EFFECTS OF SUPPLEMENTING MODERATE-QUALITY TO LOW-QUALITY GRASS HAY WITH MAIZE AND (OR) RUMEN-UNDEGRADABLE PROTEIN ON GROWTH OF WETHERS

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 rume n undegradable protein (MR) on growing (70 days) and subsequent finish ing (98 days; 85% concentrate diet) performance and body composition. During the growing phase, wethers consumed bermudagrass (EER) or brome grass (BRO) hay ad libitum, and 0.35% body weight of soybean meal. Emp ty 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 l ive weight gain (195, 199, 174, 186, 217, 218, 191 and 204 g day(-1) f or BER-control, BER-M, BER-R, BER-MR, BRO-control, BRO-M, BRO-R and BR O-MR, respectively; SE 6.7) was depressed (P < 0.05) by supplementatio n 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, BE R-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 supplem entation. Supplementation with rumen undegradable protein during the g rowing phase decreased finishing live weight gain, which was accompani ed by loss of the improvement in protein deposition achieved during gr owing. Conversely, the effect of maize on empty body protein was only slightly less after the finishing than after the growing phase, and th e effect on empty body fat was slightly greater after the finishing th an after the growing phase.