Effects of dietary protein sources and nisin on rumen fermentation, nutrient digestion, plasma metabolites, nitrogen utilization, and growth performance in growing lambs1

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.