 |
Rural Industries Research & Development Corporation |
|| Home || Search || Contact || Publications Eshop || Privacy Statement ||
Rural Industries Research & Development Corporation
Safe and Effective Grain Feeding for Horses
A report for the Rural Industries
Research and Development Corporation
by James Rowe, Wendy Brown, and Simon
Bird
November 2001 RIRDC Publication No 01/148 RIRDC Project No UNE-62A
Cereal grain is an important feed ingredient for most intensively managed horses and although cereals provide a valuable source of digestible energy their feeding to horses is always associated with some risk. The danger in feeding cereal grain to horses lies in the risk of incomplete digestion of starch in the small intestine and the possibility that significant amounts of starch can pass through to the caecum and colon (large intestine, or hind gut). Starch entering the hind gut is fermented very much more quickly than roughage and this rapid fermentation leads to accumulation of acidic end products and low pH. Just how the acid build up in the hind gut affects the horse is not clear but there is no doubt that acid accumulation in the hind gut is the primary cause of laminitis as well as many of the behavioural changes commonly associated with feeding grain to horses.
At the start of this project there was no simple method for determining the intestinal or pre-caecal starch digestibility of different grains and/or the effectiveness of various processing methods designed to make cereal grains more digestible and therefore safer for horses. Several researchers have made measurements of pre-caecal starch digestion using inert markers as references or mobile nylon bags removed from the caecum but these methods are time consuming and subject to variability between animals. A simple and repeatable estimate of pre-caecal digestibility is essential if we are to understand and improve the safety of grain feeding and the development of such an assay was a primary focus for this project. An objective measurement of the starch digestibility characteristics of a raw or processed grain sample is a valuable tool in that it is not complicated by animal to animal variation or the level or method of feeding. Such a tool allows us to quickly build a data base on different feeds and the consequences of different processing techniques.
Two in vitro assays were developed during the project. The first is an enzyme-based assay designed to predict pre-caecal starch digestibility and the second was established to measure the rate of fermentation. The theory behind these two assays is that we need to understand the risk of starch entering the hind gut as well as the rate at which that starch is likely to ferment when it comes into contact with the gut microbes. Once the two assays were developed we analysed a set of 55 samples selected to represent different grains, a range of different cultivars of each grain and, with selected cultivars, samples taken from geographically distinct locations. The results were analysed by comparing the enzyme digestibility of each grain with its potential rate of fermentation. What we were looking for was grains that were highly digestible in the enzyme assay (low risk of starch reaching the hind gut) or grains that had a reasonable level of enzyme digestibility and low rate of fermentation.
By and large the grains with a high level of intestinal (enzyme) digestibility were also those that fermented most rapidly but there were a few exceptions. Two cultivars of triticale stood out as having the highest enzyme digestibility of all grains tested and far higher than would be expected from their rate of fermentation. On the basis of this result we went on to examine the digestibility of triticale in horses to confirm that the cultivar difference observed in vitro was also reflected in actual digestibility in the horse. We were very pleased that this was the case. Further in vitro testing of triticale has confirmed that the cultivars of Madonna and Abacus are significantly more digestible than Tahara.
Studies of starch digestibility of the two triticale parents, Durum wheat and rye show that the digestibility of triticale lies in between that of wheat and rye with the higher digestibility cultivars such as Abacus being far closer to rye than Durum Wheat. This finding is one that will be of interest to plant breeders, feed manufacturers and to horse owners purchasing grain for supplementary feeding.
The in vitro assays showed that oat grain starch was very highly digestible and also very rapidly fermented. This suggests that while oats is probably one of the safest grains in terms of a low risk of starch entering the hind gut, feeding strategies should still be employed that minimise this risk as any oat starch finding its way into the hind gut will ferment extremely rapidly.
Grains were ranked by the in
vitro assay for enzyme digestion as follows:
|
|
 |
|
|
|
|
|
|
|
A second objective of the project was to examine the potential importance of oat hull digestibility in the utilisation of oat grain by horses. Studies in sheep and cattle had indicated that lignin content of the oat hull is genetically controlled and can have a significant effect (approximately 10 percentage units) on apparent digestibility. This research has been extensively reviewed as part of this final report and it is suggested that lignin content is likely to have an important effect on digestibility as well as gut fill and body weight. Unfortunately the results of the experiments on digestibility of oat grain conducted as part of this project were not clear cut and only preliminary results are reported. These results suggest that lignin could influence digestibility in the horse and that processing the oats by rolling could also be important in improving its digestibility.
Exogenous enzymes that target the non-starch polysaccharides that make up the cell walls in the cereal grain have been found to be most effective in increasing starch digestion in poultry. Wheat is consistently improved by the use of exogenous enzymes and we therefore conducted an experiment to measure the response of a commercial exogenous enzyme mix on pre-caecal starch digestion in the horse. The enzymes appeared to work very well and significantly improved pre-caecal starch digestibility.
Implications
This project has provided a new tool in the form of powerful in vitro assays. These assays will be useful for plant breeders, feed manufacturers and horse owners. It is recommended that the in vitro assays developed as part of this project be made available on a commercial basis for these user groups to test samples prior to use for horse feeding. It is expected that the in vitro enzyme assay will cost around $85/sample at this stage but could become cheaper (around $45/sample) if an NIR calibration can be developed.
The identification of high-digestibility triticale for horses is an exciting new development for the horse industry as it was previously not known that this grain was potentially suitable for horses. Further work in collaboration with feed manufacturers is indicated to explore the effect of processing methods such as steam flaking in combination with selection of the more digestible cultivars of triticale.
Unfortunately it is not possible to make a clear statement about lignin content of oat hulls and its nutritional value in horses. However, because of the importance of oat grain in the diet of horses, and the very good digestibility of oat starch, it is recommended that further work be undertaken to provide unequivocal data on this factor.
The use of exogenous enzymes to improve pre-caecal digestion of wheat in the horse was clearly shown in this project. Exogenous feed enzymes are commercially available and it should be possible for feed manufacturers to take immediate advantage of this information.
|
