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Performance and carcass attributes of Nellore heifers fed with zilpaterol hydrochloride
Greater efficiency of production is mandatory in modern beef cattle industry, and use of feed additives, such as beta-adrenergic agonists, have demonstrated positive results with Bos taurus cattle. However, there are no consistent data on the effects of these substances in Nellore (Bos indicus), which accounts for more than 70% of the Brazilian beef cattle. Therefore it was the objective of this study to evaluate the effects of zilpaterol hydrochloride (Zilmax®) on the performance and carcass attributes of Nellore heifers. Seventy-two animals with 267 kg of BW and 18 mo of age were fed in a feedlot system for 135 d. Heifers were separated into two treatment groups: Control (C) and Zilpaterol (Z), which received the same diet containing 14% of crude protein, and formulated with corn silage, ground corn, soybean meal and mineral premix. The Z group received Zilmax at 8.3 mg/kg dry matter. Heifers were allotted to 18 pens (n = 9) and assigned in a completely randomized design. Animals were weighed at 21-d intervals after 16-h fasting to evaluate growth performance. Zilmax was administrated during the last 30 d of feeding, allowing 3 d of withdraw before slaughter. All animals were slaughtered in a commercial plant, according to proper welfare guidelines. Hot carcass weight, carcass yield, kidney, pelvic and abdominal fat weight were measured. Twenty-four hours later, longissimus muscle area and backfat thickness were measured at the interface of the 12th and 13th ribs. Zilpaterol administration increased (P < 0.01) final body weight (404 vs. 387 kg), average dairy gain (1.46 vs. 1.14 kg/d), hot carcass weight (224 vs. 208kg), and dressing percentage (56 vs. 54%) compared with control. However, no effects (P > 0.10) were noted in the longissimus muscle area (73.1 vs. 83.5 cm2) and subcutaneous fat depth (5.2 vs. 4.8 mm) between C and Z group, respectively. In addition, there was a reduction in kidney and pelvic fat by zilpaterol administration compared with C (4.6 vs. 5.7% of hot carcass weight). In conclusion, zilpaterol treatment improved the performance and carcass characteristics of Nellore heifers in feedlot system.
Keywords: heifers, Nellore, zilpaterol