Effects of long-term food restriction on energy expenditure and thermoregulation in broiler-breeder fowls (Gallus domesticus)

• 1.1. From 2 to 21 weeks of age, 150 female broiler-breeder chicks received one of three dietary treatments. Fifty received an ad libitum supply of food (treatment AL). The remaining 100 were given weighed (restricted) rations once a day, 50 receiving the amount per bird recommended in the Ross 1 Parent Stock Management Manual (treatment R) and the other 50 receiving twice this recommended amount (treatment 2R). Water was provided ad libitum for all treatment groups.
• 2.2. 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 weeks to 240 g at 19 weeks, before decreasing to about 200 g at 21 weeks.
• 3.3. Median heat productions (H) per bird in the R and 2R treatment groups were, respectively, 65 and 40% lower than in the AL when adjustment was made for the reduced food intake of AL birds in the calorimeter chambers. The effects of dietary treatment on fasting H were proportionally similar.
• 4.4. Because the increasing divergence in body weights would 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 weight (1.00kg). Adjusted fasting heat production was 18 and 11% less in 2R and R birds than in those fed ad libitum.
• 5.5. 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 included, H was proportional to W^0.55.
• 6.6. Rectal temperature was 0.7°C higher in AL birds at ambient temperatures of both 23 and 28°C. All treatment groups had a higher rectal temperature at 28°C than at 23°C, with the AL birds most affected.
• 7.7. Foot surface temperature of R birds at an ambient temperature of 23°C was 8°C lower than that of the 2R and AL groups, indicating peripheral vasoconstriction.
• 8.8. Polypnea (panting) and wing-extension occurred 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.
• 9.9. It was concluded that broiler breeder fowl responded to restricted food intake by a reduction in heat production over and above that resulting directly from reduced metabolism of food and reduced body weight. The reduced metabolic rate per unit of weight conferred a thermoregulatory advantage at high ambient temperature.