Chromium Propionate and Zilpaterol Hydrochloride Supplementation in Finishing Lambs: Growth Performance, Body Composition, Carcass Characteristics, and Meat Quality

The objective of this study was to evaluate the effects of chromium propionate (Cr-Pr) and zilpaterol hydrochloride (ZH) supplementation on growth performance, performance-derived estimates of dietary energy utilization, body composition, carcass traits, wholesale cut distribution, and meat quality of finishing lambs. Forty intact male Dorper × Katahdin lambs were blocked by initial body weight (38.21 ± 1.72 kg) and assigned to a 2 × 2 factorial arrangement (n = 10/treatment): Control (0 Cr-Pr + 0 ZH), ZH (0 Cr-Pr + 7.2 mg ZH/lamb/d), Cr-Pr (1.2 mg elemental Cr/lamb/d + 0 ZH), and Cr-Pr + ZH (1.2 mg elemental Cr/lamb/d + 7.2 mg ZH/lamb/d). The experimental period lasted 45 d; Cr-Pr was supplemented throughout d 1–45, whereas ZH was administered during d 15–42, followed by a 3 d withdrawal period (d 43–45). Under the conditions evaluated, Cr-Pr, ZH, and their interaction did not affect growth performance or performance-derived estimates of dietary energy utilization (p > 0.05); however, both compounds produced specific changes in body composition and carcass traits. Supplementation with Cr-Pr reduced omental, visceral, and perirenal fat by 21.8, 18.6, and 18.7%, respectively (p ≤ 0.044), and increased longissimus muscle area (LMA) by 5.3% (p = 0.013). An interaction between Cr-Pr and ZH was detected for rib fat thickness (FAT) (p = 0.050), with the ZH and Cr-Pr individual treatments showing lower FAT than Control and Cr-Pr + ZH. Supplementation with ZH increased dressing percentage by 7.2% (p = 0.048). Regarding wholesale cuts, classified according to Institutional Meat Purchase Specifications (IMPS), Cr-Pr increased shoulder (IMPS 206) and loin (IMPS 231) proportions by 10.3 and 10.6%, respectively, and reduced shoulder (IMPS 207) by 3.3% (p = 0.043), whereas ZH increased breast (IMPS 209) weight by 15.0% and its proportion of cold carcass weight (CCW) by 9.7% (p ≤ 0.042). Interactions between Cr-Pr and ZH were also detected for ribs (IMPS 209A) and flank (IMPS 232) weights (p ≤ 0.047). Supplementation did not affect meat quality traits (p ≥ 0.217). Overall, Cr-Pr was associated with reduced internal fat deposition and increased LMA and loin (IMPS 231) proportion, whereas ZH modified dressing percentage and breast (IMPS 209) weight and proportion of CCW. These responses occurred without changes in growth performance or performance-derived estimates of dietary energy utilization and without detectable changes in the evaluated meat quality traits. The interactions observed for FAT, ribs (IMPS 209A), and flank (IMPS 232) were trait-specific and did not indicate a consistent benefit of the combination.