The effect of energy intake, genotype, and body weight on protein retention in pigs when dietary lysine is the first-limiting factor

This study tested the hypothesis that the effect of lysine intake, if first -limiting, on protein retention in growing pigs is completely independent o f the effects of energy intake, differences in the protein retention capaci ty among genotypes and gender, and body weight. Protein retention, using th e nitrogen balance technique, was measured in 12 castrated male German Land race and Pietrain pigs at 44 and 77 kg of BW and at two energy intake level s (1.1 and 1.3 MJ ME/kg BW.75). All animals received a constant amount of a basal, diet that provided a protein intake of 220 g/ d and a total lysine intake of 13 gld. Appropriate amounts of cornstarch were offered additional ly to reach the intended energy intake levels. The results show that neithe r energy intake nor breed had any effect on the level of protein retention, whereas, at 77 kg BW, protein retention was significantly lower than at 44 kg(117.8 and 123.5 g/d, respectively), which can be attributed to the high er requirement for maintenance. The results of this experiment and the line arity of the relationship between protein retention and lysine intake as sh own by several authors simplify both the prediction of protein retention fr om lysine intake and the calculation of the lysine requirement for a partic ular protein retention: However, to ensure accuracy of these predictions, i t is essential to know when ratios of lysine to other amino acids and to en ergy and capacity for protein retention in the animal become first-limiting .