THE EFFECT OF GENOTYPE AND SEX ON THE PATTERNS OF PROTEIN ACCRETION IN PIGS

Protein accretion curves were derived using food intake, growth and bo dy composition data from a total of 320 pigs, which comprised castrate d males and gifts from five genotypes. The 32 pigs from each genotype/ sex subclass were offered ad libitum a series of isoenergetic diets (1 3.8 M) metabolizable energy per kg) designed to provide a nonlimiting intake of nutrients and to allow maximum protein deposition rates. Fou r pigs from each subclass were slaughtered at each of the live weights (kg) 25, 44, 65, 85, 100, 115, 130 and 150. Daily food intake (dF/dt) was described as an increasing exponential Junction of age (t), live weight (W) as an increasing exponential function of cumulative food co nsumed (F), and protein weight (Pr) as an allometric function of live weight (W). The rate of protein accretion in the body of pigs [d(Pr)/d t] was calculated as d(Pr)/dt = (dF/dt).(dW/dF).(dPr)/dW). Bootstrap p rocedures were used to estimate standard errors for the food intake, g rowth and compositional parameters and to obtain the confidence bands for the dependent variables (dF/dt, W, Pr and d(Pr)/dt). Protein accre tion rate as a function of live weight was curvilinear, increasing to a maximum, then decreasing with increasing live weight. There were sig nificant differences between subclasses in the maximum rate of protein accretion, although there was no relationship between this rate and t he live weight, stage of maturity, or age at which maximum protein acc retion occurred. Describing protein accretion as a multiplicative func tion of food intake,food efficiency and the partitioning of nutrients in the body allowed changes in the magnitude and shape of the protein accretion curve to be ascribed to one, or a combination, of the above mechanisms.