title: Effects of oscillating dietary protein on nutrient digestibility, nitrogen metabolism, and gastrointestinal organ mass in sheep.
abstract: Twenty-four wether lambs (BW = 37.5 +/- 0.8 kg) were used in a 64-d randomized complete block design experiment to evaluate the effect of oscillating dietary CP with undegradable intake protein (UIP) on diet digestibility, N retention, and gastrointestinal (GI) organ mass. Four treatments consisted of a 13, 15, or 17% CP diet fed daily or a regimen in which dietary CP was oscillated between 13 and 17% on a 48-h basis (ACP). All diets consisted of 65% bromegrass hay (10.5% CP, 61.9% NDF, 37.2% ADF) and 35% corn-based supplement, and were formulated to contain the same amount of degradable intake protein (9.6% of dry matter), plus additional UIP (from SoyPLUS) to accomplish CP levels above 13%. Beginning on d 52, N balance collections were conducted for 8 d, after which lambs were killed on d 62 and 64 of the trial for measurement of GI organ mass. Because intake was restricted to 3.0% of initial body weight (dry matter basis), dry matter intake did not differ (P > or = 0.67) and no treatment effects (P > or = 0.36) on ADG, feed efficiency, or total tract DM digestibility were observed. Increasing dietary CP from 13 to 17% linearly increased (P = 0.0001) N digestibility, but lambs fed ACP had lower (P = 0.07) total tract N digestibility than those fed 15% CP daily. Although urinary N excretion increased linearly (P = 0.0001) with increasing CP, a linear increase (P = 0.07) was observed in N retention (g/d) with increasing dietary CP. Although the quantity of N retained by lambs fed ACP was not statistically different (g/d, P = 0.19; % of digested N, P = 0.23) from those fed 15% CP daily, N retention in lambs fed ACP was 42% lower than in those fed 15% CP daily (1.8 vs 3.1 g/d, respectively). Increasing CP linearly decreased (P < or = 0.09) weights of the reticulorumen, abomasum, and small intestine, but did not affect (P > or = 0.16) liver or omasum weights. Length of the small intestine was not affected (P > or = 0.45) by treatment, but lambs fed ACP had greater (P = 0.03) small intestine weights than those fed 15% CP daily. Increasing dietary CP linearly decreased (P = 0.03) total GI organ mass, and lambs fed ACP had a greater (P = 0.03) total GI organ mass than those fed 15% CP daily. Oscillating dietary CP may increase the weights of the GI organs, which may subsequently have negative effects on N and energy metabolism in the animal. Likewise, the potential for decreased GI organ mass in response to increased supply of CP with UIP deserves further investigation.
authors.affiliation: Department of Animal Sciences, University of Wyoming, Laramie 82071, USA. ludden@uwyo.edu
authors.forename: P A
authors.initials: PA
authors.lastname: Ludden
authors.forename: T L
authors.initials: TL
authors.lastname: Wechter
authors.forename: B W
authors.initials: BW
authors.lastname: Hess
mesh_terms: D000821:Animal Feed; D000818:Animals; D031724:Bromus; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D004063:Digestion / Q000187:drug effects*; D004064:Digestive System / Q000187:drug effects / Q000254:growth & development*; D004305:Dose-Response Relationship, Drug; D005243:Feces / Q000737:chemistry; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D011897:Random Allocation; D012756:Sheep / Q000254:growth & development* / Q000378:metabolism; D003313:Zea mays
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen