Relationships of temperament, endocrine, reproductive, and behavioral parameters measured during performance testing of bulls

The aim of this study was to examine relationships between bull temperament, behavior, growth, endocrine, and reproductive parameters measured over an 84 d test period. Bulls (n = 65) were reared in 6 pens separated on BW and age. Pen scores were assigned on d -1, 27, 55 and 83. On d 0, 28, 56, and 84, exit velocity, BW, time it took each bull to leave the chute, bull order through chute, and hair and blood samples were recorded or collected. Frame score was calculated, carcass ultrasounds and breeding soundness exams were performed on d 84. ADG was calculated for each period (period 1 = d 0-28; period 2 = d 29-56; period 3 = d 57-84) and over the 84 d. Bulls (n=30; 3 pens) received dataloggers to measure activity during period 1 and 3. Bulls were categorized into three temperament (pen score + exit velocity / 2) categories (docile, intermediate, and temperamental).

Temperamental bulls tended (P=0.07) to enter the chute system prior to docile bulls on d 84 and weighed less (P<0.05) than docile bulls on d 0, 28, and 56. Frame score was less (P<0.05) for temperamental bulls than docile bulls on d 84 (5.88 ± 0.13 vs. 6.34 ± 0.18). Bulls categorized as intermediate on d 56 had greater (P<0.05; 2.10 ± 0.04 kg/d) overall ADG than docile (1.94 ± 0.06 kg/d) and temperamental bulls (1.92 ± 0.06 kg/d).

Docile bulls had greater serum (P=0.06) and hair testosterone (P<0.05) and lower (P<0.05) serum cortisol concentration than temperamental bulls on d 56. Docile and intermediate bulls tended (P=0.07) to have a lower percentage of primary spermatic defects (20.58 ± 4.86 %) than temperamental bulls (38.01 ± 8.06 %) on d 84. Serum testosterone measured on d 28 and 56 was positively correlated to BW (r = 0.47 and 0.39; P<0.01). On d 28, BW was positively correlated (r = 0.32; P<0.05) to hair testosterone and negatively correlated to hair cortisol (r = -0.31; P<0.05).

In conclusion, selecting bulls based on docility could increase BW, frame score, serum and hair testosterone concentration, and lower serum cortisol concentrations.