Effect of early feed restriction on growth, feed conversion, and mortality in broiler chickens.

Two floor pen and two battery experiments were conducted to determine the effects of early feed restriction on the performance of commercial broilers. Feed restriction was induced in all experiments by providing chicks with 40 kcal of ME per bird per day, commencing at 4 days of age. Male chicks were feed-restricted for 7 (Experiments 1 and 2) or 6 days (Experiments 3 and 4), whereas broiler females were restricted for 5 days (Experiment 1). Ad libitum feeding was resumed after the restriction periods, and continued through the conclusion of the experiments at 49 (Experiments 1 and 2) or 28 (Experiments 3 and 4) days of age. Broilers provided ad libitum access to feed for the entire experimental period served as the controls in each study. Broilers subjected to an early feed restriction had significantly (p less than or equal to .05) lower mean body weights than controls for all ages measured in the four experiments. However, feed conversion ratios for restricted broilers were significantly lower at 28 (Experiments 1 through 4) and 49 (Experiments 1 and 2) days of age than for birds consuming feed ad libitum. Through regression analyses, it was estimated that male broilers in Experiments 1 and 2 would require approximately 2 additional days to obtain body weights similar to those observed in control broilers and would still maintain a lower feed conversion ratio at this older age. In Experiments 1 and 2, weekly body weight gains for restricted broilers were significantly lower than for controls from 0 through 28 days of age. However, restricted broilers (7 days) in Experiment 2 had significantly higher rates of gain from 29 to 49 days of age than unrestricted controls. Total pen body weights for restricted and ad libitum groups were similar at 49 days of age in Experiments 1 and 2, which reflected the significant difference in mortality observed between the two groups.