Over Christmas it’s quite normal for us to indulge in a variety of unusual food and drink. Some of us overdo it and pay the consequences with digestive disturbance, but many of us are quite tolerant to dietary variation, providing the amounts eaten are reasonable. Horses, on the other hand, don’t cope with sudden dietary changes due to the nature of their digestive tracts.
The large population of beneficial gut micro-organisms and the adjustment of digestive enzymes are the reasons why horses’ diets should be changed gradually.
Horses rely on beneficial micro-organisms including bacteria, protozoa and fungi – mostly in their enlarged hindguts – to break down dietary fibre, releasing nutrients that can be absorbed. These microbes rely on a consistent supply of feed to maintain healthy populations, and if their feed supply is interrupted, their populations will suffer. Furthermore, if non-fibre carbohydrates such as starch are available in the large intestine due to an overload of the small intestine, acid-producing bacterial populations will flourish, creating an acidic environment that fibre-digesting (fibrolytic) bacteria find hostile. Hindgut (large intestine) disturbance will result, which, if mild might not cause any symptoms, but if severe could cause colic, laminitis and even death. Beneficial gut microbes can adapt if their feed supply is adjusted gradually, sufficient fibre is fed and no more than 1 g of starch per kilo of body weight is fed per meal (and introduced gradually).
Digestive enzymes produced by the gut also need time to adjust to new feeds so this is another reason to change a horse’s diet gradually.
All new feeds including forages such as pasture grass, hay, haylage and supplements should ideally be introduced gradually. Many owners are aware of changing concentrate feeds such as starchy coarse mixes gradually, but don’t consider that a change in forage should also be done gradually.
Supplements fed in small daily amounts e.g. up to 50 g can be given without introducing gradually, but ideally others fed in greater daily amounts should be introduced gradually. Doing so allows the horse time to get used to the taste as well as allowing the gut to adapt.
If your horse has a sudden change of diet that can’t be helped, such as a change of pasture due to breaking out, or a break into the feed room, the vet should be called if the horse shows any signs of colic (abdominal discomfort). A plain hay diet should ideally be given – along with a small amount of usual pasture grass if the horse has access – and a probiotic supplement given for a couple of weeks. Probiotic supplements can be used for any digestive disturbances and during dietary changes for sensitive horses.
Making all dietary changes – including forages such as grass, hay and haylage and supplements fed in large quantities – gradually ensures that beneficial gut microbes and digestive enzymes have time to adjust and potential digestive disturbance is avoided.