If your horse is too thin, there is always a reason, but it’s not always visible from the outside. That’s why your vet works step by step: first, simple and common causes such as parasites and dental problems are ruled out, then a deeper look is taken with blood tests and, if needed, gastroscopy (stomach examination). In this article, you’ll read how your vet builds up such a systematic work-up and what information each test provides. This way you better understand why all those steps are necessary and you can work together to more specifically search for the cause of the weight loss.
General clinical examination
With a thin horse, your vet starts with a general clinical examination. Your horse is checked from head to tail, with extra attention to the body condition score (BCS), the teeth, the manure, locomotion (how the horse moves) and the respiratory tract. At the same time, your story is very important: since when has your horse been thin, are there any other symptoms (for example diarrhoea, coughing, lethargy, changed behaviour, colic), what does the diet look like, …?
Based on this first examination, your vet can decide which additional tests are needed: often this involves faecal examination (parasites), blood tests (organs, inflammation, proteins, hormones) and, if the symptoms justify it, gastroscopy to look directly into the stomach. Step by step, this builds a complete picture of why your horse is losing weight.
Deworming and faecal examination
An important step in investigating a thin horse is taking and analysing a manure sample and checking the deworming status. Your vet will check when your horse was last dewormed and which product was used. Some worms are resistant to certain products, which can make deworming less effective. That’s why the manure sample is still examined under the microscope to check whether parasites are still present. Based on this faecal examination, your vet can also determine which types of worms are involved. The following parasites can cause weight loss in horses.
Small Strongyles (Cyathostominae)
These are the most common parasites in adult horses. They feed on blood and tissue fluid in the intestinal wall, which causes bleeding. The larvae can remain dormant in the intestinal wall for months and then suddenly emerge in large numbers, leading to inflammation, diarrhoea, colic and weight loss. Regular manure checks and strategic deworming are therefore essential (Khan et al., 2015).
Large Strongyles
This type of worm is less common thanks to modern deworming, but is still serious. Their larvae migrate through blood vessels to the intestines, which can cause blood clots and intestinal damage (Khan et al., 2015).
Roundworms (Ascarids)
Roundworms are mainly found in foals and young horses. They live in the small intestine and can cause blockages and colic. Typical symptoms are a bloated belly, dull coat and slow growth (Cain & Nielsen, 2022).
Tapeworms
Tapeworms attach themselves at the junction between the small intestine and the caecum. They cause digestive problems and gradual weight loss.
Based on the faecal examination, a personalised deworming plan is drawn up. Horses that graze a lot or are often in contact with other horses benefit from a strategic deworming schedule.
Dental check
A good dental check is an essential part of examining a thin horse. If your horse cannot chew properly, it cannot make good use of the feed offered, no matter how good that feed is.
Your horse’s teeth grow continuously. To wear them down naturally, your horse needs a lot of fibre in its diet. Without sufficient roughage, the teeth do not wear evenly and sharp edges or hooks can form, which make chewing painful and can ultimately lead to weight loss. In older horses there is an extra factor: they often already have (partially) worn-down or missing teeth and molars. As a result, they can grind roughage less finely and absorb it less well, which is a very common cause of becoming or staying thin.
These are the most common dental problems a vet looks for in thin horses:
-
Hooks on the molars: cause pain while chewing and make it difficult to grind roughage properly.
-
Wave mouth / step mouth: caused by uneven wear, reducing chewing efficiency.
-
Loose or missing teeth: horses have less grip on feed.
-
Caps in young horses: baby teeth that stay on too long and hinder chewing.
-
Diastemata (spaces between molars): food gets trapped, causing pain and inflammation.
-
Fractured or split molars: cause acute pain and refusal of hard feed.
-
Root infections: cause severe pain and poor appetite.
-
Uneven wear due to EOTRH (especially in older horses): horses have pain when biting off feed (Graham, 2002).
Have your horse’s teeth checked at least once a year; for thin and older horses, twice a year. This reduces the risk of dental problems, weight loss and loss of condition.
Blood tests
When the most obvious causes, such as diet, parasites and dental problems, have been ruled out, your vet can move on to blood tests.
The blood is sent to an accredited laboratory. Based on the blood values, your vet can see whether there are indications of problems with digestion, metabolism or inflammatory processes somewhere in the body.
In the next article we will go into more detail about which blood values are important and what they mean for your thin horse.
Gastroscopy
Sometimes it is useful for your vet to look inside your horse’s stomach to see whether there are ulcers or other problems. This examination is called a gastroscopy.
This test is often suggested if your (thin) horse also shows one or more of these signs:
-
frequent yawning
-
grinding its teeth
-
sensitivity when tightening the girth
-
a dull coat
-
regular (mild) colic
-
tucked-up abdomen
During a gastroscopy, a thin, flexible tube with a small camera is passed through the nostril into the stomach. Your horse receives light sedation so it remains calm. On a screen, the vet can then directly examine the stomach lining.
Among other things, the vet will look for:
-
Stomach ulcers (red or irritated areas, sometimes bleeding)
-
Glandular ulcers (ulcers near the exit of the stomach)
-
Inflamed or thickened areas of the wall
-
Excess mucus or feed residues
-
Scars or other abnormalities
Stomach ulcers and intestinal inflammation lead to reduced appetite, pain when eating and poor absorption of nutrients, which can result in gradual muscle loss and a dull coat.
Gastroscopy provides visual proof of these conditions and helps in choosing the right treatment (Stämpfli & Oliver, 2006).
In a nutshell
If your horse is losing weight or not gaining weight despite good feed, there is always a reason. Parasites, dental problems, internal diseases or stomach ulcers are the most common causes.
The best approach is a systematic examination: ruling out potential causes step by step. With the right diagnosis and treatment, most horses regain their condition within a few months.
