Effects of oscillating dietary protein on nutrient digestibility, nitrogen metabolism, and gastrointestinal organ mass in sheep1,2

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.

The influence of oscillating dietary protein concentrations on finishing cattle. II. Nutrient retention and ammonia emissions

“…Similarly, Cole (1999) noted an increase in N retention in lambs by oscillating the CP concentration of the diet over 48-h intervals. However, Ludden et al (2002a) did not observe an improvement in N retention with oscillating CP concentrations when sheep were fed at relatively high dietary CP concentrations (13 to 17%). Dietary CP (Ludden et al, 2002a) was likely in excess of needs for those lambs, such that any effect of oscillating diets on N metabolism may have been masked by the increased N that was excreted.…”

“…However, Ludden et al (2002a) did not observe an improvement in N retention with oscillating CP concentrations when sheep were fed at relatively high dietary CP concentrations (13 to 17%). Dietary CP (Ludden et al, 2002a) was likely in excess of needs for those lambs, such that any effect of oscillating diets on N metabolism may have been masked by the increased N that was excreted. Ludden et al (2002a) also noted a decrease in overall N digestibility when lambs were fed oscillating CP diets, resulting in increased fecal relative to urinary N.…”

“…Dietary CP (Ludden et al, 2002a) was likely in excess of needs for those lambs, such that any effect of oscillating diets on N metabolism may have been masked by the increased N that was excreted. Ludden et al (2002a) also noted a decrease in overall N digestibility when lambs were fed oscillating CP diets, resulting in increased fecal relative to urinary N.…”

Effect of Varying Levels of Dietary Ruminal Undegradable Protein on Feed Consumption and Growth Performance of Growing Kajli Lambs

“…A positive relationship exists between dietary ruminal degradable protein (RDP) level and forage utilization (Bohnert et al, 2002). Decreasing dietary RDP supplementation frequency to ruminants consuming low quality forages not only lowered feed consumption and digestibility (Ludden et al, 2002a) but also reduced nutrient's net flux (Krehbiel et al, 1998) and animal performance (Bohnert et al, 2002;Ludden et al, 2002b). However, enhanced RDP consumption may result into excessive ruminal NH3 production, exceeding the immediate ruminal microbial population demand.…”

Effect of dietary crude protein level on visceral organ mass, cellularity, and the protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen and ubiquitin in feedlot steers

“…Effects of CP intake on ruminant visceral organ mass have been investigated previously (Wester et al 1995;Swanson et al 1999;Ludden et al 2002). The reports of visceral organ weights in response to dietary protein concentration varied depending upon the designed protein and energy levels, specific organs, animal types, etc.…”