| Popis: |
Angus crossbred steers (n = 40; 563 ± 44 kg) were used to examine the effects of handling method and fat thickness on the blood chemistry and physiology of market steers. Steers were blocked by backfat (BF) thickness and were randomly assigned to treatment groups: low-stress handling (LSH) and aggressive handling (AH). Cattle were then ran¬domly assigned to one of 5 blocks containing 4 steers from the LSH and AH treatments. Steers in the LSH treatment were walked and AH cattle were run through a course of 1,540 m. Blood samples were obtained via jugular venipuncture before handling (BASE), at 770 m (LAP1), at 1,540 m (LAP2), and at1 h (1H) and 2 h (2H) after finishing the course. Blood samples were analyzed for plasma lactate (LAC), creatinine kinase (CK), base excess (BE), blood pH (pH), serum cortisol (CORT) concentrations, and venous carbon dioxide (PvCO2) and oxygen (PvO2) pressures. Heart rate (HR), respiratory rate (RR), and rectal temperature (TEMP) were measured at the same intervals. Cattle in the AH treatment had greater (0.05) LAC than those in LSH at BASE (4.1 vs. 3.0 mmol/L), LAP1 (16.5 vs. 2.3 mmol/L), LAP2 (22.3 vs. 2.4 mmol/L), 1H (7.2 vs. 2.7 mmol/L), and 2H (4.0 vs. 2.5 mmol/L), respectively. Creatinine kinase and RR were not different (P0.14). Blood pH in AH cattle was decreased compared with that in LSH cattle (0.05) at LAP1 (7.25 vs. 7.45) and LAP2 (7.19 vs. 7.48) but was not different (0.13) at BASE, 1H, or 2H. Heart rate and TEMP were increased in AH cattle compared to LSH (0.01). Serum cortisol was increased (0.05) in AH compared to that in LSH cattle at LAP1 (87.5 vs. 58.9 nmol/L), LAP2 (144.4 vs. 93.1 nmol/L), and 1H (113.5 vs. 53.1 nmol/L). Although RR was not differ¬ent between LSH and AH, PvCO2 was decreased in AH compared to that in LSH (0.05) at LAP2 (30.6 vs. 39.3 mmHg) and PvO2 was increased at LAP1 (42.7 vs. 33.5 mmHg) and at LAP2 (51.5 vs. 36.6 mmHg). Lactate was increased in AH cattle in the thicker BF group at 1H (0.05), and blood pH was decreased at LAP1, LAP2, and 1H (0.05) compared to the thinner BF cohorts. Four AH steers became exhausted (EXH) and did not complete the course. Increased CK, decreased PvCO2, and muscle tremors occurred in EXH steers compared to non-exhausted AH cohorts. Results of this study show that AH causes physiologic and blood chemistry changes in steers, which can be potentially detrimental to cattle, emphasizing the need for low-stress handling practices. |
