Horses in a wild environment tend to graze or browse intermittently for 18 hours per day, keeping their digestive tracts filled with high-fiber forage. In a domesticated environment, it is not unusual for feeding to be restricted to large meals fed twice daily with long periods of fasting in between. This has adverse effects on the gastrointestinal tract, leading to problems such as gastric ulcer syndrome (GUS) due to loss of buffering of stomach acid during fasting, and impaction colic due to alterations in intestinal motility. 

In addition, horses that don’t have relatively constant access to hay or pasture tend to develop pica (eating of non-food materials) and might develop repetitive (stereotypic) behaviors such as crib biting, weaving and stall walking.

Other studies have demonstrated improved body condition, better fertility rates, and positive social interactions when horses have free access to forage. 

However, some horses are incapable of controlling their feed intake while others with limited exercise tend to become obese if allowed to eat their fill. There is also the opportunity for wastage with free-choice hay if too much is provided that gets trampled or spoiled rather than eaten.

Commercial feeding systems have been developed to control a horse’s intake—these “slow feeders” contain the hay in one place and make it challenging for a horse to acquire the feed, thus slowing down consumption. A horse pulls out one bite at a time from many small holes in the feeder device instead of having access to one large hole that not only allows big mouthfuls, but also distributes clumps of hay on the ground.

One study compared the behaviors of horses fed either hay on the ground, hay in a hay bag, or hay in a slow feeder in the corner of the stall [Rochais, C.; Henry, S.; Hausberger, M. “Hay-bags” and “Slow feeders”: Testing their impact on horse behaviour and Welfare. Applied Animal Behavior Sept 2017]. The researchers found that the most time spent feeding occurred with the hay bag and the slow feeder as might be expected because the horses had to work harder in search of hay in the web or wire mesh holes.

Horses experienced less frustration with the slow feeder and exhibited fewer stereotypic behaviors. In addition, eating from the slow feeder improved positive interactions with humans.

In contrast, the hay bag feeder hung at head height on the wall resulted in greater horse frustration and this led to more stereotypic behaviors, such as crib biting. Frustration in using the hay bag was observed as the horses pulled on the hay bag with teeth or pushed on it with the head. Horses fed off the ground also demonstrated frustration behavior, and they also ate more straw than horses fed with the hay bag or slow feeder.

Hay remained in the slow feeder even 11 hours after feeding whereas the hay bag and stall ground feeding systems were empty far sooner. Periods in between eating from the slow feeder were associated with relaxed behaviors.

When horses are provided with free access to forage, they tend to self-regulate better in their eating habits, taking in what they need rather than tending toward more gluttonous behavior of eating everything in front of them. Some horses need a little time to make this adjustment; others still don’t exercise good self-control, so hay must be rationed to a set amount each day. The slow feeder helps to lengthen out the time of eating, which is much better for both psychological and intestinal health.

Types of Slow Feeders

Slow feeders come in a variety of configurations, as varied as the imagination.

• Diamond shaped openings in webbed hay nets;
• Buckets that hold 15-20# of hay;
• Trough-shaped configurations that hold a bale of hay;
• More elaborate wooden constructions with wire mesh over the hay;
• Combinations of slow feeders, such as installing a hay net (with zip ties) into a box covered by a grate.

Hay nets by themselves generally have large openings that don’t really slow down intake, and the horse also tends to pull too much hay out at one time, with most of the hay landing on the ground where it is consumed quickly or stepped or urinated on and spoiled. The ideal hole opening is 1½ – 1¾ inches for an adult horse. If the holes are too small, the horse might become too frustrated to eat. You might need some experimentation to find just the right size hole for your horse.

Nets are useful for their ability to be attached to just about any surface—wall, tree or post. They are available in a number of different sizes. The disadvantages are that a horse may pull out too much hay thereby obviating them as a “slow” feeder, plus there is a risk of leg or head entanglement.

Feeders made from hard plastic or rubber seem to hold up to temperature extremes and horse antics. It is better to avoid wooden hay containers for their tendency to splinter or fragment from wear and tear by horse proximity. And, they are more easily knocked over if too lightweight. Be aware that a steel grate or grid placed on top of a homemade slow feeder creates a dangerous risk of foot or leg entrapment. Whatever form of grate or grid used, it is best for it to have rounded edges that don’t injure a horse’s mouth or teeth.

Some slow feeders or hay bags are commercially made; some are homemade from designs available on the Internet. Purchase from a commercial enterprise is likely to ensure that the feeder is made with durable, heavy-duty fabric or materials that stand up to horse abuse and are safe for the horse to use.

The best shapes for slow feeders include:

• A removable hay basket that sits inside a metal frame – the basket doesn’t sit on the ground so is able to drain;
• A barrel or box feeder that sits on the ground with hay access from the top. This allows a horse to eat in a natural head-down position.