Energy and nitrogen balances in young pigs maintained at constant weight with diets of differing protein content

Pigs of 7 kg were fed diets containing 25% (diet 25), 8% (diet 8) or 2.5% (diet 2) protein per kilogram in quantities sufficient to maintain constant body weight for 42 days. Another group was fed diet 25, but these animals were pair-fed to animals fed diet 2. The average daily metabolizable energy required for weight stasis by the pigs fed diet 2 was nearly twice as great as that taken by pigs fed diet 25. The lipid content of the pigs was approximately 107 g/kg at the start and at the end of 42 days was 195 g/kg in pigs fed diet 2, 75 g/kg in pigs fed diet 8 and only 11 g/kg in pigs fed diet 25. The gains or losses of body energy computed from the changes in body N and lipid agreed well with those estimated directly by bomb calorimetry of carcass samples. Taken as a whole, the results do not support the suggestion that diets extremely low in protein elicit an increase in heat production greatly in excess of that expected from the results of calorimetric studies with animals fed conventional diets.