.21 0.04 0.17
BG vs. Others <0.01 <0.01 0.03 0.93 0.20 0.10 -- -- <0.01 <0.01 <0.01 0.05 0.65 0.87 -- --
(BS + PG) vs. (GG + SG) 0.06 <0.01 <0.01 0.60 0.69 0.03 -- -- -- -- -- -- -- -- -- --
BS vs. PG 0.53 0.31 0.85 0.04 0.71 0.01 -- 0.94 -- -- -- -- -- -- -- --
GG vs. (SGL + SGU) <0.01 <0.01 <0.01 <0.01 0.45 0.25 -- -- -- -- -- -- -- -- -- --
SGL vs. SGU 0.97 0.49 0.47 0.66 0.93 0.52 -- -- -- -- -- -- -- -- -- --
Height (Ht): -- -- -- -- -- -- -- -- 0.74 0.42 0.44 0.10 0.36 0.54 0.73 0.40
Linear -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Lack of Fit -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
F x Ht -- -- -- -- -- -- -- -- 0.74 0.15 0.39 0.03 0.45 0.20 0.99 0.25
1 Each value is the average of multiple estimates and the mean of three years and three replicates (n = 9).
2 Each value is the average of multiple estimates and the mean of two heights, three years, and three replicates (n = 18).
3 Each value is the average of multiple estimates and the mean of six forages, three years, and three replicates (n = 54).
4 Each value is the average of multiple estimates and the mean of four forages, three years, and three replicates (n = 36).

Table 5. Proportions of leaf, stem, dead, and head tissues of herbage mass before and after grazing, data sets 3 and 4 (dry matter basis).
Treatment Set 3 Set 4
Leaf Stem Dead Head Leaf Stem Dead Head
Before After Before After Before After Before After Before After Before After Before After Before After
----------------------------------------------- % of whole-plant dry matter -----------------------------------------------
Forage:
Bermudagrass (BG) 42.71 26.91 43.71 56.41 9.01 15.61 5.71 0.91 43.22 24.62 43.52 58.02 7.12 15.72 8.52 0.72
Bluestem (BS) 53.1 30.6 38.1 47.3 8.0 22.3 0.8 0.4 49.0 27.7 41.1 49.3 8.5 23.8 1.2 0.3
Panicgrass (PG) -- -- -- -- -- -- -- -- 49.7 19.7 42.8 67.5 7.3 12.8 1.4 --
Gamagrass (GG) -- -- -- -- -- -- -- -- 72.3 50.1 22.3 37.4 5.3 12.4 0.4 --
Switchgrass (SGL) 50.3 28.4 42.9 60.1 7.0 12.4 -- -- 45.2 21.8 46.8 65.4 8.0 14.0 -- --
Switchgrass (SGU) -- -- -- -- -- -- -- -- 46.7 20.1 45.1 69.3 60.5 14.3 4.3 1.3
Height:
Short 52.23 32.23 37.43 49.53 9.63 18.13 1.43 --3 -- -- -- -- -- -- -- --
Medium 47.7 28.7 42.5 54.4 7.8 16.5 -- -- 50.94 27.24 39.54 56.04 8.34 16.74 -- 0.84
Tall 45.9 24.9 44.9 59.9 6.6 15.7 -- 0.4 51.2 27.5 41.1 59.7 5.9 14.3 -- 0.8
Significance (P):
Forage (F): 0.12 0.57 0.11 0.02 0.76 0.14 0.05 0.22 <0.01 <0.01 0.01 0.01 0.72 0.24 0.22 0.68
BG vs. Others 0.06 0.41 0.15 0.31 0.55 0.63 -- -- 0.03 0.015 0.25 0.96 0.99 0.95 -- --
(BS + PG) vs. (GG + SG) -- -- -- -- -- -- -- -- 0.10 0.01 0.19 0.76 0.37 0.15 -- --
BS vs. PG -- -- -- -- -- -- -- -- 0.88 0.02 0.67 0.01 0.62 0.05 -- --
GG vs. (SGL + SGU) -- -- -- - -- -- -- -- <0.01 <0.01 <0.01 <0.01 0.33 0.66 -- --
SGL vs. SGU -- -- -- -- -- -- -- -- 0.73 0.51 0.69 0.44 0.51 0.96 -- --
Height (Ht): 0.10 <0.01 <0.01 <0.01 0.05 0.31 0.04 0.37 0.89 0.84 0.43 0.12 <0.01 0.04 0.68 0.89
Linear 0.04 <0.01 <0.01 <0.01 0.02 0.14 -- -- -- -- -- -- -- -- -- --
Lack of Fit 0.58 0.91 0.33 0.80 0.78 0.80 -- -- -- -- -- -- -- -- -- --
F x Ht 0.88 0.97 0.26 0.02 0.53 0.18 0.08 0.32 0.69 0.51 0.71 0.29 0.67 0.26 0.59 0.51
1 Each value is the average of multiple estimates and the mean of three heights, three years, and three replicates (n = 27).
2 Each value is the average of multiple estimates and the mean of two heights, two years, and three replicates (n = 12).
3 Each value is the average of multiple estimates and the mean of three forages, three years, and three replicates (n = 27).
4 Each value is the average of multiple estimates and the mean of six forages, two years, and three replicates (n = 36).

Table 6. Proportions of leaf, stem, dead, and head tissues of herbage mass before and after grazing, data set 5 (dry matter basis).
Treatment Set 5
Leaf Stem Dead Head
Before After Before After Before After Before After
---------- % of whole-plant dry matter ---------
Forage:
Bermuadgrass (BG) 44.31 26.31 42.51 56.81 8.41 15.81 6.31 0.71
Bluestem (BS) 51.6 29.3 38.1 46.7 9.3 15.6 1.0 0.5
Panicgrass (PG) 49.3 20.7 42.4 64.7 8.3 14.6 -- --
Gamagrass (GG) -- -- -- -- -- -- -- --
Switchgrass (SGL) 46.6 23.6 44.6 61.5 8.7 15.7 -- --
Swtichgrass (SGU) 50.9 24.5 41.6 63.1 6.4 14.8 -- 1.4
Height:
Short 52.12 29.12 37.82 51.92 9.72 18.92 -- 0.92
Medium 47.1 23.0 42.6 59.3 8.7 17.5 -- 0.8
Tall 46.5 22.6 45.1 64.5 6.3 14.7 -- 0.8
Significance (P):
Forage (F): 0.30 0.07 0.24 0.04 0.82 0.26 0.32 0.69
BG vs. Others 0.11 0.34 0.68 0.50 0.90 0.62 0.15 --
(BS + PG) vs. (GG + SG) 0.51 0.56 0.15 0.07 0.53 0.22 -- 0.55
BS vs. PG 0.52 0.01 0.13 0.01 0.74 0.08 -- --
GG vs. (SGL + SGU) -- -- -- -- -- -- -- --
SGL vs. SGU 0.26 0.68 0.27 0.68 0.41 0.83
Height (Ht): 0.10 <0.01 0.01 <0.01 0.02 0.05 0.02 0.86
Linear 0.05 <0.01 <0.01 <0.01 0.01 0.02 -- 0.63
Lack of Fit 0.34 0.06 0.48 0.54 0.46 0.57 -- 0.99
F x Ht 0.60 0.34 0.50 0.14 0.83 0.60 0.08 0.47
1 Each value is the average of multiple estimates and the mean of three heights, two years, and three replicates (n = 18).
2 Each value is the average of multiple estimates and the mean of five forages, two years, and three replicates (n = 30).



The importance of the proportion of leaf, stem, and dead fractions of the canopy and what the animal selects in each mouthful is evident from each fraction’s nutritive value. It is clear that leaves have the greatest nutritive value (Table 7), followed by stems (Table 8), and least for the dead tissue (Table 9). Nutritive value differed among forages in each of the fractions, as it did between or among heights at defoliation. Frequently bermudagrass had the least nutritive value (lesser ITOD and CP and greater NDF), whereas the other forages varied depending on data set.

Steers consumed increasingly more forage with increasing herbage mass, resulting in a quadratic response when three heights were evaluated (Tables 2 and 3). The interested reader can view the forage height and herbage mass means, as well as the forage quantity consumed for the individual forages, for each defoliation treatment in Appendix Table 1. The diet selected by steers from these canopies (one evaluation of spring growth and one of summer growth), as represented by the whole masticate, differed in ITOD and nutritive value among forage species in both three-year (Table 10) and two-year (Table 11) data sets. Among the forages, masticate from bluestem was generally least in ITOD and CP and greatest in NDF. Masticate from gamagrass, on the other hand, was generally greatest in CP and consistent with its greater proportion of dry matter consisting of leaf (Tables 4 and 5).



Table 7. In vitro true organic matter disappearance (ITOD), crude protein (CP), and neutral detergent fiber (NDF) of leaf tissue from herbage mass before grazing, data sets 1 to 5 (dry matter basis).
Treatment Data Sets
Set 1 Set 2 Set 3 Set 4 Set 5
ITOD CP NDF ITOD CP NDF ITOD CP NDF ITOD CP NDF ITOD CP NDF
------------------------------------------- % ------------------------------------------------
Forage:
Bermudagrass (BG) 80.91 20.41 66.71 80.82 20.52 66.92 81.23 21.43 65.63 81.24 21.44 65.64 81.75 21.75 65.05
Bluestem (BS) 85.1 13.9 63.2 86.2 14.2 62.6 86.6 14.4 62.2 85.7 13.9 62.3 86.3 14.2 61.8
Panicgrass (PG) 83.7 16.7 68.9 -- -- -- -- -- -- 84.6 17.0 65.1 85.3 17.6 64.7
Gamagrass (GG) 77.5 16.5 68.2 79.5 17.9 66.5 -- -- -- 81.8 19.2 65.2 -- -- --
Switchgrass (SGL) 84.2 16.2 63.4 84.1 16.6 63.7 85.0 17.3 63.2 84.3 16.5 62.8 85.0 17.1 62.7
Switchgrass (SGU) 85.0 16.9 63.5 -- -- -- -- -- -- 86.5 17.1 62.1 88.0 17.6 60.9
Height:
Short -- -- -- -- -- -- 85.58 18.98 62.98 -- -- -- 86.910 18.810 61.910
Medium -- -- -- 83.37 17.87 64.47 84.0 17.4 64.3 85.19 18.19 63.19 85.3 17.6 63.0
Tall 82.76 16.86 65.76 81.9 16.7 65.4 83.4 16.8 64.5 83.0 16.7 64.6 83.7 16.6 64.2
Significance (P):
Forage (F): <0.01 <0.01 <0.01 0.04 0.01 <0.01 <0.01 <0.01 0.01 0.03 0.03 0.06 0.01 0.01 0.03
BG vs. Others 0.08 <0.01 0.09 0.16 0.01 0.01 <0.01 <0.01 0.01 0.01 0.01 0.05 <0.01 <0.01 0.03
(BS + PG) vs. (GG + SG) 0.04 0.10 0.88 -- -- -- -- -- -- 0.29 0.05 0.62 0.32 0.08 0.09
BS vs. PG 0.38 0.01 0.01 -- -- -- -- -- -- 0.38 0.06 0.05 0.28 0.02 0.03
GG vs. (SGL + SGU) <0.01 0.96 <0.01 -- -- -- -- -- -- 0.02 0.09 0.03 -- -- --
SGL vs. SGU 0.60 0.50 0.93 -- -- -- -- -- -- 0.12 0.61 0.59 0.02 0.58 0.10
Height (Ht): -- -- -- 0.02 0.02 0.05 0.01 <0.01 0.03 0.01 0.01 0.04 <0.01 <0.01 <0.01
Linear -- -- -- -- -- -- <0.01 <0.01 0.01 -- -- -- <0.01 <0.01 0.01
Lack of Fit -- -- -- -- -- -- 0.34 0.16 0.25 -- -- -- 0.99 0.69 0.85
F x Ht -- -- -- 0.04 0.19 0.06 0.20 0.14 0.78 0.20 0.34 0.63 0.29 0.82 0.34
1 Each value is the average of multiple estimates and the mean of three years and three replicates (n = 9).
2 Each value is the average of multiple estimates and the mean of two heights, three years, and three replicates (n = 18).
3 Each value is the average of multiple estimates and the mean of three heights, three years, and three replicates (n = 27).
4 Each value is the average of multiple estimates and the mean of two heights, two years, and three replicates (n = 12).
5 Each value is the average of multiple estimates and the mean of three heights, two years, and three replicates (n = 18).
6 Each value is the average of multiple estimates and the mean of six forages, three years, and three replicates (n = 54).
7 Each value is the average of multiple estimates and the mean of four forages, three years, and three replicates (n = 36).
8 Each value is the average of multiple estimates and the mean of three forages, three years, and three replicates (n = 27).
9 Each value is the average of multiple estimates and the mean of six forages, two years, and three replicates (n = 36).
10 Each value is the average of multiple estimates and the mean of five forages, two years, and three replicates (n = 30).

Table 8. In vitro true organic matter disappearance (ITOD), crude protein (CP), and neutral detergent fiber (NDF) of stem tissue from herbage mass before grazing, data sets 1 to 5 (dry matter basis).
Treatment Data Sets
Set 1 Set 2 Set 3 Set 4 Set 5
ITOD CP NDF ITOD CP NDF ITOD CP NDF ITOD CP NDF ITOD CP NDF
------------------------------------------- % ------------------------------------------------
Forage:
Bermudagrass (BG) 65.41 10.71 73.31 66.22 11.22 73.22 67.83 12.33 72.43 67.34 11.74 71.64 68.85 12.75 70.75
Bluestem (BS) 74.6 9.0 72.8 75.7 9.1 72.0 77.1 9.5 71.1 74.9 8.8 71.9 77.0 9.4 70.6
Panicgrass (PG) 69.4 9.3 72.4 -- -- -- -- -- -- 71.8 10.1 70.2 72.8 10.9 69.6
Gamagrass (GG) 70.9 8.8 73.1 72.3 10.1 71.7 -- -- -- 73.6 10.9 70.4 -- -- --
Switchgrass (SGL) 72.6 9.0 69.5 73.8 9.7 68.7 75.6 10.6 68.2 73.8 9.7 68.2 75.3 10.4 68.1
Switchgrass (SGU) 69.0 9.3 72.3 -- -- -- -- -- -- 70.5 9.7 71.5 73.9 10.6 69.5
Height:
Short -- -- -- -- -- -- 76.68 12.38 69.18 -- -- -- 77.310 12.410 67.810
Medium -- -- -- 73.17 10.77 70.67 72.9 10.5 70.7 73.89 11.09 69.59 73.5 10.7 69.7
Tall 70.36 9.36 72.26 70.9 9.4 72.2 70.9 9.6 71.9 70.1 9.2 71.7 69.8 9.2 71.7
Significance (P):
Forage (F): <0.01 0.28 0.12 <0.01 0.22 0.02 <0.01 0.02 0.07 <0.01 0.15 0.11 <0.01 0.05 0.20
BG vs. Others <0.01 0.03 0.24 <0.01 0.07 0.02 <0.01 0.01 0.07 <0.01 0.04 0.22 <0.01 0.01 0.17
(BS + PG) vs. (GG + SG) 0.32 0.80 0.26 -- -- -- -- -- -- 0.28 0.30 0.21 0.61 0.52 0.13
BS vs. PG 0.01 0.72 0.77 -- -- -- -- -- -- 0.02 0.20 0.19 0.01 0.10 0.33
GG vs. (SGL + SGU) 0.95 0.68 0.08 -- -- -- -- -- -- 0.12 0.18 0.58 -- -- --
SGL vs. SGU 0.06 0.69 0.06 -- -- -- -- -- -- 0.02 0.98 0.03 0.13 0.74 0.20
Height (Ht): -- -- -- 0.01 0.01 0.02 <0.01 <0.01 0.01 <0.01 <0.01 0.01 <0.01 <0.01 <0.01
Linear -- -- -- -- -- -- <0.01 <0.01 <0.01 -- -- -- <0.01 <0.01 <0.01
Lack of Fit -- -- -- -- -- -- 0.29 0.26 0.69 -- -- -- 0.93 0.71 0.90
F x Ht -- -- -- 0.90 0.35 0.49 0.97 0.21 0.77 0.23 0.25 0.75 0.02 0.84 0.18
1 Each value is the average of multiple estimates and the mean of three years and three replicates (n = 9).
2 Each value is the average of multiple estimates and the mean of two heights, three years, and three replicates (n = 18).
3 Each value is the average of multiple estimates and the mean of three heights, three years, and three replicates (n = 27).
4 Each value is the average of multiple estimates and the mean of two heights, two years, and three replicates (n = 12).
5 Each value is the average of multiple estimates and the mean of three heights, two years, and three replicates (n = 18).
6 Each value is the average of multiple estimates and the mean of six forages, three years, and three replicates (n = 54).
7 Each value is the average of multiple estimates and the mean of four forages, three years, and three replicates (n = 36).
8 Each value is the average of multiple estimates and the mean of three forages, three years, and three replicates (n = 27).
9 Each value is the average of multiple estimates and the mean of six forages, two years, and three replicates (n = 36).
10 Each value is the average of multiple estimates and the mean of five forages, two years, and three replicates (n = 30).

Table 9. In vitro true organic matter disappearance (ITOD), crude protein (CP), and neutral detergent fiber (NDF) of dead tissue from herbage mass before grazing, data sets 1 to 5 (dry matter basis).
Treatment Data Sets
Set 1 Set 2 Set 3 Set 4 Set 5
ITOD CP NDF ITOD CP NDF ITOD CP NDF ITOD CP NDF ITOD CP NDF
------------------------------------------- % ------------------------------------------------
Forage:
Bermudagrass (BG) 54.21 10.31 70.91 55.42 10.22 70.42 55.93 11.13 69.93 59.54 10.94 68.04 58.75 11.65 68.15
Bluestem (BS) 70.9 6.9 68.1 70.6 7.0 67.8 68.7 7.2 67.8 67.9 6.5 68.8 65.7 6.9 69.0
Panicgrass (PG) 59.4 8.6 70.8 -- -- -- -- -- -- 52.8 7.9 64.5 54.0 8.5 66.2
Gamagrass (GG) 62.2 10.7 65.2 67.1 12.2 65.4 -- -- -- 67.3 11.8 64.8 -- -- --
Switchgrass (SGL) 57.3 8.7 70.7 61.0 9.4 70.2 59.1 9.5 68.3 59.8 8.7 70.8 56.6 8.7 68.7
Switchgrass (SGU) 67.1 8.9 66.7 -- -- -- -- -- -- 67.5 9.5 66.8 69.5 10.4 65.9
Height:
Short -- -- -- -- -- -- 59.18 10.08 67.18 -- -- -- 59.710 10.210 67.110
Medium -- -- -- 65.97 10.37 68.27 63.9 9.1 69.0 63.59 10.09 65.99 61.3 9.2 65.9
Tall 61.96 9.06 68.76 61.2 8.7 68.7 60.8 8.6 69.9 61.4 8.5 68.7 61.7 8.2 69.7
Significance (P):
Forage (F): 0.04 0.01 0.22 0.12 0.02 0.29 0.11 0.04 0.73 0.27 0.03 0.58 0.07 0.02 0.75
BG vs. Others 0.03 0.03 0.23 0.05 0.47 0.28 0.12 0.03 0.47 0.51 0.06 0.78 0.45 0.01 0.79
(BS + PG) vs. (GG + SG) 0.35 0.01 0.29 -- -- -- -- -- -- 0.33 0.01 0.75 0.32 0.03 0.88
BS vs. PG 0.03 0.07 0.33 -- -- -- -- -- -- 0.07 0.29 0.30 0.04 0.10 0.40
GG vs. (SGL + SGU) 0.99 0.02 0.15 -- -- -- -- -- -- 0.54 0.04 0.28 -- -- --
SGL vs. SGU 0.06 0.80 0.15 -- -- -- -- -- -- 0.28 0.49 0.33 0.03 0.09 0.39
Height (Ht): -- -- -- 0.03 0.04 0.65 0.20 0.02 0.17 0.32 0.01 0.25 0.68 0.02 0.28
Linear -- -- -- -- -- -- 0.50 0.01 0.07 -- -- -- 0.42 0.01 0.29
Lack of Fit -- -- -- -- -- -- 0.10 0.56 0.66 -- -- -- 0.78 0.94 0.23
F x Ht -- -- -- 0.26 0.12 0.95 0.46 0.10 0.47 0.09 0.19 0.49 0.22 0.58 0.48
1 Each value is the average of multiple estimates and the mean of three years and three replicates (n = 9).
2 Each value is the average of multiple estimates and the mean of two heights, three years, and three replicates (n = 18).
3 Each value is the average of multiple estimates and the mean of three heights, three years, and three replicates (n = 27).
4 Each value is the average of multiple estimates and the mean of two heights, two years, and three replicates (n = 12).
5 Each value is the average of multiple estimates and the mean of three heights, two years, and three replicates (n = 18).
6 Each value is the average of multiple estimates and the mean of six forages, three years, and three replicates (n = 54).
7 Each value is the average of multiple estimates and the mean of four forages, three years, and three replicates (n = 36).
8 Each value is the average of multiple estimates and the mean of three forages, three years, and three replicates (n = 27).
9 Each value is the average of multiple estimates and the mean of six forages, two years, and three replicates (n = 36).
10 Each value is the average of multiple estimates and the mean of five forages, two years, and three replicates (n = 30).

Table 10. Whole-masticate in vitro true organic matter disappearance (ITOD), crude protein (CP), and fiber fractions1 (organic matter basis).
Treatment Data Sets2
Set 1 Set 2 Set 3
ITOD CP NDF ADF ITOD CP NDF ADF ITOD CP NDF ADF
------------------------------------------- % ------------------------------------------------
Forage:
Bermudagrass (BG) 83.63 17.33 67.43 29.33 83.54 17.54 67.94 29.54 84.25 18.85 65.95 28.35
Bluestem (BS) 80.2 12.3 70.4 34.6 81.5 13.4 70.0 34.3 82.2 14.0 68.5 33.5
Panicgrass (PG) 86.7 16.6 68.7 32.1 -- -- -- -- -- -- -- --
Gamagrass (GG) 83.6 22.5 63.8 28.3 82.9 20.3 64.2 28.9 -- -- -- --
Switchgrass (SGL) 85.3 16.3 64.8 29.7 85.1 16.5 65.6 30.5 85.7 16.9 65.6 30.5
Switchgrass (SGU) 85.2 15.7 66.8 32.6 -- -- -- -- -- -- -- --
Height:
Short -- -- -- -- -- -- -- -- 85.58 18.18 64.38 29.58
Medium -- -- -- -- 83.97 17.37 66.97 30.97 83.7 16.2 68.1 31.6
Tall 84.16 16.86 67.06 31.16 82.6 16.6 67.0 30.7 83.0 15.3 67.5 31.2
Significance (P):
Forage (F): 0.01 <0.01 0.06 <0.01 0.21 0.02 0.05 <0.01 0.22 0.01 0.15 <0.01
BG vs. Others 0.53 0.30 0.72 0.03 0.78 0.51 0.35 0.05 0.83 0.01 0.35 <0.01
(BS + PG) vs. (GG + SG) 0.19 <0.01 0.01 <0.01 -- -- -- -- -- -- -- --
BS vs. PG <0.01 <0.01 0.31 0.03 -- -- -- -- -- -- -- --
GG vs. (SGL + SGU) 0.32 <0.01 0.39 0.08 -- -- -- -- -- -- -- --
SGL vs. SGU 0.95 0.42 0.26 0.02 -- -- -- -- -- -- -- --
Height (Ht): -- -- -- -- 0.09 0.27 0.91 0.70 <0.01 <0.01 0.01 0.01
Linear -- -- -- -- -- -- -- -- <0.01 <0.01 0.01 0.02
Lack of Fit -- -- -- -- -- -- -- -- 0.23 0.26 0.04 0.04
F x Ht -- -- -- -- 0.19 0.56 0.73 0.61 0.21 0.07 0.15 0.11
1 NDF = neutral detergent fiber; ADF = acid detergent fiber.
2 All values are the average of two defoliations, and two masticate subsamples at each defoliation.
3 Mean of three years and three replicates (n = 9).
4 Mean of two heights, three years, and three replicates (n = 18).
5 Mean of three heights, three years, and three replicates (n = 27).
6 Mean of six forages, three years, and three replicates (n = 54).
7 Mean of four forages, three years, and three replicates (n = 36).
8 Mean of three forages, three years, and three replicates (n = 27).

Table 11. Whole-masticate in vitro true organic matter disappearance (ITOD), crude protein (CP), and fiber fractions1 (organic matter basis).
Treatment Data Sets2
Set 4 Set 5
ITOD CP NDF ADF ITOD CP NDF ADF
------------------------------------------- % ------------------------------------------------
Forage:
Bermudagrass (BG) 83.33 17.53 68.33 29.63 84.14 18.84 66.14 28.34
Bluestem (BS) 80.1 13.1 71.8 35.0 81.0 14.0 69.9 34.0
Panicgrass (PG) 87.2 17.1 68.7 31.6 87.6 17.6 67.7 31.4
Gamagrass (GG) 84.0 21.6 63.9 28.7 -- -- -- --
Switchgrass (SGL) 84.6 16.5 65.7 30.2 85.3 16.8 65.7 30.5
Switchgrass (SGU) 84.7 16.3 67.3 32.5 85.9 17.1 65.9 31.4
Height:
Short -- -- -- -- 86.36 18.36 64.56 29.76
Medium 84.45 17.55 67.65 31.35 84.3 16.5 68.5 31.8
Tall 83.5 16.6 67.7 31.2 83.7 15.7 68.2 31.7
Significance (P):
Forage (F): 0.01 0.02 0.06 0.01 0.03 0.05 0.12 0.01
BG vs. Others 0.35 0.59 0.57 0.03 0.40 0.03 0.32 <0.01
(BS + PG) vs. (GG + SG) 0.28 0.02 0.01 <0.01 0.19 0.16 0.03 0.02
BS vs. PG <0.01 0.03 0.12 0.01 0.01 0.02 0.18 0.02
GG vs. (SGL + SGU) 0.51 0.01 0.19 0.03 -- -- -- --
SGL vs. SGU 0.91 0.92 0.38 0.04 0.66 0.81 0.89 0.16
Height (Ht): 0.17 0.12 0.92 0.89 <0.01 <0.01 0.01 <0.01
Linear -- -- -- -- <0.01 <0.01 0.01 <0.01
Lack of Fit -- -- -- -- 0.18 0.18 0.04 0.03
F x Ht 0.40 0.36 0.79 0.50 0.47 0.11 0.47 0.12
1 NDF = neutral detergent fiber; ADF = acid detergent fiber.
2 All values are the average of two defoliations, and two masticate subsamples at each defoliation.
3 Mean of two heights, two years, and three replicates (n = 12).
4 Mean of three heights, two years, and three replicates (n = 18).
5 Mean of six forages, two years, and three replicates (n = 36).
6 Mean of five forages, two years, and three replicates (n = 30).


Masticate from steers offered forage at the greater heights generally showed a reduction, although not always significant, in ITOD and CP and an increase in NDF concentrations (Tables 10 and 11). Even though steers could select what they consumed, these shifts are consistent with reduced nutritive value of canopy tissue as it matures.

The reduction, or mastication, of the forage tissue selectively grazed by steers differed among forages that were compared in each of the five data sets (Tables 12 and 13). Generally, bermudagrass masticate had the least median particle size compared with the other forages, bluestem masticate had lesser particle size than panicgrass, and the two switchgrass masticates were similar in particle size. Although not compared directly, the median particle size for panicgrass masticate was of similar magnitude as that of the two switchgrasses. This is consistent with panicgrass and switchgrass being of the same Panicum genus. These differences reflect the finer leaf and stem characteristics of bermudagrass and bluestem compared with the coarser leaf and stem characteristics of the Panicum types. On the other hand, gamagrass, which is predominantly leaf (Tables 4 and 5) and with the widest leaf characteristics, had lesser particle size compared with the switchgrasses.



Table 12. Whole-masticate median particle size (PS) and proportion of masticate in particle-size classes1 of large (L), medium (M), and small (S), data sets 1 through 3 (dry matter basis).
Treatment Set 12 Set 22 Set 32
Particle-Size Class Particle-Size Class Particle-Size Class
PS L M S PS L M S PS L M S
mm --------------- % --------------- mm --------------- % --------------- mm --------------- % ---------------
Forage:
Bermudagrass (BG) 1.93 53.53 39.93 6.63 1.94 53.04 40.44 6.64 1.85 52.75 40.35 6.95
Bluestem (BS) 2.3 62.8 31.2 6.1 2.2 60.0 32.8 6.3 2.1 59.5 33.8 6.6
Panicgrass (PG) 3.9 69.7 22.9 7.4 -- -- -- -- -- -- -- --
Gamagrass (GG) 2.9 64.4 28.2 7.4 2.9 64.9 28.1 6.9 -- -- -- --
Switchgrass (SGL) 4.4 71.7 21.6 6.7 4.1 70.1 22.9 7.0 4.1 70.5 22.8 6.6
Switchgrass (SGU) 4.6 73.0 20.3 6.8 -- -- -- -- -- -- -- --
Height:
Short -- -- -- -- -- -- -- -- 2.68 60.18 32.98 6.98
Medium -- -- -- -- 2.77 61.47 31.97 6.77 2.6 60.0 33.2 6.8
Tall 3.36 65.96 27.36 6.86 2.9 63.1 30.2 6.7 2.8 62.7 30.9 6.4
Significance (P):
Forage (F): <0.01 <0.01 <0.01 0.80 <0.01 0.01 <0.01 0.70 <0.01 0.46 <0.01 0.87
BG vs. Others <0.01 <0.01 <0.01 0.77 0.01 <0.01 <0.01 0.75 0.01 0.01 <0.01 0.62
(BS + PG) vs. (GG + SG) 0.01 0.05 0.01 0.74 -- -- -- -- -- -- -- --
BS vs. PG <0.01 0.02 <0.01 0.24 -- -- -- -- -- -- -- --
GG vs. (SGL + SGU) <0.01 <0.01 <0.01 0.49 -- -- -- -- -- -- -- --
SGL vs. SGU 0.67 0.61 0.37 0.95 -- -- -- -- -- -- -- --
Height (Ht): -- -- -- -- 0.26 0.45 0.38 0.95 0.63 0.46 0.43 0.60
Linear -- -- -- -- -- -- -- -- 0.50 0.30 0.31 0.33
Lack of Fit -- -- -- -- -- -- -- -- 0.51 0.50 0.44 0.84
F x Ht -- -- -- -- 0.51 0.84 0.90 0.63 0.83 0.83 0.88 0.32
1 L = >1.7 mm; M = <1.7 and > 0.5 mm; S = < 0.5mm.
2 All values are the average of two defoliations, and two masticate subsamples at each defoliation.
3 Mean of three years and three replicates (n = 9).
4 Mean of two heights, three years, and three replicates (n = 18).
5 Mean of three heights, three years, and three replicates (n = 27).
6 Mean of six forages, three years, and three replicates (n = 54).
7 Mean of four forages, three years, and three replicates (n = 36).
8 Mean of three forages, three years, and three replicates (n = 27).

Table 13. Whole-masticate median particle size (PS) and proportion of masticate in particle-size classes1 of large (L), medium (M), and small (S), data sets 4 and 5 (dry matter basis).
Treatment Set 42 Set 52
Particle-Size Class Particle-Size Class
PS L M S PS L M S
mm --------------- % --------------- mm --------------- % ---------------
Forage:
Bermudagrass (BG) 1.83 51.43 41.93 6.63 1.84 51.54 41.74 6.94
Bluestem (BS) 2.1 58.9 35.1 6.0 2.0 56.9 36.5 6.7
Panicgrass (PG) 4.3 72.2 21.5 6.3 4.0 70.7 22.8 6.5
Gamagrass (GG) 2.9 65.1 28.4 6.5 -- -- -- --
Switchgrass (SGL) 3.9 69.5 23.8 6.7 3.8 69.3 24.2 6.5
Switchgrass (SGU) 4.7 75.0 20.0 5.0 4.2 73.3 21.5 5.2
Height:
Short -- -- -- -- 2.76 62.26 31.16 6.86
Medium 3.25 64.35 29.65 6.15 3.3 64.2 29.7 6.1
Tall 3.4 66.5 27.3 6.3 3.5 66.7 27.2 6.2
Significance (P):
Forage (F): 0.01 0.01 <0.01 0.47 0.01 0.01 <0.01 0.20
BG vs. Others <0.01 <0.01 <0.01 0.46 <0.01 <0.01 <0.01 0.24
(BS + PG) vs. (GG + SG) 0.09 0.12 0.07 0.88 0.02 0.02 0.01 0.16
BS vs. PG <0.01 0.07 <0.01 0.80 0.01 0.01 <0.01 0.80
GG vs. (SGL + SGU) 0.02 0.67 0.05 0.43 -- -- -- --
SGL vs. SGU 0.29 0.18 0.23 0.11 0.34 0.22 0.28 0.08
Height (Ht): 0.32 0.32 0.20 0.78 0.06 0.15 0.11 0.32
Linear -- -- -- -- 0.03 0.06 0.04 0.21
Lack of Fit -- -- -- -- 0.57 0.89 0.69 0.39
F x Ht 0.86 0.84 0.84 0.86 0.69 0.84 0.82 0.67
1 L = > 1.7 mm; M = < 1.7 mm and < 0.5 mm; S = < 0.5mm.
2 All values are the average of two defoliations, and two masticate subsamples at each defoliation.
3 Mean of two heights, two years, and three replicates (n = 12).
4 Mean of three heights, two years, and three replicates (n = 18).
5 Mean of six forages, two years, and three replicates (n = 36).
6 Mean of five forages, two years, and three replicates (n = 30).

Separating masticates into large, medium, and small particle-size classes, showed bermudagrass to generally have the least proportion of large particles and the greatest proportion of medium particles (Tables 12 and 13). Whereas the Panicum types (panicgrass and switchgrass) generally had the greater proportion of large particles and the least of medium particles. The proportions of small particles were generally similar among masticates of all the forages. The noted exception is gamagrass, which had the greatest proportion of small particles.

It is noteworthy that neither the median particle size nor the particle-size classes of masticates were altered by forage height, despite differences in their nutritive values.

Experiment 2

The greater number of defoliations during the season occurred for the Short treatment, as noted in Experiment 1, averaging 7.5 compared with 6.3 defoliations for the Tall treatment (Table 14). The three lowland cultivars (Alamo, BoMaster, and Performer) were defoliated, on average, a similar number of times—ranging from 7.3 to 7.5. The frequency of defoliations was influenced by growing conditions. Because Year 1 had a more favorable growing season than Year 2, the lowland cultivars were able to exhibit their growth potential, averaging 10.3 defoliations for the Short treatment and 8.3 for the Tall (Appendix Table 2). This compares with only five to six defoliations for Cave-in Rock. In Year 2, under more droughty conditions, all four cultivars were defoliated similarly, ranging from four to six times, with little difference in defoliation frequencies among defoliation heights.



Table 14. Average defoliation (DEF) number, extended height (ExHt), bulk height (BkHt), herbage mass (HM), and forage grazed (GR) including HM and stand scores post-experiment.
Treatment DEF Before After Post Exp.1
ExHt BkHt HM2 BkHt GR2 HM Stand
No. -- lb/acre -- inches inches -- lb/acre -- %
Cultivar:
Cave-in-Rock (CIR) 5.0 22.63 6.73 40803 4.33 19153 8644 40.44
Alamo (ALA) 7.5 22.0 7.2 5490 5.8 2625 1569 58.7
BoMaster (BOM) 7.7 21.8 6.5 4685 5.1 2069 1187 38.7
Performer (PER) 7.3 21.6 6.4 4690 5.1 1660 1109 39.4
Height5:
Short 7.5 19.66 5.76 37426 4.36 18016 8927 32.87
Tall 6.3 25.6 7.7 5731 5.9 2333 1472 55.6
Significance (P):
Cultivar: -- 0.33 0.03 0.21 <0.01 0.80 0.43 0.41
CIR vs. Others -- 0.09 0.87 0.12 <0.01 0.82 0.23 0.61
PER vs. (ALA + BOM) -- 0.97 0.16 0.41 0.10 0.94 0.68 0.39
ALA vs. BOM -- 0.53 0.01 0.20 0.01 0.40 0.29 0.18
Defoliation (DEF) -- <0.01 <0.01 0.01 <0.01 0.35 <0.01 <0.01
Cultivar x DEF -- 0.19 0.93 0.77 0.46 0.80 0.64 0.79
1 Evaluated May 6 after termination of the experiment.
2 Oven dry-matter basis.
3 Each value is the average of multiple estimates and the mean of two heights, two years, and four replicates (n = 16).
4 Each value is the average of multiple estimates and the mean of two heights, and four replicates (n = 8).
5 See Materials and Methods for targeted heights.
6 Each value is the average of multiple estimates and the mean of four cultivars, two years, and four replicates (n = 32).
7 Each value is the average of multiple estimates and the mean of four cultivars, and four replicates (n = 16).

Characteristics of the forages evaluated differed, and differences were of similar magnitude among cultivars (no significant cultivar × defoliation interaction). As expected, extended canopy height and bulk height differed between the defoliation heights prior to grazing. Also, the bulk height differed between Alamo and BoMaster, with BoMaster least (Table 14). Herbage mass at offer was also similar among cultivars, averaging 4,736 lb/acre, with the Short herbage mass averaging lesser than the Tall (3,742 vs. 5,731 lb/acre). It is noteworthy that prior to grazing, the nutritive values among the four cultivars were generally similar (Table 15). The only exception was CP concentration, which was greater in forage from the Short compared with forage from the Tall defoliation heights. This is consistent with the similarity among cultivars in the proportion of leaf and stem before defoliation and the greater proportion of leaf and lesser proportion of stem in the Short vs. the Tall defoliation treatment (Table 16). Before defoliation, the leaf proportion averaged 48.3% and the stem proportion averaged 44.3% for the cultivars, whereas the leaf proportion was 52.4% for the Short defoliation and the stem proportion was 47.6% for the Tall defoliation. Any differences noted in leaf and stem proportions before defoliation were essentially removed by defoliation (see Prop–A, Table 16).



Table 15. Nutritive value1 of herbage mass before and after grazing (dry matter basis).
Treatment ITOD CP NDF ADF CELL Lignin
Before After Before After Before After Before After Before Before
------------------------------------------- % ------------------------------------------------
Cultivar2:
Cave-in-Rock (CIR) 73.0 71.6 11.2 10.4 62.5 73.7 32.6 39.4 34.3 3.80
Alamo (ALA) 79.0 72.9 13.5 10.5 71.1 71.6 35.5 37.4 32.1 3.44
BoMaster (BOM) 81.0 74.7 14.3 11.3 72.2 72.6 36.4 38.0 32.9 3.49
Performer (PER) 81.9 76.7 14.9 11.7 71.0 71.2 35.6 37.7 32.5 3.29
Defoliation3:
Short 83.0 75.4 15.1 11.8 68.5 71.0 34.2 37.0 33.7 3.39
Tall 74.4 72.6 11.8 10.1 69.9 73.5 32.7 39.1 32.2 3.62
Significance (P):
Cultivar: 0.47 0.31 0.28 0.31 0.53 0.09 0.70 0.26 0.97 0.41
CIR vs. Others 0.18 0.19 0.10 0.26 0.20 0.04 0.31 0.09 0.68 0.16
PER vs. (ALA + BOM) 0.91 0.97 0.96 0.78 0.85 0.13 0.80 0.55 0.89 0.63
ALA vs. BOM 0.62 0.20 0.47 0.15 0.99 0.55 0.98 0.87 0.93 0.60
Defoliation (DEF) 0.08 0.13 0.01 0.01 0.68 <0.01 0.30 <0.01 0.63 0.28
Cultivar x DEF 0.65 0.89 0.59 0.08 0.95 0.28 0.93 0.74 0.39 0.62
1 ITOD = in vitro true organic matter disappearance; CP = crude protein; NDF = neutral detergent fiber; ADF = acid detergent fiber; CELL = Cellulose.
2 Each value is the average of multiple samples and the mean of two defoliations, two years, and four replicates (n=16).
3 Each value is the average of multiple samples and the mean of four cultivars, two years, and four replicates (n=32).


Table 16. The proportion of leaf and stem before (Prop-B) and after (Prop-A) defoliation (dry matter basis), and their nutritive value1 before defoliation (organic matter basis).
Treatment Leaf Stem
Prop-B Prop-A ITOD CP NDF Prop-B Prop-A ITOD CP NDF
------------------------------------------- % ------------------------------------------------
Cultivar2:
Cave-in-Rock (CIR) 49.63 21.2 85.6 17.3 68.3 43.6 62.6 74.2 9.5 76.5
Alamo (ALA) 48.4 21.8 86.6 17.8 68.8 43.2 64.0 73.2 9.5 74.0
BoMaster (BOM) 47.5 19.1 88.4 18.5 69.6 45.8 67.7 75.1 10.4 75.0
Performer (PER) 47.8 18.5 88.5 19.1 68.5 44.4 69.0 77.2 10.9 73.8
Defoliation3:
Short 52.4 20.5 89.6 19.5 68.8 40.9 65.0 77.7 11.4 73.8
Tall 44.3 19.8 85.0 16.9 68.8 47.6 66.6 72.1 8.8 75.8
Significance (P):
Cultivar: 0.73 0.44 0.66 0.51 0.94 0.53 0.54 0.43 0.15 0.43
CIR vs. Others 0.35 0.46 0.37 0.29 0.75 0.59 0.33 0.63 0.17 0.18
PER vs. (ALA + BOM) 0.76 0.59 0.73 0.99 0.67 0.27 0.79 0.95 0.67 0.46
ALA vs. BOM 0.77 0.21 0.51 0.34 0.91 0.53 0.35 0.16 0.07 0.89
Defoliation (DEF) <0.01 0.60 0.06 0.01 0.99 <0.01 0.39 0.02 <0.01 0.04
Cultivar x DEF 0.25 0.29 0.76 0.67 0.86 0.18 0.53 0.97 0.22 0.40
1 ITOD = in vitro true organic matter disappearance; CP = crude protein; NDF = neutral detergent fiber.
2 Each value is the average of multiple samples and the mean of two defoliations, two years, and four replicates (n = 16).
3 Each value is the average of multiple samples and the mean of four cultivars, two years, and four replicates (n = 32).

The diet selected by steers was apparently masticated similarly as median particle sizes were similar among cultivars and between heights at defoliation averaging, overall, 3.55 mm (Table 17). Further, we detected no differences among cultivars or between defoliation intensity in the masticate particle-size classes with large particles averaging 71.5% of the dry matter, followed by medium-sized particles at 21.7% and small particles averaging 6.8%. The masticate ITOD approached being significantly (P = 0.06) different among cultivars. Masticate from Alamo was least in ITOD and different from BoMaster. Performer had the greatest ITOD, but not different from the other lowland cultivars. As expected, masticate from forage offered in the Short treatment was greatest in ITOD, averaging 88.0% compared with 86.9% for masticate from the Tall defoliation treatment. The CP, NDF, and ADF were generally not altered by cultivar or by defoliation intensity averaging 15.9% CP, 61.3% NDF, and 30.9% ADF. A significant cultivar ×defoliation interaction was noted for ADF and associated with small crossovers and considered of little biological importance.


Table 17. Median particle size (MPS), particle-size (PS) classes, and nutritive value1 of whole masticate (dry matter basis).
Treatment MPS PS Classes2 Nutritive Value
Large Medium Small ITOD CP NDF ADF
mm ----------------------------------------------------- % ----------------------------------------------------------
Cultivar3:
Cave-in-Rock (CIR) 3.39 70.7 22.5 6.9 87.4 15.0 59.7 30.4
Alamo (ALA) 3.46 69.8 22.9 7.3 86.0 16.3 62.7 31.5
BoMaster (BOM) 3.97 74.4 19.7 5.9 87.6 15.8 61.7 31.1
Performer (PER) 3.41 71.1 21.8 7.0 88.7 16.7 61.1 30.7
Defoliation4:
Short 3.61 72.0 21.3 6.7 88.0 16.3 60.8 30.6
Tall 3.50 71.0 22.1 6.8 86.9 15.6 61.8 31.3
Significance (P):
Cultivar: 0.73 0.60 0.57 0.69 0.06 0.53 0.20 0.28
CIR vs. Others 0.67 0.70 0.62 0.89 0.98 0.25 0.09 0.17
PER vs. (ALA + BOM) 0.36 0.27 0.26 0.31 0.52 0.52 0.83 0.95
ALA vs. BOM 0.93 0.72 0.66 0.85 0.02 0.72 0.21 0.18
Defoliation (DEF) 0.55 0.28 0.33 0.70 0.03 0.38 0.25 0.09
Cultivar x DEF 0.37 0.89 0.94 0.79 0.09 0.16 0.11 0.05
1 ITOD = in vitro true organic matter disappearance; CP = crude protein; NDF = neutral detergent fiber; ADF = acid detergent fiber.
2 Large = > 1.7 mm; Medium = < 1.7 and < 0.5 mm; Small = < 0.5 mm.
3 Each value is the average of multiple samples and the mean of two defoliations, two years, and four replicates (n = 16).
4 Each value is the average of multiple samples and the mean of four cultivars, two years, and four replicates (n = 32).

Assessment of canopies following grazing reveals the extent of selective grazing. The leaf proportion after grazing averaged only 20.1% compared to the 50.2% before grazing (Table 16). On the other hand, the stem proportion increased to 65.8% from a before grazing level of 44.3%. The differences in leaf and stem proportions noted between defoliation treatments before grazing were essentially eliminated during grazing. The reduction in leaf proportion and increase in stem proportion is also reflected in the nutritive value of the forage after defoliation with reductions in both ITOD and crude protein concentrations.

Examination of the stands in May of Year 3 (post-experiment), after two years of defoliation, reveals that herbage mass (HM) was the least for Cave-in-Rock, but differences in favor of the lowland types were not significantly greater (Table 14). The influence of more frequent defoliation, as noted for the Short treatment, resulted in lesser dry matter production, with the HM averaging 892 lb/acre compared with 1472 lb/acre for the Tall defoliation treatment. Stand scores (as percentages of ground occupancy) were not different among cultivars, but stand scores were altered by defoliation intensity, with the Short defoliation averaging only 32.8% of ground occupancy compared with 55.6% when defoliated less frequently. The defoliation frequencies and associated dry matter yield and ground occupancy percentage for each cultivar by defoliation height and year are presented in Appendix Table 2.

Summary

Experiment 1

  • Before defoliation, all forages within each of the five data sets averaged similar in herbage mass (lb/acre): 4401 in data set 1, 3891 in data set 2, 3387 in data set 3, 3844 in data set 4, and 3027 in data set 5.
  • The proportion of leaf and stem of the herbage mass on-offer varied among forages in data sets 1, 2, and 4, but not in data sets 3 and 5.
  • Forages compared and defoliation treatments imposed generally resulted in canopy fractions (leaf, stem, and dead) that differed in nutritive value (namely ITOD, CP, and NDF).
  • One or more constituents of the nutritive value (ITOD, CP, and NDF) of the diet selected by steers was altered by either forage species (depending on data set) or by defoliation treatment when all three treatments were evaluated.
  • The diet selected by steers from among the forages within a data set were generally masticated differently, with bermudagrass having the least median particle size of 1.8 to 1.9 mm and panicgrass and the switchgrasses greatest at 3.7 to 4.7 mm, with little difference associated with treatment height.
  • The proportion of the masticate consisting of large and medium particle-size classes showed similar responses within data sets as noted for median particle size, with the proportion of small particles remaining similar.
  • The nutritive value of the whole masticate reveals that the diet selected from among the forages within a data set generally differed. Diets selected from bermudagrass and bluestem were somewhat inferior (lesser ITOD and greater NDF) to the other forage species. This difference may be reflected in daily animal performance.

Experiment 2

  • Before defoliation the herbage mass weights of all four cultivars were similar, averaging 4,736 lb/acre.
  • The nutritive value of the forage on-offer was generally similar among cultivars, but was greater for the Short compared with the Tall defoliation treatments.
  • The proportion of leaf and stem before defoliation was similar among cultivars but generally differed between defoliation heights, with Short forage being most leafy.
  • The nutritive value of the leaf fraction was similar among cultivars and defoliation height, except for crude protein, which was greatest in leaf from the Short defoliation treatment.
  • The diet selected by steers from among the four cultivars was masticated similarly with a median particle size of 3.55 mm and generally similar in nutritive value.
  • Defoliation height altered the diet selected. Masticate from the Short defoliation was greatest in in vitro true organic matter disappearance.
  • After defoliation, bulk height was least for Cave-in-Rock—averaging 4.3 inches, compared with 5.3 inches for the lowland cultivars. But forage removed by grazing was similar among cultivars, averaging 2,067 lb/acre.
  • The diet selection exhibited by steers was generally similar among the four cultivars, and the less mature forage provided some advantage in nutritive value. This finding indicates that differences in yield potential may be the key to choosing among these cultivars for their use in animal production systems.

References

Burns, J.C., and D.S. Fisher. 2013. Steer performance and pasture productivity among five perennial warm-season grasses. Agron. J. 105:113-123.

Burns, J.C., D.S. Fisher, and K.R. Pond. 2012. Steer performance and pasture productivity of a tall fescue-bermudagrass system compared with yellow bluestem and coastal panicgrass. The Professional Anim. Scientist 28:272-283.

Burns, J.C., D.S. Fisher, and D.H. Timothy. 2009. Comparison of dry matter intake and digestion of several switchgrass cultivars and germplasms of the lowland ecotype with an upland ecotype. In Switchgrass: Establishment, management, yield, nutritive value, and utilization, pp. 63-69. Tech. Bull. 326. NC State University, NC Agricultural Research Service, Raleigh.

Burns, J.C., E.B. Godshalk, and D.H. Timothy. 2008a. Registration of ‘Performer’ switchgrass. Journal Plant Registrations 2:29-30.

Burns, J.C., E.B. Godshalk, and D.H. Timothy. 2008b. Registration of ‘BoMaster’ switchgrass. Journal Plant Registrations 2:31-32.

Appendix Tables


Appendix Table 1. Forage height (Ht), herbage mass (HM), and forage grazed (FG) at each defoliation (dry mater basis).

Treatment Set 11 Set 21 Set 31 Set 42 Set 52
Forage Ht3 Ht HM FG Ht HM FG Ht HM FG Ht HM FG Ht HM FG
inches - lb/acre - inches - lb/acre - inches - lb/acre - inches - lb/acre - inches - lb/acre -
Bermudagrass S -- -- -- -- -- -- 9.0 2,934 1,465 -- -- -- 8.8 2,589 1,483
M -- -- -- 12.3 4,121 1,590 12.3 4,121 1,590 12.2 3,648 1,688 12.2 3,648 1,688
T 14.5 4,717 2,493 14.5 4,717 2,493 14.5 4,717 2,493 13.9 4,336 2,750 13.9 4,337 2,750
Bluestem S -- -- -- -- -- -- 12.9 2,046 951 -- -- -- 12.4 1,894 858
M -- -- -- 17.2 3,028 1,419 17.2 3,028 1,419 17.0 3,134 1,278 17.0 3,134 1,278
T 22.7 4,049 2,354 22.7 4,049 2,354 22.7 4,049 2,354 21.7 4,083 2,373 21.7 4,083 2,373
Panicgrass S -- -- -- -- -- -- -- -- -- -- -- -- 13.0 1,313 549
M -- -- -- -- -- -- -- -- -- 21.8 2,277 990 21.8 2,277 990
T 30.1 4,035 1,869 -- -- -- -- -- -- 29.9 4,103 2,316 29.9 4,103 2,316
Gamagrass S -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
M -- -- -- 20.6 2,497 914 -- -- -- 18.2 2,146 632 -- -- --
T 33.1 4,955 1,811 33.1 4,955 1,811 -- -- -- 31.8 3,515 953 -- -- --
Switchgrass S -- -- -- -- -- -- 15.5 1,828 595 -- -- -- 16.0 2,015 609
(lowland) M -- -- -- 23.0 3,082 996 23.0 3,082 997 22.3 3,072 1,103 22.3 3,072 1,103
T 31.1 4,682 2,498 31.1 4,682 2,498 31.1 4,682 2,498 31.3 4,769 2,897 31.3 4,769 2,897
Switchgrass S -- -- -- -- -- -- -- -- -- -- -- -- 13.9 1,393 868
(upland) M -- -- -- -- -- -- -- -- -- 21.8 2,603 1,101 21.8 2,603 1,101
T 29.4 3,970 2,015 -- -- -- -- -- -- 30.0 4,172 2,267 30.0 4,172 2,267
1 Each value is the average of multiple estimates and the mean of three years, and three replicates (n=9).
2 Each value is the average of multiple estimates and the mean of two years, and three replicates (n=6).
3 S = Short; M = Medium; T = Tall (see Materials and Methods, Experiment 1, for target heights).

Appendix Table 2. Number of defoliations by year and post experiment dry matter (DM) yield, and stand occupancy scores.

Treatment Defoliation1 Post Experiment2
Year Yield Stand
Forage Height3 1 2 DM Change Score Change
lb/acre ------------ % ------------
Cave-in-Rock S 6 5 4654 22
T 5 4 1264 +172 55 +150
Alamo S 11 6 1357 49
T 8 5 1781 +31 69 +41
BoMaster S 10 6 818 28
T 9 6 1556 +90 50 +79
Performer S 10 6 929 30
T 8 5 1288 +39 49 +63
1 Defoliations were initiated April 24 in Year 1 and May 5 in Year 2.
2 Yield estimates and stand counts were taken May 6, Year 3.
3 S = Short; T = Tall (see Materials and Methods, Experiment 2, for target heights).
4 Each value is the mean of four replicates.

Authors:

Professor
Crop Science and Animal Science
Statistician
Syngenta Biotechnology, Inc.
Research Analyst
Crop Science

Publication date: May 6, 2015
TB-342

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