K. C SEN AND B. C. RAI SARKAR 181
have been utilized for the comparative study of vitamin-A secretion in the
daily butterfat from the various animals under different conditions. The
fat was determined by the Gerber's method and the carotene and vitamin-A
were extracted by the method of Olson, Hegsted and Peterson [1939].
Carotene was then determined colorimetrically and vitamin-A spectroscopi-
cally. The carotene content of the feeding stuff was determined by the
modified method of Seshan and Sen [1941].
RESULTS AND DISCUSSION
In tabulating the results of this investigation, both carotene and vitamin-
A are expressed in terms of International Units for the sake of convenience.
Although there still exists some confusion regarding the conversion factors
which should be used to express the amount of plant carotene and milk caro-
tene, the whole of which is not ß -carotene, the factors used in this paper
are similar to those used by Atkeson et al., namely one microgram of
vitamin A=1.56 I.U. and one microgram of carotene = 1.66 I.U.
In Table I, the results of carotene and vitamin-A estimations of the
morning and evening milk of the stall-fed animals under two levels of carotene
intake, as described previously, are shown. It will be observed that under
both levels of carotene feeding, when the data are expressed per pound of
milk, the evening milk consistently shows a higher carotene, vitamin-A and
total vitamin-A potency than the morning milk of all the animals. Thus,
taking the average values of the total vitamin-A potency for all the animals,
the evening milk is richer by 28 . 8 per cent in the case of carotene-low ration
and by 50. 9 per cent on a carotene-high ration. Attempts to explain this
phenomenon by taking into account the usual increase in the fat content
of the evening milk have not been very satisfactory. In some animals there is
a correlation between the amount of fat secretion and the vitamin-A content.
whereas in others, the evening butterfat appears to contain a slightly higher
percentage of vitamin-A. Similar results have been obtained in the case of
the second group of animals kept under dairy conditions (Table II). Here
also it will be noticed that the average vitamin-A potency of evening milk
is higher than that of the morning milk by 33.6 per cent in the case of high
carotene feed and by 27.3 per cent in the case of carotene low feed.
In Table III, the results are given of the effect of different levels of
carotene ingestion on the total vitamin-A potency of butterfat. In planning
the experiments it was decided to raise the level of carotene ingestion with
the stall-fed group of animals, whereas, in the case of the animals kept in
the dairy and as such accustomed to a fairly high carotene ingestion, the
level of carotene intake was considerably lowered during the second half of
the experiment. It will be observed from this table that with two different
levels of carotene intake, namely 20,797 I. U. and 361,980 I.U. in the case
of the stall-fed animals, the carotene content increased by 49.8 per cent
and vitamin-A by 51.7 per cent and the total potency by 51.4 per cent.
In the case of the second group of animals, a reduction in the carotene intake
from 869128 I.U. to 88175 I.U. reduced the carotene content of the butter-
fat by 67.7 per cent, the vitamin-A content by 18.7 per cent and the total
B 2