A unique problem with a horse is that he can eat himself sick or even die if allowed sudden free access to grains or other concentrates. Typically this occurs when the feed room door is left open. If he is not used to alfalfa hay or fresh green grass, he can become ill if allowed free access before becoming use to it. Eating large amounts of grain harms a horse in three ways.

• Rapid bacterial fermentation produces gas and may bloat the horse.
• Rapid bacterial overgrowth produces endotoxins which can cause fever, depression, and possibly shock.
• Endotoxemia may cause founder.

This article discusses how to determine if you are going to have a problem, treatment and prognosis. For information on adapting a horse to new pasture or feedstuffs see:

• Concentrates: an Overview
• Forages: an Overview

You come home and find you have left the feed room door open and your horse is merrily chowing down, you have two problems to solve: exactly how much feed he has eaten and then how much is too much. If you know how much feed was in the feed room you can calculate from what is left to arrive at a volume and weight.

I have never seen any published work on how much grain is too much and expect it will vary widely from horse to horse. Empirically within certain ranges large ponies and average size horses can eat twice their normal ration, one time, without serious consequences. I recommend treatment whenever:

• You are uncertain how much was consumed.
• A horse consumes more than twice what his normal ration is.
• Whenever more than 8lbs of grain is consumed.
• The horse has abnormal findings on the exam: typical would be increase gut sounds but gum color and scleral injection might be abnormal early also.

I have seen untreated horses become very sick. Clinical signs will vary depending on the amount ingested. When very large amounts of grain are ingested rapidly, the horse may bloat severely, develop shock, and die within several hours. More commonly however is within 24 hours the horse becoming colicky and developing signs of endotoxemia: elevated heart rate, gums hyperemic with a toxic line, scleral injection, dehydration. Early on there will be greatly elevated gut sounds. If the insult is large enough, this may progress to shock, recumbency and death. Most horses will respond to aggressive treatment, but this will depend on the amount of grain and how early treatment is started. Treatment before clinical signs develop is very important.