Why is My Horse Losing Weight? - Rapid Weight Loss in Horses

Updated August 14, 2024 | By: Dr. Lydia Gray

"I have an 8-year-old gelding, purchased under a year ago. He has been in pasture w/ my mare and filly they are fat and gaining weight and look good, however; he is losing weight. We have since moved him to our house and keep a constant supply of hay and grain. He eats, but gets no better. We have added some weight builder to his grain with no change and he is up to date on his deworming. No one is giving us an answer on what to do next, they just say keep feed in front of him. He continues to look worse each week and I don’t think he will last a month like this. Is there anything we can give him to help him gain weight?"

- Meg

Dear Meg,

The rapid weight loss you describe is very concerning so let’s make sure we’re on the same page. What is the body condition score (BCS) of each of your horses? The range is 1 (emaciated) to 9 (obese) with the ideal being 5.

What is the actual weight of each of your horses? Weight tapes are surprisingly accurate, especially when used by the same person in the same way each time.

What and how much are you feeding them? I recommend weighing your hay and grain to make sure he’s getting at least 2% of his body weight each day. If he weighs 1000 pounds, then that’s 20 pounds of food.

I also recommend that you keep a journal of this horse’s BCS, weight, diet, preventive care and medical work to help you get to the bottom of this alarming issue. With luck you’ll find a trend that explains his weight loss.

You say that he’s up-to-date on his deworming but if you’ve just been following a rotational deworming calendar and not taking into account fecal egg counts, resistance, and variations due to season and location, then he could still have a parasite issue.

Next, make sure his teeth are in good shape by hiring a competent veterinarian or dentist to examine his oral cavity with a full-mouth speculum, remove sharp points and correct imbalances. If you haven’t had a veterinarian out to look at him yet, schedule a visit right away. A thorough physical examination that may include bloodwork could identify a medical cause for his weight loss. If not, then specific testing may need to be done to pinpoint the problem. Some ambulatory veterinarians are equipped to handle these kinds of detailed diagnostics but others may need to refer you to a clinic or veterinary school teaching hospital.

[Editorial note: from the AAEP Ask a Vet]