Age-constant versus weight-constant feed consumption and efficiency in broiler chickens.

Weekly body weights, feed consumption (FC), and feed efficiencies (FE = gain:feed) of 148 male and 125 female broilers were measured individually between 2 and 7 wk of age. Multiple regression analyses of these traits were performed to examine the influence of body weight, weight gain or feed consumption, age, and individual broiler differences. Four different measures of FC and FE from 4 to 6 wk of age were compared within sex: age-constant FC and FE; weight-constant FC and FE; age-constant-weight-corrected FC and FE; and weight-corrected FC and FE, which estimate weight-constant measures. Much of the variation (85 to 90%) among broilers in FC and FE was due to age and body weight differences. Partial regression coefficients indicated that increased body weight at commencement of testing was associated with increased FC and reduced weight gain and FE. Correlations between age-constant and weight-constant FC were zero. This indicates the two forms have little in common. Correlations of body weights and weight gain with FC were negative (-.5 to -.8) for weight-constant values but positive (.5 to .8) for age-constant values. Hence, correlations of the correct (weight-constant) measure of FC with body weights indicate that faster growth gives rise to lower broiler feed consumption. Age-constant and weight-constant FE values were positively correlated (.8 to .9); however, the latter values had larger correlations with body weights and weight gain. These results emphasize the need to correct age-constant FC and FE for body weight differences in order to evaluate differences in efficiency among broilers more accurately.