Abstract :
Forty-eight Pelibuey×Katahdin (38.8±0.67 kg) crossbred male lambs were used in a 32-
day feeding trial (four pens per treatment in a randomized complete block design), to
evaluate the influence of zilpaterol ( 2-agonist) supplementation level on growth performance
and carcass characteristics. Lambs were fed a dry-rolled corn-based finishing
diet (3.04 Mcal/kg of ME) supplemented with 0, 0.15, 0.20, or 0.25 mg/kg of live weight d−1
zilpaterol (as zilpaterol chlorhydrate, Zilmax®, Intervet México, México City). DM intake
averaged 1.099±0.042 kg/d and was not affected (P = 0.40) by treatments. Compared with
control lambs, zilpaterol supplementation increased gain efficiency (15.8%, P < 0.03), apparent
energy retention per unit DMI (10.9%, P = 0.03), and tended to increased daily gain (16%,
P < 0.07) and total gain (17.7%, P < 0.08). Zilpaterol supplementation did not affect (P = 0.20)
carcass weight, longissimus muscle area (LM), or fat thickness, but increased (2.3%, P = 0.04)
carcass dressing percentage and reduced (36%, P < 0.01) kidney-pelvic fat. Increasing level
of zilpaterol supplementation increased total weight gain (linear component, P < 0.05),
gain:feed (linearcomponent, P < 0.01), and dressing percentage (linearcomponent, P < 0.02),
and decreased (linear component, P < 0.01) kidney-pelvic fat. We conclude that zilpaterol
supplementation enhances growthperformance and dressing percentage inlambs in amanner
comparable to that of cattle (greater muscle accretion, reduced body fat). Responses to
zilpaterol was optimal when supplemented at 0.20mg of zilpaterol/kg of live weight d−1.
