As it is well known, barber pole larvae show increased resistance to commercial anthelmintics drenched to small ruminant livestock, and producers are looking for other alternatives. What about bypassing the livestock entirely and applying a larvicidal product directly on the pasture itself?
Laboratory studies we conducted at North Carolina State University showed that 96.6% L3 barber pole larvae were not moving or dead when immersed in solutions of liquid nitrogen fertilizer (containing 32.7% urea and 42.2% ammonium nitrate (21.1% ammonium and 21.1% nitrate), corresponding to field applications of 30 lb of nitrogen per acre. Another laboratory study showed that a 10% solution of household bleach (5.25% sodium hypochlorite) resulted in 99.1% of L3 larvae not moving or dead. Higher solutions of household bleach caused lysis (disintegration) of the larvae.
The larvicidal action of liquid nitrogen fertilizer has been attributed to the toxic qualities of ammonia and nitrate, as well as to the increased osmotic pressure created with an accompanying water loss when in direct contact with L3 larvae. Do you remember as a child how water leaked out of slugs when dribbling table salt on them?
One agricultural practice recommended by North Carolina Cooperative Extension is to apply 50 lb of nitrogen fertilizer per acre to cool-season grasses such as fescue and orchardgrass both in early spring and late summer, and one or several applications during summer for warm-season grasses such as bermudagrass, millet and sorghum. So, could we pop two balloons with one dart by fertilizing pastures with liquid nitrogen fertilizer to promote forage growth and at the same time reducing pasture nematode larvae population, their subsequent ingestion by grazing animals and ultimately reducing gastrointestinal parasite loads?
We conducted 3 experiments to test this hypothesis on predominantly tall fescue pastures, one in spring and two in fall. In each of these experiments, a field was grazed by does heavily infected with gastrointestinal parasites for 21 to 26 days until the ground was well covered by fecal pellets. The goats were then removed from the field, which was immediately flail-chopped (forage was cut and moved off-site) to a height of 5 inches. Then, according to experimental principles that took into account differences in slope, soil, etc., the fields were divided into several sub-pastures so that each experimental treatment was replicated 3 or 4 times. Sub-pastures within each replication were then randomly assigned to be either treated with liquid nitrogen fertilizer or untreated (control). Granular urea was applied to the untreated (control) sub-pastures to ensure that forage would grow at an equal rate in all sub-pastures and because granular urea has a very limited negative effect of L3 larvae survival. As infective L3 larvae migrate up the blades of forage crops during mornings and evenings with the dew, we sprayed pastures with liquid nitrogen fertilizer starting at 6:30 AM or after 4PM depending on weather conditions. Large amounts of liquid nitrogen can be lost from evaporation to the atmosphere if applied under full sun, and may also burn the tip of leaves.
Five days after applying liquid nitrogen or urea, ‘clean’ goats were randomly assigned to each plot and control-grazed. Why the 5-day delay? Because we were concerned with nitrate poisoning if goats had been turned immediately into the sub-pastures that had been sprayed with liquid nitrogen. Fecal egg counts were performed on all goats as they were entering the sub-pastures to get a baseline count. We also took blood samples to determine packed cell volume (cellular constituents of whole blood), and FAMACHA-scored the lower eyelids of each goat. All sampling and scoring took place on a weekly basis.
Results and Discussion
Results from Expt. 1 showed promise as fecal egg counts, starting at a baseline average count of 136 eggs per gram of feces on 7 May, were suppressed for 7 weeks in goats grazed on the liquid nitrogen treated plots. At the end of 7 weeks (25 June), goats grazed on the liquid nitrogen treated sub-pastures showed counts of 350 eggs per gram of feces compared to goats grazed on the control plots with 775 eggs per gram of feces. During the contamination period, no more than 3 consecutive days passed without precipitation. The average maximum and minimum temperatures during the contamination period were 70°F and 48°F, respectively, all ideal environmental conditions. The average maximum temperature fell within the range of temperatures where the majority of the larvae would be found on grass leaves. Therefore, the plots were sprayed with liquid nitrogen fertilizer when the larvae would be on the leaf blades and would be in direct contact with liquid nitrogen, rather than being buried in the forage mat or soil for protection against environmental stresses.
No differences were observed in fecal egg counts in Expt. 2, starting with a baseline average count of 14 eggs per gram of feces on 23 September. On 30 September and 2 October, fecal counts averaged 233 and 626 eggs per gram of feces, respectively. Thereafter, fecal counts increased dramatically to 1789 (28 October) and 2401 (4 November) eggs per gram of feces. Conversely, no change and difference in packed cell volume were observed throughout the study, averaging 28%. During Expt. 2, the average maximum temperature was 87.8°F. Dry weather lasted from August when the field was contaminated until 28 September, followed by 4.4 inches of intermittent rainfall from 29 September through 8 October. In addition, pastures were irrigated 6 times starting on 28 September until the end of the trial to keep the soil moist and grass growing. By the time the sub-pastures were sprayed with liquid nitrogen fertilizer on 11 September, larvae had possibly migrated down to shady spots at the base of plants, or were buried in the forage or soil for protection against desiccation. In that scenario, the liquid nitrogen would not have made direct contact with the larvae. Another reason for a low fecal count followed by a dramatic increase starting between 21 and 28 October could be due to the eggs staying protected in the fecal pellets until outside conditions, such as adequate moisture, became favorable for hatching, molting and eventually migrating onto leaf blades as L3 larvae to continue their life cycle. The number of larvae emerging would be large due to the accumulation of feces on the ground during the drought period. By the time of this dramatic increase, the effects of liquid nitrogen would not be apparent because it works by direct contact, thus its effect is short-lived.
In Expt. 3, treating plots with 65 lb of liquid nitrogen per acre had no effect on fecal counts. Baseline fecal counts per gram of feces were 0 (20 September), and increased in a linear fashion to an average of 528 on the last sampling date (28 October). No difference in packed cell volume was observed during the study, averaging 28.3% across sampling date and treatment. The average minimum and maximum daily temperatures during the trial were 51°F and 72°F, respectively. The average amount of precipitation that is considered “normal” for that period is 4.2 inches. However, 15.7 inches of precipitation fell during the trial, including 6.5 inches during a hurricane on 15 and 16 September, one day after contaminating and spraying the pastures with liquid nitrogen fertilizer. Too much rainfall can move larvae onto surrounding herbage or carry them and the fecal pellets away in the runoff, thus the larvae could have been very easily washed from one plot to another or off the entire area of research. The movement of larvae off the entire research area could help explain the low fecal counts for the entirety of the trial.
A 4th experiment was conducted on bermudagrass during the summer. The differences in preparing the field compared to the previous 3 experiments were the following: the field was only contaminated for 11 days, forage was flail-chopped 3 days later, and liquid nitrogen fertilizer was only applied 11 days later. A tropical storm that dumped 6 inches of rain on 13 June during the contamination phase did not seem to have any effect as the field was really flat, and bermudagrass formed a thick thatch. Conversely, so much moisture may have speeded up the hatching and molting of larvae. Application of liquid nitrogen fertilizer had on effect on fecal counts. At the start of the experiment, fecal counts averaged 26, 65 on day 7, 702 on day 14, 861 on day 21, and increased up to 2541 eggs per gram of feces 29 days after the first sampling. FAMACHA scores remained constant during the first 3 sampling dates, averaging 1.8, then increased in a linear fashion to 3.2 by the end of the study. Conversely, PCV were similar during the first 2 sampling dates (average: 30.9%), and progressively decreased, averaging 18.9% at the completion of the study. The observed FAMACHA and PCV trends toward the end of the experiment are indicative of progressively higher gastrointestinal worm loads. The observed FAMACHA and PCV trends toward the end of the experiment are indicative of progressively higher gastrointestinal worm loads. The majority of the goats started to developed intermandibular edema (bottle jaw) by day 29, a direct result of low packed cell volume, therefore the decision was taken to end the study on that date. As the density of fecal pellets on the field was very high, the quantity of larvae incapacitated or ‘killed’ by the application of liquid nitrogen was probably large. Nevertheless, because liquid nitrogen fertilizer only acts on contact and as its action is short-lived, a large number of larvae probably hatched and molted into L3 following the loss of liquid nitrogen effectiveness.
The Bottom Line
As you have read above, nothing is simple when dealing with biology and dynamic environmental conditions that one cannot control.
- Results from experiments conducted in the laboratory do not necessarily translate into the same outcome in field situations. The field experiments described above necessitated a large amount of coordination, resources and labor, the results were obviously disappointing, and many questions remain unanswered.
- The main limitation of liquid nitrogen fertilizer is that it kills or incapacitates larvae on contact and that its effectiveness is very short-lived. In addition, as larvae can bury in the forage mat or the soil, or stay at the base of forage plants for protection from desiccation, it is important to spray liquid nitrogen very early in the morning when the dew is still present, or late in the day under cloudy skies, on forage that is not more than 5 inches in height. Therefore, another limitation is owning or having access to a flail-chopper, a tractor and a boom-sprayer. Finally, not everybody has easy access to a source of liquid nitrogen fertilizer.
- Adequate temperature and moisture are necessary for larvae to hatch, molt and migrate onto the leaves of forage crops. In the absence of rainfall during the contamination period, only a minimum number of larvae will hatch and molt, whereas the majority will stay protected in the fecal pellets and wait for outside conditions that will favor their survival.
- Spraying liquid nitrogen on pastures during dry conditions will be less effective or not effective at all due to the combination of the short effectiveness of liquid nitrogen and the low number of larvae that hatched, molted and migrated to grass blades. In addition, liquid nitrogen will have no effect on eggs still in the fecal pellets.
- Too much rain on a field having a certain slope may mean that most of the feces and larvae could be washed away and accumulate on a field located downslope. In turn that field, that may belong to you or your neighbor, could become heavily contaminated without goats having grazed it.
- Should we have used another approach, such as waiting for a longer period of time between contamination and the spaying of liquid nitrogen fertilizer to give the majority of fecal eggs the opportunity to hatch and molt to achieve a better ‘kill’? Or, should we have used split applications to also achieve a better kill? Possibly! In the case of split applications, fast forage growth may decrease the direct contct of nitrogen fertilizer with the L3 larvae. Or should we have used applications of liquid nitrogen and in addition several separate applications of household bleach solutions?
- The objectives of the experiments described herein were never to pretend that liquid nitrogen be used as the sole source of a gastrointestinal parasite control program, but that hopefully it could be included as part of an integrated program. Environmental conditions and their interaction with forage growth and the dynamic life cycle of gastrointestinal nematodes represent a complex challenge that may greatly affect outcomes.
- Howell, J. M., J-M. Luginbuhl, M. J. Grice, K. L. Anderson, P. Arasu, and J. R. Flowers. 1999. Control of gastrointestinal parasite larvae of ruminant using nitrogen fertilizer, limestone and sodium hypochlorite solutions. Small Ruminant Research 32:197-204.
- Conrad, A. P. 2000. Field applications of liquid nitrogen fertilizer for controlling gastrointestinal parasites in meat goats. 2000. MS Thesis. North Carolina State University.
- Conrad, A. P., J-M. Luginbuhl, K. L. Anderson, J. P. Mueller, A. M. Zajac, and M. J. Grice. 2001. Field applications of liquid nitrogen fertilizer for controlling gastrointestinal parasites in meat goats. J. Anim. Sci. 79 (Suppl. 2):25.
- Luginbuhl, J-M., and H. M. Glennon. 2007. Field applications of liquid nitrogen fertilizer for controlling gastrointestinal parasites in weanling meat goats. J. Anim. Sci. 85 (Suppl. 2):33.
Publication date: April 10, 2017
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