Metabolism and Nutrition II: Ingredients and Protein

This study evaluated live performance, carcass, abdominal fat and commercial cuts yields of broilers fed corn-soybean meal diets with increasing digestible valine to lysine levels from 21 to 42 days of age. One thousand five hundred and seventy-five Cobb vs Cobb 500 male broilers were raised with the same commercial mash feed until 21 days of age. Seven treatments with 9 replications of 25 birds each were used afterwards to 42 days. These had a basal corn-soybean meal all vegetable diet with 1.10% of digestible lysine formulated without CP restriction (17.57% CP) and a known deficient digestible valine to lysine ratio (0.59) supplemented with synthetic amino acids to reach the following ratios with digestible lysine: methionine + cystine: 0.75; threonine: 0.67; isoleucine: 0.67, arginine: 106 and tryptophan: 0.17. Six diets having graded supplementations of L-valine were then produced to create the following valine to lysine ratios: 0.64, 0.69, 0.74, 0.79, 0.84 and 0.89. Statistical analysis was conducted to evaluate differences between treatments. Body weight gain, feed conversion rate and abdominal fat yield data were submitted to linear and quadratic regression analysis and 95% of asymptote levels were utilized as level which maximized responses. Feed intake, percent mortality, carcass and commercial cut yields were similar between treatments. However, a valine to lysine ratio of 59% negatively affected body weight gain and feed conversion, which were maximized at 0.745 and 0.755 digestible valine to lysine ratios, respectively. Abdominal fat yield was reduced until reaching a ratio of 0.78 digestible valine to lysine.