| NUTRITION |
| STARCH v FIBRE |
• Example feeds
• Starch or fermentable carbohydrates? Whilst both are sources of energy and equally valuable to the horse, glucose from starch holds an advantage over VFAs from fermentable carbohydrates when it comes to availability during exercise. Glucose is metabolically more efficient. When working aerobically at slower speeds, glucose is metabolised at nearly twice the rate of VFAs to provide energy to the muscle for contraction. As speed and exertion increases and the horse works anaerobically, the body favours glucose as the energy source over VFAs. As such, starch is always needed in the diet of racehorses and too little starch can negatively impact on performance. The temptation may then exist to push starch intake upwards given its advantages. However, there are several drawbacks to too much starch in the diet aside from over excitability, including increased risk of disorders such as gastric ulceration, colic, tying-up and hindgut acidosis. VFAs derived from fermentable carbohydrates are available as an energy source when working at steadier speeds and contribute to daily energy requirements for basic bodily functions. They should not be discounted as less valuable. Getting the balance right between the two groups of carbohydrates can be a challenge, in which choice of hard feed plays a significant role.
• Carbohydrate profile of racing feeds Hard feed forms by weight, the largest part of a racehorse’s daily intake. The balance of carbohydrate provided through the hard feed will determine the overall balance of the daily intake. Forage, whether hay or haylage, will be a consistent source of fermentable carbohydrate. Hard feeds in contrast are highly variable in the amount of starch vs. fermentable carbohydrate provided. The fibre content of hard feeds is expressed as ‘crude fibre’, and this value can be found on all feed tags. Crude fibre is a laboratory measure that includes most of the cellulose found in the feed but only some of the hemicellulose. It also includes some lignin, an indigestible type of fibre. As such, it is not a true measure of fibre in the feed, but as all horse feeds are required to use this same measure, it allows for comparisons between feeds. Starch can be directly measured and whilst not required to be stated on the feed tag, the majority of feed companies provide this information on their websites or through their nutritional helplines.
FOR MORE INFORMATION SCAN QR CODE TO WATCH CATHERINE RUDENKO'S REVIEW OF 'CARBOHYDRATE CHOICES FOR RACEHORSES IN TRAINING' 32
TRAINERMAGAZINE.COM ISSUE 70
RACING FEED 1
RACING FEED 2
Protein g/kg
140
140
Starch g/kg
280
180
Fibre g/kg
70
130
The protein content of a feed has no correlation to the amount of starch or fibre present, and so it cannot be used as a predictor for determining whether the feed is best suited to hard and fast work or to steadier or more stamina-related work. The racing feed 1 example is a cereal-based feed and contains 28% starch (280g/kg), whereas racing feed 2 example contains cereals but in balance with more fibrous fermentable carbohydrate sources such as beet pulp and soya hulls, resulting in an 18% starch value (180g/kg). Fibre content is lower when starch is higher, as seen in racing feed 1, and increases as starch content lowers, as seen in racing feed 2. Both feeds are fortified with the appropriate vitamins and minerals so the choice becomes entirely related to the balance of carbohydrates. Combining feeds, such as the two examples above in different proportions, is often advised when wanting to slowly ‘step up’ or ‘ease off ’ horses at various stages of training. Feeds once balanced for vitamins and minerals will not become unbalanced when combined together to give flexibility around the type of carbohydrate needed.
SUMMARY There are many sources of carbohydrate that form part of the daily diet of horses in training. The site of digestion determines the source of energy produced, either glucose from the small intestine or VFAs from the large intestine. Both sources are needed on a daily basis. The balance between these sources is important as it affects behaviour, digestive health and can reduce the risk of incidence of disorders such as tying-up, colic and hindgut acidosis. By using feeds with different ratios of starch and fibre, it is possible to alter the total daily balance of ‘fast release’ and ‘slow release’ carbohydrates against type of work and stage of fitness. Use of chaff and beet pulp in the feed program also brings flexibility when needing to increase intake of ‘slow release’ fermentable carbohydrates.
Reading List •B ulmer, L. S., Murray, J. A., Burns, N. M., Garber, A., Wemelsfelder, F., McEwan, N. R., & Hastie, P. M. (2019). High-starch diets alter equine faecal microbiota and increase behavioural reactivity. Scientific Reports, 9(1), 18621. •G eor, J.G. Harris,A.P. Coenen,M. (2013) Equine Applied and Clinical Nutrition. London: Elsevier. •H oekstra,K.E. Newman,K. Kennedy,M.A.P. Pagan,J.D (1999). Effects of corn processing on glycemic responses in horses. In: Proc. 16th Equine Nutr. and Physiol. Soc. Symp. pp. 144-148.