Individual Management Key Part Of Sound Horse Growth
By Donald Stotts
STILLWATER - Leg growth disorders in young horses are a common concern of those who raise equines, a concern for which there exists no alternative to individualized, hands-on management.
Horses are individuals, with each animal having a specific genetic potential for growth rate and mature size, said Dave Freeman, Oklahoma Cooperative Extension Service equine specialist.
Many horse owners have selected for genetically fast growers in recent years because of premiums paid for these animals in yearling sales, and the need for horse use at early ages in many competitive events. It has been suggested that with this type of selection has come an increased incidence of skeletal leg disorders.
"While there appears to be some logical basis for this claim, it is difficult to accurately document this assertion because of the variation in management practices, rate of growth and leg conformation in horses with similar pedigrees," Freeman said.
Nutritional studies have indicated that both level of intake and ration composition play important roles in altering rate and composition of gain, although nutrition cannot overcome an animal's poor genetics or a poorly designed exercise program.
"While horses have been successfully developed at a variety of growth rates, rapid changes in growth rate precipitated by abrupt increases in rations are commonly accompanied with increases of leg growth disorders," Freeman said.
The generally-accepted recommendation is to maintain young horses in a moderate body condition to promote sound development of bone and muscle.
However, individual differences in genetic makeup create such a degree in variation that general rate of gain recommendations are limited in scope and accuracy.
"Since there are differences in the rate at which bone and muscle mature, a small percentage of growing horses may need to be developed at slower growth rates than others so to allow for a coordinated development of both types of tissue," Freeman said.
Individual differences are of primary importance when regulating feed intake. Weanlings may consume 1.5 to 2.5 pounds of grain mix per 100 pounds of body weight per day. Yearlings may consume one to two pounds of grain mix per 100 pounds of body weight per day. These ranges assume the weanlings and yearlings are consuming hay at 0.75 to 1.0 pound per day per 100 pounds of body weight.
"Regardless of the amount, nutrients in the feed must be balanced because most nutritionally-related leg problems that occur in growing horses result from the feeding of unbalanced rations," Freeman said.
Most weanling grain mixes contain between 1.2 and 1.4 Megacalories of digestible energy per pound. To ensure adequate intake of protein and minerals, Freeman said rations should contain about 14 percent crude protein, 0.6 percent calcium and 0.4 percent phosphorus.
Yearling grain mixes of 1.1 to 1.3 Megacalories of digestible energy per pound should contain about 12 percent crude protein, 0.5 percent calcium and 0.3 percent phosphorus.
"These rations should be combined with a high quality hay," Freeman said. "Nutrient content in the hay will affect the amount that will be needed in the grain."
There exist other mineral minerals and vitamins that can cause growth problems when fed in either deficient or excess amounts. Most documented problems have been when hay and grain are fed without mineral or vitamin supplementation as part of the mix, or when commercially-prepared grain mixes with added amounts of minerals and vitamins are over-supplemented with additional mineral and vitamin premixes on the farm.
Level, type and duration of exercise also can cause differences in rate and composition of gain. Controlled, forced exercise has been shown to increase bone in weanling and yearling horses as compared to similar, non-exercised growing horses.
"Exercise level must be large enough to stimulate the proper development of the muscle and skeletal system without over-stressing the bone or muscle system to fatigue," Freeman said.
One commonly recommended guideline has been to keep exercise intensity low by working young horses at slow speeds such as a trot. Recent studies, however, have refined this long-standing guideline to consider the length of an exercise about as much as the speed at which a young horse is worked.
"Evidence supports the idea that a long bout of any level of exercise can cause bone fatigue," Freeman said. "This fatigue may be a leading factor in fatigue of the young horse's legs."
Single exercise bouts, therefore, should be limited in duration, apply enough stress to stimulate sound muscle and bone growth without over-exertion and be adjusted for environmental variables such as hardness of the exercise surface.
"Growing horses should be exercised conservatively at first, then at an increased rate as positive responses are achieved," Freeman said. "Evidence of mild soreness or joint swelling must be recognized before becoming severe, and the subsequent level of exercise reduced until the horse responds more favorably."
Freeman said knowing what is normal for each horse, and how each responded to previous nutrition and exercise management practices will allow for adjustments that efficiently meet the individual needs of each horse.
We would like to take this opportunity to thank Oklahoma State University for allowing us to provide you with this information.
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