Variation in maintenance requirements of growing pigs in relation to body composition : a simulation study

Existing dynamic models for the simulation of growth metabolism in pigs were extended with routines to predict the energy requirements of protein turnover and thermoregulation. Protein turnover was modeled by distinguishing six body protein pools with different turnover rates and different growth curves. Thermoregulation was modeled by assessing minimum and maximum heat loss, and heat production, deciding by comparison of these whether the pig is cold or hot, and taking appropriate metabolic action.

Model output compared satisfactorily with independent data. Pig populations were modeled by stochastic simulation, imposing between-animal variation on growth potential parameters and therefore on body (growth) composition. Because protein turnover, and heat production and thermal insulation, in the model depend on body (growth) composition, between-animal variation was generated in the associated energy requirements. This leads to variation in maintenance requirements as a function of variation in body composition.

The simulated output was analysed to provide an answer on the question "to what extent can differences in maintenance requirements be attributed to differing proportions of the different organs and tissues of the body, each having different metabolic rates" ? The conclusion from this analysis is that the contribution of variation in body (growth) composition to the variation of total maintenance requirements in growing pigs is very limited, probably less than 10 % of the total variance. Experimental verification of this conclusion is desirable; the design of the required experiments is discussed, making use of the simulation results.