NRC panel updates Nutrient Requirements for Horses - DVM
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NRC panel updates Nutrient Requirements for Horses


The total daily drinking time for the horse is short, and the duration of individual drinking bouts is brief. From several studies cited by the NRC, horses drank two to eight, 16 to 21, or 18 to 39 times per day for about 10 to 60 seconds, 10 to 52 seconds or 13 to 26 seconds per bout, for stalled horses, or pregnant mares, respectively.

The balance of the chapter explains the best methods of providing fresh, clean water to horses and the drinking behavior of foals, pregnant/lactating mares, exercising horses, dependent on weather conditions, ambient temperature, sun exposure, etc. The average water consumption is estimated at 5 liters per 100 kg body weight (25 liters for an 1,100-pound adult horse).


The next chapters are excellent for equine practitioners: "Feeds and Feeding;" "Feeding Behavior" and "Unique Aspects of Equine Nutrition."

"Feeds and Feeding" discusses the chemical composition and nutrient content of forages and the specific nutrient benefits of pastures. "The feed value of pastures for horses is a function of pasture intake and forage nutrient composition, digestibility and bioavailability," the NRC states.

Estimates for voluntary dry matter intake for grazing horses averages 1.5 to 3.1 percent of body weight. Average daily DM intake for grazing mares is high in comparison with other physiological classes of horses. Mares consumed about 2.8 percent of body weight while most other horses consumed about 2 percent of body weight.

Pasture digestibility is good, depending on the grass species: in other words, the more cell-wall fiber, the lower the digestibility. Spring and summer pasture is adequate for most horses; even lactating mares can gain sufficient energy, protein and trace nutrients from pasture intake.

Vitamin E and beta-carotene (the precursor to vitamin A) are adequate in fresh grass; so are vitamin D and vitamin K (phylloquinones).

The species of pasture grasses and their nutrient benefits are discussed, as well as hay and silage. The objective of haymaking is to provide nutrient-complete forages from fresh grass. Drying begins as soon as the grass is cut and proceeds rapidly with storage.

As opposed to fresh pasture, stored forage accounts for significant fat-soluble vitamin losses – up to 80 percent or 90 percent loss in cured hay, compared to the same species of fresh grass. Beta-carotene is lost at 80 percent and vitamin E to 90 percent.

Forages "conserved as hay by desiccation should contain no more than 200g moisture/kg to prevent proliferation of micro-organisms, heating (due to microbial respiration) and subsequent reduction of nutritive quality. However, under conditions of high (90 percent to 100 percent) relative humidity, which favors microbial growth, hay stored at 200g moisture/kg can become moldy."

Other aspects of hay are discussed, including hay intake and digestibility. Further topics include ensiled forages, including intake, digestibility, problems including contamination by insects and microbes.

The NRC publication discusses grains, including common grains, their digestibility and contamination by microbes.

Oats are a main staple of the horse diet, the NRC explains. Oats are less energy-dense than corn, contain more fiber, less starch and greater protein content than corn, and oat starch is more readily digested than corn starch in the small intestine. Therefore oats may produce less starch to the large intestine.

Oats tend to be higher in protein, lysine and fat than corn, but like corn have an inverted calcium-to-phosphorus ratio. Oats are palatable to horses, but the consumption of oats often is less than sweet feed or pelleted rations.

The balance of the chapter on feeds and feeding is a discussion of supplemental fats, oils and vitamin/mineral supplements and finally a section on feed manufacturing and its effects on nutrient intake and digestibility.

The chapter on feeding behavior and general feeding considerations is pertinent to equine practitioners.

"Horses are herbivores. Therefore they require a forage supply to lessen the risks of clinical disorders such as colic, laminitis, and oral and locomotory behavior problems. By acknowledging the normal feeding behaviors of the equine, appropriate feed management decisions can be made to minimize these important clinical problems and contribute to the well-being of the horse."


Source: DVM360 MAGAZINE,
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