THE NIGHT SHIFT

What really happens between last feed and first

A look at the overnight hours, the part of the feeding day we plan the least, and what new work on the equine body clock suggests we could be doing better.

Most yards have a feeding routine that ends at evening stables and resumes at dawn. Concentrates fed, hay nets filled, lights off. What happens in the ten or twelve hours in between tends to look after itself (barring a sick horse or a disruption due to show schedule). Yet that overnight stretch is the single longest part of the feeding day, and a run of recent research suggests it is also the part we understand the least, and some of the most interesting work is not about what horses eat overnight at all. It is about when they eat, and why the timing turns out to matter more than we assumed.

The clock in the stable

A circadian rhythm is an internal cycle of roughly 24 hours that the body generates on its own and then fine-tunes against the outside world. In horses, as in us, the master clock sits in a small region of the brain called the suprachiasmatic nucleus. Light entering the eye is its main signal: the ‘clock’ reads day and night and sends timing instructions out to the organs and tissues, partly through melatonin, the hormone the pineal gland releases as darkness falls. Melatonin is, in effect, the body’s message that night has arrived.

Work led by the equine chronobiologist Barbara Murphy at University College Dublin found that the horse’s melatonin rhythm is unusually light-driven rather than strongly self-sustaining. Held in continuous darkness, horses did not keep up the normal night-and-day swing in melatonin; levels simply stayed high. Horses also reset their body clocks to an abrupt time shift remarkably quickly. The takeaway is that, in the horse, the light environment we create in the barn is not a minor detail. It is one of the strongest levers we have over the animal’s internal sense of time.

That reframes a few familiar habits we tend to practice in our yards. Bright white light switched on for a late check or an early feed sends a daytime signal at the wrong hour. Blue-rich light, the kind from many LED fittings and from screens, is particularly good at suppressing melatonin in horses. Murphy’s group has shown that doing night chores under dim red light, which the horse’s clock largely ignores, avoids that disruption, and that horses kept under red light at night tend to be calmer, rest better and eat more readily. For a yard doing a 10pm check or a pre-dawn feed before a show, the colour of the light is a cheap and easy thing to get right.

When horses choose to eat

The clock shapes appetite, too, and this is where the new research on feeding comes in. Kentucky Equine Research recently used chewing halters with sensors that record how long and how often a horse chews, to track stabled horses through the night. With hay in front of them, chewing was heaviest in the early evening, then eased off as the night wore on, with a clear rest phase developing in the small hours. They then began to eat again with more gusto around dawn. It was a small study, and the researchers are careful not to overstate it, but the shape matches older behaviour work: horses do most of their hay eating in daylight and the early evening, and most of their resting and sleeping in the second half of the night, resuming foraging behaviours around dawn.

It is tempting to read this research as permission to let the hay run out overnight, on the logic that horses are barely eating then anyway. That would be the wrong lesson, and a potentially harmful one. The taper describes a horse pacing himself when forage is always there: he eats, rests, and comes back to the hay through the night. Ultimately, eating less is not the same as needing nothing available. A horse dozing at two in the morning still has a stomach producing acid, and an empty net at that hour means an enforced fast, not a natural one, risking damage to the stomach lining in the form of ulcers. The overnight rhythm, and the early start at dawn, is a reason to keep forage trickling through the night, not a reason to withdraw it.

It is worth stating that this science is really in its infancy. The researchers who study the equine body clock are the first to point out that we do not yet know how much of a horse’s daily rhythm is hard-wired and how much is simply learned from the routine we impose on it. However, that uncertainty itself still gives us practical guidance. If routine is doing much of the work in keeping our horses regulated, then a consistent, predictable rhythm, with horses fed, checked and turned out at much the same times each day, is probably one of the most underrated tools in the feed room.

Why the gaps matter

That matters because the stomach does not rest when the horse does. The horse’s stomach is small, around seven to eight percent of the gut, and it produces acid continuously, whether the horse is eating, dozing or fast asleep. A steady trickle of forage, and the saliva that chewing produces, keeps that acid buffered, whereas long gaps do the opposite. Research has repeatedly linked low forage intake, long stretches without it, and high-starch meals to a raised risk of squamous gastric ulcers. The overnight stretch is the longest forage gap most stabled horses face, which is precisely why what we do with it is important.

The practical answer is to make forage last rather than to feed more of it. A small-holed or slow-feeder hay net can stretch a measured ration across more of the night, so the horse still has hay available to pick on when he needs as well as for his dawn appetite surge. The aim is hay that is still there in the early hours, not a net that empties by midnight.

However, it is worth noting that some horses settle happily with a net while others fret at it, so it is worth watching the individual, but the goal stays the same either way: forage available through the night, not just at the start of it.

Final thoughts

The overnight hours will probably never get the attention the morning feed does, but the emerging picture is encouraging, because almost everything it points to is reasonably affordable and within reach. If we keep the forage trickling, mind the lights and hold the routine steady, we should be giving our horses the best chance of a happy, healthy life.

References
Kentucky Equine Research (equinews) and University of Kentucky equine behaviour research
B.A. Murphy and colleagues on equine chronobiology, University College Dublin