The effect of the apparent ileal digestible lysine-to-energy ratio on growth rate and protein deposition in the body of growing pigs fed a wheat-rapeseed diet

Abstract

The experiment was conducted on 20 pigs from 25 to 70 kg body weight (BW) to determine the optimal apparent ileal digestible lysine:metabolizable energy (Lys:ME) ratio in a wheat-rapeseed diet. Gilts (synthetic line 990) were allocated to 4 groups. Group 1 was fed a basal diet containing wheat and rapeseed meal (with 4.4 mM kg-1 glucosinolates), without supplementation with any crystalline amino acids and was lysine deficient. Group 2 consumed a basal diet supplemented with 0.21% L-lysine·HCl, but was still deficient in comparison with the content of other essential amino acids. Group 3 was fed a diet supplemented with 0.42% L-lysine·HCl, 0.018% L-threonine, and 0.015% L-tryptophan. Group 4 received a diet supplemented with 0.65 % L-lysine·HCl and 0.053% DL-methionine to maintain their mutual proportion of 100:32, however the concentration of these amino acids was in excess of the requirement. Supplementation of 1rystalline lysine to the basal diet was designed to contain a differential Lys:ME ratio: 0.34 (diet 1), 0.47 (diet 2), 0.59 (diet 3), and 0.71 g MJ-1 (diet 4). The apparent digestibility of amino acids in wheat and rapeseed meal was determined in a separate experiment with surgically modified pigs. All diets were isoproteino (193 g kg-1 DM) and isoenergetic (14.5 MJ kg -1 DM). The methionine, threonine and tryptophan contents were close to the recommendations of CVB (1995) or were given in excess. The gain of chemical body components was determined using the comparative slaughter method. The animal body weight gain and protein deposition in the body were taken as the response criteria. Daily weight gain increased (P<0.05) from 673 to 808 g along with the Lys:ME ratio increasing from 0.34 to 0.59 g MJ-1. Daily protein deposition also increased (from 98 up to 133 g; P<0.05). However, increasing the Lys:ME ratio from 0.59 to 0.71g MJ-1 did not increase daily gain or protein deposition. These results indicate that the optimal Lys:ME ratio in diets containing wheat and rapeseed meal and supplemented with crystalline lysine was 0.55 g MJ-1 when referred to growth rate or 0.60 g MJ-1 if daily protein deposition in the body was considered.