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At the Equine Science Society’s Symposium 2023 in Grapevine, Texas, Jessica Seabra from the Federal University of Paraná in Brazil delivered an engaging presentation comparing slow feeders, unrestricted hay, and timed hay racks. he findings were later published in the ‘Journal of Equine Veterinary Science’.

The studies primarily focused on observing the effects of the various feeding methods, including the amount of feed consumed, weight changes, and body condition scores. Additionally, the studies investigated behavioural influences, such as group dynamics, feeding duration, and, as a secondary objective, changes in cortisol levels.

In group housing, such as in open yards, the aim is to promote calm and consequently reduce stress levels among the horses, while also ensuring efficient utilization of hay. The study also aimed to determine which form of housing is most comparable to the behaviour of wild horses, as they exhibit no abnormal behaviour, unlike what is often observed in stables.

15 horses and 15 days of different feeding

For the tests, 15 polo ponies were divided into three groups. Each pony was weighed at the start of each test series, and their body condition score was assessed. For a duration of 15 days each, the ponies in one group were provided unrestricted access to hay. In the second group, hay was also freely available, but the hay racks were covered with nets (slow feeders). In the third group, hay was dispensed using time-controlled racks. These were opened six times a day, each time for a duration of 45 minutes. After the 15 days, the groups were swapped, and the values were reassessed (‘crossover design’).

The group using slow feeders consumed the least amount of hay

As anticipated, the group with unrestricted access to loose hay exhibited the highest level of hay wastage. This group also had the highest consumption, averaging 16.6 kg of hay per horse. This aligns with other studies indicating that feeding loose hay results in hay loss ranging from 30-80%, whereas the use of hay nets can reduce hay loss to 10-20%.

Hay feeding from the hay net
The use of hay nets can reduce hay loss to 10-20%. © Adobe Stock / pholidito

In the other two groups, the amount of hay consumed was comparable: the slow feeders with constant access consumed an average of 9.3 kg of hay per horse per day, approximately 1 kg less (!) than the time-controlled hay racks, which consumed an average of 10.4 kg of hay per horse per day. In all three feeding variants, no distinction was made regarding whether the hay was actually consumed or merely wasted. However, it can be assumed that some of the hay ended up in the manure when loose hay was fed, rather than being ingested by the horse.

Weight gain with loose hay at free disposal

The group with unrestricted hay experienced the greatest weight gain (average 23.5 kg), while the other two groups showed minimal changes in weight, with an average of 1.2 kg for the timed hay racks and 0.37 kg for the slow feeders.

Additionally, it was interesting to note that not only was slightly less hay consumed with constant access to hay using a hay net, but the weight gain was also slightly lower compared to the time-controlled hay racks. This observation was unexpected, as the opposite ratio would have been anticipated.

Behavioural comparison with free-ranging horses

However, what is particularly noteworthy is how the horses allocated their time, as many of the feeding results were already anticipated based on previous studies.

With the slow feeders and loose hay, both of which were continuously accessible to the horses, they spent over 50% of their time eating, mirroring the behaviour observed in free-range horses grazing. The groups exhibited greater calmness, with reduced aggression observed within each group.

Black horse standing with other horses in an open yard in front of a covered building
Horse groups with continuous access to hay exhibit greater peace. © Adobe Stock / Annabell Gsödl

The group using the time-controlled hay racks spent, on average, only 25.8% of their time eating, yet consumed approximately 1 kg more hay per day on average than the slow feeder group, indicating very rapid consumption. During the remaining time, increased aggression within the group was observed, along with undesirable behaviours such as coprophagy (eating faeces). It was also frequently observed that the horses stood still but did not relax into a dozing state. Instead, they remained constantly alert, ensuring they didn’t miss the next opening of the hay rack.

The cortisol levels did not change with any of the three feeding methods. This is also an intriguing result, as one might have expected a different outcome given the behaviour of the group with the time-controlled hay racks.

No recommendation for time-controlled hay racks

If you want to do something beneficial for your horses, it’s advisable to avoid using time-controlled hay racks.

As a nutritionist, therapist, and owner, one often observes aspects such as horse aggression, abnormal eating behaviour, and tension in the back. Now, all of these observations have been scientifically validated. Timed feeders and automatic hay racks are suitable for ruminants, for which they were originally developed, but not for horses.

Instead, opt for slow feeders such as hay nets if you wish to control horses’ weight gain. For older horses or those that are too thin, loose hay can also be fed without restrictions, although hay loss may be somewhat higher in this case.

More articles & podcasts

How all of this can affect your horse’s health and metabolism, you can find out in our article “Are automatic hay feeders beneficial to horses and stable owners?”



Seabra JC, Hess T, Martinez do Vale M, Spercoski KM, Brooks R, Dittrich JR. Effects of different hay feeders, availability of roughage on abnormal behaviors and cortisol circadian rhythm in horses kept in dry lots. J Equine Vet Sci. 2023 Aug 23:104911. doi: 10.1016/j.jevs.2023.104911. Epub ahead of print. PMID: 37625626.