Can Fat Help Horses Gain Weight in Winter?

Q: My new mare’s previous owners said she’s a hard keeper during the winter and recommended adding fat to her diet in the colder months to help maintain her weight. But when I looked online, I found many recommendations about different supplements, oils, and grains, and I’m not sure where to start. What’s the best way to add fat to a horse’s diet, and which products are most effective?

A: When adding fat to the diet for weight gain it is important to ensure the diet remains well-balanced. Therefore, the most nutritionally complete way to add a fat source to your horse’s diet is to use a higher fat fortified commercial feed fed at the recommended daily intake level. These feeds often having 10-12% crude fat, not only adding fat to the diet but also essential vitamins and minerals, protein, and other nutrients.

Oils are a great way to add fat calories to a ration but provide only calories, not other nutrients. Depending on the rest of the horse’s diet, it is possible when supplementing oil to provide your horse with adequate calories but create a diet that is deficient in other key nutrients, especially minerals and vitamins. This could hinder weight gain, as these essential nutrients are necessary for proper functioning of metabolic pathways. Another benefit of using fortified high-fat feeds is that they tend to contain sources of highly digestible fiber, such as beet pulp and almond hulls, so you have the benefit of adding cool calories from two different sources: fat and fiber.

Rice bran is a popular choice due to a fat content of more than 20% on a dry matter basis. Rice bran should be stabilized and typically has added calcium carbonate to balance its otherwise high phosphorus content. However, few rice brans are otherwise fortified, so are unlikely to help with the overall provision of other necessary essential nutrients. Some better-quality rice-bran products will have added vitamin E. This in part helps maintain the product’s shelf life; horses with higher fat intakes also have higher vitamin E requirements. For this reason, if you compare feeds that have, say, 6% versus 12% crude fat, you will typically find that the 12% crude fat feed has a higher vitamin E content.

It is tempting and easy to pour oil over an existing diet, which will certainly increase calorie intake; however, feeding large amounts of oil can backfire. If you overwhelm the small intestine’s ability to digest and absorb fat it will pass into the cecum and large colon where it can disrupt fiber fermentation. This could actually result in weight loss as the horse would not be able to get as much nutritional benefit from the forage in the diet. With very high intakes or sudden introductions of larger amounts of oil, manure can become oily. For these reasons, introduce oil slowly over 10 to 14 days, increasing by no more than a quarter cup every two to three days until you reach the desired amount.

Oils all have different compositions of fatty acids, and recently omega-3 versus omega-6 fatty acids have gained a lot of attention. This is because these fatty acids play important roles in cell membrane fluidity, inflammation, and immunity. Both are necessary for these important functions, but relative amounts of each might influence overall response. As a result, corn oil is no longer as desirable as those oils with higher omega-3 contents such as canola oil. Flax oil and camelina oil provide more omega-3 than 6 fatty acids and are good choices; however, in large amounts cost might be inhibitive.

An 8 fluid ounce measuring cup holds approximately 200 g of vegetable oil, which provides 1.8 Mcal of digestible energy, which is about 10% of a 500 kg (1,100 pound) horse’s maintenance requirements and is comparable to the energy provided by just over a pound of oats. Even though the horse’s natural diet is relatively low in crude fat, horses appear to utilize fat well and have been fed up to 230 g of fat per kilogram dry matter consumed as corn oil. However, the National Research Council cautions against feeding soybean oil at intakes exceeding 0.7 grams per kilogram body weight per day. Therefore, it is likely best to keep supplemental oil intake at no more than about 2 cups per day for an average sized horse.

Lastly, consider whether increasing fat is actually the best feeding option for preventing weight loss in winter. Many horses lose weight in the winter due to the additional calorie expenditure used to keep warm. Feeding extra hay not only increases calorie intake but also generates internal heat due to the fermentation process necessary for digestion in the horse’s hind gut. Therefore, increasing forage for horses that have good dentition is always my first choice.