Growth performance,serum parameters,inflammatory responses,intestinal morphology and microbiota of weaned piglets fed 18%crude protein diets with different ratios of standardized ileal digestible isoleucine to lysine

The present study was to explore the Ile requirement of piglets fed 18%crude protein(CP)diets.Two hundred and fifty 28-day-old Duroc×Landrace×Yorkshire piglets(8.37±1.92 kg)were randomly divided into 5 dietary treatments(10 piglets per replicate,5 barrows and 5 gilts per replicate)with 45%,50%,55%,60%,65%standardized ileal digestible(SID)Ile-to-Lys ratios,and the SID Lys was formulated to1.19%.The experimental design consisted of two phases(d 1 to 14 and d 15 to 28).Results showed that average daily gain(ADG)had a tendency to quadratically increase as the SID Ile-to-Lys ratio increased(P=0.09),and the optimum SID Ile-to-Lys ratios required to maximize ADG were 48.33%and 54.63%for broken-line linear model and quadratic polynomial model,respectively.Different SID Ile-to-Lys ratios had no significant effects on average daily feed intake and gain-to-feed ratio.Dry matter(P<0.01),CP(P=0.01),ether extract(P=0.04),gross energy(P<0.01)and organic matter(P<0.01)digestibility increased quadratically.Serum total cholesterol levels decreased linearly(P=0.01)and quadratically(P<0.01);aspartate aminotransferase(P<0.01),interleukin-1β(P=0.01),and tumor necrosis factor-a(P<0.01)levels decreased quadratically;immunoglobulin G(P=0.03)and immunoglobulin M(P=0.01)concentrations increased quadratically.Serum Ser levels decreased linearly(P<0.01)and quadratically(P=0.01);Glu(P=0.02),Arg(P=0.05),and Thr(P=0.03)levels decreased quadratically;Gly(P<0.01)and Leu(P=0.01)levels decreased linearly;Ile(P<0.01)concentration increased linearly.Duodenal villus height(P<0.01)and villus height to crypt depth ratio(P<0.01)increased quadratically.The deficiency or excess of Ile decreased short chain fatty acid-producing bacteria abundance and increased pathogenic bacteria abundance.Overall,taking ADG as the effect index,the optimum SID Ile-to-Lys ratios of piglets offered 18%CP diets were 48.33%and 54.63%based on two different statistical models,respectively,and the deficiency or excess of lle negatively affected piglet growth rates and health status.