Diet-induced thermogenesis and feed intake in poultry: broiler versus layer cockerels

Research with adult mammals has shown that the diet-induced thermogenesis (DIT) related to the oxidation of macronutrients has a negative feedback on feed intake (FI), depending on the nutrient considered: proteins are combusted first, then carbohydrates and finally fat, corresponding to their satiating ability. However, previous studies revealed no significant differences in DIT between broilers reared on isocaloric low protein-high fat or high protein-low fat diets. The link between DIT and FI might be less distinct in broilers, which are characterized by a voracious appetite compared to layer strains. This study aimed to investigate the role of DIT in the regulation of FI in broiler and layer chickens. Also, the strain effect on plasma metabolite and hormone levels was studied. Day-old male broiler (Ross) and layer (ISA Brown) chicks were reared under standard conditions on a commercial broiler diet. From 22 days of age, twice per week, 3 broilers and 6 layers were placed in six open circuit respiratory chambers. After adaptation, the animals were fasted for one day, and fasting heat production (HP) was measured by indirect calorimetry. During the subsequent 7 hour refeeding period, FI as well as DIT was measured. Blood samples were taken after fasting and refeeding. During fasting and refeeding, the cockerels had a significantly higher HP per metabolic body weight (kg, MBW) than the broilers. This suggests that the broiler chickens use a greater proportion of the metabolisable energy intake for growth. The DIT per MBW and per FI was on average 320 % higher for the cockerels than for the broilers. However, FI per MBW was significantly higher in the cockerels. Thus, no feedback effect of DIT on FI per MBW was observed and the model formulated for adult mammals, relating DIT to FI could not be corroborated. The level of 3,5,3’-triiodithyronine in the plasma of the cockerels was elevated compared to the broilers, which was statistically verifiable after fasting, confirming the higher HP in the layer cockerels. Circulating uric acid, glucose, triglyceride and free fatty acid levels were significantly elevated in the layer cockerels. As the diet was formulated according to the requirements of broilers, these higher metabolite levels of the layer cockerels might reflect a relative oversupply of dietary nutrients.