Metabolic utilization of energy and maintenance requirements in growing pigs: Effects of sex and genotype

An experiment was conducted in which the metabolic utilization of energy wa s measured in individually penned pigs from seven groups that differed in g enotype and(or) sex and ranged in body weight between 20 and 107 kg. The an imals were fed a diet containing, on a DM basis, 14.7 MJ ME and at least 21 % CP. Heat production was measured in an open-circuit calorimeter, and ener gy, nitrogen, and fat balances were determined at regular intervals over th e growing period; a total of 177 measurements were performed. Body composit ion of the animals was measured by serial slaughter, and these data were us ed for estimating the body composition of an animal at a given weight; thro ugh allometric regression. A factorial analysis procedure was used to estim ate the utilization of ME: by regressing the ME intake on the observed prot ein and lipid deposition rates. The intercept of this equation is the maint enance energy requirement (MEm) and was represented either as a function of body weight with group-specific parameters (MEm = a(i) BWb) or as a functi on of the muscle and visceral I-mass with an additional additive group effe ct (MEm = a(M) muscle(b) + a(V) viscera(b) + G(i)). With BW as dependent va riable, the exponent b was close to .60 and differed significantly from .75 . The regression coefficient (a(i)) averaged 1.02 MJ ME/kg(.60) but it was different for most groups, indicating that different groups of animals have different maintenance requirements. Fixing the exponent to .75 consistentl y underestimated the maintenance requirement. When the-exponent b was not f ixed to .75 but estimated, the partial efficiencies for protein and lipid d eposition were .62 and .84, respectively. Body muscle and visceral mass cou ld explain a large pare of the variation in MEm. Viscera contributed three times more to MEm (per kilogram of mass raised to the .70 power) than did m uscle. Even though the muscle mass exceeds to a large extent the visceral m ass in animals, the contribution of muscle to MEm was lower than that of vi scera for most groups.