Effects of dietary threonine:lysine ratios on growth performance, blood urea nitrogen, and nitrogen balance in weaned pigs

Two experiments were conducted to evaluate the effects of different levels of threonine: lysine (Thr:Lys) ratios on growth performance, blood urea nitrogen (BUN) concentration, and nitrogen balance in weaned pigs. In Experiment 1, a total of 90 weaned pigs (Landrace x Yorkshire x Duroc) with an initial average body weight (BW) of 6.57 +/- 0.46 kg were allocated into three treatments for 35 days. Each treatment had six replicate pens with five pigs per pen. Diets were formulated with different apparent ileal digestible (AID) Thr: Lys ratios of 0.62, 0.67, and 0.72. Dietary AID of Lys and Thr concentrations were set at 10.8 and 6.7, 7.2, 7.8 g/kg, respectively. Throughout the experiment, average daily gain, average daily feed intake, and feed: gain ratio were not influenced (P > 0.05) by dietary Thr: Lys ratios. However, BUN concentration was increased (linear, P = 0.01) as the Thr: Lys ratio increased at day 35. In Experiment 2, a total of 24 weaned pigs with an average BW of 8.57 +/- 0.32 kg were individually housed in metabolic cages and fed for 10 days. Dietary treatments were the same as in Experiment 1. Nitrogen intake, nitrogen excretion in feces and urine, and nitrogen retention were not influenced (P > 0.05) by dietary Thr: Lys ratios. In conclusion, increasing dietary AID Thr: Lys ratio (0.62, 0.67 vs. 0.72) could not improve the growth performance and nitrogen balance in weaned pigs.