What's the Best Weight Loss Plan for My Horse?

Q. My dominant gelding is also an easy keeper, and he’s managed to pack on the pounds this summer, ballooning from a body condition score (BCS) of 5 to 7. When your farrier asks if your gelding is pregnant, you know you have a problem! I’ve now separated him from my herd in an attempt to control his weight. His diet is forage-based, with only a handful of alfalfa pellets to mix with his supplements. What recommendations do you have for a “reduction diet,” and how quickly should I expect him to lose weight?

A. First of all, kudos to you for taking action, because obesity in horses can lead to serious health risks.

The first part of a management plan—which you’ve done—is performing a body condition score so that you can determine just how overweight he is. It also gives you a starting point from which to work. While we used to say that a BCS of 4 to 6 was an ideal range, more recent work has shown that a 7 is in fact obese. Therefore, a 6 is headed in that direction, so staying in the 4 to 5.5 range (I award half scores for horses that aren’t quite one score or the other) is recommended. (Editor’s note: Learn about body condition scoring in our article “Evaluating Your Horse’s Body Condition.”) Once you have performed the BCS and identified the problem there are a number of steps to take:

  1. Determine your horse’s body weight. Nutritional requirements are based on body weight and physiologic state such as light work, growth, pregnancy, etc. Weight tapes are a good tool for estimating weight and showing a relative gain or loss over time. However, for greater accuracy, I like to use a calculation based on heart girth circumference and length from point of shoulder to point of buttock. Calculate body weight every month to track progress.
  2. Measure heart girth circumference and belly circumference. Initially these might be better indicators of weight loss than BCS. Studies suggest that you might find over the first couple of months that you do not see that great a change in BCS, but you could find a difference in heart girth and belly circumference indicating weight loss. Being able to track these changes when BCS doesn’t appear to be changing can help keep you motivated on your horse’s weight-loss management path. Repeat these measurements every month to track progress.
  3. Weigh everything that you’re currently feeding your horse. As a starting point reduce hay intake to 1.5% of your horse’s current body weight. This will reduce calories while maintaining ample intake for gastrointestinal health. If after two months no weight loss has occurred, reduce hay intake to 1.25% of body weight. But, don’t reduce total forage intake to less than 1% of body weight, because this can lead to gastrointestinal issues as well as boredom, both of which can cause wood chewing or bedding and/or feces consumption. If you’re already feeding 1.5% of body weight or less, consider looking for a forage with lower nutritional quality (see below).
  4. Remove all grain and excessive treats. While one carrot a day likely isn’t going to do much harm, every calorie counts and it’s better to make more calories available from hay rather than consuming daily calorie intake as treats. So cut back on unnecessary treats for your horse and deduct any treat calories from his overall calorie intake. Additionally, remove all other sources of calories such as sweet feed, senior feed, beet pulp, rice bran, and even low nonstructural carbohydrate feeds from the ration. The one exception is a ration balancer. One big problem with reducing feed intake to limit calories is that you’re not just reducing calories, you’re also reducing the intake of protein and vital minerals and vitamins. If the forage has low nutritional value, a supplemental source of quality protein and vitamins and minerals is needed. In fact if adequate protein is not provided, you might see a loss in lean muscle mass. Commercial ration balancer pellets are typically relatively low in calories and high in protein, vitamins, and minerals. If forage quality is good, then your horse only needs a source of vitamins and minerals. You might want to consider feeding a ration balancer instead of your alfalfa pellets.
  5. Choose your forage sources wisely. Ideally, have your hay tested so you know exactly what you’re feeding. This is very important when you are limiting intake. Good hays for overweight horses have a lower leaf to stem ratio and lower overall nutritional quality. This does not mean that the hay is moldy or dusty; rather it means the farmer harvested it at a later stage and so it’s more mature and less nutritious. You’ll be able to feed more of this kind of hay than a leafier hay that was harvested at an earlier stage. Grass hays are a good choice for overweight horses. Alfalfa has a higher calorie content per pound than grass hay, so avoid feeding it to overweight horses. Also avoid grain hays. I’ve recently tested several timothy hays that were quite mature and had low nutritional value and would work in your situation. But, generally, no one grass hay is better than another; it’s going to depend on the horse’s maturity at cutting and harvesting practices.
  6. Limit pasture access. When trying to manage calorie intake pasture can pose a problem because you have no way of knowing what or how much your horse is consuming. And, unfortunately, we can’t rely on horses  to limit their intake. Reducing turnout hours can lead to faster consumption rates and no weight loss. However, turnout gives more freedom of movement, and movement is a good thing, especially for an overweight horse. Therefore, consider using a grazing muzzle if you turn your horse out on pasture, as this has been shown to make significant reductions in pasture intake and, thus, calories. Many owners find the idea of using a muzzle cruel; however, I would counter that if you’ve ever witnessed a horse recovering from laminitis, you’d likely consider a grazing muzzle a humane alternative. The muzzle allows for pasture access, movement, and social interaction, while controlling intake.
  7. Get moving. If your horse has a clean bill of health and can be worked start, increase his work load and build gradually to incorporate lots of trot and long, slow canter sets. Out of everything you do, this might have the biggest impact. To lose weight calorie intake has to be less than calories burned. While reducing calories consumed is often necessary, increasing calories burned each day you will potentially mean not having to decrease intake as much. Restricting feed intake can cause the horse’s metabolic rate to drop—essentially their bodies learn how to get by on less making weight loss difficult. Exercise helps bump up metabolism and might allow you to maintain feed intake at a higher level while your horse still loses weight.
  8. Consider removing bedding. For horses stalled and housed on straw or shavings, you might need to remove this bedding and have only rubber mats. Horses will ready eat straw, and on weight-loss diets they’ve been shown to eat alarming amounts of shavings. Neither will help your attempts at calorie restriction and, in the case of shavings, could have some undesirable intestinal consequences.

As for how long until you start to see results, this varies with each horse. Don’t get in too much of a hurry—weight loss should take time. Researchers estimate that one BCS score is equivalent to consuming 400 Mcal’s of digestible energy. If a pound of better quality grass hay is about 1 Mcal; this means that if you reduce your horse’s hay intake by 2 pounds a day it will take him 200 days to drop from a BCS of 7 to 6. You might find it tempting to reduce daily intake by greater amounts, but keep in mind a horse’s need to consume at a minimum 1% of body weight as forage per day to maintain gastrointestinal health.

Rapid weight loss can also lead to hyperinsulinemia, which can damage the liver and kidneys. If after several months your horse has not lost weight, your veterinarian might prescribe a short course of levothyroxine to stimulate metabolism and weight loss. Additionally, working with a qualified equine nutritionist can help you to more precisely determine nutritional needs and calorie intake for better results.