Swelling on the neck in horses – is it dangerous and what can you do?

A concerned horse owner recently asked this question:

"My mare has a noticeable swelling on the underside of her neck – it's soft and she doesn't seem sore, but I'm still worried. Could it be the feed? Or something dangerous?"

The question is not unique – and it raises some important points that many horse owners will be able to nod in recognition to. In this post, you will get an overview of possible causes, what you can do yourself, and when it is time to contact the vet.

1. What can cause a swelling in the neck?
There are many possible causes – and fortunately most of them are not serious. Here are the most common explanations:

Lymphatic fluid accumulation (edema)

– often seen with changes in feed, temperature or hormonal fluctuations (e.g. heat).
– the swelling is usually soft and movable, and the horse does not seem bothered.

Reaction to parasites or vaccination

– the swelling is typically located close to a puncture site or along the lymphatic pathways.
– can occur as a natural body reaction and often disappears spontaneously.

Reaction to certain feed ingredients

– especially food with a high sugar content or sharp changes in the feeding schedule.
– in some horses, for example, alfalfa, corn or yeast can cause reactions, especially if the microbiome is out of balance.

“We see it most often in horses where the gut microbiome is challenged – for example after antibiotic treatment, parasite infestation or feed change. Here the body's reactions can occur in different places – especially in the neck and jaw area.”
– Eva Lydeking, nutritional therapist and consultant

2. Is this a sign of metabolic problems or EMS?

Another horse owner asked:

"My Icelandic has had a thick neck for a long time – it's not soft, but hard. Is it the same?"

It is important to distinguish. A soft swelling is not the same as fat storage (e.g. "cresty neck", typical of EMS or insulin resistance).
The latter is hard, firm and does not disappear within 24 hours. It requires a change in diet and possibly weight loss.

If you are unsure, take pictures over a few days and feel the area. Soft swellings change often – fat does not.

3. What can you do here and now?

✅ Wait and observe

– if the horse is unaffected and the swelling is mild, you can wait 2–4 days and monitor the development.

✅ Check the feed

– have you changed anything? Added new products?
– consider, in consultation with your feed advisor, taking a break from new supplements and going back to basics: roughage, salt and possibly a little + Fiber Mash.

✅ Support lymph and digestion

– choose food with fermentable fiber, prebiotics and appropriate vitamins and minerals, such as Regulator Completes Supreme Minerals , to support healthy intestinal function.
– movement also helps. Walking and running are very beneficial for lymphatic circulation.

4. When should you contact the vet?

📞 Call the vet if:

• the swelling becomes warm, tender, or grows rapidly
• the horse seems depressed, withdraws, eats less
• there is a fever or other symptoms

Summary: You need to remember this

Do you need help with a feeding plan?

We are ready to help you review your horse's feeding plan if you are in doubt - or just want some advice on feeding .