Are some horses more prone to colic than others?

Are some horses more prone to colic than others? There are several factors which contribute to increased risk that you should be aware of.

Significant weather changes usually mean quick changes to the way we manage our horses, for example in bad weather going from grazing 24/7 to stabled, at least at night. It also heralds a seasonal [spring & autumn] rise in colic cases, but why? This month's topic is Colic, is it really that important?

If you’ve had a horse with even mild colic it can be extremely upsetting, never mind the worry [and expense] of a more serious case. So for the average owner and definitely for the horse, it probably is. Colic affects about 5 horses in every 100 each year and they vary in seriousness. Some will resolve with no treatment, the majority are sorted with simple treatments and some will require surgery and for some, it is fatal.
 
There are a few risk factors, some we are familiar with and others that may be a bit more of a surprise. Let’s start with the obvious, cereals. As you can see from the graph below, the more hard feed you feed, the higher the risk.

The horse's small intestine has a very limited capacity to digest starch, different grains not only have different levels of starch they also have different digestibility, so not all starch is the same. Whole oats for example are about 53% starch, which is 85% digestible; Barley is on average 60% starch, which has a digestibility of 20% and the other common cereal is maize, which contains a whopping 73% starch which is about 29% digestible. If barley and maize digestibility is so low why do we use them in horse rations? Sneakily, if you treat cereal grains by rolling, milling and cooking, you improve the digestibility significantly. So the digestibility of popped maize for example, increases from 29% to 90%! To be safe, the rule of thumb is don’t feed any more than 1g of starch for every 1kg of body weight, per feed. So for your average 500kg horse you should have no more than 500g of starch per feed. If you are feeding oats with 53% starch, that means in round figures a maximum of 1kg per feed. Bear in mind that starch figures are usually averages and it is possible that your oats may have significantly more starch in them and you also have to add in starch from other sources, including forage.
If you get it wrong does it really matter? Unfortunately it does. Undigested starch getting into the large intestine makes it go nuclear. The bacteria that digest starch multiply like mad producing gases, froth and lactic acid which causes a reduction in pH [more acid]. This reduction in pH kills the fibre digesting bacteria [who prefer a more alkaline environment] which then release toxins causing all sorts of problems [notably laminitis] in addition to increasing the risk of colic. So play safe and feed little and often if you need to feed a lot of straight cereals or hard feed.
What about grazing? Another graph and it shows that the more time horses spend grazing, the lower the risk – no surprise really, after all that’s what they are designed to do.

Does this tell us anything else? Possibly. It may be telling us that when horses spend the majority of their time grazing they don’t have big fluctuations in their diet. The location of grazing may have an impact, fields that have significant shaded areas can have larger variations in sugar levels [driven by sunlight] and particularly Fructans. These simple sugars can cause hindgut problems, which is not only important from the laminitis perspective, it can also contribute to variation in the hindgut microflora. There is no doubt that the horses digestive system does best when it doesn’t have change. Last month we talked about how we feed our horses, in particular the hard feed, grazing, hard feed, hay rotation we often use. For the bacteria in the hind-gut this is not ideal, they tend to be specialists and require different environments. As I eluded to earlier, the bacteria that are most efficient at digesting sugar and starch prefer a more acid environment. Fibre digesters don’t. You can see the quandary. The other thing to bear in mind is that what is good for colic may not be good for laminitis or weight control! The limited time grazing may be leading to colic because of inadequate consumption, or too much in too short a time. There are other colic risks from grazing too - grass sickness, tympanitic colic and sand colic – so it’s not all good news.
Colic [impaction] is also associated with poor quality forage like straw. Essentially forages should ideally be good/moderate quality which is defined as being more than 8DE/kg and more than 8% protein. Again you have to set this against problems with obesity and laminitis etc.
The type and quantity of cereal, forage and grass are obviously all important factors in the cause of colic. However the most important factor is DIETARY CHANGE, especially changes in hay. We tend to think of all hay as being similar, but research by Prof. Andy Durham has shown that the difference between batches of hay is enough to cause significant disturbance to your horse’s digestive system.
 
He recommends the following to minimize the risk of colic:-

• Remove or limit cereals to 1g/kg bodyweight of starch per meal
• Allow more than 12 hours grazing per day
• Give free access to good/medium quality forage when not grazing
• If more energy is required [working, lactation or thin] then use high fibre feeds first [Alfa A Oil, sugar beet etc]
• Implement dietary changes [including grazing and batch changes of hay/haylage] over 2 weeks or more
• If you still need more energy use vegetable oil [up to 1ml/kg bodyweight per day] and/or cereals/hard feed with the maximum in point 1 above.
• Remember what suits the intestine, may not suit the overall health of the horse [obesity, ems, laminitis etc]

I would add one more tip to this list – feed a pre/probiotic like Protexin either daily, or when you are making changes and during times of stress. It helps keep your horse’s hindgut firing on all cylinders.