Effects Of Lower Protein Diets Supplemented With Tryptophan On Performance And Hypothalamic 5-Hydroxytryptamine Concentration For Piglets

Three experiments were conducted to study the effect of tryptophan on piglets performance and its modulating mechanism of improving feed intake in this reasearch. In Exp. 1, 90 piglets with initial BW of 8.1 kg were fed one of five diets in a randomized block design for 28d. Three pigs were fed in one pen as one replicate resulting in 6 replicates per treatment. From the 1st diet to the 4th, dietary crude protein levels were 18.37% and consisted of a control (no synthetic tryptophan) or supplemented with 200, 400, or 600 g/t synthetic tryptophan, which resulted in the tryptophan concentration in diets were 0.22%, 0.24%, 0.26%, and 0.28%, respectively. In the 5th diet, the crude protein and tryptophan concentration were 21.59%, and 0.24%, respectively. Although the ADG and ADFI of piglets were not significant by dietary trypothan concentration, the performance of piglets low protein supplemented with 600 g/t tryptothan in the 4th group were almost equal to that of the high protein diet in the 5th group. Compared with the higher protein diet, the urinary N concentration of serum were significantly reduced by lower protein diet, which was about 16%. In Exp. 2, 54 piglets with initial BW of 9.9 kg were fed a lower level tryptophan (0.11%) diet, normal level tryptophan (0.19%) diet, and higher level tryptophan (0.24%) diet in a randomized block design for 28d. Three pigs were fed in one pen as one replicate resulting in 6 replicates per treatment. With increasing of dietary tryptophan concentration, the performance of piglets was significantly improved (P < 0.05), especially for the ADFI. Moreover, with dietary tryptophan concentration increasing, the hypothalamic 5-hydroxytryptamine concentration and serum were significantly increased, which indicated that the ADFI improving by tryptophan might modulated by increasing the hypothalamic 5- hydroxytryptamine. In Exp. 3, 72 piglets with initial BW of 10.2 kg were fed one of five diets in a randomized block design for 28d. Three pigs were fed in one pen as one replicate resulting in 6 replicates per treatment. From the 1st diet to the 4th, dietary tryptophan levels were 0.28% and consisted of a control (no synthetic large neutral amino acids) or supplemented with 0.39%, 0.81%, or 1.32% synthetic large neutral amino acids, which resulted in the large neutral amino acids concentration in diets were 5.34%, 5.73%, 6.14% and 6.66%, respectively. The ADG of piglets were not significant by dietary large neutral amino acids concentration. With increasing of dietary large neutral amino acids concentration, the ADFI of piglets was significantly improved. The hypothalamic 5-hydroxytryptamine of piglets was not significantly changed by dietary large neutral amino acids concentration.