Effects of castration on eating pattern and physical activity of Holstein bulls fed high-concentrate rations under commercial conditions.

A total of 132 animals (initial BW = 220 ± 22 kg and age = 166 ± 0.4 d) were used to study the effect of castration on eating behavior and physical activity. Animals were randomly allocated to 6 pens with 2 pens for each of the 3 treatment groups: 44 intact bulls, 44 steers castrated (3 mo of age) before the study began, and 44 bulls castrated (CAS) at 8 mo of age (at d 69 of the study). The study finished when animals reached 292 d of age. Each pen held 22 animals, and had 1 computerized concentrate feeder (GEA WestfaliaSurge, Germany), 1 feed trough for straw, and 1 water source. Concentrate and straw were offered ad libitum. Animals were weighed every 14 d and eating pattern at which animals consumed concentrate was averaged for each 14-d period. A pedometer was placed on the left hind leg of 86 animals randomly distributed among treatments to estimate physical activity from d -5 to 10 relative to surgical castration (d 65 to 79 of study). The statistical model included initial BW as a covariate, treatment, period, and the interaction between treatment and time (14-d), as fixed effects, and pen and animal as random effects. For physical activity data, day was the repeated measure. The CAS animals exhibited reduced ADG and concentrate DMI (P < 0.001) during the first 2 wk after castration than bulls or steers. Eating behavior throughout the study differed among treatments. Meal size (1.3 ± 0.05 kg) and meal duration (12.4 ± 0.47 min) were greater (P < 0.001) in bulls during the 2 wk after castration than in steers (1.0 ± 0.05 kg and 9.7 ± 0.46 min, respectively) and CAS animals (0.8 ± 0.05 kg and 7.8 ± 0.47 min, respectively). In contrast, bulls visited the feeders less frequently (5.3 ± 0.34/d) during these 2 wk than did steers (6.7 ± 0.34/d) and CAS animals (7.7 ± 0.34/d). In addition, daily intake, meal size, and eating rate increased (P < 0.001) with time. Lying time in CAS animals was reduced (P < 0.001) for the 5 d after castration compared with bulls and steers. Bulls were more active (steps/h) than steers, and activity of recently castrated animals decreased (P < 0.001) for at least 10 d after castration. Although 2 wk after castration differences in eating pattern across treatments were observed, the long-term effects of castration and gender (bull vs. steer) on eating behavior were difficult to interpret. Castration effects on total feed intake and lying time are temporary, whereas castration has a lasting reduction on physical activity.