Supplementation of pig starter diets with carbohydrate-degrading enzymes - stability, activity and mode of action

Authors

• Johan Inborr University of Helsinki, Department of Animal Science, FIN-00014 University of Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.72724

Abstract

A total of five experiments were conducted to investigate the stability of feed enzymes to steam pelleting and the proteolytic conditions in the gastrointestinal (GI) tract of pigs and poultry, and to try and elucidate the mechanisms behind the improved performance of pigs fed enzyme-supplemented barley/wheat-based diets. The results of the pelleting stability experiment showed that the commercial feed enzyme employed maintained most of its activity in conditioning temperatures up to 85°C.Furthermore, it became evident that measuring enzyme recovery in pelleted feeds by in-vitro assay methods underestimated the actual activity. For this purpose in-vivo models such as that based on gut viscosity measurements in broiler chickens gives a more accurate estimate. Gut viscosity also correlated highly with live weight gain (r2=0.624) and feed utilisation (r2=0.616) of broiler chickens. The in-vitro incubations using conditions similar to those of the GI tract showed that enzymes are not readily denatured and inactivated in such conditions and indicated that wheat and wheat gluten, and possibly similar feed ingredients, may help to maintain the activity longer either due to their buffering capacity or by providing substrates for the enzymes. This was supported by the results of the in-vivo measurements. In the stomach of pigs, 10-20per cent of the xylanase and β-glucanase activities added to the diets could still be recovered 4 hours after feeding. In the ileum, proportionally more added enzyme activities were recovered between 4 and 6 than 0 and 2 hours after feeding. In broiler chickens fed an enzyme-supplemented barley-based diet, β-glucanase was fully recovered in the proximal part of the small intestine, giving further proof of the stability of the enzymes employed to the conditions of the GI tract. When a mixture of fibre- and starch-degrading enzymes were added to a diet based on wheat and barley, β-glucan, starch and dry matter digestibilities were significantly (P<0.05) improved in the last quarter of the small intestine of early-weaned pigs but did not translate into improved growth or feed utilisation. However, the results showed that enzyme supplementation increased the rate of digestion and more nutrients were absorbed higher up in the small intestine. In a similarly designed experiment, adding a single β-glucanase preparation to diets based on either a low- or a high-β-glucan barley, improved live weight gain (P=0.074) and feed utilisation (P=0.058) of early-weaned pigs over a three-week experimental period. Although there was no significant improvement in nutrient digestibility, enzyme supplementation reduced digesta viscosity (P<0.03) and the concentration of digestive enzymes (P<0.08) in the three proximal quarters of the small intestine. Thus it appears that conditions for a more efficient digestion were brought about due to the reduction of digesta viscosity, enabling less production of pancreatic enzymes without affecting digestibility. Further analysis of the digesta samples showed a significant (P=0.044) reduction in the concentration of VFAs in the distal small intestine and hind gut of the pigs fed the enzyme-supplemented diets. This further indicates that enzyme supplementation leads to fewer nutrients escaping digestion and absorption in the small intestine such that less readily fermentable material was available for microbial growth.