Abstract
An evaluation of the effects of feeding programs with three amino acid (AA) densities given to males and females from a fast growth broiler breed was conducted. A total of 1200 Cobb×Cobb 500 broilers were distributed across 6 treatments in a 2×3 factorial arrangement (Sex×AA Density) with 8 replications of 25 birds per pen. Maize–soybean meal, provided from 1 to 7, 8 to 21, 22 to 35 and 36 to 42d of age, was formulated without crude protein restriction maintaining minimum ratios between essential AA and Lysine (Lys) in a true digestible (dig) basis as follows: total sulfur AA, 0.75; threonine, 0.65, valine, 0.75 (from 1 to 21d) and 0.78 (from 22 to 42d). Experimental treatments were Low (L), Moderate (M) and High (H) AA density diets with M having dig Lys of 1.25, 1.19, 1.09 and 1.05% in the pre-starter to withdrawal phases, respectively. Diets L and H had reductions and increases of 12% dig Lys in relation to the Moderate diet. There were no effects of treatments on mortality (P>0.05) and males had an overall better performance than females (P<0.001). No interactions were observed between Sex×AA density, with the exception of feed intake (1–42 days) and abdominal fat, which were further reduced with males as AA density increased than with females (P<0.01). Body weight gain was affected by AA density (P=0.0308) with birds fed L diets being lighter than those fed H and M diets. Feed conversion ratio (FCR) was improved (P<0.05) as AA density increased. Carcass and breast meat percentages were higher for females (P<0.01) and percent breast yield was highest for the H diet and lowest for the L diet, whereas the M diet was in between. Abdominal fat was reduced with H diet (P<0.05) for males but not for females. The decision making process to change AA density in the diet towards a higher density AA diet will depend on the price of feed ingredients and broiler meat.
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