The Fat Farm: Nutrition for the Overweight Horse

Is your mare looking a bit rotund lately? Does her gait have a waddling roll to it? Has her spine disappeared in a dimpled groove along her back? Has she outgrown her girth, her winter blanket, and the stall door? If she’s not due to foal, then she’s definitely suffering from an expanding waistline.

Now, we all like to see our horses in good flesh, but it’s possible to provide too much of a good thing. Excess dietary energy, in the form of calories, combined with too little exercise, does for horses exactly what it does for humans--creates chubby waists, thunder thighs, and broadening rumps. For some equines, it seems extraordinarily easy to become overweight. Ponies, in particular, have a problem because they usually evolved in very harsh conditions and thus were designed to get the maximum nutritive value out of very sparse, coarse forage. As a result, their metabolisms are unusually efficient. Certain horse breeds have a predisposition towards being "easy keepers" (Quarter Horses and Morgans come immediately to mind, although they’re certainly not alone!).

Several factors can combine to create an overweight horse. Inadequate exercise is a common one, as is deliberate overfeeding for show or sale (this is less common than it once was, but there still are many owners and trainers who believe that a little extra fat can hide a multitude of conformational sins.). Sometimes, chubbiness is the result of misplaced owner affection. Many of us get considerable satisfaction from making our horses happy, and one of the things that makes them happiest is food. Many owners also mistakenly believe that broodmares need extra nutritional support throughout their pregnancies; in fact, it’s only in the last two to three months of pregnancy, and during lactation, that a broodmare’s feed intake should increase.

Finally, in a group feeding situation, there always will be horses which are dominant, and those which are submissive. Dominant horses get to eat first, and often will bully more subservient pasturemates into giving up their portions. So, you might be able to identify the boss mare in your field simply by her proportions. Remember, too, that horses are grazing animals, designed to eat constantly for up to 16 hours a day. What we interpret as "greed" simply is a natural and constant hunger, which is genetically programmed into all equines. Some are just better at satisfying it than others.

Motivations For Getting Buff

Should you worry about your mare being overweight? Yes, for several reasons. First and foremost, if she is too fat, she’ll be a far less efficient athlete. She’ll have lowered exercise tolerance, will break into a sweat at the slightest exertion, and her extra body weight will mean increased stress on all of her bones and joints. Being overweight means she’ll have increased oxygen needs--but her body’s ability to take in oxygen will be compromised because the additional mass against her chest wall makes respiratory effort more difficult.

Overweight horses have a particularly difficult time in the hot summer months, when their extra fat layer compromises the body’s natural cooling system. Higher heart and respiratory rates due to increased exertion needed to move the greater bulk around result in a high plasma lactate concentration when exercising. This possibly can increase the risk of tying-up. (In winter, however, an extra fat layer is less of a problem; it even can be a bonus when temperatures become really bitter.)

Obesity also is a problem if your mare is pregnant, or if you plan to breed her. While being overweight won’t affect her reproductive efficiency, the duration of her pregnancy, the placental weight, or the degree of difficulty she has in foaling, it can decrease her milk production—and that can adversely affect the growth rate of her foal. (Unlike some other species, horses don’t seem to suffer an increased incidence of labor complications when they’re obese.) It also can affect her ability to get back in foal.

Stallions, too, experience difficulties when they’re fat. Some studies have indicated that overweight stallions experience reduced fertility. It has been suggested that the reason for this is that fat deposits around the haunches and gaskins increase the body temperature around the testes, and that leads to lessened motility and malformation of sperm.

Most veterinarians agree that obese equines, especially ponies, run an increased risk of founder, or laminitis. This is thought to be due to a relative insulin resistance commonly seen in obese equine animals that is similar to adult onset diabetes in humans. In these animals there is excessively high insulin response after a meal of grain. It has been reported that the insulin response decreases to more normal levels if the horses lose weight. There also is an increased risk of strangulation colic due to pedunculated lipomas.

In humans, and in a number of other domestic animals, obesity has been linked to an increased risk of heart disease, cancer, and circulatory, digestive, and skin disorders. Obesity also has been demonstrated to decrease resistance to some kinds of infectious diseases. The overall effect is a shorter lifespan. Whether these same effects exist in horses isn’t known, but it could be possible.

For all of these reasons, it’s a good idea to put your overweight mare on a diet. And don’t bother calling Jenny Craig or Weight Watchers, there are no magic formulas or secret diets that will do the trick. The answer for overweight horses, alas, is the same as it is for us: eat less and exercise more.

Strategies For Weight Loss

There’s really only one way to correct obesity: your horse’s dietary energy intake must be less than her energy utilization. You can accomplish this either by decreasing the amount of feed she gets, or by increasing her exercise regimen. The best approach is to do both.

Very few horses will voluntarily maintain a fit body weight if given excess food and free exercise. Most are genetically programmed to maintain a condition score over seven to save up for the cold winter months. Only "hot blooded" breeds might have lost this tendency. That’s why a horse which is overfed is likely to be "wired for sound." He’s asking for the chance to work off some of those extra nutrients! If that opportunity is denied him, his body will convert the calories to fat and store them.

A severely overweight horse, of course, will find exercising difficult and uncomfortable, so you will have to increase your demands very gradually. At first, just long stretches of trail riding at a walk might be enough. Or try providing him with a larger turnout field in which to self-exercise, preferably with some lively companions to motivate him.

Regular turnout, in a paddock big enough for exercise, will play a big part in your horse’s slimming regime. If she’s really obese, however, you might have to seek out a paddock with a minimum of edible pasture or she might pack on the calories as quickly as she works them off! Many owners of chronically "easy keepers" find that their horses or ponies maintain a healthy physique only when kept on a dry lot (a dirt paddock with no grazing). If your "easy keeper" is kept in a grass pasture, you’ll have to ensure your horse exercises by longeing, riding, or driving her on a regular basis and with steadily increasing demands.

The other half of the equation is modifying the diet. First, you want to decrease the amount of dietary energy your horse is taking in. Carbohydrates and fats, found in grains, are the principle culprits here, as they are far more energy-dense than forage or hay. So cutting back--or even eliminating--the grain your horse receives is a good step to take.

Before you do that, however, consider the other nutrients your grain ration provides to your horse. In addition to energy, a grain feed, whether it be oats, corn, sweet feed, a pellet, or an extruded ration, also supplies a number of essential vitamins and minerals. If you suddenly eliminate that nutrient source from her diet, will she be in danger of suffering deficiencies? Starving your horse of nutrients will, in the long run, do more harm than good—so if you’re going to remove that vitamin/mineral source from her diet, make sure that you’re replacing those nutrients in some other way.

Start by getting your hay analyzed, if you haven’t done so already. Once you know the approximate protein content, and calcium and phosphorus ratio, you’ll have a better idea of where the diet will fall short. While you’re at it, avoid feeds with added fat levels (more than 3.5% crude fat). This is one instance where your horse won’t benefit from having extra fat levels in her diet.

If you intend to eliminate grain from your horse’s diet entirely, look for a vitamin/mineral supplement designed to balance the deficiencies in hay. Such a supplement, usually fed in very small amounts, can help ensure you’re not robbing your horse of essential nutrients while she’s losing weight.

Assuming you’ve got your overweight horse on a dry lot or poor pasture, the bulk of her diet will be hay. As much as possible, try to feed a relatively coarse, long-stemmed, high-fiber grass hay, possibly cut a little later than optimum. This sort of hay requires more chewing to process, and will occupy your horse for a longer period of time, thus staving off those inevitable hunger pangs. Avoid legume hays, such as alfalfa or clover, or young, leafy grass hay. Those generally are much more energy-dense, flake for flake. While you might want to select an over-mature hay, be careful that it’s still otherwise of good quality (no weeds, mold, or dust).

How much should you feed? The general formula of feeding a horse between 1.5% and 3.0% of her body weight in total feed per day still stands. However, with an overweight horse you should steer toward the 1.5% of the equation. Don’t allow the quantity to drop below that, however, or you risk delivering too few nutrients and creating a malnourished horse.

Just as in humans, rapid weight loss is unhealthy and rarely provides lasting results. A horse which drops a great deal of weight in a short time-frame is at risk for vitamin/mineral deficiencies, protein deficiency, hormonal disturbances, and most dangerously, hyperlipemia, a condition particularly common among ponies. In hyperlipemia, the body perceives itself to be starving, so it releases large quantities of stored lipids into the bloodstream, generally more than the horse can use. At the same time, the system seems to say "no more" and it shuts down the appetite. A horse or pony suffering from hyperlipemia might be drowsy, or depressed, and might suffer muscle twitching, incoordination, colic, and diarrhea. Hyperlipidemia causes impaired liver function, which can be life threatening. Hyperlipemia can appear rapidly and has a high fatality rate. It is difficult to treat because the only cure is to feed a high-energy, low-fat diet for a period of one to three weeks, to a horse with little enthusiasm for food. Enticing the pony with beet pulp or chaff (chopped hay or oat straw) with molasses, laced with fruit juice, apples, or carrots, sometimes does the trick, but obviously the best approach is not to risk hyperlipemia at all.

Gradual weight loss (monitored by eye and with regular use of a heart-girth weight tape) is always a better bet than a crash diet.

The Chewing Compulsion

One of the challenges of putting an overweight horse on a diet is managing to keep her from chewing the barn down when her abbreviated mealtimes don’t satisfy her hunger. Sarah Ralston, VMD, PhD, Diplomate ACVN, equine nutritionist with the Department of Animal Science at Rutgers University in New Jersey, suggests you make your horse work harder for her meals by placing her hay inside two haynets, or even better, a haynet inside a canvas hay-bag. This little strategy will slow down her consumption rate considerably.

In addition, she says, you can consider feeding chopped straw "if your horse is chewing the barn down." Straw largely is made up of indigestible fiber, and provides little in the way of nutrients, but it likely will satisfy your horse’s munching instincts and do something to convince her she’s not being sorely deprived. However, even the straw you offer should be limited. So if you use straw as your bedding, consider switching to something inedible, such as shavings or peat moss.

Another suggestion from Ralston: If your horse is really missing her grain, try feeding a few large, bulky hay cubes soaked in water to make a mush. This makes a substantial volume of food to dump in the feed tub, "and it gives the mother in you the feeling that you’re feeding more, too," she says. A lower-protein, lower-energy hay cube based on grass, or hay plus whole-plant corn, is a better bet than an alfalfa cube.

Although beet pulp is a low-protein feed, says Ralston, she doesn’t usually recommend it for horses on weight-reduction regimes because it’s not particularly low-calorie. That’s because its fiber is quite fermentable, so your horse will still extract quite a lot of food value from it. However, it is lower in calories and energy than grain, so it can be used in small quantities to give to a horse who’s upset that everyone else in her shedrow is getting a grain meal when she’s not. Most horses readily accept it as a substitute.

When your horse first goes on her diet, she might spend a lot of time giving you baleful glares, designed to push all your guilt buttons and make you feel unbelievably cruel. Try not to cave. Remember that your efforts (and hers) will leave her feeling healthier and more athletic in the long run--and that’s how a horse should be.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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