Effect of Met+Cys Supplementation to a Low- Protein Diet on the Growth Performance and Fat Accumulation of Broiler Chicks at Starter Period

Abstract

This experiment was conducted to determine the effects of feeding a low-protein diet supplemented with DL-methionine-plus-L-cystine (Met+Cys) on growth performance and fat accumulation of female broiler chicks during the starter period (0-21 days). A low-protein diet (17% Crude Pretein (CP); 3,017 Metabolizable Energy (ME) kcal/kg) was fortified with Met+ Cys at 0.64%, 0.93%, 1.25% and 1.50%. Another diet (23% CP; 3,017 ME kcal/kg) served as the control. All the birds were given feed and water ad libitum. The body weight gain of the birds fed the 17% CP diet supplemented with Met+Cys at 1.50% was comparable to that of the 23% CP diet group. The feed conversion ratio was better in chicks fed the 23% CP diet. However, the protein efficiency ratio, feed intake and energy intake were not significantly different among the experimental groups. The abdominal fat weight was high in chicks fed the 17% CP diet; however, it decreased as the amount of added Met+Cys in the diet increased. The fatty acid synthetase activity in the liver of chicks fed 17% CP diets supplemented with Met+Cys was significantly higher than that of the 23% CP diet group. The acetyl-CoA carboxylase was not affected in all the experimental groups. The triglyceride contents in the liver and breast muscle were decreased by the increased level (1.50%) of Met+Cys supplementation. The free cholesterol in the serum and in the breast muscle was not influenced by the level of dietary protein. That in the liver, though, was significantly higher in the 23% CP diet group than in the 17% CP diet group. The phospholipid in the liver was not influenced by the protein level or by Met+Cys supplemeta-tion; however, breast muscle phospholipid tended to increase in chicks fed the 17% CP diet supplemented with Met+Cys. The results of this study suggest that a 17% CP diet, if supplemented with a right quantity of Met+Cys might improve the growth performance of starter broiler chicks during the first 21 days. The data further suggest that fat deposition in the chicks fed the 17% CP diet could be mitigated by proper Met+Cys supplementation.