Branched Chain Amino Acids: Requirements and Antagonism in the Male Broiler Chick

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Experiments were conducted to study the effect of feeding the branched-chain amino acids (BCAA), leucine (Leu), isoleucine (Ile) and valine (Val) to 7-21 day old male broiler chicks. Using the central composite rotatable design, the results of response surface regression analysis showed that optimum body weight gain (BWG) and feed conversion values (FC) would be obtained with dietary levels of 1.16, 0.81 and 0.90% for Leu, Ile and Val respectively. Chicks fed a Val deficient diet ad libitum exhibited a ricket-like condition which was characterized by a low Ca content in the bone. The value was 134 as compared to 156 and 172 mg/g dry bone for chicks fed a diet deficient in the three BCAAs and a Val supplemented diet respectively. similar results were obtained when equal amounts of the three diets were given to the birds by using pair feeding and force feeding techniques. Although birds fed the Val deficient diet and those pair fed the BCAA deficient diet had similar BWG, bone measurements (bone ash, dry bone, and bone Ca) were significantly lower (p < 0.05) for the Val deficient group. Serum ca (mg/dl) was not significantly different. Excretion of urinary ca, however, was enhanced by feeding a Val deficient diet as compared to the Val supplemented treatment suggesting that a proper ratio of the BCAAs may be required to form the bone matrix which serves as a base for mineral deposition. Feeding a Val deficient diet significantly (p < 0.05) lowered the protein content of the feathers. The value was 82.7% as compared to 85.0 and 88.0% for all BCAA deficient and Val supplemented diets respectively. Valine deficiency also changed the pattern of feather amino acids by increasing the levels of aspartic acid, glutamic acid, methionine, tyrosine, histidine and lysine. Cysteine level, however, was decreased. High dietary Leu(≥ 3.0%) depressed BWG and FC of ad libitum fed birds. When Ile and Val were simultaneously added to the diet the growth rate and FC were similar to the controls. The ketogenic property of Leu was tested by measuring β-OH-butyrate level in the plasma (mg/1) and found to be nonsignificant.