The effects of supplementing feedlot diets with ionophores and breed type were assessed on growth rate and carcass characteristics in hair lambs. Twenty four intact males, 12 Pelibuey × Dorper (PDo) and 12 Pelibuey × Damara (PDa) lambs, 17.9 ± 3.7 kg initial weight, were housed in individual pens for a 60-d feeding trial. The lambs were assigned randomly into four diets: control without additives (C); 25 µg/g monensin (M); 28 µg/g salinomycin (S); 28 µg/g S for 20 d, and 25 µg/g M for the next 40 d (SM). Each diet was supplied to six lambs. Data were analyzed as a randomized complete block design in a 4 × 2 factorial arrangement, with four diets and two breed types of hair lambs (PDo and PDa). All diets were formulated to contain 14% CP and 2.6 Mcal ME/kg dry matter. At the end of the feeding trial carcass images were recorded in the last intercostal space (12th and 13th ribs) using ultrasound equipment to measure the Longissimus dorsi muscle area and subcutaneous fat (SF). The average daily gain (ADG), daily dry matter intake, feed:gain ratio, subcutaneous fat and Longissimus dorsi area were not affected by ionophore supplementation.. The Pelibuey × Dorper group tended to show better average daily gain than Pelibuey × Damara (262 g/d and 235 g/d, respectively). Daily dry matter intake, feed:gain ratio and subcutaneous fat were not affected by breed type. The Pelibuey × Dorper lambs had greater Longissimus dorsi area (16.74 cm²) than the Pelibuey × Damara (14.29 cm²) lambs. The growth rate was not influenced by the inclusion of ionophores. Pelibuey × Dorper lambs showed better average daily gain and carcass characteristics than Pelibuey × Damara lambs.
feed additives; hair lambs; fattening; Longissimus dorsi; subcutaneous fat
