Determining the optimal lysine : calorie ratio for growth performance of 10 to 25 kg nursery pigs

Two studies were conducted to evaluate the effects of increasing dietary lysine and energy density on performance of Genetiporc nursery pigs. Experiment 1 was organized as a combination of two simultaneous experiments with one set of diets consisting of five treatments with increasing true ileal digestible (TID) lysine (0.99, 1.07, 1.14, 1.22, and 1.30%) and the second set of diets consisting of five treatments with increasing energy density (2,952, 3,093, 3,236, 3,377, and 3,520 kcal of ME/kg). The highest level of both lysine and energy (1.30% and 3,520 kcal/kg, respectively) was combined as one diet for a total of 10 treatments. Pigs were randomly allotted to 8 replications with 5 pigs per pen. Increasing TID lysine linearly (P<0.01) improved ADG and G:F. While increasing energy density had no effect on ADG, ADFI decreased (linear, P<0.01) which resulted in a quadratic (P<0.08) improvement in G:F. Regression analysis of the response surface indicated the optimal lysine:calorie ratio was 3.7 g lysine/Mcal ME. In Exp. 2, pigs were fed diets with two different energy densities (2.95 or 3.28 Mcal ME/kg) with TID lysine:calorie ratios ranging from 3.1 to 4.1 g/Mcal ME. There was an energy density by TID lysine:calorie ratio interaction (P<0.03) for ADG. The greatest ADG was achieved for pigs fed a lysine:calorie ratio of 3.60 for pigs fed the low energy diets and 3.36 for pigs fed the high energy diets. Feed efficiency improved (quadratic, P<0.01) as lysine:calorie ratio increased for pigs fed the low energy diet with the best G:F observed at 3.87. Pigs fed the high energy diets had a quadratic (P < 0.07) improvement in G:F as the lysine:calorie ratio increased with the best feed efficiency at 4.07; however, little improvement were observed when the ratio was increased above 3.36. Based on these results, the optimal lysine to calorie ratio seems to be 3.30 to 3.87 g of TID lysine/Mcal ME for pigs in these facilities.