The effects of supplementing a low-protein threonine-deficient diet with different sources of non-essential amino acids on nitrogen retention and gut structure in young pigs.

A threonine-adequate control diet and four Thr-deficient (80% of requirement) diets were formulated to contain similar amounts of digestible lysine and the recommended pattern of other standardised ileal digestible essential amino acids (except Thr). Threonine-deficient diets were supplemented with different amounts and sources of non-essential amino acids, namely 0, 20, and 40 g wheat gluten (WG) protein per kg diet or 17.6 g monosodium glutamate (MSG) per kg diet. Each diet was fed for 28 days to six piglets (initial BW 15 kg). Supplementation of the Thr-deficient diet with WG or MSG had a positive effect on N retention (5.9-8.5%) in younger, but not in older, pigs. Furthermore, it reduced the plasma Thr level and increased threonine dehydrogenase activity in the liver and pancreas. The treatment effects on intestinal morphology differed according to the histological criteria used. It may be concluded that non-essential amino acids added to the low-protein diet deficient in Thr seem to improve utilisation of these amino acids for protein deposition in very young pigs, whereas their effects on the structure of the small intestine are equivocal.

Apparent precaecal digestibility of nutrients and level of endogenous nitrogen in digesta of the small intestine of growing pigs as affected by various digesta viscosities.

Sixteen male growing pigs of about 24 kg BW were fitted with both a duodenal re-entrant and a post-valve T-shaped cannula inserted in the caecum. The animals were divided into four groups. Each group received one of the following diets: corn starch-soybean protein isolate-based diet without (diet C) and with carboxymethylcellulose (diet CMC) or a rye-wheat-based diet without (diet RW) and with xylanase addition (diet RWX). The diets provided similar levels of apparent precaecal digestible crude protein (CP), lysine, methionine + cystine, threonine and tryptophan. Additionally, [15N]-yeast was given with the diets during the first 10 days of the experiment. For estimation of digesta viscosity, N-flow of dietary and endogenous origin, apparent precaecal digestibilities of dry matter (DM), CP, amino acids and non starch polysaccharides (NSP) (only in pigs fed diets RW and RWX), ileal and duodenal digesta were quantitatively collected on day 16 and 17, respectively. The endogenous N-proportion was measured by the ratio of 15N enrichment in the digesta and urine. The duodenal and ileal digesta supernatant viscosity increased as carboxymethylcellulose was included into the diet. Xylanase addition to the rye-wheat based diet reduced the viscosity in the ileal digesta. There were no differences in precaecal digestibilities of DM, CP and amino acids between diet C and CMC. The precaecal digestibilities of DM and soluble and insoluble NSP increased from 69.5% to 73.9%, from 1.3% to 47.9% and from 17.0% to 35.4%, respectively, as xylanase was added to the rye-wheat-based diet. The apparent precaecal digestibility of most essential amino acids increased by 2 to 5 percent units. The amounts of endogenous N at the duodenal level were estimated to be 158, 233, 313 and 276 mg per 12 h per kg0.75 BW of pigs fed diets C, CMC, RW and RWX, respectively. The corresponding values at the ileal level were 95, 107, 164 and 150 mg per 12 h per kg0.75 BW. For endogenous N amounts, significant differences were observed between diets C and CMC (duodenum) and also between semi-purified and cereal-based diets (duodenum and ileum). Methodological aspects for the estimation of endogenous N using the isotope dilution technique are discussed. Obviously, the digesta viscosity per se does not affect the nutrient absorption and endogenous N flow within the small intestine of pigs. Other properties of complex dietary fibre, digesta passage rate or bacterial activity probably contribute to the observed changes.