Does fat-tail docking and Zilpaterol hydrochloride (ZH) supplementation affect feedlot performance and carcass characteristics of finishing lambs?

The present study aimed to examine the implementation of either fat-tail docking and/or Zilpaterol hydrochloride (ZH) supplementation on feedlot performance, carcass characteristics and selected blood metabolites of fat-tailed Afshari lambs. In a 2 x 2 factorial design, 32 male lambs (41.0 +/- 5.8 kg, 180 days of age) were allocated to two experimental groups consisting of 16 intact and 16 fat-tail docked lambs. Within each group, lambs were randomly assigned to two dietary treatment groups for 28 days as follows: G1; intact lambs with no ZH supplementation, G2; intact lambs with 10 mg ZH/day, G3; fat-tail docked with no ZH supplementation and G4; fat-tail docked with 10 mg ZH/day. ZH supplementation or fat tail docking did not change total body weight gain (P > 0.10). Dry matter intake was significantly increased by fat-tail docking (P < 0.01), but it was not affected by ZH supplementation. Fat-tail docking did not influence feed efficiency, while ZH improved feed efficiency only in intact lams with no significant effect on docked lambs (P = 0.05). ZH tended to decrease backfat thickness (P = 0.06) and tended to increase longissimus dorsi muscle depth only in intact lambs (P = 0.08). ZH supplementation, fat tail docking, or ZH x fat-tail docking interactions did not affect whole carcass weights and lengths (P > 0.10). Fat-tail docking resulted in a nearly 2-fold increase in fat thickness covering longissimus dorsi muscle in docked lambs with no ZH supplementation; however, ZH supplementation prevented this increase in longissimus dorsi muscle fat thickness (P = 0.03). In summary, fat-tail docking did not notably affect feedlot performance and carcass characteristics; however, it increased dry matter intake and subcutaneous fat thickness as well as visceral organs weights and visceral fat deposits. ZH supplementation did not influence feedlot performance but significantly improved carcass characteristics, as indicated by lower fat and higher muscle and protein content of carcass both in docked and intact lambs.