by Dr. Kris Hiney

Just like in people, many horses suffer from obesity related health issues. Overweight horses can have more trouble with joint issues, suffer from exercise intolerance and can even develop metabolic problems. While many horse owners know the risks of having an overweight horse, it may be difficult to reduce weight in these horses – certainly the horse is usually an unwilling participant!  In this article we will address management techniques and dietary strategies designed to reduce weight, but still keep the horse physically and mentally healthy.
 
First of all, which horses are good candidates for losing weight? Ideally most performance horses should have a body condition score around five. Horses that are slightly overweight, or have a body condition score of 6 or 7, shouldn’t be at a great risk for health issues, but certainly will perform better at a condition score of 5 or 5 1/2. Horses above a 7 have more risk of developing health issues such as insulin resistance, metabolic syndrome, or even Cushings in their later years. If the horse with a high body condition score also has uneven fat distribution, he is more likely to have metabolic issues, and may even be harder to remove weight from than a horse with a more even fat distribution (personal observation). Horses that have cresty necks, substantial amounts of fat over the tailhead, enlarged abdomens and fat in the area of their mammary glands or sheath fit this category.   It is more critical for these individuals to lose weight. Now that we have identified the horses which need to lose weight, let’s address a healthy weight loss plan.
 
One of the first issues to address is the quality of the horse’s forage. Ideally we will feed dieting horses harvested forage/hay, rather than pasture as it is easier to monitor their intake. Horses that are overweight will do better on mature grass hay which has less caloric density than alfalfa or alfalfa-grass mix. When selecting hay, look for more mature hays that have been cut at a later stage of growth. Typically these will be coarser stems and have seed heads present in the hay. However, when looking for lower energy hays, don’t sacrifice the overall quality of the hay – it should not contain weeds, debris, dust, mold, etc. We are just looking for fewer calories, not hay that your horse shouldn’t eat! Once we have the correct hay type, the owner will have to limit their horse’s intake. This can often be confusing, as we typically teach owners to feed based on a percentage of the horse’s body weight. However, in this case, we have a horse that weighs too much, and is consuming more hay/forage than it should. Let’s take a look at the math involved to determine how much the horse should eat.
 
For an example, we will start with a 1300 lb horse who has a body condition score of 8. If we looked up this horse’s energy requirements for maintenance, it would need 19.7 Mcals per day. But that energy requirement is based on a horse that is in a lean body condition. Remember that it takes more calories to maintain metabolically active tissue like muscle than it does fat.   So even if we fed our horse at its maintenance requirement, it is still receiving too much energy for its body type. We will now assume that for every body condition score we want the horse to lose, it should lose about 45 lbs. For our 1300 lb horse, our target weight is actually closer to 1165 lbs [1300 lbs-(45lbs x 3 body condition units)]. The maintenance requirement for the lean 1165 lb horse is 17.7 Mcal per day.    Using these numbers, we will calculate out how much hay this horse would need to provide that amount of energy. For this example, I will use a grass hay of advanced maturity with a caloric density of .86 Mcal/lb as fed. The amount of hay the horse would consume using our 19.7 Mcal figure would be 23 lbs of hay (19.7 Mcal/0.86 Mcal/lb), while the horse would receive 20.6 lbs of hay if we intend to provide 17.7 Mcal (17.7 Mcal/ 0.86 Mcal/lb). Let’s compare that with the standard feeding guidelines for horses based on body weight. If the target weight of our horse is 1165 lbs, and we fed at 2% of the target body weight, our horse would receive 23 lbs of hay. That certainly wouldn’t work because that would provide enough calories to maintain his current weight of 1300 lbs! So how much do we need to reduce his hay intake? If we feed the horse at 1.75% of its target body weight, the horse would receive 20.4 lbs of hay per day. However, even feeding at this rate will probably not get us to their target weight. Therefore, in order to really achieve weight loss in our horse, we should probably feed closer to 1.5 % of the horse’s target weight. That means our horse would only be eating 17.5 lbs of hay per day. For the horse owner, this means that in order to successfully achieve weight loss, we need to get a scale out to the barn, and physically weigh out the amount of hay the horse will consume in one day. While this may be time consuming, it is the most accurate technique to deliver the correct and consistent amount of calories.
 
Now let’s talk about some other practical issues. A horse that is only consuming 1.5% of its target body weight is going to have some “free time” that it is not used to having. We need to provide mental stimulation for this horse or it may development unwanted stereotypies such as cribbing or wood chewing. Continual stalling would not be ideal as this will certainly lead to a great deal of boredom and frustration. If possible, the horse should be kept in a dry lot (free access to pasture certainly won’t help!) with secure fencing. Do not underestimate the horse’s ability to get through the fence to graze! Also, providing other horses with which to interact, stable toys, etc. will help relieve boredom. If you find your horse finishing his meals too quickly, putting the hay in a hay net which is tightly woven may also slow down his rate of intake and alleviate boredom. While these strategies may sound tedious, it is important in order to improve the overall health of your horse.
 
Next month we will continue to discuss the dietary needs of a horse in a weight loss program, as well as how to safely use an exercise program to encourage weight loss.