BACKGROUND: Leucine is one of the subgroups of amino acids, which play an important role in the anabolism of muscles, adipose tissue, and the liver by stimulating insulin secretion.OBJECTIVES: Effects of different levels of leucine were investigated on carcass yield, characteristics, and quality, and expression of insulin-like growth factor (IGF-1) and insulin genes in male broilers.METHODS: Five levels of L-leucine (100, 110, 120, 130, and 140 % of Ross strain requirements) were tested with 250 male one-day-old chicks in a completely randomized design with five treatments and five replicates (containing 10 chicks each). On day 42 of their age, the blood samples of two birds from each replicate (10 birds per treatment) were taken to determine serum IGF-1 gene expression. Subsequently, these birds were slaughtered for analysis of carcass characteristics and quality, and collecting the samples of liver and breast for expression of IGF-1 and insulin genes.RESULTS: Body weight increased by consumption of 140 % of leucine as compared to 100 %. Reduction in feed conversion ratio was observed by feeding 140 % of leucine level. The IGF-1 gene expression of breast and liver increased by 110 % of leucine level. Moreover, feeding 110 % of leucine level caused a higher expression of insulin gene in breast and liver. Consumption of 130 % of leucine improved the meat protein, fat, and ash contents. Furthermore, consumption of 110 % of leucine increased the serum IGF-1 concentration.CONCLUSIONS: Consumption of leucine in broiler diets was found to increase the expression of IGF-1 and insulin genes and consequently, improve the performance and carcass quality. It also decreased the abdominal fat in broiler chickens.

To investigate premium palm kernel cake (PKC) based diet’s effect on amino acid digestibility, this study conducted a feeding trial. Four groups of 150 day-old broiler chickens in every group were given four isocaloric diets using these formulation: Diet 1 - commercial feed for both starter and grower phase Diet 2 - broiler feed that contains 30% PKC for starter phase + commercial grower, Diet 3 - commercial starter + broiler feed that contains 45% PKC for grower phase (and Diet 4 - broiler feed that contains 30% PKC for starter phase + broiler feed that contains 45 % premium PKC for grower phase. During the experiment’s day 31, bird faeces’ samples were collected based on group diets in order to estimate the availability of amino acid as well as the digestibility of amino acids using balance experiment. Ultra-Performance Liquid Chromatography with photo-diode array detector was used to analyse amino acid. The findings showed no significant difference in digestibility of amino acids with p<0.05 in the feed broiler chickens’ comparison with commercial feed in terms of different levels of PKC based diet. This study shows that by including 30-45% premium PKC in poultry diet, it could contribute as protein source in broiler feed production with suitable supplementation of essential amino acid. Further studies are encouraged to combine the analysis of excreta, ileal digesta and growth performance in order to achieve more concrete findings.