Maintaining high levels of nutrition plays an important role in a cow’s reproductive performance, but recent research from two separate studies indicates that nutritional management immediately following artificial insemination have an impact on heifer reproductive efficiency. Results from the studies conducted at the University of Wyoming and Purdue University, and South Dakota State University and University of Minnesota were presented at the Range Beef Cow Symposium held in South Dakota in December.
According to the research paper accompanying the studies, many spring-born heifers are developed from weaning to breeding in a dry-lot system and fed a diet of forage and concentrate to gain approximately 1.5 pounds per day, with the goal of achieving 65 percent of estimated mature body weight at the time of breeding. Typically, immediately following AI, heifers are moved to pasture where they are allowed to eat spring forage. The researchers hypothesized that feeding high moisture pasture forage and limiting dry matter intake caused temporary weight loss during the critical stages of early embryonic development and maternal recognition of pregnancy. Further, they hypothesized that maintaining the same plane of nutrition for at least 25 days after breeding to ensure the embryo fully attaches to the uterus will increase first-service conception rates and improve herd fertility and longevity.
The first study, conducted at Purdue University and the University of Wyoming, examined the role of post-insemination nutrition on AI pregnancy rates in heifers. At locations at both universities, from weaning to breeding, heifers were fed a diet that resulted in approximately 1.5 pounds per day gain. Then, immediately following breeding, heifers were divided into three groups: 1) maintain pre-breeding plane of nutrition (GAIN); 2) 100 percent of maintenance requirements (MAINTAIN); and 3) 80 percent of maintenance requirements (LOSE). Heifers stayed on those diets for 21 days following AI. When comparing pregnancy rates of heifers at both locations, the results showed that heifers in the GAIN group had greater AI pregnancy rates compared to the MAINTAIN and LOSE groups, suggesting that failing to maintain the pre-breeding plane of nutrition following AI reduces the probability of AI pregnancy success.
The second study, conducted by South Dakota State University and the University of Minnesota’s North Central Research and Outreach Center, examined the direct effects of an immediate change in nutrition at insemination on embryonic development. At locations at both universities, all heifers were on a common diet from weaning to breeding and were estrous synchronized and artificially inseminated. Immediately following AI, heifers were divided into two groups at both universities: 1) half continued the pre-AI diet at 125 percent of maintenance requirements; and 2) half were fed at 50 percent of maintenance requirements. These dietary schedules were fed until embryo collection was done six days after AI. Results showed that nutrition restriction immediately following AI resulted in poorer quality embryos that were developmentally retarded as indicated by being at an earlier stage of development and having fewer blastomeres, suggesting that early embryo development is sensitive to immediate changes in nutrition.
While it is well established that maintaining a cow’s nutrition pre-partum and post-partum is critical to overall reproductive performance, these studies indicate that maintaining pre-breeding nutrition is critical immediately following breeding in heifers.
To read the full studies, click here.