Pork production contributes to environmental pollution through the emission of nitrogen and phosphorus compounds. In addition, pig fattening in Europe usually requires imports of soybean, since the protein requirement of feed cannot be easily met by domestic plant-protein sources alone. It is therefore desirable to improve protein efficiency, i.e. to achieve a similar protein uptake in the carcass with a lower intake of dietary protein, through selective breeding. For a preliminary evaluation of the potential of breeding for higher nitrogen efficiency in this population, we used the results of previous experiments with protein-reduced feed to estimate genetic parameters of nutrient efficiency in Swiss Large White pigs. Protein efficiency could be determined by using automated feeders with individual pig recognition system allowing for detailed information of individual lifetime consumption. We determined protein contents of the feed and of the body fractions after slaughtering with wet-chemistry analyses. Heritability of protein efficiency in the whole body (including organs and cleaned gastro-intestinal tract) was estimated at 32% and in the carcass (including the head but entrails removed) at 16%. The common environment played a minor role in shaping nitrogen efficiency. Positive phenotypic correlations between the two traits suggest that selection for one trait will lead to an increase in the other trait. However, since protein-efficient pigs took longer to reach the target slaughtering weight, a slight delay in the growth of protein-efficient pigs might be expected. We have just begun a more thorough investigation of nutrient efficiency with studies yielding higher sample sizes to improve the quality of estimates and to conduct genetic correlation analyses with production traits. We further aim at obtaining information on the genes underlying nutrient efficiency in pigs as well as their functions.
