Effect of L-threonine and DL-tryptophan supplementation to the low protein practical broiler finisher diet.

Three feeding experiments were conducted to investigate the effect of L-threonine and DL-tryptophan supplementation on the low protein practical finisher diet supplemented with L-lysine•HCl and DL-methionine using commercial broiler chicks housed in open bird houses at three local farms (facility: A 1800 birds×10 houses, B 1800 birds×9 houses, C 5000 birds×4 houses and 7000 birds×3 houses). Crude protein content of the high protein diet (HC diet) was 19% and that of the low protein diet (LC diet) was 16%. ME was 3200-3300 kcal/kg in both diets. The feed conversion was improved by the L-threonine addition to the LC diet supplemented with L-lysine•HCl and DL-methionine but no effect was observed in tryptophan supplementation. The third limiting amino acid of the LC diet was threonine and its requirement might be not less than 0.63% for finisher broilers. The tryptophan requirement for finisher broilers might be less than 0.17%. In conclusion, the protein con-tent of the broiler finisher diet could be reduced by 3% when L-lysine•HCl (0.22%), DL-methionine (0.08%) and L-threonine (0.04%) were added to the diet.No difference in the weight of abdominal and liver fat was observed between the diet treatments, whereas significant sex difference was observed. The liver and gizzard weight were not significantly different between treatments and between sexes.