It seems that the minimum quantity of vitamin A needed per pound of body weight to maintain good health, growth, and a normal level of vitamin A in the blood lies between 18 and 34 micrograms a day per pound of body weight. If an arbitrary average of 25 is chosen, and this figure doubled for optimum results under practical farm conditions, a 100-pound calf would require 5,000 micrograms of vitamin A or about 20,000 I. U. a day.

How can these requirements be met practically? First of all, because a cow's first milk after calving, or colostrum milk, is very high in vitamin A, calves should be left with the cow or fed the colostrum milk for the first 3 days. The following tabulation, based on studies at the Maryland Agricultural Experiment Station, shows the effect of colostrum on the blood-plasma vitamin A and carotene of newborn Holstein calves:

Number of Vitamin A Carotene Age (days) animals (micrograms) (micrograms)

0 (birth) 17 3.3+0.48 1.8+0.11 1 17 15.6+1.80 14.9+0.64 2 16 16.8+1.34 17.4+0.63 3 17 15.9+1.32 18.8+0.59 4 16 15.0+1.44 19.1+0.77 5 15 14.4+1.47 18. 7+0.56 6 16 13.2+1.26 17.4+0.44 7 13 13.8+0.84 16.5+0.41 The blood plasma is very low in vitamin A at birth, but the colostrum milk causes about a fivefold increase.

T. S. Sutton and H. E. Kaeser, of the Ohio station, report that colostrum milk furnishes the generous supply of 32,100 I. U. a day for the first 3 days of the calf's life. At Beltsville we found that the vitamin A content of colostrum milk varies with the carotene intake of the cow. Cows on pasture yielded colostrum milk up to 12 times richer in vitamin A than cows that had No. 3 grade of timothy hay. Many dairy farms discard the extra colostrum milk, a wasteful practice.

After the colostrum period, whole milk is usually fed at the rate of about 1 pound per 10 pounds of body weight, but this amount is gradually decreased after 30 days. Average winter milk contains about 640 I. U. a pound, according to a national survey by the Department. Thus, a 100-pound calf receiving a maximum of 10 pounds of whole milk a day would receive 6,400 I. U. a day. A calf up to 4 weeks of age consumes little hay, so that the intake of vitamin A from the whole milk would not appear to be adequate, when compared with a requirement of 20,000 I. U. If the calf is weaned or changed from whole milk to skim milk at 6 to 8 weeks of age, the total supply of vitamin A must come from the carotene in the roughage. If the roughage is of poor quality, it is doubtful whether the intake of vitamin A is adequate.

There may, therefore, be a need for supplementation of the young calf's ration if the quality of hay is low. The amount and method remain to be established. Conflicting data come from several States about the use of capsules containing 5,000 I. U. of vitamin A plus niacin and ascorbic acid. Until we get further information, then, it seems best to recommend 20,000 to 25,000 I. U. for young calves for the first 4 to 6 weeks where difficulty with scours and pneumonia is encountered. That amount is contained in about three-fourths of an ounce of ordinary cod-liver oil for animal feeding. Calves will consume sufficient hay of good quality ( after the first or second month) to meet the requirements.

Of course, just giving a calf extra vitamin A will not overcome poor Management. It is still as necessary as ever to have the pails clean, to feed regularly, and to give the calves the right quantities of milk at the correct temperature. Pens must be dry, bedding ample, and stalls free from draughts.

Some research workers suggest that young calves cannot utilize carotene efficiently. But among the calves raised at Beltsville without whole milk after the colostrum period of about 3 days were 50 calves that received no vitamin A as such, except from the colostrum. These calves, which made adequate gains, received skim milk with a carotene supplement starting on the third or fourth day after birth and continuing to at least 6 months of age. Thirty of them received carotene as carotene in oil, and 20 had grated or finely ground garden carrots as the source of carotene. Calves fed skim milk after the colostrum period but without any vitamin A or carotene supplement died before 100 days of age.

Carotene is the only natural source of vitamin A for growing dairy cattle after they no longer receive any whole milk. The minimum requirements as found by different investigators vary considerably depending upon the criteria used. A summary of these requirements is given in the table at the top of the next page.

Of course, the amount of hay or silage necessary to meet minimum requirements depends upon its carotene content. Several workers at Beltsville determined that various kinds of roughage differ widely between grades and have a wide range of carotene content within grades.

Under practical conditions the minimum carotene requirement should at least be doubled. If 30 micrograms of carotene per pound of body weight is considered about a minimum and this figure is doubled, the amount of hay of various grades to be fed to cattle of various weights can be obtained from the facing table. The carotene content of the average hay on dairy farms approximately equals that of No. 2 hay.

Tests made at various stations show that growing calves need from 14 to 57 micrograms of carotene each day per pound of body weight.

Vitamin A deficiency in growing dairy cattle under practical farm conditions probably does not occur often. But it has been observed when the dairyman feeds too much grain in proportion to roughage, in an attempt to get rapid growth; in drought years when the range is short and of poor quality; and in the feeding of poor or a limited quantity of roughage for a long time. A brown late-cut timothy hay, a 2-year-old hay, or No. 3 quality hay would fall in this classification.

We learned at Beltsville that cows that get 80 to 100 milligrams a day of carotene give birth to normal calves. A. H. Kuhlman and W. D. Gallup, working with Jersey cows at the Oklahoma Agricultural Experiment Station, considered a daily intake of 40 to 45 micrograms of carotene per pound of body weight about the minimum needed for normal calving. Large quantities of poor hay must be fed in order to meet the requirements, but only a small portion of good roughage is necessary. Good pasture furnishes an excellent supply of carotene and is the best roughage available for this purpose.