OPTIMIZATION OF SELECTION FOR FOOD-INTAKE CAPACITY IN PIGS

Optimum selection directions for average ad libitum food intake capacity (FIC) in growing pigs were derived by means of a biological growth model based on the linear/plateau relationship between protein deposition and food intake. Breeding goal traits were minimum fat to protein deposition ratio (R), maximum protein deposition rate (Pd(max)) and FIC. The selection index included FIC, daily weight gain (DG), backfat thickness and proportion of lean meat in the carcass of a full-sib. Selection indexes were developed for three alternative levels of FIC. If FIC was too low to realize Pd(max), the economic weight of FIC was positive and optimal selection emphasis should be mainly on FIC, resulting in a rapid increase of DG. If FIC was higher than necessary to realize Pd(max), the economic weight of FIC was negative, and short-term selection resulted in increase of carcass leanness but decrease of FIC and DG. If FIC was just sufficient to realize Pd(max), selection should be for R and Pd(max). In this third alternative, the gain in FIC should follow the gain in R and Pd(max) in an optimal way and selection should best be carried out with a desired gains index, which results in improvement of DG and carcass leanness. It was shown that, in cases where FIC was higher than necessary to realize Pd(max), selection with a desired gains index should be preferred because this was more profitable in the long term. From the model calculations, it followed that future profit from selection of growing pigs for production traits is likely to decline because of the necessity to increase FIC.