The Most Profitable Feeding Level

Experiments by colleagues in the Department have shown the relative increases in production by good cows fed liberally on roughages and concentrates at various levels above those suggested in feeding standards: As the feeding level is increased the production also is increased, but at a progressively smaller rate. A cow fed at 110 percent of the standard may be expected to yield 0.8 pound of milk for each additional pound of concentrate. Thus by heavier feeding of concentrates, more milk can be obtained from the same number of cows. The extent to which heavier feeding can be practiced profitably depends entirely on the feed-milk price ratio. This ratio, obtained by dividing the price of a pound of feed by the value of a pound of milk, should be followed closely for best results. When the value of the extra milk obtained from feeding an additional pound of concentrate is worth more than the concentrate, then it is profitable to feed at the heavier rate. With each additional input of concentrate, the output of milk per unit of input decreases.

Cows can utilize large quantities of roughage because they have a large paunch, the rumen, where the material is stored as it is eaten and until it is returned to the mouth for' masticating. It has another important function. The rumen contains micro-organisms like bacteria, yeasts, molds, and protozoa, some of which break down the fibrous portions of foodstuffs into material the animal can use. The organisms also make certain vitamins like the B-complex vitamins. It is therefore unnecessary to include these vitamins in the ration. Certain micro-organisms also make usable and digestible protein from the nonprotein nitrogen that is naturally in the feed or is added to the feed in the form of urea or ammonium carbonate, and from nitrogen that becomes available through protein and amino acid decomposition. This newly made protein apparently has high biological value.

Use of Urea as a Protein Feed

This knowledge that rumen micro-organisms utilize inorganic nitrogen to build protein has made it possible to use substances like urea as part of the cow's protein supply.

The amount of urea that should be used depends on the protein content of the rest of the feed supply. One pound of urea feeding compound contains enough nitrogen to make about 2.6 pounds of protein. The micro-organisms take the nitrogen and combine it with carbohydrate material, which must come from the regular feed supply, to form protein. For each pound of protein made from urea, about 0.9 of a pound of carbohydrate feed is used. Since natural high-protein feeds contain considerable energy, which urea does not furnish, additional carbohydrate feed is needed when the urea is used to replace the natural feeds.

Urea usually is added to the concentrate mixture to increase the protein content. Thus, by adding 2 pounds of urea to 100 pounds of a 10-percent protein concentrate mixture, the protein equivalent is increased to 16 percent. When a mixture contains as much as 18 to 20 percent protein, however, added urea is poorly utilized. Most of the urea used for feeding dairy cattle has been mixed in commercial feeds. It can be used in amounts up to 3 percent of the mixture without harmful effects to the animals. Large amounts make the feed unpalatable and it may be toxic. For this reason, it is important to limit the amount used and to make sure that it is thoroughly combined throughout the mixture. The use of urea as a source of protein for cows, of course, should be limited to its economic advantages compared with other sources of protein.

THE AUTHORS

R. E. Hodgson is assistant chief of the Bureau of Dairy Industry. During 1942-43 he conducted a survey of dairying in seven Latin-American countries; in 1939 he received the Borden award for outstanding research in dairy production. Dr. Hodgson is a graduate of the University of Wisconsin.

W. J. Sweetman is associate dairy husbandman in the Bureau of Dairy Industry. He is a graduate of Michigan State College.