Effects of growth-promoting technology on feedlot cattle behavior in the 21 days before slaughter

There is growing interest in the animal welfare implications of growth-promoting technology used in feedlot cattle, namely hormonal implants, ionophores, antibiotics and β2-adrenergic agonists. Previous studies have focused on the effects of implants on aggression, but little work has evaluated other behavioral changes anecdotally reported with β2-adrenergic agonists, such as an increase in lateral lying, a posture seen when cattle rest. The objectives of the present experiment were to quantify the effects of these technologies on lying and agonistic behavior in the 21 days before slaughter and to examine the sampling strategy required to measure lateral lying. Angus crossbred steers were assigned to 16 pens of 10 animals each. Treatments were applied in an additive manner to represent the decisions that feedlot managers would likely make about technology use. They were: (1) control (CON; no technology application), (2) monensin and tylosin phosphate (MON), (3) MON and growth implant (trenbolone acetate and estradiol, IMP) and (4) IMP and zilpaterol hydrochloride, a β2-adrenergic agonist (fed day 24-3 before slaughter; BAA). Agonistic (pushing, displacements) and bulling behaviors were recorded on day 21, 17, 12, 7 and 3 before slaughter and lying behavior, including time and number of bouts of lateral and sternal lying, was measured on day 12, 7, and 3. These time points were chosen to overlap with the feeding period for zilpaterol. BAA cattle spent 31% more time lying laterally, compared to all other treatments (BAA: 2.4 vs. others: 1.7 h/24 h, SE: 0.18 h/24 h, P = 0.020), perhaps because of changes associated with muscle growth. Continuous measurement is needed to measure lateral lying; estimates generated with instantaneous scan sampling never met all of our criteria for accuracy (R2 > 0.9, slope = 1, intercept = 0). BAA cattle engaged in more pushing and displacements than MON or CON (P ≤ 0.05); IMP also increased pushing compared to MON or CON, but only during day 12, 7 and 3 before slaughter (IMP and BAA 12.5 pushes/steer/h vs. MON and CON 6.8 pushes/steer/h, SE 1.4 pushes/steer/h, P = 0.007). Together, these findings indicate that combined use of growth-promoting technologies tested in this experiment affected both agonistic and lying behavior.