Research-Based Horse Feeding Considerations

It’s one of the most common questions an owner asks: What should I feed my horse? Equine nutritionists look both to research and their own experience to answer this question. Besides considering life stage and activity level, they must weigh variables such as environment, climate, genetics, and health conditions, which can alter the horse’s needs and lead to, perhaps, the most appropriate answer to this question: “Well, it depends.”

The Kentucky Equine Research (KER) Conference 2018, held Oct. 29-30, in Lexington, ended with a roundtable session on putting feeding requirements—particularly those outlined in the National Research Council’s (NRC) Nutrient Requirements of Horses Sixth Revised Edition, 2007—into practice around the world. Pat Harris MA, VetMB, PhD, Dipl. ECVCN, MRCVS, from the WALTHAM Centre for Pet Nutrition and MARS Horsecare, based in the U.K.; Peter Huntington, BVSc, MANZCVSc, director of nutrition at KER’s Australasian facility, in Victoria, Australia; and Laurie Lawrence, PhD, professor of equine nutrition at the University of Kentucky, in Lexington, fielded questions posed by moderator Joe D. Pagan, PhD, founder and president of KER, with main headquarters in Versailles, Kentucky.

Here are five take-home messages for horse owners from this session.

1. Stop and consider whether you’re overfeeding your horse or pony.

“(Horse owners) generally do believe that their horse/pony is doing more work than they actually are,” said Harris. “They can be putting in the inappropriate (work level into the NRC’s diet calculation) and throwing it all off.”

This extends to active performance horses, too. Pagan said, “When we were measuring the eventing horses in training (during trials with KER’s performance-tracking app), we were surprised at how little they trained. There’s a bit of a disconnect between how hard people are actually training or not training their horses.”

Lawrence said the NRC adapted its tool from three exercise-load categories—light, moderate, or intense (heavy)—to four, adding very heavy work, “to better separate out the horses that were truly in light exercise from those that were moderately working, with the idea that the very heavy work category would be the horses that were racing, elite three-day (event) horses, elite polo horses.”

Even if they’re correctly classified, it’s important to remember that some horses simply seem to be able to maintain condition on fewer calories than others. And, Harris added, researchers have confirmed that certain animals can be weight-loss-resistant.

On the other hand, you’ll see horses that struggle to keep weight on, even they aren’t in work. “Horses are individuals just like us and there are some animals that seem to need more energy than you would think just to maintain their condition, although, if this persists or gets worse, it is always worth getting your veterinarian to check there is no underlying clinical problem,” said Harris.

2. Take it very slow and steady when reintroducing feed to the severely underweight horse.

Feeding the very emaciated horse too many calories too quickly can lead to a condition known as refeeding syndrome, in which the horse can suffer heart and respiratory problems, as well as muscle damage, in part due to abrupt electrolyte imbalances. Veterinary advice is, therefore, always needed in these cases. However, even for the thin rather than the chronically starved animal, dietary changes—in quantity and/or quality—need to be made gradually.

A slow approach can make it seem like it takes ages to see the horse gain weight, said Harris, but once they start to, often the increase can be surprisingly rapid.

“If there’s no clinical reason (i.e., sickness/abnormality) why they’ve lost weight, they often will put on more weight than required when fed for weight gain—hence, the continued need to monitor and adjust your feeding program,” she said.

“Interestingly, weight loss studies in obese animals have shown that whilst more severe restriction might increase the rate and extent of any weight loss, these animals were more likely to put weight back on more rapidly (when fed the same diet that was needed to maintain their obesity originally) than if they were restricted more moderately,” she added. “Weight-loss diets need to take this into consideration and balance the level of restriction (and, therefore, rate of weight loss) with the need to provide sufficient fiber/forage over the 24-hour period–the maximum weight loss we recommend is 1% of body weight (BW) per week (after the first week), and we do not recommend feeding less forage than 1% BW in dry matter (with veterinarian involvement and with strategies to extend foraging time).”

3. Feeding Thoroughbred and Standardbred racehorses coming off the track, whether going to the breeding shed or into performance training programs, can take time and patience.

“Horses that come home to the farm and they’ve been in race training … we try to put them on a high-forage diet,” said Lawrence. “It takes them at least two weeks, and usually a month, before they actually start eating as much hay as you would expect a normal horse to eat. That’s just my observation; they come home, and they pick at their hay and they’re used to eating grain. It takes a long time for them to figure that part out.”

Consider the mare that comes from the track at a body condition score (BCS) of less than 5 in the fall, she said. You’d like to breed her, so you must increase her BCS to above 5 by February. “To increase one BCS unit, you have to feed more than a maintenance level of calories,” she said. “How far above maintenance depends on how fast you want her to gain weight and how big the change in BCS is going to be … one unit or two units, etc.

Research-Based Horse Feeding Considerations

“In general for a Thoroughbred mare, changing BCS in about 60 days takes 5-6 pounds of regular concentrate above her normal maintenance ration,” she said. “So if she is at a stable BCS of 4.5 and she is getting ad lib high quality hay/pasture and 3 pounds of concentrate per day, then you are going to increase the concentrate to 8-9 pounds per day to achieve the weight gain in 60 days.

“Ideally you might want to achieve the weight gain more gradually … say 90 days. Then you can feed 3-4 pounds above maintenance per day (so, a total of 6-7 pounds per day). The other advantage of starting earlier if you live in cold climates is that you can take advantage of milder weather and probably better pasture. In all cases, diet changes should be made gradually.”

Huntington added, “There’s definitely a lag phase with the retired racehorse. And that could be the maiden mare that’s going to stud … but also in the retired gelding that’s going to be owned by a girl who wants it as a riding horse and they’re worried about temperament, No. 1, and also putting weight on them, and often the two things don’t go well together.”

4. Be sure horses fed in groups are getting their rations.

“You need to keep in mind that some horses eat fast, others slow, and mares, especially maiden mares who have just come off the racetrack and are low in the group pecking order, might not be getting enough in groups,” said Huntington.

Keep this in mind with groups of broodmares with foals at their sides, too.

“Remember with the older foal, if it can, it’s going to be eating some of the mare’s food,” said Huntington. “So if you’re calculating how much you’re going to feed a lactating mare, you’ve got to factor in that the foal might be having 20-25% of the dam’s feed.”

Harris added, “Some older horses can’t get their heads down to graze or they can’t move to get to the grazing or problems with their teeth or jaw mean they cannot chew properly. So you think they’ve got plenty of forage and, if the owner reports the horse is losing weight, it might just mean they’re not able to use it.”

Or, they might simply eat concentrate much more slowly than the other horses do, added Lawrence.

5. Consider pasture intake and hay wastage when calculating a horse’s forage intake. Also, consider whether you’re feeding horse or pony.

Diets are built around forage first, but it can be challenging to know exactly what the horse is consuming. Lawrence said she generally estimates hay intake to be 2% of body weight.

“We’ve measured hay intakes in horses that could be 2.8% of body weight, and we’ve measured other horses that eat 1.3% of body weight, so there’s a lot of individual range that you need to keep in mind there,” she said.

She calculates pasture the same way, thinking about total dry matter intake and, of course, the horse’s pasture access.

“When (horses and ponies are) not time-pressured we have some data on kilograms of dry matter per hour, but the biggest thing that’s going to affect how much pasture they’re going to eat is how much pasture is there,” said Lawrence. “So, if they have to wander from one plant to the next on the range, that’s a lot different than if they’re in a beautiful Central Kentucky pasture that’s eight inches tall and dense.”

As for whether horses are consuming enough pasture, her solution is to throw hay to the pastured horses. “If they eat it, there’s not enough pasture out there,” she said. “And if I take them hay and they leave it, then there’s enough pasture.”

But Harris said this can depend on the grass and the individual: “When we’ve got very, very rich, low-fiber pasture, horses will sometimes eat hay because they seem to want the fiber. Some horses might ignore really wonderful grass in favor of some more fibrous hays.”

Either way, remember that ponies seem to have the potential to eat more as a proportion of their body weight than do horses.

“If you turn them out for half an hour and they’re a Thoroughbred, they might buck, run around, and not eat much,” said Harris. “If it’s a pony, especially a native, many will just put their head down and eat   grass! So … for a horse, if they’re out for just an hour, it probably doesn’t count very much to their daily energy requirements (depending on the quality of the grass) But if a pony, it probably will. We have seen that ponies/natives can eat up to 1% of their BW in dry matter when out at grass in just three hours and nearly 5% over a 24-hour period, whereas horses more typically eat around 2-2.5% BW in DM (dry matter, all nutrients minus water) per day. But they are all individuals–so, again, monitoring is key

Huntington reminded attendees to always put out at least one more hay feeder/pile than there are horses, and place them in a circle, rather than a line, to help the natural pasture politics play out, even while everyone gets to eat.

Bottom line: Allow for 10% wastage, he said, as well as that variation with individual intake, while also considering the variability of digestibility and metabolism; remember there can be large individual variation in the response to a “standard” feed. Adjusting the feeding program to a horse’s individual needs is vital.