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.</p

Variance components for survival of piglets at farrowing using a reduced animal model

Farrowing survival is usually analysed as a trait of the sow, but this precludes estimation of any direct genetic effects associated with individual piglets. In order to estimate these effects, which are particularly important for sire lines, it is necessary to fit an animal model. However this can be computationally very demanding. We show how direct and maternal genetic effects can be estimated with a simpler analysis based on the reduced animal model and we illustrate the method using farrowing survival information on 118 193 piglets in 10 314 litters. We achieve a 30% reduction in computing time and a 70% reduction in memory use, with no important loss of accuracy. This use of the reduced animal model is not only of interest for pig breeding but also for poultry and fish breeding where large full-sib families are performance tested

Body composition in non reproduction adult males and females in long-term selection experiment for litter in mice

Earlier studies have shown that adult mice from a line selected for high litter size (S-line), in particular females, had higher residual food intake (RFI) than mice from a non-selected control line (C-line). It was suggested that this increase in RFI, in particular the mature selected females, may anticipate the metabolically stressful periods of pregnancy and lactation. The present study investigated whether body composition at maturity has been changed as a correlated response to selection, in order to support the offspring during pregnancy and lactation. Furthermore, part of the observed differences between individuals in RFI may be attributable to differing proportions of body protein and lipid. For these reasons, differences in body composition at maturity between males and females of the S-line and the C-line were investigated. Lipid percentage was similar for C-line animals and S-line females; S-line males had a significantly lower lipid percentage. Males had a higher protein percentage than females, in particular S-line males. The results show that body composition in adult non-reproductive females has not been affected as a correlated effect of selection for high litter size. Furthermore, the results suggest that the high lean content in S-line males may explain part of the high RFI compared with C-line animals. Body composition in S-line females probably does not explain the high RFI compared with S-line males and C-line animals. Factors other than protein and lipid levels must be responsible for the differences found between the lines and sexes in RFI