Optimal dietary lysine to threonine ratio in pigs (30–110 kg BW) derived from observed dietary amino acid efficiency

Optimal ratio of lysine (Lys) to threonine (Thr) in diets for growing barrows [genotype: Piétrain × (Large White × German Landrace)] was established at 30, 50, 70, 90 and 110 kg body weight (BW). N balance studies were conducted with diets based on constant mixture of wheat, barley, soybean meal and field peas. Supplementation of crystalline amino acids (AA) provided diets with Lys (diet A) and Thr (diet B) in first limiting position. For each BW range, totally 28 individual N balance data were utilized for assessing model parameters (exponential N utilization model) of dietary efficiency of Lys and Thr, respectively. Observed maximal dietary efficiency of Lys and Thr provided the database for conclusion of optimal dietary Lys to Thr ratio. Based on applied experimental conditions, BW dependent Lys to Thr ratio could not be concluded. On average, the dietary ratio Lys to Thr = 1:0.61 ± 0.02 was obtained as optimal for growing pigs.