14
Carotene Content of Grasses.
on the dry matter can be conserved with ease. Quick drying of hay is the
least damaging as far as the contents of A, D and C vitamins are concerned
[Rygh, 1934]. Silo fodder with a hydrogen ion below 4.2 is considered very
good, but when the pH is above 4.9 it is considered poor [Kniest. 1934].
Exposure to sunlight and air causes a rapid decrease in the carotene content
of forage [Guilbert, 1934]. A good field-cured product may approximate a
dehydrated meal in "Vitamin A " value. There is little or no loss of caro
tene after vacuum drying for three hours at 100°C. Alternatively, by means
of machine drying, it is possible to preserve grass cut at an early stage of
growth and preserve the nutrients in a much larger amount than can be
obtained by hay-making. They can be cut several times during the season
and in this way the pigments contained in young growing stage can be re
tained. They contain carotene, xanthophyl and chlorophyl. The first is
the precursor of vitamin A and the last two are responsible for quality.
Gillam and others' experiments [1933] show that the relatively high propor
tion of carotene, xanthophyl and vitamin A present in summer butter can
be maintained during the winter period of stall feeding by the use of arti
ficially dried grass.
The carotene and vitamin A contents of milk and butter of cows have
been found to be influenced by the breed and the diet of the animal. Caro
tene was highest in Guernsy cows, 10.3γ per kg. of fat; and lowest in
Holstiens, 4.3 γ. Vitamin A content varied inversely, being 5.1 in
Guernsy and 10.2 in Holstien. On a low carotene diet, 3.3 per cent appeared
in milk, and 1.3 per cent on a high carotene diet as vitamin A. However,
individuals of the same breed differed upto 100 per cent among themselves.
Increasing the carotinoid content of the diet increased, but not proportionately
the carotene and vitamin A in the milk. Watson et al [1934] found that
when 25 per cent of the concentrated foodstuff was replaced by dried grass,
no improvement in the yellow colour of butter was noted. Inclusion of 50
per cent of dried grass caused distinct improvement in carotinoid colour ;
the inclusion of A. I. V. fodder had also the same effect.
Fraps and others [1934] have carried out experiments on the vitamin A
requirement of dairy cows. They found that vitamin A recovered from the
feed in the butter-fat was approximately 47 per cent in a cow receiving 8,500
units daily from yellow corn, 21 per cent in a cow getting 60,000 units for
alfalfa, and 10 per cent for a cow getting 11,600 units for alfalfa and yellow
corn 17,000 units daily was not enough to maintain a cow in health. One
unit of vitamin A in butter required 11 units in the feed over the maintenance
ration. Silage, hays and fodder will not supply enough vitamin A to main
tain a high potency in butter-fat. Green growing pasture grasses are needed
to maintain a high percentage of vitamin A in butter-fat.
It will be seen from the above that the estimation of carotene content
of grasses and fodders is essential for a proper study of the nutrition of dairy
cattle. It will then be possible to meet the carotene demand of the milch
cattle with a suitable combination of feeding materials. This can also help