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The Effects of High-stress verses Low-stress Cattle Handling at the Time of Shipping to Slaughter on Physiological Responses in Cattle fed Ractopamine Hydrochloride
Feedlot cattle (n = 80; BW = 668 ± 36 kg) were used to measure the effects of handling at the time of shipping on physiological response, blood parameters, and carcass quality in cattle fed ractopamine hydrochloride during the summer in a Kansas commercial feedlot. Eight phenotypically similar steers were selected from 10 pens. Within each pen, cattle were stratified by weight and randomly assigned to 1 of 2 handling treatments: 1) Low-stress handling (LSH) or 2) High-stress handling (HSH). For the LSH treatment, 4 penmates were walked a course of 1,600 meters. Penmates from the HSH treatment were kept at a minimum of a trot over the 1,600 m course. Rectal temperature (RT), heart rate (HR), and respiratory rate (RR) were recorded prior to handling (baseline) and post-handling. Blood samples were collected at baseline, post-handling, and during exsanguination at the abattoir. Steers on the HSH treatment had higher HR than LSH cattle post-handling (100.4 vs. 86.7 beats/min; P = 0.01). There was no difference between treatments on post-handling RR (76.7 vs. 75.7 ± 2.6 breaths/min, P = 0.80) or RT (40.5 vs. 40.3 ± 0.09 ºC, P = 0.17). Blood pH, bicarbonate, and base excess were all decreased post-handling in the HSH cattle (P < 0.0001). Blood lactate was greater in the HSH cattle post-handling (15.1 vs. 5.2 ± 1.93 mmol/L, P = < 0.0001), while the LSH handled cattle tended to have greater blood lactate at exsanguination (12.2 vs 11.0 ± 0.43 mmol/L; P = 0.06). High-stress handled cattle had greater post-handling levels of plasma epinephrine (2,408 vs. 1,598 ± 232.8 pg/mL, P = 0.02), norepinephrine (3,434 vs. 2,010 pg/mL ± 523.4; P = 0.0004), and cortisol (136 vs. 114 ± 16.7 nmol/L; P = 0.01) than LSH cattle. However, no differences were observed in these hormones at exsanguination (P > 0.05). High-stress handled cattle had greater serum glucose post-handling (260 vs. 102 ± 10.3 mg/dL; P < 0.0001) than LSH cattle, however there was no difference at exsanguination (137.9 vs. 155.8 mg/dL; P = 0.30). There was no effect of handling treatment on blood creatine kinase at post-handling or exsanguination (P > 0.05). No differences in carcass quality were observed between treatments (P > 0.05). High-stress handling increased HR and stress hormones, also causing exhaustion of the respiratory system resulting in acute acidosis. However, HSH cattle recovered and no differences were seen in blood parameters at exsanguination.
Keywords: Beta-agonists, lactate, cattle-handling