Growing Pains: Growth problems in horses

In 2004, the 2nd European Workshop on equine nutrition was held in Dijon. The theme of the workshop was the 'growing horse', which gave researchers throughout Europe a chance to present their latest findings into developmental problems. It was a fascinating few days that ultimately revealed there are still many more questions than answers. Some of the main points are summarised below.

What are Growth Disorders?

Developmental Orthopaedic Disease (DOD) is the umbrella term used to describe any growth-related problem. These can be very obvious and easily recognisable such as contracted tendons where the foal appears to be walking on tip-toes, or they can be much more subtle and difficult to definitively diagnose such as Wobbler Syndrome.

Why do Growth Problems Occur?

One of the main points to come out of the Dijon conference is that DOD is a multi-factorial problem and that some of the factors are easier to influence than others. One of the most difficult to control is that of genetics and so it is important to consider that sometimes problems will occur regardless of how much effort you put in to try and avoid them. A contributing factor that can be influenced however, is nutrition.

How Does Diet Influence Growth Problems?

The growth of the foal begins at the point of conception and the diet needs to take account of this. In breeds where mares generally hold their weight easily, extra calories are not required. It is therefore common for mares to receive little additional feed to keep calorie intake down. In practice this often means that they don't receive any additional minerals either, which can cause problems.

The foetus accumulates mineral stores that it can draw on during the first few months after birth when it is growing very rapidly. If DOD occurs during this time it is often an indication that the foetus wasn't able to accrue sufficient stores. This can be due to a number of reasons, the most usual one being that the mare didn’t receive additional minerals in the diet and so couldn't pass them to the foal. Sometimes the health of the placenta is compromised by infections or old age and this can impair the transfer of nutrients to the foetus. This doesn't mean that you shouldn't breed from older mares - you just have to accept that there is an increased risk of problems.

One myth that has well and truly been dispelled is that excessive protein causes DOD. It is now generally agreed that the most dangerous type of diet is in fact one that is high in energy and low in minerals as this stimulates a rapid rate of growth without supplying the building blocks to support it. Straight cereals are an obvious culprit as they provide lots of energy but have a poor vitamin and mineral content. However, if a supplement or balancer is used alongside and cereals are fed in moderation, they can be a cost-effective way to feed.

When adding minerals to the diet the crucial factor is that they are balanced. Feeding more of one mineral in isolation is not necessarily a good thing as it upsets the balance of others. For instance, limestone is frequently added as a source of calcium as most people are aware that calcium is required for bone development. Although calcium is important, feeding too much can block the availability of other minerals such as zinc and copper, which are also vital for growth and development. Copper, for example, is an important constituent of the enzymes that are needed to give tendons their elasticity. Supplements and balancers formulated specifically for breeding stock are low in calories but contain optimum levels of minerals and other essential nutrients making them ideal for good-doers.

One of the most interesting but largely unexplored ideas is how the time of year the foal is born could influence development. Foals would naturally be born in late spring and summer when the mare has access to plenty of grass with a high nutritional value, which allows her to produce the most milk when the foal most needs it. Breeding foals early, in January or February as routinely happens in the Thoroughbred industry, means that the foal arrives when there isn't much grass available to the mare. To compensate for the lack of grass, large amounts of supplementary feed have to be given which increases the risk of digestive upsets, such as colic, and is not particularly cost-effective. Crucially, it also means that by April or May when lots of grass is available and the mare is likely to be producing lots of milk, the foal is three to four months old and starting to become less reliant on the mare as a source of nutrition. Some researchers believe that the milk may provide too much energy when the foal doesn’t need it, which may lead to growth problems.

How to Manage DOD

The advice for dealing with DOD has usually been to shut the foal in the stable and just give it hay and water. Although there are still many questions unanswered, one thing that is known is that hay and water is not good enough. Just as you wouldn't expect a child with a developmental problem to improve on bran flakes and water, foals need a balance of essential nutrients to repair damage. A supplement or low calorie balancer fed at the recommended levels alongside hay will provide the nutrients needed to build healthy tissues.

Hopefully this has given you an insight into why DOD can occur and some guidelines for trying to avoid it. Unfortunately there are no guarantees, but if you provide a balanced diet of vitamins and minerals and avoid over-feeding, you’re on the right track. Arguably the most important message is that if you try to mess with Mother Nature by breeding early or from older mares, problems are more likely to occur. It doesn’t mean you shouldn't do it - you just need to be prepared to deal with the consequences.

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