Improvement of energy and nitrogen utilisation in pork production : genetics and growth models

Expansion ofdemand for porkis expected to meet the nutritional requirements of an increasing world population. However, higher levels of pig production are using limited feed resources and are often associated with higher levels of environmental pollution, which provide substantial challenges for pork producers. Therefore, strategies that simultaneously improve feed efficiency and increase production with reduction of environmental pollution of pork production (e.g. per kg product) is necessary. The general aim of the current project was to investigate opportunities for improvement of energy usage and nitrogen excretion at different stages of growth in pigs, and to determine their phenotypic and genetic background in association with other performance traits as well as to provide the basis for developing strategies for improvement of these traits using biological growth models.Feed efficiency was characterised by residual energy intake (REI) as the surplus of energy intake which is not used for protein and lipid deposition along with maintenance throughout growth to 140 kg BW whereas nitrogen excretion was estimated as the difference between nitrogen intake and retention. The results of phenotypic analyses indicate that nitrogen excretion increases substantially during growth of pigs and can be reduced most effectively by improving feed efficiency and to a lesser extent through the improvement of weight gain and/or body composition. Results of genetic analyses indicate that REI as a measure of feed efficiency is highly heritable (h2= 0.44), suggesting great potential for genetic improvement. REI has different genetic background at different stages of growth, suggesting that genetic improvement of REI should consider the stage of growth. In addition, REI explains a large portion of variance in nitrogen excretion, suggesting that selection for lower REI is expected to reduce nitrogen excretion of pork production as well as improve feed efficiency. Genomic analysis showed that different genes are responsible for efficiency of feed utilisation at different stages of growth.The results further suggest that only a small proportion of the variance in REI was explained by variation in feed intake, whereas underlying factors of feed utilisation, such as metabolism and protein turnover, are likely to have great influence on REI. A biological growth model was used to characterize a crossbred population regarding feed energy and nitrogen efficiency in comparison to two purebred population selected for different performances. The results of the biological growth model can be used to developed optimal genetic, nutritional and production strategies, e.g. the impact of reduction in slaughter weight on marginal energy efficiency and nitrogen excretion was estimated. Furthermore, based on the results of the biological growth model, the influence of changes of production traits during growth on energy and nitrogen efficiency can be estimated to optimise genetic strategies. Furthermore, opportunities for further improvement of energy and nitrogen utilisation have been outlined.