The Effect of Food Restriction During Rearing on Fasting Heat Production of Layer Strain Pullets and Hens

ABSTRACT Fasting heat production was measured in darkened respiration chambers at three chronological and three physiological ages during rearing and laying in a layer strain to determine the effects of food restriction during rearing. There were three rearing treatments (42 to 162 days of age) in which birds were allowed ad libitum food intake (F) or were restricted by time (TR), in which birds were allowed con-tinuous ad libitum food intake for about 24 hr in every 72 hr, or by proportion (PR), in which birds were offered each day 60 to 70 % of the quantity consumed by F birds the previous day. Liveweight at 163 days of age was reduced by 19 and 15 % for TR and PR birds, respectively, compared to F birds. Ad libitum food consumption was allowed during the laying period. Chronological age measurements were carried out at 140 days of age (prelay), 332 days of age, and 370 days of age. Physiological age measurements were carried out at sexual maturity (first egg), peak production (28 days after first egg) and postpeak production (98 days after first egg). Fasting heat production, measured under conditions that minimized physical activity, was not altered after correction for liveweight changes by the food restriction treatments. Based on this and other published studies, it was postulated that physical activity may play an im-portant role in determining the effects of food restriction in poultry. (Key words: fasting heat production, food restriction, pullets and hens