1275 Effects of temperament on physiological and reproductive responses of Bos Indicus beef cows.

This experiment evaluated the effects of temperament on physiological and reproductive responses of Bos indicus cows. A total of 954 lactating, multiparous, non-pregnant Nelore cows (age = 99 ± 1.6 mo; days post-partum = 51.4 ± 0.3 d; BCS = 5.34 ± 0.04; BW = 430 ± 2 kg), allocated into 8 groups of approximately 120 cows each, were utilized. Groups were assigned to an estrus synchronization + timed-AI protocol from d 0 to 11. On 11, cows were inseminated, blood samples were collected, and cow temperament was evaluated via chute score and exit velocity. Individual exit score was calculated by dividing exit velocity results into quintiles and assigning cows with a score from 1 to 5 (exit score: 1 = slowest; 5 = fastest cow). Temperament scores were calculated by averaging cow chute score and exit score, and cow temperament type was defined according to temperament score ( ≤ 3 = adequate temperament, ADQ, > 3 = excitable temperament, EXC). Pregnancy status was verified 30 d after timed-AI via transrectal ultrasonography. Cows not pregnant to AI were assigned to a second timed-AI protocol. Cows that still remained non-pregnant were exposed to natural breeding for 60 d. Cow age, BW, BCS, and days post-partum on d 0 were similar (P ≥ 0.27) between ADQ and EXC cows. On d 11, EXC had greater (P < 0.01) plasma cortisol but similar (P = 0.89) plasma haptoglobin concentrations compared with ADQ cows (48.9 vs. 38.4 ng/mL of cortisol, SEM = 1.0). Pregnancy rate to the first timed-AI tended (P = 0.10) to be less in EXC vs. ADQ cows (41.0 vs. 47.2%; SEM = 3.5), whereas pregnancy rates to the second timed-AI, natural breeding, and final pregnancy rates (AI + natural breeding) were similar (P ≥ 0.23) between ADQ and EXC cows. However, calving rate was less (P = 0.02) in EXC vs. ADQ cows (66.9 vs. 74.9%; SEM = 2.5), which can be associated with the greater (P = 0.04) pregnancy loss (based on final pregnancy status and actual calving) detected in EXC vs. ADQ cows (11.3 vs. 6.4%; SEM = 1.6). Results from this experiment indicate that B. indicus cows with excitable temperament have impaired reproductive performance during a breeding season based on timed-AI + natural breeding compared to cohorts with adequate temperament.