Pregnancy Loss in Beef Cattle
The United States has the world’s largest beef production industry, as the country is both the largest consumer and exporter of beef products (Gleason and White 2019; USDA-ERS 2023). Cow-calf operations are an essential portion of the beef industry, as they are the key component to supply the demand for beef products (Mejia Turcios 2022). An efficient cow-calf operation strives to produce a weaned calf yearly per cow and therefore has a calving interval closer to 12 months (Mejia Turcios 2022). However, maintaining this calving interval is challenging due to poor reproductive efficiency. A recent meta-analysis reported that, given one opportunity to become pregnant, a mature cow has a 48% chance of losing the pregnancy within the first 30 days of gestation (Reese et al. 2020). This early loss requires producers to make a greater investment in resources to ensure that cows will be pregnant by the end of the breeding season (Diskin and Kenny 2016). At the end of the breeding season, even if a large number of cows are pregnant, there is a decreased efficiency in cows that rebred later in the breeding season because those cows will wean younger and lighter calves. In addition, these cows will struggle to breed back because they will have less time to recover between calving and the following breeding season. Besides the financial burden, poor reproductive efficiency can lead to a 34% increase in water use, a 44% increase in land use, and a 39% increase in CO2 footprint per female that fails to reproduce yearly (Davis and White 2020; Baruselli et al. 2023). Collectively, decreased reproductive efficiency impairs the profitability, vitality, and sustainability of beef production systems.
Reproductive efficiency has the largest economic impact on cow-calf operations (Pohler et al. 2020). Several components go into maintaining increased reproductive efficiency, including genetics, nutrition, bull fertility, and overall health of the cow or heifer and the bull (Diskin and Kenny 2014). Nutrition is a crucial aspect of reproductive efficiency; both a surplus or a deficit of energy can lead to decreased pregnancy outcomes (Roche 2006). Therefore, adequate energy intake is needed for the growth and development of reproductive organs and the continuation of ovarian activity to support pregnancy (Rajendran et al. 2022). With this objective in mind, several cattle producers alter their feeding management to accommodate the increased nutritional requirements needed to support the cow and the embryo (Rajendran et al. 2022). Recently, lipids composed of monounsaturated and polyunsaturated fatty acids have been reported to be a key component in early embryonic development (Ribeiro 2018); therefore, supplementing lipids in the diet could contribute to improved reproductive efficiency in cow-calf operations by supporting early embryonic development.
During the first month of pregnancy, there is a period of exponential embryonic growth in which the embryo grows from 0.12 to almost 10 inches in size (Figure 1). This rapid growth occurs between days 15 and 18 of pregnancy, which is around the same time as maternal recognition of pregnancy (Mathew et al. 2022). This period is crucial, as it is the time when the growing embryo alerts the cow of the pregnancy, which prevents her from continuing her estrous cycle and allows the pregnancy to be maintained (Mathew et al. 2022). This communication is signaled by the secretion of interferon tau—the maternal recognition-of-pregnancy "messenger"—by the growing embryo (Bazer et al. 1997). Collectively, the amount of messenger the embryo secretes to alert the cow of the pregnancy depends on the length of the embryo; a bigger embryo translates into a better chance of the cow recognizing the pregnancy messenger.
Recently, it has been found that there is an increase in various lipids inside the uterine environment (the location where the embryo develops) near the period of exponential embryonic growth (Figure 1) (Ribeiro et al. 2016a). At the same time, the growing embryo also exhibits an increased uptake of these lipids (Ribeiro et al. 2016b). It is plausible that supplying lipids in the uterine environment when an embryo is growing could favor early embryonic growth and mitigate early pregnancy loss. To test this theory, we conducted an experiment to determine if the lipid content in the uterine environment could be altered by supplementing unsaturated fatty acids and choline in the diet of mature cows. Our goal was to provide unsaturated fatty acids and choline to be used as building blocks for lipid formation in the uterine lumen.
Figure 1. Embryonic development during the first 20 days of gestation. The contents of the highlighted box indicate the uterine environment between days 16 and 19 and consist of enzymes, cytokines, hormones, amino acids, fatty acids, and various types of phospholipids that will provide energy and building blocks for tissue formation.
Source: Megan Bahr.
Materials and Methods
To address this research question, we used 100 multiparous Angus cows. At the beginning of the experiment, cows were ranked by body condition score and days post-partum and randomly assigned to receive either (1) TARG: a supplement providing mostly rumen-inert monounsaturated and polyunsaturated fatty acids, plus rumen-protected choline (n = 50 cows) or (2) CON: a supplement providing mostly saturated fatty acids (n = 50 cows). All cows were fed the same base diet, which was a total mixed ration (TMR) containing predominantly corn silage and soybean meal. Figure 2 is a schematic of the experimental design. Supplementation was top-dressed on TMR from 30 days before timed artificial insemination (TAI) to 30 days after TAI. The reproductive management consisted of a 7-day Co-synch + CIDR protocol and TAI. Fourteen days after TAI, a uterine swab (cytobrush) was collected to identify the concentrations of metabolites (for example, fatty acids, phospholipids, and methyl donors) inside the uterus of the pregnant cows. These metabolites are important because they are the only source of nutrients to support early embryonic development and growth. On day 16 post-timed artificial insemination, we collected a sample of the uterine cells to determine if there were any changes in the expression of genes involved in regulating pregnancy recognition or lipid synthesis, metabolism, and transport. Some of these genes can reflect how the embryo communicates with the cow during the period of maternal recognition of pregnancy.
Figure 2. Dietary supplementation started on day -30. Estrus synchronization started on day -10. Timed artificial insemination occurred on day 0. A uterine sample (cytobrush) was collected on day 14 to analyze the concentration of metabolites in the uterine lumen and on day 16 to analyze the gene expression in endometrial cells.
Source: Megan Bahr.
Results and Conclusion
On day 14 post-timed artificial insemination, 23 metabolites had different concentrations between the two treatments, with the concentration of 21 metabolites being greater in the TARG supplementation strategy. The TARG treatment had an increased concentration of two fatty acids, docosahexaenoic acid (DHA) and linoleic acid. In the uterine environment of the cows fed the TARG treatment, there was also an increased concentration of choline, betaine, and seven phospholipids, including phosphatidylcholines. The results also showed an increased concentration of two different amino acids, serine and alanine. Figure 3 summarizes the findings of our experiment as a graphical abstract (the green text indicates where there was an increased concentration of metabolites or upregulation of the gene in the TARG treatment; red indicates a decreased concentration of metabolites or downregulation of the gene in the TARG treatment).
On day 16 post-timed artificial insemination, 379 genes had greater expression in the TARG treatment, and 39 genes had decreased expression in the TARG compared to the CON treatment. Genes involved in the production of long-chain fatty acids, such as DHA, were more highly expressed in the TARG treatment, as was a gene involved in the production of phosphatidylcholines. In addition, genes involved in the regulation of pregnancy were more highly expressed in the TARG treatment.
Our findings demonstrate the feasibility of altering the concentrations of several metabolites in the uterine environment, such as fatty acids and methyl donors, through a maternal dietary supplementation strategy. This study lays a foundation for further investigations during the first month of gestation and nutritional supplementation strategies to reduce the problem of early pregnancy loss. It is important to note that this was a terminal study in which overall pregnancy rates were not measured; therefore, a fertility study would need to be conducted to determine the overall effects this supplementation strategy would have on pregnancy rates.
Figure 3. The left side of the figure shows a variety of metabolites that changed in concentration between the two supplementation strategies on day 14 post-artificial insemination; the right shows different classes of genes (general function) and specific genes that were altered between the two strategies on day 16 post-artificial insemination.
Source: Megan Bahr
Acknowledgments
The authors would like to thank the staff at the Butner Beef Cattle Field Laboratory for their help with animal husbandry and assistance with this project.
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Publication date: March 18, 2026
AG-1004
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