Bad Combination for Heifers

ANGUSJournal ■ August 2008 I is hard enough breeding heifers under the best of conditions, so when heat stress and endophyte-infected fescue are added to the mix, reproductive systems, pregnancy rates and the long-term bottom line are all bound to suffer. Dave Patterson, University of Missouri Extension researcher and reproductive specialist, notes that reproductive performance is the most important economic trait in a beef cow herd, and anything a rancher can do to reduce his percentage of open and late-bred animals will pay off handsomely at sale time. He adds that this premise is particularly relevant to the breeding of heifers in today’s production environment, one which demands that cows conform to an increasingly narrow breeding window. “It is an issue of labor and economics,” he says, adding that if a heifer falls behind the herd in breeding there is a strong likelihood she will remain behind the herd in breeding back the rest of her productive life. So how does endophyte-infected fescue enter this critical equation? As early as 1986, researchers from the Alabama Agricultural Experiment Station in Auburn reported in their documented study, “Fescue Toxicity and Reproduction in Beef Heifers,” that weaned beef heifers who were assigned to pastures with low, medium or high levels of infection and received hay of similar infection levels during winter had decreased pregnancy rates as the infection level in the forage increased. These decreases in pregnancy rates could hardly be considered insignifi cant, with fi rsttime pregnancy rates dropping from 96% for heifers that consumed 0%-5% toxic fescue to 82% for animals with a diet of 25%-60% fescue to 55% for heifers that ate 80%-99% Researchers identify direct links between high ambient temperatures, the consumption of toxic fescue and impeded ovarian development in heifers.