046 Relationships among temperament, endocrinology, and reproductive soundness of performance-tested Angus bulls

Excitable cattle exhibit greater concentrations of cortisol than calm cattle, which can negatively impact an animal's reproductive performance. The aim of this study was to examine the relationships among temperament, endocrinology, and reproductive soundness of Angus bulls consigned to an 84-d post-weaning performance test. Bulls (n= 60; 263 ± 36 d of age) arrived at the University of Tennessee Bull Testing Station on d -14 and were housed in 6 pens based on age and weight. Pen scores (PS; 1 (calm) to 5 (excitable)) were assigned on d -1, 27, 55, and 83. Exit velocity (EV; m/s) was evaluated on d 0, 28, 56, and 84 and serum and hair samples were collected on the same days. All hair samples were collected from the same region on the bull. Breeding soundness exams were performed on d 84. Hair and serum samples were analyzed for testosterone and cortisol concentrations via ELISA and RIA, respectively. Bulls were categorized as PScalm (PS = 1 or 2) or PSexcitable (PS = 3 or 4) based on initial PS. Bulls were also categorized as EVcalm or EVexcitable based on the fastest 20 and slowest 20 initial EV. A mixed model ANOVA with repeated measures was performed (SAS 9.3). Scrotal circumference did not differ (P>0.10) between PScalm and PSexcitable or EVcalm and EVexcitable bulls. Cortisol and testosterone concentrations in serum and hair did not differ (P>0.05) between temperament categories, but day differences occurred. Hair testosterone concentrations were the greatest (P<0.01) on d 0, but remained constant from d 28 to 84. Hair cortisol concentrations were the greatest (P<0.01) on d 0, decreased from d 28 to 56, but remained constant between d 56 and 84. Serum testosterone increased (P<0.01) from d 0 to 28, decreased from d 28 to 56, while d 84 did not differ from d 0, 28, or 56. Serum cortisol concentration did not differ (P>0.10) over the testing period. In summary, after the initial hair clipping, hair testosterone accumulation was consistent throughout the testing period and hair cortisol accumulation leveled over time as bulls acclimated to the testing center.