A comparison of three xylanases on the nutritive value of two wheats for broiler chickens

Abstract

Three xylanase products, xylanase A derived from Thermomyces lanuginosus, xylanase B from Humicola insolens and xylanase C from Aspergillus aculeatus, were examined for their effects on the nutritive value of wheat. The study investigated the effects of enzyme addition to broiler diets based on a low-metabolisable-energy (ME) wheat and a normal-ME wheat, with the emphasis on changes in composition of the NSP along the digestive tract in broiler chickens. There were significant (P>0·01) enzyme and wheat effects on the apparent ME, but there was no wheat×enzyme interaction on apparent ME. Weight gain and feed conversion efficiency (except xylanase C for normal wheat) were also significantly (P>0·01) increased by the xylanases. The enzymes differed in their effect on a number of important nutritional parameters. Xylanase A reduced (P>0·05) the excreta moisture level from 77·1% in birds fed the normal-ME wheat control to 73·4% and from 77·4% in those fed the low-ME wheat to 73·0%. The other two enzymes did not affect excreta moisture levels. The digesta viscosity in the duodenum, jejunum and ileum of birds fed both types of wheat was reduced (P>0·01) by xylanases A and C, but was increased (P>0·01) in the jejunum and ileum by xylanase B. The digestibility of the soluble NSP was mostly negative in the small intestine. The digestibility of the insoluble NSP differed (P>0·01) between the two wheats, with those in the low-ME wheat being more digestible (14 v. 28%). When supplemented with xylanase A, the ileal digestibility of the insoluble NSP in the normal- and low-ME wheats was increased by 28 and 42?%, respectively. Xylanases B and C did not affect the digestibility of the insoluble NSP regardless of wheat type. It may be concluded that wheats with low or normal ME values vary in their responses to xylanase supplementation. Apart from having an elevated level of soluble NSP, low-ME wheat may also contain insoluble NSP, which in the present study appeared to be more easily degradable in the gut of the chicken.