EFFECTS OF LONG-TERM FOOD RESTRICTION ON ENERGY-EXPENDITURE AND THERMOREGULATION IN BROILER-BREEDER FOWLS (GALLUS-DOMESTICUS)

1. From 2 to 21 weeks of age, 150 female broiler-breeder chicks receiv ed one of three dietary treatments. Fifty received an ad libitum suppl y of food (treatment AL). The remaining 100 were given weighed (restri cted) rations once a day, 50 receiving the amount per bird recommended in the Ross 1 Parent Stock Management Manual (treatment R) and the ot her 50 receiving twice this recommended amount (treatment 2R). Water w as provided ad libitum for all treatment groups.2. The daily allowance for R birds increased from 26 g per bird at 2 weeks of age to 94 g at 21 weeks. The intake of AL birds meanwhile increased from 65 g at 2 w eeks to 240 g at 19 weeks, before decreasing to about 200 g at 21 week s.3. Median heat productions (H) per bird in the R and 2R treatment gr oups were, respectively, 65 and 40% lower than in the AL when adjustme nt was made for the reduced food intake of AL birds in the calorimeter chambers. The effects of dietary treatment on fasting H were proporti onally similar. 4. Because the increasing divergence in body weights w ould have made a large contribution to differences in H per bird, the results were adjusted to the median weight of 2.03 kg and to unit weig ht (1.00 kg). Adjusted fasting heat production was 18 and 11% less in 2R and R birds than in those fed ad libitum. 5. If age was included as a variate in the logarithmic multiple regression, H was proportional to body weight (W, kg) raised to the power 0.73; if age was not includ ed, H was proportional to W0.55. 6. Rectal temperature was 0.7-degree- C higher in AL birds at ambient temperatures of both 23 and 28-degrees -C. All treatment groups had a higher rectal temperature at 28-degrees -C than at 23-degrees-C, with the AL birds most affected.7. Foot surfa ce temperature of R birds at an ambient temperature of 23-degrees-C wa s 8-degrees-C lower than that of the 2R and AL groups, indicating peri pheral vasoconstriction. 8. Polypnea (panting) and wing-extension occu rred frequently in the AL birds, which also had a greater water intake . It was also observed that the restricted birds tended to aggregate, while the AL groups tended to space themselves evenly about the pen. 9 . It was concluded that broiler breeder fowl responded to restricted f ood intake by a reduction in heat production over and above that resul ting directly from reduced metabolism of food and reduced body weight. The reduced metabolic rate per unit of weight conferred a thermoregul atory advantage at high ambient temperature.