Stochastic simulation of growth in pigs: Protein turn-over-dependent relations between body composition and maintenance requirements

A dynamic model for simulation of growth in pigs, that was extended by a module to describe protein turn-over, was made stochastic in order to simulate groups of pigs with among-animal variation in the maximum daily protein deposition (P-dep,P-max), in the minimum lipid to protein deposition rate (R(L/P,min)), and in the distribution of body protein over protein pools (muscle, connective tissue, and other proteins). As a result, these simulated pigs show among-animal variation in body protein content and composition. This in turn leads to among-animal variation in energy requirements for protein turn-over and this causes among-animal variation in maintenance metabolizable energy requirements (ME(maint)) as a result of variation in body composition. Simulated population means for P-dep,P-max were varied in seven steps from 100 to 250 g/day, with an among-animal variation coefficient of 0.10; the feeding level was also varied in seven steps. Dependent on the levels of these input variables, 100-kg pigs showed within-population standard deviations in body protein and lipid content of 0.31 to 0.54 kg and 1.22 to 2.17 kg, respectively. ME(maint) showed a protein-turn-over-related, within-population coefficient of variation of 0.014 to 0.02. Comparisons over populations suggests that a 1.50 proportional increase in P-dep,P-max (from 100 to 250 g/day) would increase protein-turn-over-related ME(maint) by 11 to 15%, from between 470 and 486 to 541 kJ ME per kg body weight(0.75) per day. The inferences that can be made from this with regard to experimental design are discussed.