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The tryptophan requirement of piglets as influenced by the threonine level

Warnants, N., Oeckel, M.J., Bekaert, H., Paepe, M., Boucqué, Ch.V.
Journal of animal physiology and animal nutrition 1997 v.78 no.1-5 pp. 49-59
Belgian Landrace, ancestry, animal performance, crude protein, diet, feed intake, hybrids, ileum, lysine, piglets, threonine, tryptophan, weaning
SUMMARY: The tryptophan (Trp) requirement was investigated in post weaning piglets from 5 to 10 weeks of age (7-20kg). Three feeding trials were conducted. All piglets were randomly alloted according to age, sex, weight, pre-weaning growth and ancestry to the different dietary treatments. Ad libitum feed intake (per 6-7 pigs) and daily gain (individual) were recorded at 5 and 10 weeks (end of experiment). In the first trial 72 Belgian Landrace (BL) and 60 Piétrain × Seghers Hybrid (P × SH) piglets were used for two dietary treatments. The basal diet, 16% crude protein (CP), 1.06% lysine (Lys) and 0.14% Trp, was supplemented up to 0.19% Trp. This trial revealed a significant improvement in daily gain from 0.14% (0.10% ileal digestible Trp) to 0.19% Trp (0.15% ileal digestible Trp). The second trial was based on a lower CP content (14%) and a similar Lys level. Trp was increased in steps from 0.16% to 0.18, 0.21 and 0.24%. One hundred and fifty-eight BL and 147 P × SH piglets were divided over the four feeding regimes. No improvement in growth was obtained for the levels above 0.16% Trp (0.11% ileal digestible Trp). It was presumed that Thr was the limiting factor. A third trial was conducted, which consisted in a 3 × 3 factorial experiment, using the same CP level as in trial 2, but a lower Lys level (1.03%) and combined three Trp levels (0.18, 0.21 and 0.23%) with three Thr levels (0.65, 0.72 and 0.79%). Nine groups of 49 animals (all P × SH) were used in this experiment. Only a slightly favourable tendency of Trp towards increasing daily feed intake was found and the growth and feed: gain ratio were not affected at all. The Thr, on the contrary, led to increasing growth figures. The optimum Thr level seemed to have been reached by the 0.72% total Thr or 0.57% ileal digestible Thr level, yielding a ratio of 65% of Thr:Lys. For Trp, the requirement was difficult to predict in the conditions of the experiment, as no optimum appeared for Trp from the animal performance results.