Fibrous foods are major sources of energy and protein for equids. The potentially energy yielding fraction of dietary fibre consists of non-starch polysaccharides (NSP). NSP cannot be digested by equine enzymes and in order for the animal to obtain energy from NSP it must be fermented by the gut microflora to yield volatile fatty acid. This fermentation process is less efficient in terms of yield of ATP than the digestion of starch to glucose, and is generally believed to occur solely in the large intestine. Plant protein may be associated with the NSP or the protoplast. However, horses can only utilize that protein which has been digested and absorbed in the small intestine. Thus, knowledge of the site and extent of nutrient degradation is important to enable the accurate formulation of diets for horses. Therefore in the current study the site and extent of NSP and crude protein (CP) degradation from four fibrous foods commonly given to horses in the United Kingdom were determined in caecally fistulated ponies using mobile bags.
The trial was a 4 X 3 incomplete Latin square design with three caecally fistulated Welsh X pony geldings (ca. 250 kg live weight) and four botanically diverse sources of dietary fibre. The ponies were maintained on a basal diet of hay and grass nuts and water was available ad libitum. Bags (6X1 cm) of monofilament polyester mesh pore size 4 μm were filled with 350 mg of either unmolassed sugar-beet pulp (SB), hay cubes (HC), soya hulls (SH) or oat hulls : naked oats (2:1) (OH: NO), which had been ground to pass a 1-mm steel mesh. On two consecutive mornings 20 bags were introduced into the ponies via a naso-gastric tube. Each bag contained two 100 mg steel washers which enabled their capture by a magnet placed inside the caecal fistula: the cannulae were positioned just posterior to the ileo-caecal junction. Between 10 and 16 bags were recovered on the magnet, the remaining bags were allowed to continue through the hind-gut and were subsequently collected in the faeces.