0
Threonine (Thr) is often the second or third limiting amino acid (AA) in cereal-based diets for pigs. In comparison with the other essential AA, Thr requirement for maintenance is high and this may be explained by special functions of Thr in the intestine. It was found that the intestine utilize about 60% of dietary Thr. This AA is incorporated in the intestine proteins which are mostly secreted into the lumen. Deficiency or excess of Thr reduces the synthesis of intestinal mucosal protein and mucins as well as muscle protein in weaned pigs. The aim of the study was to investigate the effect of increasing dietary Thr level on performance, N retention, morphology and goblet cell types in the small intestine, and threonine dehydrogenase (TDG) activity in the liver and pancreas of young pigs (from 13 to 22 kg of BW) with a high lean gain potential. Four experimental diets were formulated: one unsupplemented, Thr-deficient and three diets supplemented with crystalline Thr. Diets contained 6.46, 7.43, 8.37 and 9.32 g Thr per kg. Each diet was fed to six male pigs for 19 days and N balance was determined at 15 kg BW. Tissue samples of the small intestine were taken for histological and histochemical measurements.
No significant effect of increasing Thr level on ADG and F/G was observed (P > 0.05). In pigs fed Thr-deficient diet, N retention (g per day) was lower (P < 0.05) than on diets containing 7.43 and 9.32 g Thr per kg. Experimental diets had no effect on weight of the segments of the small intestine (P > 0.05), while they modified their morphometry. Villi length differed only between pigs fed Thr-deficient diet and Thr-supplemented diets and was the lowest in the duodenum (P < 0.001) and highest in the mid-jejunum (P < 0.05). Tunica mucosa thickness and number of goblet cells (in villi and/or in crypts) containing neutral mucins were smaller (P < 0.05) on Thr-deficient diet than on other diets. Dietary treatments did not affect the weight of liver and pancreas and TDG activity (P > 0.05).
It can be assumed that the level of dietary Thr amounting about 7.4 g per kg covers the requirement of piglets from 10 to 25 kg for rapid growth and maximal N retention as well as for supporting gut barrier function. Whether this level of Thr is optimal for intestinal health, it remains to be proved.
E Dwidch, M Boryczka, M Taciak and L Buraczewska, 2011. The effect of graded levels of dietary threonine on nitrogen retention and structure of the small intestine in young pigs. Journal of Animal and Feed Sciences, 20: 350-360.