Protein and Protein Replacers for Dairy Cattle
Abstract
The common standards for feeding dairy cattle in the U.S. and Canada are those based upon the1971 edition of Nutrient Requirements of Dairy Cattle (NRC- ISBN 0-309-01916-8), or, the 22ndedition of Feeds and Feeding (Morrison, 1956-nolonger in print; 9th edition, ab1idged of same work,1962, is still available and contains same tabular material). The NRC data is based upon consideration of the amounts of crude protein and digestible protein for dairy animals of various ages, physiological status, and production, whereas the Morrison values are based solely on digestible protein, on the same considerations.
It is well-known that a lack of protein will depress perfo1mance of animals, and in dairy cattle a severe lack will lower not only the yield of lactating cows, but also will affect the solids not-fat content of the milk. A large excess of protein, on the other hand, is not toxic but is uneconomical, particularly at present-day prices for protein ingredients (or their substitutes). A high level of protein may increase milk protein slightly, but does not increase milk yield, provide the animals already receive required minimal levels.
In general, the present NRC requirements for milk production furnish about 150% of the amount of crude protein in the milk. The Morrison standards are not set figures but give range values, and these are about 130-165% of the protein in the milk produced.
Personally, my belief is that calculation of needs on the basis of DP is far superior to a system based upon CP.
When considering protein requirements of cattle it is necessary to remember that well-fed dairy animals have the ability to store protein, particularly during the dry period, and then they are able to catabolize body protein stores to synthesize milk during lactation. Naturally, the degree to which this is done is dependent upon many factors, but it is of critical value when high-producing cows are incapable of consuming enough feed to meet both their protein and energy needs during early lactation.
