PAUCITY OF HORSE NUTRITION RESEARCH
A recent report revealed that the following man years( One man year refers to one person working an entire year) were devoted to U. S. animal research in 1961- 1962:
Dairy cattle ________ 235.9 Poultry _____________ 184.1 Beef cattle __________ 124.6 Swine _______________ 95.6 Sheep and goats _____ 63.0 Fur animals _______ 9.9 Horses _____________ 0.9
It’ s small wonder, therefore, that the“ unknowns” far outnumber the“ knowns” when it comes to horse nutrition.
In many cases, we have either( 1) proportioned the ration of draft horses down to the size and weight of light horses or( 2) extrapolated or calculated estimated horse requirements from those of cattle or other classes of farm animals. Of course, the chief fallacies to this sort of thing are: Draft horses are quiet, work at a walk, and are under little stress; and cattle differ from horses anatomically and physiologically— horses have a smaller digestive tract, and their cecum( the primary seat of bacterial action) is on the wrong end. As a result of this situation in the horse, perhaps microbial activity gives only a limited assist in synthesizing proteins and vitamins, and there is reason to question the efficacy of absorption so far down. For these reasons, in giving the nutritive requirements of horses, they are usually prefixed by such confidence-shaking words such as calculated, estimated and assumed.
In the discussion that follows, frequent reference is made to National Research Council( NRC) publication 912, Nutrient Requirement of Horses. At the outset, I wish to compliment the authors on having done so much with so little, and to acknowledge that no one could have done more.
Digestibility of Feeds
Few digestion experiments have been conducted with horses. In using digestion data obtained with cattle and sheep, it is assumed that fiber digestibility is lower in horses, but there may be other digestibility differences. Thus, the digestibility of the most common horse feeds needs to be determined. Metabolism
Little is known about the changes which take place in nutrients after they are absorbed from the horse’ s digestive tract. How are they used for growth and repair, and how are nutrients oxidized for the production of heat and work?
Energy Requirements
NRC Pub. 912 states that energy required for maintenance is judged to be equal to twice the basal metabolism rate; and the energy requirements for light and for medium work are assumed to be 3.0 and 3.5 times, respectively, their basal metabolic rate.
It is obvious, therefore, that these figures can only serve as rough guides to feeding practices. Also, the nutrient requirements of horses at work are based almost entirely upon draft animals pulling heavy loads at slow speeds. Yet, light horses at fast speeds for short periods( as in racing) may use up to 100 times the energy used at rest.
Data on milk yield of mares are scant, and largely based on draft mares. Extrapolating from the cow, it is assumed that the horse converts digestible energy into milk energy with 60 per cent efficiency. Likewise, the energy requirements for growth are calculated from beef cattle and based on certain assumptions. Protein Requirements
Nutritionists recognize that protein and energy requirements go hand-in-hand; thus, as the carbohydrate portion of the ration is increased with severity of work, the protein portion should be increased simultaneously. This points up the likely need for higher protein content rations than have usually been fed to horses in hard use. Also, it would appear that higher than normal protein levels for breeding horses may be in the nature of good insurance, because it is recognized( 1) that a protein deficiency may affect mare and stallion fertility adversely and( 2) that the daily protein requirement increases in the last quarter of gestation.
In NRC Pub. 912, it is estimated that mare’ s milk averages 2 per cent protein; then it is recommended that an allowance of 35 per cent protein in excess of that appearing in milk will provide adequate digestible protein for lactation. Further, the protein requirements for growing, young horses is calculated from cattle and based on the assumption that 50 per cent of the digestible protein fed above maintenance will appear in the gain. Mineral Requirements
Few experiments upon which to base horse mineral requirements are available, despite the fact that $ 7,000,000 is spent annually for minerals for equines. It is known that horses can perform work for extended periods on rations of grass hay, farm grains and salt. From this, NRC Pub. 912 goes on to say that it is assumed that horses are less sensitive to trace element deficiencies than are ruminants.
( Continued on Page 31)
28 VOICE of The Tennessee Walking Horse