Article by: Betsy Wagner, PhD PAS
On every bag of livestock feed is a label reporting the guaranteed analysis of the feed inside the bag. At a minimum that label reports crude protein, crude fat, and crude fiber content. It is these values that are used to estimate the energy content of the feed, but a lot of that depends on the source of the fiber. Not all fiber sources are created equal. Some are very digestible and provide a good balance of energy and other nutrients while others fall short. One such ingredient that can be found in low-cost feeds in the Southeastern United States is peanut hulls.
Peanut hulls are a by-product feed, meaning they are left over from the processing of some other feed or food ingredient. This makes it a relatively cheap feed ingredient and cattle producers have long used peanut hulls as an affordable, low-quality roughage or fiber source for growing cattle when hay may be lacking. It makes sense then that peanut hulls are often found in “All-Stock” and other generic, low-cost sweet feeds that can be fed to cattle, goats, and/or horses.
Just because something can be fed to a horse doesn’t mean it’s the best option. And yes, there are times where small amounts of peanut hulls can be added to a horse’s diet as cheap filler, such as when hay supplies start running low. The emphasis is on the concept of “filler”. Peanut hulls contain 70% or more of the fiber compounds cellulose and lignin. Cellulose can be digested in the cecum and large colon of the horse, but the digestion is not as efficient as what cattle and goats can accomplish. The lignin portion is practically indigestible, and some studies have reported as much as 30% lignin content in peanut hulls. By comparison, good quality Bermuda grass hay usually contains 35-40% cellulose and lignin, with less than 5% of that coming from lignin.
With so much of the peanut hulls taken up by this poorly-digested fiber there is little room for anything else of nutritional value. The proportion of readily digestible fiber and other energy sources is low. The ash or mineral content is about 3-5%, much lower than what is typically found in hay. Protein content is variable, with one study reporting about 5% protein content while another reports 9% protein. That variation can be explained by differences in the machinery used to remove the hulls from the peanuts and how much broken peanut kernel material mixes in with the peanut hulls.
Aside from poor nutritional quality peanut hulls have another concern regarding horse health. Depending on the soil and weather conditions at the time of harvest and storage, peanuts are sometimes contaminated with the fungi Aspergillus. The same fungi also may be found in cereal grains, cottonseed, and other feeds, again depending on weather conditions at harvest and care in storage. These fungi may produce aflatoxins, which have been associated with liver damage and death in horses. It is important to note that Aspergillis is found in the peanut kernel, not the hull itself, so depending on how carefully the peanut hulls are screened to remove peanut pieces there may be a risk of aflatoxin. Reputable feed manufacturers have safeguards in place to detect aflatoxins, and reject feed ingredients if they are found to be contaminated.
So what is a good quality fiber source in horse feeds? Today’s better quality, high fiber feeds often contain beet pulp, soybean hulls, and other readily digested fiber sources. In addition to having low levels of lignin the fiber fraction in these feedstuffs contain a greater proportion of hemicellulose, a type of fiber that is readily digested and converted into energy. These readily digestible fiber sources have another advantage in that they contain more calories and other nutrients on a pound-for-pound basis, so it takes less feed to get the same results as when offering a feed with a low-quality fiber source.
In conclusion, though peanut hulls can be an economic way to increase the fiber content of sweet feeds the fiber is poor quality and poorly digested by horses. The feed itself may cost less at the less per bag but generally it will take more of this low-cost feed to maintain the horse’s weight than if the horse was fed a better quality sweet feed or pelleted concentrate from the beginning.