Eating Manure - Natural or Not?

Well if you're a youngun eating Mom's fresh manure is normal. 

It's called coprohagia and it gets the foal's digestive system in working order. 
The manure provides "starter" bacteria baby needs for the system of fermentation and digestion that allows his intestinal tract to handle solid food. In addition, the environmental bacteria in the manure stimulates the foal's immune system, reducing the chances he'll get sick as he gets older.  

If it's fresh manure, there is less of a chance the foal will be infected by his dam's parasites, as the eggs need to pass through to maturation in the manure before they're infective.

In any event, you will be making sure baby is wormed properly as well.

This behavior usually ceases by the time the foal is five months of age. But if you see this happening in adult horses, then alarm bells should be going off in your head.  If your adult horse is eating manure it has become a habit - and a very hard one to break.  If it is a habit, then it usually has to do with inappropriate feeding, boredom and/or a lack of exercise.

It seems studies have been done that show if a horse is not getting enough roughage he may eat his own manure just for something to do. The same studies say it's extremely important and necessary for a horse to use his lips, picking through grasses and other kinds of forage. If there's not enough forage, he'll start using his lips, picking through and eating manure.  Ewwwww!  Well, yes indeed.  There are other reasons for them eating manure though.

If a horse has been ill, and antibiotics have been used, the drugs may have killed off the good bacteria, present in the gut of all horses that help prevent invasion by harmful bacteria or fungi. Eating manure may help the horse replenish the good bacteria.  If the eating manure just doesn't do it for you then try feeding probiotics.  They're a source of live naturally occurring microorganisms.

Bottom line?  Always make sure your horse has enough forage to keep him happy, healthy and munching. Horses are grazers and if you have them in a pen all day with nothing to eat in between morning and evening feedings, you're asking for trouble.  Also make sure they have something to do and aren't standing all day doing nothing.  A horse is a highly social animal and needs the company and companionship of other horses.