Pros, cons, and surprising facts about slow-feeding devices for horses, such as haynets, hay bags, and hay boxes

Horse owners use slow-feeding devices for a variety of reasons. For instance, utilizing a slow-feed haynet can aid in controlling a horse's weight by reducing feed intake while keeping the horse occupied. Alternatively, owners could use other types of slow feeders to extend feeding times when their horses are stalled for a substantial portion of the day. In both cases slow feeders can help promote normal foraging behaviors, which might decrease the risk of developing stereotypies -- repetitive behaviors that have no apparent purpose, such as cribbing.

You might be interested in slow feeders to extend feeding times to decrease the risk of equine gastric ulcers, especially squamous ulcers (those in the upper portion of the stomach). Finally, slow feeders could help reduce feed intake while keeping horses busy, leading to weight loss, which could potentially reverse or reduce the risk of equine metabolic syndrome.

Another reason to consider slow feeders is to reduce feed wastage. Bordin et al. (2024) cite a report that horses waste up to 57% of loose hay provided, and feeding costs represent one of the greatest expenses on horse farms (Alabama Cooperative Extension System).

We have a wide variety of slow-feeding devices available, each with the potential to make our horses happier and slimmer. As we will see, researchers on several recently published studies affirm that slow feeders do extend feeding time. However, not all slow-feeding devices perform equally well, and there are potential drawbacks to using them. Here we'll relay the most up-to-date data on the topic of slow-feeding devices, including haynets, hay bags, and boxes.

Horses stabled for most of the day often have extended periods of fasting. This occurs despite recommendations from veterinary experts that horses should not fast for longer than four or five hours (Bordin et al., 2024).

"Prolonged fasting periods may cause gastrointestinal or behavior problems in horses, such as increased risk of gastric ulcers, development of stereotypies, and the ingestion of bedding substrate," explains Clara Bordin, MSc, a research fellow in the Department of Veterinary Science, University of Turin, in Italy.

To determine the effect of various methods of feeding hay on feed intake rate, Bordin and colleagues studied nine healthy adult ponies, both Shetland type and Welsh/Cob type. They used four different feeding types: (1) fully filled small perforated haynets (3.5 x 3.5 cm holes); (2) partially filled small perforated haynets; (3) a hay box devised and patented by the research team with the haynet stretched over the top; and (4) hay provided on the ground.

As expected, ponies fed off the ground had a significantly higher intake rate than ponies fed using any of the slow feeders. The partially filled haynet resulted in the lowest intake rate, while the fully filled haynet and hay box yielded similar intake rates.

"The expression of frustration behaviors, such as the bite and pull, was exacerbated with the use of the haynets, but this is not surprising because they are hung and thus very mobile," explains Bordin. "With the hay box, however, we recorded a higher expression of frustration in terms of bite and ripping behavior."

When choosing a slow-feeding device, Bordin recommends considering that each animal is unique and many factors influence the intake rate, including breed. For example, they noticed that Welsh Cob ponies showed a higher expression of frustration behavior when compared to Shetland ponies, which could be an effect of the breed temperament.

"There is no one-size-fits-all solution," says Bordin.

She also notes that the hay box needs additional testing, but so far it seems to be a good compromise to enforce a restricted diet and reduce forage waste, while allowing a natural grazing posture.

Hart and fellow researchers from the Department of Animal and Dairy Science at the University of Georgia's College of Agriculture and Environmental Sciences report: "No research has yet demonstrated whether haynets cause the horse to increase their chewing frequency and chewing duration, or whether the slowing effect observed in some research is simply due to restriction in the amount of forage they can ingest per bite."

They investigated whether feeding Bermuda grass hay from a haynet alters chewing frequency compared to feeding from the ground and studied chewing patterns of horses fed from three types of haynets.

Eight horses acclimated to a chewing halter ate from a haynet with a single large bottom hole, a large-hole haynet (132.24 cm openings), a small-hole haynet (30.25 cm openings), or directly from the ground. The research team analyzed data collected over a 24-hour period for each treatment to calculate the chewing duration, chewing frequency, and the number of chews in the first 120 and 240 minutes.

They found haynet use did not influence overall hay consumption, with all horses consuming 1.4% of their body weight. Type of feeder also did not affect chewing frequency. However, chewing duration, calculated to measure the amount of time (in minutes) spent chewing each day did differ based on feeder type. Notably, chewing duration was significantly longer when feeding from the small-hole haynet compared to the control group (off the ground). Further, the researchers noticed a more rapid intake in the morning than the evening and from the bottom-hole haynet than the small-hole haynet. The authors reported it was interesting that the rate of intake did not differ between the small-hole haynet and either the large-hole haynet or off the ground.

"The increased rate of consumption noted with the bottom-hole net, especially given that the loose hay did not have this effect, potentially indicates that raising hay off the ground and closer to the (horse's) head level while providing a large opening may in fact increase the rate of consumption as compared to no intervention at all," wrote the researchers.

Tanja Hess, MV, MSc, PhD, professor of animal sciences, and Jéssica Carvalho Seabra, PhD, a postdoctoral fellow, both from Colorado State University, in Fort Collins, along with colleagues from the Federal University of Parana, Brazil, acknowledge that free-choice roughage could indeed be the best option for horse welfare.

Seeking to better understand the effects of various feeding devices on equine behavior, Seabra and her collaborators divided 15 horses into three groups. One group was fed using an automatic hay box that offered unrestricted hay for 60 minutes six times daily. The second group was fed using a traditional elevated V feeder offering unlimited access to hay. The third group had unrestricted access to hay through a slow feeding device called a Hayhut with a 1 ¼-inch-hole haynet over a square bale. After 15 days the horses' behaviors were video recorded and analyzed by animal scientists specializing in equine behavior.

Horses in both the free-choice and slow-feeder treatment groups were able to spend more than 50% of their day foraging, generating a time distribution like feral horses in their natural environment. Horses consumed and wasted more hay from the traditional free feeder than the automatic box feeder and the slow feeder.

Not surprisingly, the free-fed horses experienced a significantly greater change in weight over the study period compared to the box- and slow-feeder groups. Therefore, free-choice hay should not be recommended to owners of overweight horses. The researchers saw no difference in consumption or weight change between horses feeding from the box and slow feeder. However, the box feeder treatment had a negative influence on horse behavior, decreasing the time horses spent eating to 25.81% of their day and increasing the time spent on other unwanted activities, such as aggression and coprophagy (eating manure).

"Our study shows that restricted access to resources like food and space can increase competition and aggression between horses housed in groups," says Seabra. "The horses in the box-feeder group had a higher number of negative social interactions (e.g., biting and kicking), corroborating with previous studies reporting that aggressive behavior between horses increases when hay availability decreases."

On the other hand, the free-choice treatment resulted in lower levels of aggression and was the only group where the researchers observed allogrooming, a positive social interaction involving mutual grooming.

"Our study therefore shows that providing more foraging opportunities can increase the frequency of positive social interactions between horses kept in groups, decrease aggression, promotes expression of natural behavior, and decreases the chances of horses developing abnormal behaviors," says Seabra.

Andrea Ellis, PhD, with UNEQUI Ltd., in Notts, U.K., has conducted extensive research on slow feeders and haynets. In one of her recent studies (Hodgson et al., 2022), Ellis and colleagues examined how the height at which haynets are hung affects the pressure needed to pull forage from single- or double-layered haynets.

Horses without evidence of back or neck pain were included in this study and acclimated to the haynets. On the testing days horses were fasted 45 to 60 minutes before being offered forage in the haynets. The haynets were connected to a force meter linked to a laptop to collect pull force data. They were hung either low (2.5 centimeters above the withers) or high (30 cm above the withers) in the pilot study, and single and double haynets were used in the main study hung at the high level.

"Key findings of this study were that horses pulled harder on low-hung haynets compared to high-hung haynets and on the double-layered haynets compared to the single-layered haynets," says Ellis. "The pull pressure on the teeth was equivalent to around 2 kg (4.41 lb) for hay, which was not worrying, but it could go up to 6 kg (13.23 lb) in very resistant forages like haylages."

The researchers reported they were not surprised to find that feeding from double-layered nets involved increased pressure.

"As haynet fill decreased, ingestion time increased, making it harder to take larger bites of hay for the horses," explains Ellis. "In the pilot study, shorter-cut brittle hay was used, and this did not extend intake time much on single-layered haynets. Filling multiple haynets and hanging them at the right height can increase intake time and foraging behavior considerably."

Researchers on this and a previous study (Ellis et al., 2015) also assessed the horses' behaviors while using the single-, double-, and even triple-layered haynets. Some horses exhibited frustration behaviors such as flinging the haynet, particularly when double haynets were used. A few horses even gave up on the triple-layered nets.

"Offering the initial hay in single haynets and hanging some up in doubles to keep them busy for later on (e.g., overnight) may be a good strategy," explains Ellis.

"Individual horses will respond differently so first observe your horse and its reaction to double haynets," she adds. "If the horse gets very frustrated or makes wide neck movements by flinging the haynet, you could tie this down at the bottom, as we tested that option, and it did not increase pressure on teeth much at all."

Ellis and colleagues also looked at back and neck posture. They used markers placed on the horses' necks and backs to evaluate angles while feeding.

"Low-hung haynets created a lot greater posture changes as horses lifted the haynet upwards and had to pull upwards to extract the hay," she says. "This can be avoided by hanging the haynet so its bottom reaches no lower than the shoulder of the horse. We used hangers 30 cm above withers so horses can pull downwards, which allows gravity to help them."

Bordin adds that some horses adopt an unnatural neck and back posture while eating from high-hung haynets.

Indeed, haynets can lead to unnatural neck and back posture if hung too high or low from the floor and not adjusted for the individual horse. But haynets might still be an optimal solution when owners or managers need to reduce horses' intake rate (i.e., overweight horses or ones prone to metabolic disorders) and increase their feeding consumption time, says Bordin. They might also help reduce waste which impacts hay costs.

"As suggested above, a ground slow feeder such as the hay box can be a good compromise when looking for a restrictive feeding method and at the same time allowing a natural feeding posture," she says.

Using haynets and slow feeders can be more complex than it seems at first glance. These tools aim to extend feed intake time while promoting equine welfare, a balance scientists continue to refine through ongoing research.

"As a research group, we are still testing and looking for new, practical solutions to improve feeding management of stabled equids," says Bordin. "Further research is needed if we aim to help owners and caretakers to improve welfare of their horses and ponies." Ellis adds, "According to the latest recommendations by Harris et al. (2017), horses should be allowed to forage a minimum of eight hours in 24 hours. Therefore, haynets hung correctly or doubled up will increase intake time by around 30%, and slow feeders on the ground can also achieve this. Hanging multiple haynets at lower fill rates or doubling up larger haynets can also lead to increased and more natural intake times in stables."