Underweight Horses

Every year we see many horses who are underweight. Often their owners are already trying to help the horse get to their optimal condition, or even some are not aware that their horse is at all underweight. Weight loss or an inability to maintain optimal condition can be the result of various factors, so many in fact that we understand how it is easy for the owner to miss something.

Malnutrition is a leading cause for horses being underweight. There are several reasons as to why a horse may be malnourished:

Lack of Feed

Essentially, horses require 1-2% of their ideal body weight in dry matter to simply maintain their condition. Some breeds require more, as do horses who are more active. So for a 500kg quarterhorse who is just kept in the paddock, then at least 5kg of dry feed per day would be needed to maintain his current condition. To start off you need to weigh your dry feed to determine how much the horse is getting. If he is underweight and is getting less, or around the 1-2% mark, then you need to increase his feed, slowly. Increasing too quickly can upset his gut and lead to colic. You need to estimate the dry matter content of the feed. For example, green grass is only 20% dry matter, hay and chaff can be anywhere from 55% to 85%. Pellets are often closer to 100%. As you’re probably aware, the equine market is flooded with many different feeding products and it can be difficult to determine which is best for your horse. If making any change, as above, do it slowly. Adding vegetable oil to feed is sometimes a good way to speed up the fattening process. Increase in small increments up to a total of one ml per kg of bodyweight. If pasture is sparse then you need to seriously consider supplementing your horse’s diet with more roughage, in the form of hay.

Poor Teeth

We cannot stress enough how vital a good set of teeth is to the grazing animal. It is no longer acceptable to think teeth take care of themselves because domesticated horses have different feeding patterns to wild ones, and also because we expect them to live longer and with more vigor. If a horse is unable to properly chew its food (due to pain or a dental obstruction), the first stage of the digestive process is disrupted, and thus the horse is not going to efficiently process nutrients. If feed is not chewed correctly, and passes through partly undigested, or in some cases completely undigested, the gut can become irritated and colic can result. Therefore when presented with an underweight horse the oral condition will be one of the first things assessed. It is very important for all horses to have their teeth done at least annually from 6-12mths of age. Horses who are under 6 need to be seen every 6 months, as do performance horses. In Queensland a vet is the only person who can legally sedate your horse and use dental motorised tools (such as a powerfloat). If a person who is not a vet does either, then your insurance and legal claims are void). It is actually quite easy to do damage to a horse’s teeth and the surrounding structures, in some cases rendering your horse unable to eat. That’s why we always stress the importance of having a highly trained professional to do the job, the risk just isn’t worth it.

Worms & Other internal Parasites

We know this is a bit of an old message, but please keep up worming regimes. If you are concerned about your wormer’s affect on dung beetles (generally mectin c\wormers are to blame), then alternate wormers, using the mectin ones when dung beetle activity is less. Parasites compete for feed and damage the internal lining of the gut, therefore reducing nutrient absorption. Your vet can do a faecal float to determine if worms are a problem for your horse.


Internal cancers can also interfere with the gut’s functioning, leading to a decreased inability to process feed, and therefore resulting in weight loss. It can be difficult to diagnose, sometimes blood tests cane pick these up if damage has occurred (especially in the case of leukemia).

As you can see, due to the vast array of things that can result in a horse being underweight, it is often a good idea to get your vet to assess your horse to determine its dietary requirements and if anything is interfering with the horse’s ability to digest.