Feeding Horses to Reduce Weight or Body Condition
By Shannon Pratt-Phillips, MSc, PhD • Jul 04, 2016 • Article #24676
Because of the significant health risks associated with obesity in horses, owners may need to put their horses on a diet. This is a very difficult task to accomplish, in part not only because most horses are pets, and owners do not want to stress their pets, but also because feeding a balanced diet for all nutrients except for energy at rates sufficient to maintain a healthy digestive tract and satisfy feeding behavior is difficult. Feeding to obtain negative energy balance such that a horse will lose weight and body condition is not easy for either the owners or the horses, and takes time and commitment to the horse’s overall well being.
Similarly to humans, the only way a horse can lose weight is to take in fewer calories than it expends. Therefore, it can consume fewer calories, expend more (through exercise), or combine the two methods.
Energetics of Weight Loss
One body condition score requires a dietary energy intake difference of approximately 400 Mcal. As it does with gaining weight, feeding your horse to lose weight will take time. In fact, it will probably take more time for an animal to lose weight than to gain weight simply because we need to be more careful about drastically cutting calories for horses.
So, rather than taking 100 days at reducing the intake by 4 Mcal per day, it may take 200 days with a reduction of 2 Mcal per day, or somewhere in between. However, unlike offering more hay to help a horse gain weight, you can’t just take hay away from a horse. Remember, horses need at least 1% of their body weight in forage, and feeding a lesser amount can cause some serious digestive problems. Furthermore, decreasing the amount of feed runs the risk of not providing enough “other” nutrients such as protein, vitamins, and minerals. For these reasons, simply reducing feed intake may not always be appropriate.
Also, there is often a question of whether a horse should be fed at his current requirements or at his desired weight. It is usually recommended that protein, vitamins, and minerals be fed at the current weight requirements while energy be fed at the desired weight requirements—and often at rates lower than that. Usually feeding between 70% to 90% of current energy requirements is enough to generate weight loss.
One study examined feeding obese (BCS of 8–9) ponies to achieve weight loss. The desired rate of loss was approximately 1% of the ponies’ goal weight per week (for example, if the goal weight was 200 kg, the ponies needed to lose 2 kg per week). The ponies were initially fed 70% of their energy requirements, but had to be further restricted to 35% to 50% of energy requirements to achieve the desired rate of weight loss.
However, feeding below 70% of energy is not recommended unless under the strict supervision of a veterinarian. After losing an average of 16% of their initial body weight, the ponies had improved glucose metabolism and insulin sensitivity.
While not confirmed in the horse, it is well accepted in human nutrition that restricting energy causes the body to be more efficient in using it, thus making it even harder to lose weight. Therefore, it is possible that while it may take 400 Mcal difference to gain one body condition score, it may take a reduction of more than that to lose one body condition score. Exercise is also extremely important to increase the overall caloric expenditure by the horse.
Feed Selection for Weight Loss
When an owner wants a horse to lose weight, the first thing to do is look at its current diet very critically. Calculating the overall total intake may reveal that calories, and potentially even protein, vitamins, and minerals, are being fed above their requirements. Often, the first thing that should be considered is removal (or decrease) of any grain or pasture access.
Because grain mixes are usually fed to increase caloric intake, it seems logical that these mixes would not be required if a horse is being fed to lose weight. However, regular concentrate mixes may need to be replaced with some kind of ration balancer to replace any protein, vitamins, and minerals, especially if the hay is lower quality. (If the hay is decent quality, as determined by a hay analysis, you may be able to feed only a vitamin/mineral supplement). Recall that good-quality hay often provides enough calories and protein for most horses, but may have variable amounts of vitamins and minerals.
Grazing muzzles effectively allow a horse the benefits of being at pasture (including the access for free exercise and social interaction with other horses) while limiting its ability to consume rich pasture grasses.
Photo: Erica Larson
Pasture is often another “diet disaster,” particularly if horses are allowed to graze freely. Horses are not very good at regulating feed intake and will often overeat if given the opportunity. Further, if you are counting your horse's calories, it is difficult to estimate feed intake from pasture, and therefore pasture caloric intake. A grossly obese horse should not have access to any pasture, while a moderately fat horse should have only limited access at most, either through management (reducing the hours per day a horse gets on pasture) or through the use of a grazing muzzle. Grazing muzzles effectively allow a horse the benefits of being at pasture (including the access for free exercise and social interaction with other horses) while limiting its ability to consume rich pasture grasses (including sugars and fructans). Many owners look at grazing muzzles as cruel contraptions, but for those who have seen a horse founder, grazing muzzles are a humane alternative.
With the prospect of removing or replacing grain in a diet, the hay needs to be examined carefully. A hay analysis will provide details about its nutritional quality, which is extremely important if you are going to be limiting intake. Often feeding hay at 2% of body weight will provide more calories than required, especially if the horse is not in work. Thus, it may be possible for some horse owners to reduce intake to 1.75% or even 1.5% of body weight. If total feed intake is reduced below 1.5% of body weight, it is possible that the horse may develop some boredom-related vices such as wood chewing or pawing. For horses with a history of such vices, it may be worth finding a hay source with lower nutritional quality (though still free of mold, dust, foreign objects, etc.). Lower nutritional quality hay could be fed in slightly higher amounts, potentially offsetting boredom.
For example, moving from a hay with 2.2 Mcal/kg to 1.7 Mcal/ kg means a horse needing 15 Mcal/day could get 8.8 kg of hay rather than 6.2 kg of feed (providing other nutrient requirements are met either with the hay or a balancer type of product). Some horses on limited feed intake may also exhibit coprophagia (the consumption of feces). While this is an abnormal behavior, it is not considered dangerous to the horse. Coprophagia does not necessarily mean the diet is lacking in nutrients (especially since the diet should have been carefully analyzed to ensure only energy intake is reduced) and is likely due to boredom.
Many horse owners have trouble with the idea of reducing a horse’s feed intake, particularly if concentrate is removed. This is especially difficult if other horses in the facility are fed some kind of concentrate, and the overweight horse becomes stressed when not fed. However, owners can use a few tricks to appease their dieting horses. Offering something like timothy hay cubes at feeding time can fool horses into thinking they are getting their meal without adding more calories to the diet (if you decrease hay fed to compensate for the cubes). Another method might be to offer some non-molasses beet pulp, especially if other supplements such as vitamin-mineral mixes need to be fed. In fact, it may be wise to feed an obese horse something such as a small amount of flaxseeds, due to the protein and omega-3 (anti-inflammatory properties that may be useful to counteract the obesity-associated inflammation) content.
Also, many feed companies offer lower-calorie or even extruded types of feeds. Because of their low nutrient density (nutrients for a given volume), it is often possible to feed a small amount of these feeds without greatly offsetting the diet. Working with a nutritionist can help horse owners calculate the overall intake and determine what can be fed to optimize their horses’ situation. Often, however, the horse owner just needs to be a little tougher.
As with all changes where diet and nutrition are integral, weight loss in horses should be gradual. Some potentially serious health consequences can result if horses lose weight too rapidly. Most notable is hyperlipemia, a condition characterized by excessive fat mobilization from the adipose tissue that results in high lipid concentrations in the blood (hyperlipidemia, with triglyceride concentrations being greater than 500 mg/dl) and can cause serious liver and kidney damage. Hyperlipemia is most common in animals such as donkeys and miniature horses, but can occur in all horses. Therefore, it is prudent to minimize stress during weight loss and to achieve the changes to the diet slowly. The rate of weight loss achieved in the pony study described earlier (van Weyenberg et al.) did not result in hyperlipemia and is therefore likely a safe rate of loss.
The best advice for horse owners to remember when looking to help their horses lose weight is to keep at it and to be tough. Though it may be difficult to have the fat pony muzzled and get limited feed, owners should realize it is in the horse’s best interest.