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Don’t Risk Poisoning Your Horses with Cattle FeedBy Dr. Clarissa Brown-Douglas · May 26, 2011

Many farmers around the world have more than one type of animal on their property, and it is not unusual for horses to be housed on properties with other livestock such as cattle and sheep. A common practice in multi-livestock situations is to feed one concentrate feed to all livestock on a property, regardless of species.

Many farmers see no harm in this because at first glance, the feeds all look similar. Often the main ingredients of livestock feeds are the same; the nutrient specifications are similar, especially protein content; and the feeds smell similar. So farmers sometimes see no harm in saving time and some money, and feeding one feed to all. Unfortunately, despite often looking and smelling similar, not all livestock feeds are the same. In fact, feeding cattle feed to horses can be fatal.

Although both are designed to thrive on high-fibre diets, cattle and horses have completely different digestive tracts. Cattle are ruminants, and they possess a four-chambered stomach that ferments fibre efficiently before enzymatic digestion and absorption in the small intestine. Horses, however, are hindgut fermenters and ferment fibre at the end of the digestive tract after digestion and absorption of other nutrients, which makes them less efficient. Because cattle are more efficient at digesting fibre, they are able to extract greater nutrition from poor-quality feedstuffs. This means that horses generally require higher quality forage than cattle. This also explains why cattle tend to graze pastures evenly, whereas horses pick and choose the most digestible areas to graze, often resulting in uneven pasture cover.

Because of these differences in digestive tracts, cattle and horses have quite different nutrient requirements, which feed companies take into account when formulating feed. Although they often use the same base ingredients, there are some fundamental differences that should be noted.

Vitamin and mineral fortification. Cattle feed tends to be lower in vitamins and minerals, as cattle have lower requirements than horses. Horses, especially those that are breeding and exercising, have greater requirements of nutrients and thus horse feed contains greater concentrations of nutrients, especially trace minerals and B-vitamins, when compared to cattle feed. Horses also lose electrolytes through sweating, which cattle do not, so horse feed also contains higher levels of electrolytes than cattle feed.

If feeding ruminant feed to horses, the lack of trace minerals is often not the greatest issue. More concerning is that the balance of these nutrients is incorrect for horses. Feed designed for certain ruminants, particularly sheep, is very low in copper, while some cattle feed can contain excessive levels of iodine for horses.

Ingredient quality. Horses can be fussy eaters, whereas cattle tend to eat most feed they're offered. Cattle feed often contains lower quality grains, and ingredients sometimes have minimal screening during processing. As a result, cattle feed can frequently contain foreign objects like rocks, sticks, lumps of dirt, weeds, and dusty fines. Cattle generally have no problem with these objects in feed, but the presence of foreign material can be dangerous to horses.

Fat source. Although horses and cattle can digest and utilize fat as an energy source, their differences in digestive tracts mean that the type of fat used in their feeds is often quite different. Both cattle and horses digest and absorb fat in the small intestine, however cattle rumen bacteria (that reside before the small intestine) do not tolerate large amounts of fat and thus cattle feed often contains a protected fat source (usually hydrogenated tallow termed “rumen-protected” or “rumen-inert”) to bypass the rumen and ensure digestion in the small intestine. This rumen-protected fat is indigestible by horses and in some cases has proven fatal. Most fat in horse feeds is in the form of plain vegetable oil (corn, soy, or canola) or plant fats such as rice bran, which are efficiently digested and absorbed in the small intestine before bacterial fermentation.  

Crude protein. Often cattle and horse feed have similar protein levels, but the source of the protein in each can differ markedly. Cattle are more efficient than horses at digesting and absorbing amino acids from protein, as this process occurs after fermentation and breakdown of feed in the rumen. Furthermore, cattle are more efficient at synthesizing protein from many sources other than plant and vegetable material, and thus cattle feed can contain cheap protein sources such as urea. Horses are able to utilize some urea for protein but they're not as efficient at this as cattle. The available protein in cattle feed is often substandard for horses, especially those with increased protein requirements such as breeding and growing horses.

Feed additives. Cattle feed usually contains additives that are toxic to horses. The most common and harmful additives are ionophores, commonly known as monensin sodium (Rumensin) and lasalocid (Bovatec), which are antibiotic-like medications. Ionophores are added to cattle feed to alter rumen fermentation and aid in digestion and absorption of feed. However, ionophores are extremely toxic to horses, and feeds containing these ingredients should never be fed to horses.

Levels of monensin sodium as low as 1 mg/kg of body weight have resulted in the death of horses. Cattle feed designed to be fed at a high intake is generally formulated with 3.3-5.5 ppm, which means a 500-kg horse would need to consume a few hundred kilograms of cattle feed to be toxic. Horses often eat this type of cattle feed with no toxic result. However, problems can occur if the feed manufacturer makes an error in formulation or when horses eat more concentrated cattle pasture supplements. Affected horses usually exhibit restlessness, colic, sweating, and death, with postmortem examination showing severe damage to the heart muscle. Because of this risk, never feed cattle feed containing ionophores to horses.

Most feed manufacturers know the danger of ionophores to horses, and will take good measures to prevent contamination of feed by making cattle feed in separate areas, correctly cleaning equipment, and not transporting cattle and horse feed in the same trucks. It is a good idea to ask your feed company whether it makes medicated cattle feed and its policy to prevent contamination.

In summary, horses can survive on many types of cattle feed, however it is unlikely that they will thrive. Despite the addition of additives toxic to horses, there are many reasons not to feed cattle feed to horses. Horses fed cattle feed may be getting less than ideal levels of energy and lower quality protein, resulting in weight loss, low growth rates, poor performance, poor milk production in broodmares, and stunted growth in young horses. They will likely not be getting enough vitamins or minerals to meet their requirements, which can result in deficiencies leading to poor bone and cartilage development, compromised cell function, and general ill-thrift.

The negative effects of feeding cattle feed will be more apparent in horses gazing low-quality pasture, or those requiring superior nutrition such as broodmares, lactating mares, foals, weanlings, yearlings, and horses in work. Because of the negative effects of reduced performance and the high risk of toxicity when feeding horses cattle feed, Kentucky Equine Research (KER) recommends to always feed a grain feed specifically formulated for horses. It will be worth the investment.

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