LAUSR

This study investigated the effects of dietary protein sources and nisin on rumen fermentation, nutrient digestion, plasma metabolites, N utilization, and growth performance in growing lambs. Thirty-two male Hu lambs (23 ± 2 kg initial BW) were assigned to four dietary treatments in a randomized block design with a 2 × 2 factorial arrangement. Two protein sources, soybean meal (SBM) and dried distillers grains with solubles (DDGS), and two levels of nisin, 0 and 30.5 mg of nisin/kg of feed, were used to formulate four isonitrogenous and isoenergetic diets. No interaction (P ≥ 0.16) of protein × nisin was found except on apparent digestibility of DM, OM, NDF, and ADF (P ≤ 0.02). Lambs receiving DDGS had lower (P ≤ 0.04) concentrations of ruminal acetate and butyrate, but propionate concentrations did not differ (P = 0.39), compared with those fed SBM, leading to a trend for reduced total VFA concentration (P = 0.07). Ruminal NH3-N and total branched-chain VFA concentrations were lower (P ≤ 0.01) in the lambs fed DDGS than in those fed SBM. The DDGS-fed lambs had less (P < 0.01) CP, but greater (P < 0.01) ether extract apparent digestibility than those fed SBM. For plasma metabolites, only blood urea N and albumin concentrations were lower in the DDGS-fed lambs (P < 0.01) than in those fed SBM. Nitrogen excretion pathway was altered when DDGS replaced SBM, with fecal N excretion (% of N intake) being greater (P < 0.01), while urinary N excretion (% of N intake) tending to be less (P = 0.06) from the DDGS-fed lambs than those fed SBM. Protein sources affected growth performance in an age/time-dependent manner. From weeks 1 to 4, DDGS resulted in less (P = 0.03) DMI and ADG than SBM. From weeks 5 to 8, DDGS did not affect (P ≥ 0.23) DMI or ADG but resulted in a greater (P = 0.04) G:F than SBM. Final BW did not differ (P = 0.58) duo to protein source. Providing nisin had no impact on DMI (P = 0.44), ADG (P = 0.84), or G:F (P = 0.73). Nisin addition only affected plasma uric acid concentration (P = 0.04). It was concluded that DDGS could substitute for SBM as a nitrogen source to growing Hu lambs to reduce N excretion via urine without adverse effects on animal performance, but nisin supplementation probably had no additional benefits.