In the May 2008 edition, I discussed weight loss in horses and some of the causes thereof. I talked about nutrition and parasites as the main causes of "skinny horses". In this article I will discuss the role that teeth, liver disease, lameness and cancer can play.

The quality and quantity of the feed must always be scrutinised fully, no matter how cheap or expensive, how nice it looks and smells, and how good the packaging looks! Once you are happy with the quality (and quantity), you now need to ensure that the horse can make good use of the ration.

I will get to the function of the teeth in a moment, but first, and this applies especially to owners of many horses who are grouped together, bullying and competition is a more important aspect than is perceived. Remember that there doesn't need to be vicious fighting in order for competitive food denial to be a serious factor.

And even though I said that this applies to owners of large groups of horses, I have seen a "group" of two horses interact, without a bite, kick or squeal, and watched one of the horses lose a massive amount of body condition – so always watch your horses carefully for subtle "bullying".

Teeth, as obvious as it may sound, are crucial in the process of grinding up the food (grazing or a fed ration) and is one of the most important causes of weight loss in horses (especially middle-aged and older horses).

Thorough checking

There is more to checking your horse's teeth than putting your hand in the side of its mouth and feeling for a "hook" or a sharp edge or two. Even if it requires a bit of sedation, it's important to thoroughly check the horse's mouth for defects. The molars are primarily responsible for grinding the feed to a particle size that is easily fermented and absorbed in the intestine. If this does not happen, some of the feed passes through undigested.

The molars move in a side-to-side motion, with a circular-like backward and forward motion as well. Therefore, as a lateral angle develops, so the efficiency of the side-to-side motion of the molars is reduced significantly. Also, occasionally a "wave mouth" develops where the molars are of different lengths from front to back, thus reducing the ability to effectively chew or grind in a subtle front to back direction/motion.

A well-balanced diet will help prevent these teeth problems, i.e. enough coarse fibre to encourage chewing for a long enough time – which is why zebras and veld horses don't often develop these problems. Lovely soft teff, lucern and easy-to-eat concentrate pellets do not really encourage extensive chewing.

But more importantly, horses of "these days" need a dental check every 6-24 months – such a broad timespan frequency, because a thorough examination and filing every year or two is better than a twice-yearly wishy-washy check by "someone who thinks they know everything about horses"!

Also, if your horse's teeth need attention, it may require two or three "sessions" to get them right, and then the right food and regular checks should maintain a healthy "chew-worthy" mouth! So when you next organise to get your vet out to do the flu and horsesickness vaccinations – don't be afraid to ask if he or she is confident and capable of doing a thorough equine dental check while paying you a visit.

Neoplasia (cancer) is also a very important potential cause of weight loss. This happens because of a few reasons: If the tumour has invaded the gastro-intestinal tract, it will probably inhibit proper fermentation, digestion and absorption, leading to weight loss. Another reason is that some tumours can become so big and/or invasive, that they actually consume more energy and nutrients than the body can provide. Cancerous tumours generally have a very high growth rate – thus the high demand for nutrients.

Also bear in mind that a horse is big, and big tumours can go for many years without being detected – on post mortem of a horse that had died of horsesickness, I saw two rugby ball sized tumours in the horse's abdomen, without any "apparent" ill-effects visible to the owner – prior to the horsesickness of course!

Thirdly, certain cancerous tumours affect organs, or are in places that may be very painful – and pain is a very, very important cause of weight loss. Pain causes weight loss not just because the horse is so uncomfortable that food is the last thing on its mind, but also, because the horse is too sore to move around. This may not be that much of an issue in a small space with plenty of food at a neck's length, but is a very real issue if the horse needs to graze.

As mentioned in Part 1, there is a very long list of potential causes of weight loss in a horse. Even if one ignores very important causes such as neoplasia (cancer) and liver disease (which can be a bit trickier to diagnose), then by addressing what the horse eats; strategic deworming with good quality products; making sure the horse can chew effectively with well-maintained teeth and eliminating any source of pain, by doing these basic things (which, as a deserving and responsible horse owner you should be doing anyway!), you would have covered 90-95% of the causes of loss of body condition of your beloved equine friend.