A few days ago you brought your gelding in from the pasture where he’s been living 24/7. Because you have a show in a few weeks, you’ve decided to stall him during the day so you two can polish your skills. Today, however, he seems dull and is off his feed, with mild colic signs. The sudden change from pasture to hay and grain must have upset his digestive system. You’ve always made the springtime shift to pasture from hay and grain gradually but, as it turns out, the reverse transition should be gradual, too.
This is just one example of how our feeding practices can greatly affect our horses’ gastrointestinal (GI) health. To understand how to shape our management techniques to benefit our horses, we need to first look at the diet horses adapted to eat from an evolutionary standpoint.
The Horse in Nature
Horses evolved in an environment where they grazed more or less continuously—about 14 to 18 hours a day, says W.B. (Burt) Staniar, PhD, associate professor of equine nutrition at Pennsylvania State University, in State College.
And for good reason—digestion in horses is less efficient than digestion in ruminants, says Staniar, so the horse’s feeding strategy is to eat a lot of forage to get the necessary nutrients. “This forage … has a relatively rapid rate of passage through the tract, producing lots of feces,” he says. “As long as the horse has plenty of forage, this (rapid rate of passage) doesn’t matter.”
This strategy works well for horses, which wander, graze, and eat continually except when resting. In fact, locomotion (e.g., traveling, grazing) is natural and necessary for the equine GI tract to function properly.
“There was a study that showed that horses in stalls maintained a lower pH in the stomach (a more acidic environment) than the horses allowed to move around in paddocks,” says Kathleen Crandell, PhD, an equine nutritionist with Kentucky Equine Research, in Versailles. “The movement also helps gut motility. This is why confinement is one of the risk factors for colic.”
Another thing that affects digestion in natural settings is social contact, which Crandell says gives horses a sense of security so they can settle down and eat. Being herd animals, the comfort of being together reduces their stress levels and allows them to follow each other in normal grazing behavior.
“Those are the three aspects (free movement, foraging, and social interactions) of normal equine behavior that we have interfered with when we started putting them in stalls or small pens,” she says. “We limited their locomotion and meal-fed them. They have lost some of that foraging behavior, and even if they can see other horses when they are in stalls, it’s not the same as having continual social contact.” This also adds stress to their daily lives.
These changes can affect horses in several ways. Some of them adopt abnormal behavioral stereotypies such as cribbing, weaving, and stall-walking. They might also develop health issues such as gastric ulcers, colic, or laminitis due to the unnatural conditions, feeds, and practices of modern horse-keeping.
The horse’s small stomach, designed to handle modest amounts of high-fiber food continually, works best if the horse is eating a little bit throughout the day and night. It can’t hold a large meal eaten all at once; it’s smaller than a cow’s rumen or a human stomach, relative to the rest of the digestive tract.
The horse’s gut also works different from ours. Humans, like other predatory species, eat nutrient-dense meals (such as meat) and don’t have to eat again for quite a while, whereas a prey animal like a horse is eating a larger proportion of fibrous material all the time to gain an equal amount of nutrients and is constantly on the move, on the lookout for predators.
“We’ve imposed our type of eating on the horse, thinking a horse can eat meals like us, which is unnatural and also detrimental to his well-being and gut health,” says Crandell. “It is convenient for us to feed the horse just twice a day; we don’t stop to think about the horse’s natural feeding behavior and how the digestive tract works.”
Increase Chew Time
Foraging behavior—that is, grazing for 50 to 70% of the day—translates into buckets of time spent chewing. “The horse spends a lot more time chewing forage than eating grain,” says Crandell. “One study showed that for 1 kilogram (2.2 pounds) of hay, a horse chews 3,400 times and takes 40 minutes to eat it. If the horse is chewing 1 kilogram of oats, he only chews 850 times and finishes it in 10 minutes.”
Crandell cites another study in which researchers looked at how many times horses chew per day when given constant access to hay: 43,000. By contrast, a horse consuming a pelleted diet chewed only a quarter of that amount, around 10,000 times per day.
All this chewing is important because the saliva it produces helps buffer the stomach from ulcer-causing acid. We can increase chew time by making conscientious feeding adjustments, says Staniar.
“Horsemen can use a concept from dairy nutrition called physically effective fiber,” he says. “This is a characteristic of diet centered around how much the feedstuff causes the animal to chew.
“More physically effective fiber makes the animal chew more and also results in a biphasic makeup within the digestive tract,” he says. “This means the solid and liquid portions readily separate. The fiber tends to float on top with the liquid underneath. There are also large and small particle sizes.”
In contrast, if a horse consumes a 100% pelleted diet, there’s not much physically effective fiber, which leaves the particle size in his GI tract very small. “The horse doesn’t have to chew pellets very much, and you’d have a very uniform mix of food within the tract,” Staniar says. “That homogeneous mixture will increase the risk for ulcers, and it will not move through the GI tract in the same way that a nonuniform mixture would move through,” because there’s not enough bulk to help keep things moving along properly.
Related Content: Journey Through the Equine GI Tract
Staniar describes a study in which researchers at the Marion DuPont Scott Equine Medical Center, at the Virginia-Maryland Regional College of Veterinary Medicine, in Leesburg, Virginia, studied feedstuff characteristics in the cecums of cannulated horses (those with surgical portals created through the abdominal wall through which researchers can access the cecum).
High-grain diets resulted in more homogenous material in the cecum, lacking good solid and fluid separation, says Staniar. The researchers, who were interested in how this might increase colic risk, noted that this mixture was also frothier and trapped more gas.
They theorized that the anatomy where the cecum and colon come together at the pelvic flexure is geared toward the high-fiber feedstuffs that horses eat in nature. The more uniform mixture caused by modern diets might not fit as well, says Staniar, possibly increasing the risk for gastrointestinal disturbances.
So horses with minimal chew time are prone to not only gastric ulcers but also colic due to gas, impaction, or other issues, he says.
Chewing also has a calming effect. Crandell says horses that chew more during the day are less likely to develop stereotypies and, if they are happily eating, are content, less stressed, and healthier.
Several things, however, can diminish a horse’s ability to chew. “If a horse has poor tooth alignment, tooth loss, or arthritis in the jaw—which can all happen in older horses—he will chew less, with higher risk for gastric problems,” says Crandell. “If the horse can’t chew fiber effectively, then you have to make changes in the diet and provide something that’s easier to chew,” such as hay cubes, pellets, chaff, beet pulp, and/or a complete feed.
A Provisions Paper Trail
W.B. (Burt) Staniar, PhD, associate professor of equine nutrition at Pennsylvania State University, in State College, recommends owners keep precise records of what and when they feed. “If you could look back and see what you’ve been feeding your horse over the past year, it might help you determine what might have caused a gastrointestinal problem.”
This might include the type and amount of grain, hay type and weight, feeding frequency, and diet changes.
“You also need to know the body condition of your horse and vital signs,” he says. Taking these periodically will make you familiar with his normal temperature, pulse, and respiration rate when he’s healthy, so you can recognize problems early—for instance, if he goes off feed and his heart rate is increased.
“If any of these things are abnormal for that horse, this can be indicative of a gastrointestinal problem,” he adds.
While many horse owners think they know exactly what’s going on with their horses, Staniar says a notebook or a diary is more concrete evidence than a recollection.
—Heather Smith Thomas
Reduce Meal Size
Remembering horses’ small stomach size, concentrate meals should never be too large. The old rule of thumb was that a 1,000-1,200-lb (500-kg) horse should consume no more than 5 pounds (2.3 kg) of concentrate feed per feeding.
“There are some new rules of thumb that seem to help—these have more to do with the amount of starch” in the feed, says Crandell. “If you are trying to decrease incidence of gastric ulcers and still need to feed a high-starch meal to a horse that needs a lot of energy, it can make a difference if you limit grams of starch per kilogram of body weight. These horses should have no more than 1 gram of starch per kilogram of body weight in any single meal.”
So, if your feed is 20% starch, your 500 kg horse should consume 2.5 kg (5.5 lbs)of feed per meal. If the feed is 40% starch, his meal should be half that size, or about 1.25 kilograms (2.7 lbs). This helps reduce gastric ulcer risk.
If you feed more than 2.5 kg of concentrate in one meal, your horse might also be at risk of hindgut (the large intestine and colon) acidosis or colic. “Hindgut acidosis occurs when we overwhelm the small intestine with too much starch,” says Crandell. “It does not get enzymatically digested and ends up in the hindgut. There are bacteria in the hindgut that love to digest starch and the end product of their starch digestion is lactic acid, and this makes the hindgut more acidic. This increases risk for colic and indigestion.”
She says these horses might lose weight and develop stereotypies. “If you keep a concentrate meal under 2 grams per kilogram of body weight, this may prevent hindgut acidosis,” she adds.
- Feed More Frequent Meals
Increasing the number of meals per day is a management strategy that helps reduce gastric ulcer and colic risks, but it can be a challenging practice for people accustomed to only morning and evening feeding—before and after work.
Many horse owners put a pile of forage in front of the horse first thing in the morning or at night, thinking he’ll eat on it until the next feeding, says Staniar, but “most horses eat it all at once and by mid-morning or late evening the hay is gone.”
Try grouping smaller, more frequent fiber-rich meals closer together. “If you have a nibble net or slow feeder for hay and incorporate some kind of chopped fiber (or chaff) into the grain or concentrate feeding, this will slow the eating and make the horse chew more,” says Staniar. “If this is combined with some pasture access during the day, the horse will probably have less risk for gastrointestinal problems.”
In fact, if you are trying to get more calories into a horse, you are better off feeding smaller meals more frequently. “If you are trying to feed just 1 gram of starch per kilogram of body weight, and the horse needs 5 kilograms per day (to keep weight on or provide energy for hard work), you should be feeding several meals,” says Crandell. “If you are feeding oats, which are about 40% starch, that means you would feed four meals per day to keep it under 1.25 kilograms per meal.”
Some of today’s commercial concentrate feeds are helpful because they are high-fiber, or high in fat and fiber and lower in starch and sugar (less than 20% starch). The typical meal size (2.3 kilograms of concentrate) rule of thumb works for these feeds because they are low in starch.
Many stalled horses spend as little as 30% of their time eating. Dividing food into more meals for these animals, so they can eat more often, is healthier for the GI tract than going so long between meals. Abnormal behaviors such as eating manure and bedding, along with stereotypies such as chewing wood, are primarily due to the horse’s inability to graze, lack of chew time, insufficient fiber in the diet, and not feeling full. The horse resorts to trying to eat or chew other things.
- Make Diet Changes Slowly
As we mentioned earlier, when making any changes to your horse’s diet, do so slowly and gradually. Make the change (e.g., from hay to pasture or pellets and vice versa; from one kind of hay to another; or in concentrate ration, content, or quantity) over a couple of weeks.
Related Content: Switching Horse Feeds Safely
“Even moving from one part of the country to another, where feedstuffs might be different, can be a challenge for horses,” says Staniar. “Many people on the East Coast go from north to south every year for showing, racing, etc. When making these moves, bring a little feed (both the hay and concentrate) along that the horse is accustomed to eating, and make a gradual change after the horse arrives in his new environment.”
Some horses adjust readily, others don’t, so always err on the side of caution. “Horses are a lot like humans in that there are variations in how different individuals handle change or different foods,” says Staniar. “Two people might go on a trip together to a foreign country, and one might get sick and the other doesn’t eating the same food. It’s the same with horses—a combination of genetic factors, the microbes in the gut, and little differences in … ability to handle different foods or changes in food” contribute to differences among horses.
For optimum gut health, our feeding and management practices should mimic nature as much as possible because unnatural conditions can adversely impact horses’ GI tract health and function. This means paying attention to what we feed (nutrient and fiber levels) and how we feed, in terms of meal size, frequency, and ways to increase eating and chew time.