Effects of supplementing moderate- to low-quality grass hay with maize and (or) rumen-undegradable protein on growth of wethers

Abstract

Crossbred wethers ( N = 80, 4 months of age, average live weight of 25 ± 0.2 kg) were used to determine effects of supplementing grass hay with ground maize (M; 0.7% body weight), a mixture of feedstuffs high in rumen undegradable protein (R; 0.2% body weight) or maize plus rumen undegradable protein (MR) on growing (70 days) and subsequent finishing (98 days; 85% concentrate diet) performance and body composition. During the growing phase, wethers consumed bermudagrass (BER) or bromegrass (BRO) hay ad libitum, and 0.35% body weight of soybean meal. Empty body fat (4.28, 5.91, 5.20, 6.64, 4.18, 5.17, 4.96 and 6.20 kg; SE 0.357) and protein (4.45, 5.02, 5.05, 5.32, 4.57, 4.84, 4.93 and 5.21 kg; SE 0.074) for BER-control, BER-M, BER-R, BER-MR, BRO-control, BRO-M, BRO-R and BRO-MR, respectively, increased ( P < 0.05) after growing when maize or rumen undegradable protein was supplemented. Finishing live weight gain (195, 199, 174, 186, 217, 218, 191 and 204 g day −1 for BER-control, BER-M, BER-R, BER-MR, BRO-control, BRO-M, BRO-R and BRO-MR, respectively; SE 6.7) was depressed ( P < 0.05) by supplementation with rumen undegradable protein. Empty body fat (14.0, 16.3, 14.2, 17.5, 14.7, 16.0, 14.7 and 16.7 kg; SE 0.936) and protein (6.65, 6.92, 6.62, 7.07, 6.78, 6.88, 6.82 and 7.00 kg; SE 0.093) for BER-control, BER-M, BER-R, BER-MR, BRO-control, BRO-M, BRO-R and BRO-MR, respectively, were increased ( P < 0.05) after the finishing phase by maize supplementation. Supplementation with rumen undegradable protein during the growing phase decreased finishing live weight gain, which was accompanied by loss of the improvement in protein deposition achieved during growing. Conversely, the effect of maize on empty body protein was only slightly less after the finishing than after the growing phase, and the effect on empty body fat was slightly greater after the finishing than after the growing phase.