188
Vitamin-A Potency of Cow's Milk
It was mentioned previously that carotene in butter contributed but
a small part of the total vitamin-A potency but Atkeson et al. could raise the
potency due to carotene to about 35 per cent of the total vitamin-A potency
by heavy green fodder feeding (141.3 lb. green rye per head per day). This
they considered to be typical of pasturage conditions. Baumann and Steen-
bock fed about 50 lb. of green fodder daily, considering this to be typical
summer feeding, and obtained a carotene potency of about 32 per cent of the
total. Although it is difficult to estimate the average pasture consumption
of Indian cows during the best part of the pasture season, it is likely that the
daily consumption of green fodder may be more than 50 lb. which would be
roughly equivalent to 1.5 to 2 million International Units of carotene.
As a little less than one million units were fed to one group of animals, it was
thought of interest to find out the ratio of carotene to vitamin-A in the butter-
fat of the two groups of animals. The data are given in Table VII. It will
be noticed that, although in some cases the individual variations are wide,
the activity due to carotene is 14 per cent of the total vitamin-A potency
in the butterfat of the stall-fed animals, while, in the case of the second
group of animals on a high carotene ration, the percentage activity due to
carotene is 27 of the total vitamin-A potency. It is probable that, with a
still higher carotene ingestion in the form of green feed, a value similar to that
obtained by Atkeson and others might be obtained. This raises the question
as to whether the total vitamin-A potency of butter could be still further
increased. It will be noticed from the figures given in Table VI, that the
highest vitamin-A potency of butterfat which has been obtained in our experi-
ment is with the group II animals, the average value found being 9,745.90
I.U. per lb. of butterfat. A separate experiment with other animals in the
Institute dairy herd at Izatnagar has given a value of 13,900 I.U. (January
butter) on the pooled milk of 18 animals getting, in addition to 28 lb. of
berseem, a certain amount of grazing on dub grass, which is particularly rich
in carotene. The activity due to carotene in this sample is 35 per cent of
the total vitamin-A potency. It appears, therefore, that it is possible by
suitable feeding to increase the vitamin-A potency of the butter of the dairy
animals in this country to a level comparable to that of the dairy animals in
other countries.
SUMMARY
1. An experimental investigation has been carried out to study the effect
of different levels of carotene ingestion on the carotene and vitamin-A potency
of milk and butterfat.
2. It has been found that, when the potency is expressed per pound of
milk, the evening milk shows a higher concentration of both carotene and
vitamin-A.
3. When a carotene-low ration is replaced by a carotene-high ration
both the carotene and vitamin-A content of butterfat show a considerable
increase. Similarly, when animals on a carotene-high ration are placed
on a carotene-low ration, there is a fall in the total vitamin-A potency of
the butterfat, the carotene part of it showing an immediate change.