FEEDING STANDARDS

Waikato Times, Volume 127, Issue 21248, 19 October 1940, Page 20 (Supplement)

FEEDING STANDARDS

GUIDES TO PRODUCERS FARM FEEDING PROBLEMS From the earliest days of the scientific study of farm feeding problems efforts have been mad-fe to arrive at “standards” that would serve as guides to the most efficient adaptation of food supply to the needs of the animal. In an article on this subject in an issue of The Journal of the English Ministry of Agriculture, Dr. Charles Crowther. of the Harper Adams Agricultural College, points out that, in drawing up a feed standard, it is customary to assess separately the requirements for maintenance and production. This is done on grounds of convenience and is not intended to imply any sharp discrimination by the animal in the use it makes of the various feeding-stuffs included in the ration; each probably contributes to both maintenance and production, though in different proportions. The distinction between maintenance and production makes it easier, however, for us to adjust our standards to different sizes of animal and different levels of production.

The first essential, therefore, for arriving at a “standard” is accurate knowledge of the basic requirements of the animal for maintenance, which represent the first charge to be met by the food before the needs of production can be supplied.

Reduced to its simplest terms, the maintenance requirement is measured by the energy necessary to maintain the body temperature constant. to make good wear and tear, and to provide for the “internal work” of the body. The heat requirement is affected by the external temperature if this should be below a certain point, the “critical temperature,” which varies with different classes of animal. The “internal work” comprises not only the normal work of such organs as the heart and lungs, but also the work involved in masticating and digesting the food. It also includes muscular exertion of any other kind, voluntary of involuntary, which will be greater when the animal is standing up than when lying down, and also when awake than when asleep. Body Size In practice, the live-weight is a more convenient basis than body surface on which to assess the variation of maintenance requirement with varying size of the animal, and for this purpose it is usually assumed that body surface, and. therefore, the maintenance requirement, varies as the two-thirds power (square of the cube root) of the live weight. Other ratios differing slightly from this have been suggested, from time to time, on the basis of measurements of groups of animals, but the “twothirds power” rule is most generally used. The practical effect of the rule is that the maintenance requirement per 10001 b live-weight tends to fall as the live-weight of the individual animal rises, and to rise as liveweight falls. For example, ten cattle each of 9 cwt live-weight require together more food for maintenance than nine, each of 10 cwt live-weight, although the total Jiveweight to be “maintained.” 90 cwt, is the same in each instance. The rule is, probably, fairly reliable with adult animals of the same class, where the range of variation in individual weights is not very large. Its validity for young, growing animals would appear to be doubtful, especially where, as with pigs, the changes in live-weight are very rapid.

Condition of the Animal

Another factor that influences the

maintenance requirement in practice is the “condition” of the animal, the requirement (per 10001 b liveweight) tending to rise as the animal passes from poor into good condition. This is indicated by the common experience of feeders that a fat animal needs more food to prevent loss of live-weight than a lean animal of the same weight. This point has also been verified in American experiments in which the maintenance requirements of two Aberdeen-Angus steers were measured at various levels of food supply ranging from starvation to double the maintenance ration. As the food supply was raised from zero up to half of the maintenance requirement little increase took place in the heat production (and, therefore, in the maintenance requirement), but from this point onwards the maintenance requirement (per 10001 b liveweight) gradually rose until the food supply reached the maintenance level, and then rose further at a more rapid rate as the food supply was increased beyond this point. Towards this exxra maintenance requirement at the higher levels of feeding some contribution is made, however, by the heat coming from the food given in excess of the maintenance requirement. The specific provision for maintenance in a heavy ration may thus actually be lower than with light rations. In the light of the various considerations that have been outlined, it is evident that, in giving a “standard” for the maintenance requirement of a particular class of animal, we should indicate the conditions to which it is intended to apply. For

the standards in common use the implied conditions are that the standards are intended to apply to the average animal in store condition and on store rations, protected from undue exposure and allowed not more than the amount of exercise desirable in the interests of health. Where these conditions do not obtain some adjustment must be made, the nature and extent of which must be left to the discretion of the rationer.