In the article "Fat, Fiber and the Future," (EQUUS 289) there is a mention of mixing cottonseed oil with pellets or grain. I have access to large amounts of high-quality cottonseed oil. It is premium grade and fit for human consumption as cooking oil. However, I have been told that cottonseed oil is not good for horses and stopped adding it to my pellets as a result. I was told it could "build up" within the horse and cause problems. Please advise me on this matter as I like what the oil did for the coats, skin and weight of my mares.
I have little personal experience with cottonseed oil, but research at Virginia Polytechnic and State University included five preference trials that compared the palatability of 15 different oils, fats and blends tested. Of the substances tested, only two ranked lower than cottonseed oil in acceptability to horses: inedible tallow and fancy bleached tallow.
At the other end of the scale, corn oil was found to be the most well accepted by horses. In fact, corn oil acceptance was set at 100 percent, while the acceptance of cottonseed oil, relative to corn oil, was only 10 percent. By comparison, the acceptance of soybean oil was 45 percent.
As far as "build up" of oil is concerned, I believe that sensible use of oil supplements will not cause problems. We worry about exceeding 30 percent fat in our own (human) diets. If we do, we have a "high fat" diet, and we need to worry about such things as high-density lipoproteins, low-density lipoproteins and cholesterol. A "high fat" horse diet generally contains 5 to 10 percent fat/oil from the total intake (forage and grain), probably not enough to cause concern.
So, in answer to your question--If your horses will actually eat the cottonseed oil, then I see no harm in adding some to their diet. Please keep in mind that adding oil is good in moderation, but adding too much oil could lead to loose manure and may reduce the digestibility and absorption of some nutrients.