Components of feed efficiency in broiler breeding stock: is improved feed conversion associated with increased docility and lethargy in broilers?

Two trials were conducted to test the hypothesis that broilers classified as good rather than poor feed converters (low vs. high feed-to-gain ratios, respectively) would show decreased activity (increased lethargy) and reduced fear of human caretakers. In both trials birds were reared to juvenile selection age when the 192 males with the "best" breast and leg conformation were placed into individual bird cages (46 x 60 cm), and their feed conversion ratio (FCR) was measured. In trial 1, birds remained in the cages for 7 d for assessment of feed conversion. During the feed conversion testing period, the birds were subjected to three behavioral tests. First, approach-avoidance responses to a novel object placed in the feeder were observed when feeding would be expected. Second, behavior patterns of individual birds were assessed by recording feeding, drinking, walking pecking, preening, standing, and resting. Third, the 20 birds showing the best FCR and the 20 showing the worst were induced into tonic immobility (TI). Feed conversion was not related to either the novel object or the TI measures of fearfulness. Neither was FCR related to feeding, drinking, walking, or pecking. However, FCR was positively correlated with both standing and preening and negatively correlated with resting behavior. In trial 2, the FCR test lasted for 11 d. The birds were assessed for behavioral patterns (feeding, drinking, walking, pecking, preening, standing, and resting) as in the previous trial. As in trial 1, FCR was positively correlated with standing and negatively correlated with resting behavior. Contrary to expectations, the results of these two studies suggest that broilers with good FCR were actually less lethargic and no more fearful than those that showed poor FCR values.