Influence of undegraded intake protein on intake, digestion, serum hormones and metabolites, and nitrogen balance in sheep

In Exp. I, 20 ewes of mixed breeding were fed grass hay : straw mixtures, a ssigned to one of four supplemental treatments and evaluated during six col lection periods. Supplemental treatments were control (no supplement), and low, medium, and high levels (5.2%, 22.1%, and 41.3% of DM, respectively) o f undegraded intake protein (UIP). Supplements were formulated to be simila r in degraded intake protein (DIP; 21%). Digestibilities of DM, OM, and CP were increased (P < 0.10) with protein supplementation and in medium and hi gh compared with low UIP supplemented ewes. Digestibility of CP also was in creased (P < 0.10) in ewes on high compared with medium treatments. Serum i nsulin was not influenced (P > 0.10) by UIP treatment, except in collection period four. In contrast, serum glucose and growth hormone were not influe nced (P > 0.10) by UIP treatment. In Exp. 2, four wether lambs fed the same treatments as in Exp. 1, were used in two 4 x 4 Latin squares trials. In t rial 1 lambs received a grass hay diet (6.7% CP) and in trial 2 lambs were fed 40 : 60 blend (6.6% CP) of grass hay and spring wheat shaw. In both tri als, N intake, urinary N, N digestion, apparent N absorption, and N retenti on were increased (P < 0.10) with protein supplementation. In addition, in trial 1, urinary N, N digestion, and apparent N absorption were increased ( P < 0.10) in medium and high compared with low UIP and also in high compare d with medium UIP treatments. In trial 2 of Exp. 2, total feed intake (g/kg BW), digestibility of DM and OM, BW, and fecal N were increased (P < 0.10) with protein supplementation. Organic matter digestion, BW, N intake, and N retention were increased by medium and high compared with low UIP. Fecal N, BW, N intake, and N retention were increased (P < 0.10) in high compared with medium UIP. These data indicate that increasing levels of UIP supplem entation increases DM, OM, and CP (N) digestibility, serum urea N concentra tion, and N retention in sheep fed low quality forage. (C) 2000 Elsevier Sc ience B.V. All rights reserved.