This series of articles has highlighted that many of the metabolic disorders in horses are diet related. These disorders include hot or fizzy behaviour, colic, laminitis, insulin resistance, obesity, and tying up, and are related to the high levels of sugar and starch in the feed. The sugar and starch content is called the non structural carbohydrate content (NSC).  This can be measured by laboratories such as Dairy One. 

What is the ideal NSC content?

You must consider the NSC content of the total diet (ie what is the total NSC from the hay, the pasture, and the pellets or whatever else is being fed?).  You must also consider how much work you horse is doing.

NSC content in pastures will vary throughout the day, with the type of pasture, and on seasonal conditions (see www.safergrass.org). It is considered that horses require a NSC content of 10-12% in the total diet. With horses in work, with higher energy demands, the NSC level can be much higher.  Remember, the key is feed?work related?do not over feed and under work.

The NSC content of commercially available horse feeds varies considerably, and is not truly reflected by the name as shown by the following study.  The term ?Cool? has now become a misnomer, since some of the feeds tested had very high NSC levels (above 40%). By comparison oats, barley and wheat have NSC levels between 45-70%.

THE NON-STRUCTURAL CARBOHYDRATE CONTENT OF SOME COMMERCIALLY AVAILABLE HORSE FEEDS IN AUSTRALIA
NERIDA RICHARDS
Equilize Horse Nutrition, Newcastle, NSW Australia

Non-structural carbohydrates (NSC) can have serious negative impacts on some horses including those with insulin sensitivity, insulin resistance and Cushing?s disease. It is believed that the negative impact on these horses is elicited through the effect of NSC on post feeding blood insulin concentrations. Recent research (Asplin et al. 2007) has shown that prolonged hyperinsulinaemia was enough to precipitate laminitis in otherwise normal ponies. The nutritional management of these metabolically sensitive horses therefore relies heavily on avoiding feeds that will cause significant changes in post feeding blood insulin parameters.

Several studies, summarised by Kronfeld et al. (2004) have determined the post feeding glycaemic response of horses when fed common horse feeds. While glycaemic responses in horses are often unpredictable and difficult to interpret (Richards 2003), feeds that caused the largest post-feeding changes in blood glucose concentration were observed to be those that are expected to contain appreciable amounts of NSC. While post feeding insulin responses were not reported, it can be assumed that given the well established biological relationship between post feeding blood glucose and insulin, the feeds which cause high post feeding glycaemic responses will also cause high post feeding insulin responses.

Therefore, feeds which contain low amounts of NSC should be preferentially selected as feeds for metabolically sensitive horses. The difficulty for horse owners is selecting a suitable low NSC feed, as currently NSC is not a labelling requirement. To explore the levels of NSC in Australian feeds, a range of commercially available feeds, targeted at the ?pleasure and equestrian? segments of the Australian horse industry were sub-sampled from point-of-sale. They were analysed by Dairy One Forage Laboratories (NY, USA) for starch, water soluble carbohydrate (WSC) and ether soluble carbohydrate (ESC). The results are shown in Table 1.

Table 1: The starch, water soluble carbohydrate (WSC), ether soluble carbohydrate (ESC) and total non-structural carbohydrate (NSC; equal to starch + WSC) content of commonly available horse feeds.

 While a ?safe? NSC content has not been formally established for metabolically sensitive horses, a level of <10% to 12% NSC seems to be generally accepted. Feeds with levels of NSC >20% should almost certainly be avoided for these horses. While debate has recently emerged over whether ?total NSC? or ?starch + ESC?, which forms the enzyme digestible NSC component, are the most important carbohydrate parameters to consider, providing starch, WSC and ESC levels on labelling would assist horse owners to select suitable feeds for metabolically sensitive horses.

KRONFELD, D., RODIEK, R. AND STULL, C. (2004) Glycemic Indices, Glycemic Loads and Glycemic Dietetics. Journal of Equine Veterinary Science 24, 399 ? 404.

ASPLIN, K.E., SILLENCE, M.N., POLLITT, C.C. AND McGOWAN, C.M. (2007) Induction of laminitis by prolonged hyperinsulinaemia in clinically normal ponies. The Veterinary Journal 174, 530 - 535  
RICHARDS, N. (2003) Enhancing starch digestion in the equine small intestine. PhD Thesis, UNE.