Growing and finishing performance by lambs differing in growth potential consuming diets during growing varying in levels of corn and lumen undegradable protein

Forty-eight 3.5-month-old lambs were used (2x2x2x2 factorial arrangement) t o determine effects of corn and rumen undegradable protein (R) levels in gr owing diets on growing (56 days) and subsequent finishing (47 days) perform ance by lambs differing in growth potential. During the growing phase, the basal diet consisted of bermudagrass (Cynodon dactylon L.) hay (8% CP) cons umed ad libitum and 0.3% BW of soybean meal. Factors investigated were: 1.0 vs 2.5% BW (LC and HC, respectively) of ground corn; 0 vs 0.5% BW (S and S R, respectively) of a mixture of fish, feather, and blood meals (36, 27, an d 37%, respectively); ewes vs wethers (17.91+/-0.63 and 19.2+/-0.66 kg init ial BW, respectively); and Romanov (RV) x St. Croix vs Suffolk (SU) x St. C roix (18.2+/-0.61 and 18.7+/-0.63 kg initial BW, respectively). During the finishing phase, all lambs consumed ad libitum the same 80% concentrate, 20 % CP diet. Dry matter intakes during growing (0.83, 0.96, 0.97, and 0.97 kg /day; SE=0.023) and finishing (1.47, 1.67, 1.66, and 1.56 kg/day for LC-S, LC-SR, HC-S, and HC-SR, respectively; SE=0.052) were affected by interactio ns (p=0.05) between corn and R levels. Corn and R levels increased (p less than or equal to 0.02) mass of fat (4.68, 5.82, 6.25, and 7.02 kg; SE=0.271 ) and protein (3.91, 4.11, 4.15, and 4.40 kg for LC-S, LC-SR, HC-S, and HC- SR, respectively; SE=0.031) after growing, although effects, particularly t hose of corn level, varied with sire breed [fat: 5.49, 5.01, 6.13, and 7.15 kg (SE=0.286); protein: 4.07, 3.96, 4.18, and 4.37 kg for RV-LC, RV-HC, SU -LC, and SU-HC, respectively (SE=0.065)]. Dietary corn level during growing increased accretion of empty BW [268, 258, 289, and 276 g/day; SE=9.3 (p=0 .10)] and fat [151, 152, 167, and 164 g/day for LC-S, LC-SR, HC-S, and HC-S R, respectively; SE=5.9 (p=0.08)] during finishing. In conclusion, differen t concentrate levels and types during growing may comparably affect growth during growing, but can have dissimilar impact on finishing performance, an d such effects are more likely to vary with growth potential as affected by genotype than gender. (C) 1999 Elsevier Science B.V. All rights reserved.