334 The impacts of temperament and stress on reproductive efficiency in beef females.

Abstract Cattle temperament is classified as the behavioral response animals express when handled by humans. Such behavioral response is often classified as stress, since animals considered to have excitable temperament consistently have great circulating concentrations of cortisol, indicating a more activated hypothalamic-pituitary-adrenal axis. Noteworthy, beef females classified as having excitable temperament have decreased reproductive efficiency as evidenced by decreased pregnancy rates to the breeding season, often resulting in decreased calving rates and decreased weight of calves weaned per cow exposed when compared to adequate temperament cohorts. Subfertility is the main cause of economic loss for cow-calf operations and has been estimated to cost the American beef industry approximately $2.8 billion every year. While docility has been estimated to have low to moderate heritability, and expected progeny differences (EPDs) for docility traits are available, genetic selection for this trait would be slow, and more of a long-term approach to improve temperament. Strategies aimed at improving environmental conditions and stressors have been explored and are efficient at improving temperament and reproductive efficiency of beef females. One strategy that has been explored is acclimation to human handling. Enrolling beef heifers into an acclimation protocol after weaning has resulted in decreased cortisol concentrations, hastened puberty, and a greater proportion of acclimated heifers that became pregnant earlier during their first breeding season when compared to non-acclimated cohorts. Estrous synchronization protocols (ES) followed by timed-artificial insemination (TAI) are a readily available technology to promote improved reproductive efficiency in cow-calf operations. While several factors influence TAI success, our research group has previously reported that heifers with excitable temperament have decreased fertility to TAI when compared to adequate temperament cohorts. Additionally, excitable heifers that failed to become pregnant with TAI had increased cortisol concentrations at TAI when compared to excitable heifers that became pregnant with TAI. Nevertheless, cortisol concentrations decreased for all heifers as the handling events of the ES progressed, indicating that heifers were acclimated to handling. More recently, our research group explored acclimating beef heifers during the handling events of the ES by exposing them through the handling facilities without individual restraint prior to each ES event. Results indicate that acclimated heifers had improved phenotypic measurements of temperament by termination of the ES and increased conception rates to TAI when compared with non-acclimated counterparts. While cattle temperament impacts reproductive efficiency of cow-calf operations, strategies to alleviate the detrimental effects of temperament on reproduction are efficient and should be further explored.