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

Forty-eight 3.5-month-old lambs were used (2x2x2x2 factorial arrangement) to determine effects of corn and rumen undegradable protein (R) levels in growing diets on growing (56 days) and subsequent finishing (47 days) performance by lambs differing in growth potential. During the growing phase, the basal diet consisted of bermudagrass (Cynodon dactylis L.) hay (8% CP) consumed 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 SR, respectively) of a mixture of fish, feather, and blood meals (36.27, and 37%, respectively): ewes vs wethers (17.9 +/- 0.63 and 19.2 +/- 0.66 kg initial BW, respectively); and Romanov (RV) x St. Croix vs Suffolk (SU) x St. Croix (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 interactions (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 those of corn level, varied with sire breed [fat: 5.49, 5.01, 6.13, and 7.15 kg (SE = 0.286): protein: 4.07, 3.06, 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, 157, and 164 g/day for LC-S, LC-SR, HC-S, and HC-SR, respectively; SE = 5.9 (p = 0.08)] during finishing. In conclusion, different concentrate levels and types during growing may comparably affect growth during growing, but can have dissimilar impact on finishing performance, and such effects are more likely to vary with growth potential as affected by genotype than gender.