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Vitamin A Potency of Cow's Milk and Butter Fat
I. Effect of replacement of a carotene-poor ration
(dry hay) by a carotene-rich ration (oat grass and
berseem) on the compositon of milk
Four cows were arranged in two groups of two
in each. Group I consisted of animals, No. 70
(B. W. 900 lb.) and No. 42 (B. W. 942 lb.), each
of which was in the third month of lactation,
the number of lactations being six and nine, and
the daily milk yields being 20.5 lb. and 14 lb.
respectively. Group 2 consisted of animals No. 64
(B. W. 1044 lb.) and No. 21 (B. W. 908 lb.), which
were in the first and third month of lactation,
the number of lactations being six and nine, and
the milk yields being 23 lb. and 12.5 lb. re-
pectively. For a fortnight before the start of
this experiment, all the cows had received the
regular herd mixture and hay containing very
little green material.
The feeding experiment was divided into three
periods.
Period I. The animals continued to receive hay
and the proportionate amount of concentrate
mixture, according to their milk yields, for a
further period of ten days. Milk samples were
collected from individual animals after this on the
last day the last seven days also being used as the
faecal collection period. A daily analysis of the
feed was not considered necessary, as, it being a
poor source of carotene, the rate of carotene
destruction in the ration was not appreciable.
The hay contained 0.64 mg. of carotene per pound
of material and the concentrate mixture 0.17 mg.
per pound. The faeces in aliquots from seven
days' collection was analysed for the computation
of carotene balance. A composite sample of butter
was prepared from the mixed milk of all the
four animals from the last day's milk samples by
separating the cream from the milk with the help
of a cream separator. The cream was then
shaken in a closed bottle at a temperature of
about 15ºC. for nearly two hours when the fat
completely separated from the liquid. It was
washed several times with fresh water, pressed
inside a muslin cloth and then preserved in the
refrigerator. This material was used for the
determination of the Reichert-Meissl value, the
Polenske value and the saponification and iodine
numbers. The individual milk samples were also
analysed for fat, total solid, solids-not-fat, protein
and ash. On the day the milk samples were collect-
ed, all the animals were bled and the plasma
was analysed for both carotene and vitamin A.
Period II. After the collection of milk, faeces
and blood samples in period I, the feeding was
continued for another 13 days, but the hay
was replaced by 60 lb. of green berseem
in the rations of the animals of group I and by
60 lb. of green oat grass in the rations of the
animals of group 2. The milk and faeces were
then collected, as in the previous period, and ana-
lysed. The animals were not, however, bled at
this stage, nor was a composite butter made.
The average carotene contents of the berseem
and of the oat grass, which were analysed daily,
were 25.13 mg. and 21.55 mg. per pound of the
green material respectively, the dry matter per-
centages being 13.26 and 17.38.
Period III. The feeding experiments were
continued for another 13 days during which
the animals of group 1 received 120 lb. of green
berseem and those of group 2, 120 lb. of green
oat grass daily. During this period the green
feeding was in reality ad libitum and consequently
no concentrate mixture was given. After the
feeding period was over, the usual last day's
milk and faecal samples from the last seven day's
collection from all the animals were analysed.
Butter was also prepared as before from the milk
of individual animals and subsequently analysed.
The animals were also bled for the determination
of plasma carotene and vitamin A. The carotene
contents of green berseem and oat grass during
this feeding period were on the average 13.75 mg.
and 17.33 mg. per pound respectively, the per-
centage dry matter being 12.45 and 13.66.
RESULTS AND DISCUSSIONS
No significant change has been found to take
place in the chemical composition of milk of the
two groups of animals in the three periods
(Tables I and II). Although a decrease in the
milk yield (36 per cent in the case of the animals
of group 1 and 32 per cent in the case of No. 21 of
group 2) was found in the third period, this was
not unexpected, partly because of the lactation
period crossing the peak at this time, and partly
because of the supply of insufficient nutrient,
especially the starch equivalent, owing to the
withholding of concentrates. This, however, did
not affect our experiment in any way, as it was
designed to study the composition of milk under
these very conditions. The animals tended,
therefore, to maintain a constant composition of
milk except in the case of No. 42 in period III
where the change in fat percentage appears to be
due to causes other than that of green fodder
ingestion. A similar conclusion was arrived at
from the data of Das Gupta [1942] who fed Hissar
cows and Murrah buffaloes with varying amount
of green berseem and found no significant change
in the amounts of total solids, ash, protein and fat
percentage of the milk. In Table III, the data
are given showing the change in the chemical
composition of butter fat under heavy green
feeding. It will be noticed from the results that
in the case of both berseem and oat grass feeding,