PS8-9. Effects of Temperament on Growth Performance and Metabolic and Hormonal Profile of Bos Indicus-influenced Heifers.

Abstract The objective of this study was to evaluate the effects of temperament on metabolic and hormonal profiles and growth performance of grazing Bos indicus-influenced heifers. A total of 104 heifers (initial BW = 247 ± 3.4 kg; age = 9 ± 40 d) were evaluated over two years (yr 1, n = 47; yr 2, n = 57). Approximately 30 days post-weaning (d 0), individual temperament was assessed using exit velocity, chute score, and pen score. An overall temperament score was calculated as the average of these traits, and heifers were classified as having adequate temperament (ADQ; score < 3) or excitable temperament (EXC; score ≥ 3). Across years, 65 heifers were classified as ADQ and 39 as EXC. Heifers had free-choice access to Bermudagrass hay and received a supplement at 1% BW until d 56, after which they grazed cool-season forages until d 140. Body weight, hip height, temperament assessments, and blood samples were collected on d 0, 14, 28, 42, 56, 84, 112, and 140. Serum was analyzed for albumin, total protein, urea nitrogen, glucose, creatinine, IGF-1, and cortisol. Data were analyzed using PROC MIXED of SAS, with heifer as the experimental unit and year as a random effect. Temperament × year × day and temperament × year interactions were not detected for growth or physiological variables (P ≥ 0.18). ADQ heifers were heavier on d 56 (284 vs 277 ± 9.67 kg; P = 0.04) and tended to be heavier on d 84 and 140 (298 vs 290 ± 4.38; P = 0.06). Average daily gain was greater for ADQ heifers from d 0 to 28 (0.74 vs. 0.53 ± 0.09 kg/d; P = 0.02) and from d 0 to 56 (0.71 vs. 0.59 ± 0.09 kg/d; P = 0.04), with a tendency for greater ADG from d 0 to 84 (P = 0.06). A greater percentage of ADQ heifers reached 65% of mature BW by study end compared with EXC heifers (51.3 vs. 30.9 ± 7.61%; P = 0.04). No differences were detected between treatments for albumin, total proteins, creatinine, urea nitrogen, or globulins (P ≥ 0.22). EXC heifers exhibited greater concentrations of glucose (temperament × day; P < 0.001) on d 0, 14, 28 and 56 compared to ADQ heifers. EXC heifers exhibited greater concentrations of cortisol on throughout the study (P = 0.01) compared to ADQ heifers. ADQ heifers exhibited greater concentrations of IGF-1 (P = 0.04) on d 56 compared to EXC heifers. In summary, heifers with adequate temperament demonstrated greater early-period BW and ADG, lower glucose and cortisol concentrations, and greater IGF-1 compared with excitable heifers, indicating improved physiological status and growth performance.