Studies on energy and tryptophan requirements of growing pigs
With this study it has been shown that fattening pigs kept under commercial housing conditions need a considerable amount of energy for other purposes than maintenance and growth (MEx). MEx can be used as a sensitive indicator for the efficiency and quality of production systems. Enhanced physical activity is likely the main responsible factor for MEx in our study, while environmental temperature, genotype, and immune responses might have contributed to a smaller extent only. However, further studies are needed to identify and to quantify the factors responsible for MEx to provide more precise recommendations for the energy supply to growing pigs. Estimates of the optimum Trp:Lys ratio differ between the mathematical model used to analyze experimental data, on the chosen response parameter as well as on the intended performance level. A more critical discussion about suitable models to describe dose-response relationships, about the performance level to be aimed for in the commercial production, and about the parameters to be chosen is necessary to avoid conflicting recommendations for optimum AA supply which lead to an uncertainty of farmers and the feeding industry. (ii) Trp requirement is influenced by feed ingredients when using standard values for precaecal digestibility of Trp. Further studies are needed to identify the responsible factors for this effect to allow for more diet specific recommendations for the adequate Trp supply to growing pigs.