Cereal starch, protein, and fatty acid pre-caecal disappearance is affected by both feed technological treatment and efficiency of the chewing action in horses

摘要

Horses have a digestive tract adapted for digesting a continuous flow of grasses with high fibre and low starch contents. However, to meet the energy requirements of performance horses, diets often contain energy dense and starch rich cereals. This is a practise, which can cause digestive disorders due to shifts in the environment of the digestive tract and the digestion profiles of various dietary constituents, due to limited secretion of amylase and a short passage time through the small intestine, which limits the capacity for starch digestion in horses. To enhance the starch digestibility of cereals in horses, different feed technological treatments can be applied which alter the physical properties of cereal kernels, including starch granules, and change their site and/or course of digestion. In the present study a mobile nylon bag technique was used to study pre-caecal disappearance of dry matter, starch, protein, and fatty acids from maize (Zea mays) and barley (Hordeum vulgare) subjected to different feed technological treatments together with different types of untreated black and yellow oats (Avena sativa). However, degradation of feed in the gastrointestinal tract is not solely determined by feed technological treatment. Efficient chewing of the feed is essential for herbivores ability to meet their relatively high energy demands from high fibre containing diets and the efficiency of the chewing action can also influence the physical structure of kernels and influence their digestion. To study the impact of chewing on the pre-caecal disappearance of dietary constituents, feed samples were subjected to either milling through a 1 mm screen or blending for 2 s. on a sample mill, to model the chewing action of grain fed horses with healthy teeth or neglected teeth, respectively. Correlations were found between nylon bag passage time and observed pre-caecal disappearances of dietary constituents, hence all digestibilities were interpolated to pre-caecal disappearances at 7 h (average passage time) prior to statistical analysis. Heat treatment, chemical treatment, and physical destruction of seed coats generally increased the pre-caecal disappearance of dietary constituents from cereals. However, the effect of the feed technological treatments changed with different modelled chewing actions. The effect of the feed technological treatments was most pronounced in blended samples, which mimicked the chewing action of hasty eaters or horses with neglected teeth, probably due to the relatively smaller area open for enzymatic degradation compared to samples milled through a 1 mm screen.