Obese Pony

Photo by Bigstock

If the rainwater pools along his back, your horse is fat. If his neck makes him look like he should be posed outside a P.F. Chang’s, your horse is fat. If his withers have been swallowed by his shoulders and neck, your horse is fat. No, he is not well-muscled, stocky, deep in the heart girth, or even pleasingly plump. But it may not be his fault. It may not even be yours.

Easy keepers have been a stable staple for generations. Evolutionarily, there are advantages to being a horse that “gets fat on air.” In fact, for centuries, in the heyday of the work horse, humans selected horses for just this trait: the ability to maintain body condition and do heavy labor even when feed resources were scant.

Unfortunately, evolution is a slow process; we didn’t emerge from the sludge overnight. While for the most part our horses no longer haul large wagons, pull plows, or function as our major source of transportation, feed ‒ though subject to some whims of climate ‒ is largely abundant and affordable. The result: calorie-efficient animals housed in boxes or on irrigated and maintained pastures, fed nutrient-rich diets, and exercised for maybe a couple of hours per day. Hmmm….I wonder if there’s any correlation between that and a species housed at desks, fed stuff out of microwaves and drive-throughs, and using treadmills to hang laundry.

At the extreme end of energy conservation (I’m talking about horses who can function on very few calories, not horses who remember to turn out the barn lights) we have the horse affected with equine metabolic syndrome (EMS). These horses appear to have some metabolic glitches including a propensity toward obesity and associated insulin resistance. Researchers investigating the possibility of a genetic component to EMS suspect that while genetics may play a role in EMS, most likely the expression is complex and has more than one gene involved. In other words, there probably isn’t an EMS on/off switch. But wouldn’t it be cool if someday someone could tell you if that scrawny, spider-legged foal was at risk for turning into a hippopotamus on the wrong feed?

Ok, why do we care about EMS and obesity in horses, anyway? Isn’t a round croup (rump) a sign of a well-fed animal? Isn’t it bad for horses to be too skinny? Well, I’d like to convince myself that my croup looks better when well rounded, too, but my knees say otherwise. Human medicine has done a great job of making the public aware of the risks of obesity. We may not pay attention, but we know the stops along the obesity road: heart disease, joint disease, diabetes, etc. Small animal practitioners have done an equally exemplary job over the years counseling clients about overweight pets. I don’t know that the percentage of dogs who are wider than tall has dropped any over the past few decades, but I suspect that it is easier to make the case for diet dog food when you weigh the pet at every visit. But horses are just so darn hard to fit on that exam-room scale.

A feedlot mentality still seems to persist in the horse industry. Despite broad marketing of new “low NSC” (that’s non-structural carbohydrate for those not reading horse magazines) feeds, horse owners still seem perpetually concerned with “underfeeding” their horses. Yet the consequences of obesity in horses are as severe as in any species, and in the case of laminitis, rapidly disastrous.

Horses who are overweight for any reason run a high risk of health problems. Aside from being mistaken for something that Victorian hunters would have shot while on safari, overfed horses are being managed far outside their true needs. The horse is a grazer, designed to walk throughout the day and forage on a diet of mixed grasses. Feeding large quantities of alfalfa, hay, and concentrate feeds to a horse is like sitting humans down at an all-you-can eat buffet. Marathoners might be able to burn off buckets of pasta and fried chicken, but it’s a bit hard on most of us. For horses with EMS, a poorly regulated diet is closer to feeding a Type II diabetic that same pasta, fried chicken, and soft-serve ice cream feast.

While EMS horses are not strictly diabetic (they don’t dump sugar into their urine), these horses do typically have difficulty properly processing sugars and their blood work is generally characterized by insulin resistance. This means that while the body does just fine at producing insulin, the receptors that would normally say, “Hey there, insulin, come on over and give me a hand with these sugars” are instead sulking and have gone on strike.

In horses, this glitch in sugar processing often leads to another physiologic upset: the condition known as laminitis. Laminitis is an inflammatory condition of the lamellae, sensitive tissues that connect between the hoof wall and the coffin bone. When these lamellae become inflamed several things can happen:

1. Pain-ever had an infected toenail? Ok, now say you weighed over 1000 pounds and your entire foot was that toe. Now, now make it both feet. And you're wearing pumps. Half a size to small. For men, just drop something heavy on your bare foot. A couple of times and then put on a dress shoes. (Sorry, thats the best I can do.)

a. Rotation of the coffin bone (that funny triangle-shaped bone inside the horse’s hoof) – The lamellae balance the forces of the flexor tendons to keep the coffin bone in place within the foot. When    lamellar integrity is compromised, the coffin bone can rotate or sink within the foot, sometimes even penetrating the sole – GAME OVER.

b. Vascular compromise – Circulation in the equine foot is more intricate than some patterns of lace; screw it up even a little and you get tissue death pretty quickly. 

2. Physiologic stress – pain isn’t good for the body. Chronic pain causes cortisol release, which makes the animal more susceptible to infection, among other things. Also, horses with severe laminitis tend to spend a lot of time lying down. Wouldn’t you? However, even humans can get bedsores and muscle damage from lying in place for too long, and most of us don’t weigh half a ton or more.

Ok, so, EMS=badness; obesity=badness; laminitis=badness; overfeeding=badness. Fine, you say. I can cut back on the grain, maybe switch from alfalfa to grass hay, take my horse on a few more rides, but what do I do if my horse truly does have EMS and isn’t just kinda plump?

First, only your veterinarian can help you determine the cause of your horse’s weight or health issues. Talk to him or her about your horse’s body condition. Ask your veterinarian to teach you how to measure your horse’s body condition score so that you can better monitor his weight. Ask your veterinarian for tips on nutrition and feeding. If you have an overweight horse with a history of laminitis, ask about followup care. Chances are your veterinarian may recommend restricting pasture access and feeding a low NSC diet. But remember your vet isn’t just the person to call when you have a problem. Prevention is most of the battle when dealing with EMS and EMS-associated laminitis. Once a horse develops laminitis, it is too late; damage is permanent. Your veterinarian can help you work with your horse to slim that cresty neck and rounded croup. And your horse will look great in that little black dress! (Oh, wait. That’s my goal – sorry.)