Relationships Between Carcass Fatness and Feed Efficiency and Its Component Traits in Broiler Chickens1

ABSTRACT Weight gain, feed consumption, and feed efficiency (gain/feed) from 28 to 48 days of age were measured in conjunction with initial weight (at 28 days) and percentage carcass fat of 59 male and 54 female broiler chickens from two stocks slaughtered at 49 days. Relationships among these traits were examined in terms of simple and partial correlations and of multiple regression analyses. Feed efficiency improved with rapid weight gain but declined with greater carcass fatness and initial weight. Within broiler strain, sex, and cage type subclasses, 65 % of the variation in feed efficiency was accounted for by differences in these variables; gain, 36%; carcass fatness, an ad-ditional 25%; and initial weight, the final 4%. In some instances, differences between simple and corresponding partial correlations were observed. The —.48 correlation between carcass fatness and feed efficiency became —.62 after adjusting for differences in weight gain. Similarly the.40 correlation between carcass fatness and feed consumption rose to.63 after adjustment for differences in weight gain. The low correlation of.01 between initial weight and feed efficiency became —.38 after adjusting the data for dif-ferences in weight gain and carcass fatness. Hence, results from age constant feed efficiency tests should be corrected for differences in initial weight to reflect "true " differences in efficiency. (Key words: feed efficiency, growth, fatness