The horse is a grazing animal, designed to spend most of his waking hours eating. Feeding hay free choice can duplicate this to some extent, and it definitely has a favorable impact on behavior. Horses who are allowed to eat as much hay as they want are generally more relaxed and content, and 24-hour access to horse hay tends to reduce vices such as wood chewing.
However, before you open up the hay smorgasbord, there are some things you need to keep in mind about feeding hay free choice.
First, consider that fresh grass is about 90% water, 10% nutrients, fiber and minerals, while hay is the other way around. It's predominately dry matter. Horses on hay-only diets need about 3.6 liters of water for every 2.2 pounds (1 kg) of hay they consume. In hot weather, or when being worked, it's much more. If feeding hay free choice, it's imperative to make sure the horses have constant access to unlimited clean water to avoid problems with dehydration or impaction colic.
At first, your horses may seem to have insatiable appetites, spending nearly all their waking hours at the feeder. However, once the novelty of all-you-can-eat dining wears off, a normal horse will reduce its hay consumption to an amount needed to maintain a normal body condition score of between 5 to 6.
• When feeding free-choice hay, provide your horse with an endless supply of fresh water.
• If weight gain or insulin resistance is a concern, have the hay analyzed for sugar and starch content. (It should be less than 10%).
• Limit or eliminate your horse's grain intake.
• Monitor free-choice hay for freshness, keeping an eye out for contaminants such as foul bacterial growth, dust or mold.
If your horse continues to eat large amounts of hay and gains weight rapidly, he should be checked for insulin resistance. You may still be able to feed free-choice hay, but you will have to make sure that the forage you are feeding is very low in sugar and starch (less than 10% sugar and starch combined) by having the hay analyzed. Don't rely on guesswork here or you could have other health issues on your hands.
Excess weight gain may also occur if you continue feeding grain to horses that are being fed hay free choice, especially if they get little to no work. Most horses will not need any grain at all. Work with a nutritionist to determine what protein and mineral supplementation the horses will need, based on the hay type, and feed a pelleted supplement instead of grain.
A horse on free-choice hay may also take on a fuller look through the abdomen, but he should not develop a prominent "hay belly." A hay belly is a sign of parasitism or poor fermentation of the hay and is never normal.
If feeding free choice, every attempt should be made to find a suitable grass hay. The next best choice would be a grass/alfalfa mix. Alfalfa or grain hays (such as oat or rye) can be fed free choice too, and most horses will probably regulate their intake of these as well. But there are some problems with these. Alfalfa and oat hays are often somewhat higher in calories so will put weight on many horses. Extreme care is needed with the grain hays in horses that are known to be easy keepers and those who may be insulin resistant, because the soluble carbohydrate level in grain hays is much higher than in grass hays. This may also cause a problem with hindgut acidity.
The extra protein in alfalfa can also cause problems with bloating or diarrhea if it is not completely digested and absorbed in the small intestine. Horses on straight alfalfa also have the highest requirements for water to process metabolites of the extra protein through their urine. It is not true, however, that the high protein intake is harmful to the kidneys. Both grain hays and alfalfa also have very unbalanced mineral profiles that will require careful supplementation.
You may also need to consider the economics of feeding hay free choice, as compared to providing a predetermined hay ration. How expensive it will be will depend on several factors. In areas where hay is in short supply, it may be more expensive to feed hay free choice, especially if you have been carefully doling it out.
When figuring how much hay you'll need to buy in order to provide a constant supply, you can assume the horse will eat about 2% of his body weight in hay as a ballpark figure. Then you'll need to add another 10% to 20% as waste. In other words, if your horse actually eats 20 pounds per day, you'll need to buy 22-24 pounds per day, factoring in the leftovers. Compare that to the daily cost of your previous feeding program. If you were already being generous with hay, the horse probably won't consume much more than he was before, but he will enjoy having it available whenever he wants it.
Depending on the feeding system you use, you can expect some waste. Feeding off the ground in bunkers or putting it into hay racks prevents loss of hay at ground surface, but the horses won't be as careful to clean up everything they drop as they are when the hay ration is limited.
Using large round or "square" (actually rectangular) bales can provide a considerable cost saving. But big bales have their drawbacks. They need to be carefully protected from the weather, or there will be considerable loss of quality on the exterior surfaces of the bales. They also require special equipment to move. Most important are some safety issues. Unless put up under very dry conditions, the interiors of large bales can support growth of harmful bacteria and fungi. Also of concern is the possibility of small animals like rabbits or mice getting accidentally baled into the hay, leading to a high risk of botulism.
When feeding large bales, keep a close eye on the horses for any change in weight, appetite or attitude. Bales should also be closely examined on a regular basis, preferably daily, to check for areas of molding, discoloration or an off-odor.
If horses have sufficient high-quality free-choice hay to meet their needs, they will do their best to avoid unappetizing components. This can work well for potentially toxic weeds. However, with dust and mold, it is often a matter of the horses selecting from the "less dusty or moldy" areas of the bale, rather than the horses eating only what is truly "dust- or mold-free." Bales containing sections that are obviously moldy or dusty (and that "dust" may very well be mold) should be discarded, so it's important to keep inspecting the quality of hay as horses work their way through it, especially when feeding big bales that may last a period of days or even weeks. Reputable vendors/dealers will take these bales back and give you a replacement or refund.
Around-the-clock hay is a luxury that most horses enjoy. It can also ease management pressures, especially for horses being maintained on pasture during cold weather when grass has gone dormant. Even so, you'll want to monitor horses daily to make sure they're eating and drinking, and that their hay supply is nutritious. If you weigh these advantages against the added cost, feeding horses free-choice may still make sense at your stable, farm or ranch.