Energy balance of laying hens selected on residual food consumption

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Abstract
1. Energy balance of adult hens divergently selected for high (R + ) or low (R- ) residual food consumption was investigated using indirect calorimetry. Three experiments were conducted: feeding behaviour of individual hens, hens having free access to food or fasting and hens tube-fed at 70, 100 or 130% of the control intake of both lines. 2. R + hens ate significantly more than R- (+ 48%). This difference was maximum at the onset of the light (+ 120%) and not significant during the rest of the light period. Although both lines spent the same total time eating, R + hens exhibited more frequent but shorter meals than R- ones, suggesting a higher feeding activity in R + hens. 3. True metabolisable energy (TME) intake was 28% greater in R+ than in R- birds. Basal heat production did not differ significantly between genotypes. Heat increment of feeding (HI) or diet-induced thermogenesis was significantly enhanced in R + birds: + 23.9 vs 13.7 kJ/100 kJ TME intake in R- . 4. When tube-fed and placed in darkness, restricted-fed R + hens had the same HI as R- birds. When fed at 100% and 130% of control intake, R + hens demonstrated a regulatory thermogenesis, which allowed them to dissipate the excess of energy ingested compared to R- hens. 5. No significant modification was observed in plasma triglyceride, phospholipid, uric acid, glucose or insulin concentrations between lines, suggestive of the use of similar thermogenic pathways. While plasma triiodothyronine (T3) concentrations did not differ between genotypes, plasma thyroxine (T4) appeared higher in unfed R + birds and equal in fed conditions in both lines. 6. A regulatory part of HI allowed R + hens to get rid of their excessive energy intake. An increased turnover of lipids could be involved.