Mg. Macleod et al., EFFECTS OF LONG-TERM FOOD RESTRICTION ON ENERGY-EXPENDITURE AND THERMOREGULATION IN BROILER-BREEDER FOWLS (GALLUS-DOMESTICUS), Comparative biochemistry and physiology. Part A, Physiology, 106(2), 1993, pp. 221-225
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.