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The objective of this research was to determine the impact of zilpaterol hydrochloride (ZH) on movement behavior of calf-fed Holstein steers fed in confinement as well as understand the optimal slaughter end point for a calf-fed Holstein by use of biometric measurements. Calf-fed Holstein steers (n = 135) were randomized to 11 pre-assigned slaughter groups (254, 282, 310, 338, 366, 394, 422, 450, 478, 506, and 534 days on feed) consisting of 10 steers per group. Steers were assigned to one of three pens each containing a feed behavior and disappearance system (GrowSafe, Airdrie, AB Canada) which had four feed nodes per pen. A fourth terminal pen was divided in half with one side containing five steers fed a ration supplemented with ZH and the other half containing five steers fed a control ration without ZH supplementation. Steers placed in the fourth terminal pen were fed in 28 d feeding periods; d 1 to 5 included no ZH supplementation, d 6 to 25 included ZH (8.33 mg/kg dietary DM) supplementation, and steers were withdrawn from ZH during d 26 to 28. Objective movement behavior of each animal was monitored during the 28 d prior to harvest using an accelerometer (IceQube, IceRobotics, Edinburgh, Scotland, UK) attached to the left hind leg of each animal. The accelerometer recorded standing time (min), lying time (min), number of steps taken, and number of times lying down (lying bouts). These variables were accumulated in 15 min intervals. Data use began at 1200 h on d 1 to remove variation from movement caused by handling the animals and ended on d 28 at 2400 h. Biometric measurements were takenon the same group of calf-fed Holsteins to allow for understanding of the maximal slaughter point based on hip height. Hip-height was measured every 28 d from 226 to 422 days on feed. Hip-height was a dependent variable modeled via linear regression procedures, utilizing days of age and live weight as independent variables. Additionally, logistic regression was used to estimate the probability of a steer exceeding a hip-height of 147.32 cm (58 inches) from independent variables of days of age and live weight. No ZH x slaughter group interaction (P > 0.05) was detected for any variable. No difference (P > 0.05) was observed between ZH supplementation treatment groups in the quantity of minutes spent standing (0 d ZH = 15,831; 20 d ZH = 15,470), minutes spent lying (0 d ZH = 23,769; 20 d ZH = 24,130), or number of steps taken per 28 d period (0 d ZH = 46,118; 20 d ZH = 46,914). The number of lying bouts tended to be different (P = 0.09) between treatment groups; cattle supplemented ZH exhibited 302 lying bouts whereas those not supplemented ZH had 326 bouts over the 28 d period. There was no day of period x ZH interaction (P = 0.44) for any of the behavior outcome variables. There was a difference (P < 0.05) between treatments in the amount of time spent standing (0d ZH = 571; 20d ZH = 541 min) and lying (0d ZH = 869; 20d ZH = 883 min) within day of a 28 d period. A difference (P < 0.05) occurred between treatments in numbers of lying bouts (0d ZH = 11.3; 20 ZH = 10.8) within day over the 28 d period. Interactions (P < 0.01) were observed for time x treatment for each one of the outcome variables when expressed in 15 min intervals during a 24 h period. The results indicated similar objective movement outcomes for calf-fed Holstein steers supplemented ZH when compared to those not supplemented ZH. The linear relationship of live weight to hip height had an R2 value of 0.7116, and on average the calf-fed Holstein steers grew 1.0 cm per 16.9 kg of live weight gain during the finishing phase. The 10, 50, and 90% probability of a steer exceeding 147.32 cm (58 inches) of hip height was achieved at 563, 653, and 743 kg of live weight, respectively. The linear relationship of days of age to hip height had an R2 value of 0.6691, and the calf-fed Holstein steers grew 1.0 cm for each 10.7 days of age during the finishing phase. The 10, 50, and 90% probability of a steer exceeding 147.32 cm (58 inches) of hip height was achieved at 408, 459, and 510 days of age, respectively



Behavior, Biometric


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