Optimum tryptophan: Lysine ratio in diets for growing pigs: Analysis of literature data

摘要

Optimum tiyptophan supply in diets for glowing pigs shows considerable variation between studies; therefore, an attempt was made to analyse all available data reported in the literature. Due to the fact that, in most studies, lysine was the second-limiting amino acid, which means that lysine limits growth at a certain level of tryptophan intake, optimum supply has to be expressed as a ratio to lysine. The database was too small to give optimum supply as a concentration in the diet or as a daily amount. In total, 33 experiments were found, where tiyptophan intake was offered in graded levels resulting in a tryptophan-dependent and -independent response phase An additional 13 experiments showed either no dependent or no independentphase, which did notallow an optimum determination. The optimum tryptophan: lysine ratio (T: L_(opt)) was defined as the beginning of the plateau response-phase in feed intake or body weight gain. Mean T: L_(opt) was 0.174 (SD=0.023; n = 3.3) and seemed to be unaffected bybody weight, growth rate, lysine and protein concentration in the diet, or genetic improvement of the animals. However, precise detection of the optimum ratio is generally restricted due to the relatively large intervals between the ratios tested in therespective studies. Mean difference between T:L_(opt) and the nearest T:Lratiotestedbelow(T:L_(opt-1))wasO,028(SD=0.011;n=32). Therefore, it is likely that the true optimum ratio is below 0.174, and that the mean of both ratios ((T:L_(opt)+T:L_(opt-1) 0/2) can be taken as a good estimation (mean=0,,160; SD=0.024;n=33). Withrespect to feedformulationforgrowingpigs,itwas concluded that a figure of 0.17 for the optimum T:Lratio includes a safety margin large enough to cover most of the biological variations.