GEORGE H.
HART
87
is constituted an average daily storage
30 mg. in excess of requirements.
There was a concentration of 500 blue
fits per g. of liver tissue which is com-
prable to the amount present in the liver
1 to 2-year old cattle kept under
optimum conditions. These results com-
pare favourably with those obtained in the
t by Davies and Moore [1934]. In one
Guilbert and Hart's experiments it had
been shown that animals receiving 1 lb.
ily of a fairly green chopped alfalfa hay
addition to a basal ration low in vita-
min A did not show clinical symptoms of
deficiency after a period 7 months longer
an was required to deplete similar ani-
mals on the basal ration alone, but as
two of these animals secreted milk so
ficient in vitamin A that their nursing
lves developed night blindness their
take must have been below the mini-
mum.
MINIMUM REQUIRMENTS OF VITAMIN A
A study was also made by Guilbert
and Hart of minimum requirements for
cattle with the cure of night blindness as a
st for sufficiency. Experiments were
rted when the animals exhibited com-
plete night blindness in semi-darkness,
and frequently other nervous symptoms
addition. Small amounts of chopped
alfalfa hay or dehydrated alfalfa meal of
own carotene content were supplied and
e quantity increased at intervals until
normal weight increases occurred and
clinical symptoms were cured. After 3
years' work, data were accumulated making
evident that the minimum daily require-
ment of carotene as supplied by alfalfa
by between 26 and 33 γ per kg. liveweight.
ay containing carotene, cod liver oil and
alibut liver oil given orally were equally
effective. Corotene, dissolved in olive oil
d injected subcutaneously was less effec-
tive. Data were presented on animals
carying in size from the rat to the cow
nich showed that utilization was related
bodyweight rather than to energy re
quirements and that in mammals 20 to 30 γ
per kg. bodyweight constituted the daily
requirement. The observations indicated
that minimum requirements for chickens
and turkeys are higher than
for
mammals.
Further work by Guilbert, Miller and
Hughes [1937] on minimum vitamin A and
carotene requirements of cattle, sheep and
swine showed this to be 6 to 8γV vitamin A
or 25 to 30 γ carotene daily per kg. body-
weight. The minimum requirements for
swine were within the range found by
Dunlop [1935]. Evidence was presented
that, at low levels of intake, vitamin A
and carotene approach, weight for weight,
biological equivalence and that the ratio
widens as the dosage is increased.
Goss and Guilbert [1939] have recent
ly revaluated the vitamin A in the oil used
in the above experiments by spectrophoto
metric measurement, using the extinction
coefficient at 328 mµ of crystalline vitamin
A as prepared by Holmes and Corbet[1937]
as standard, and on this basis the values
6 to 8 γ vitamin A per kg. bodyweight
become 4.6 to 6.1 γ per kg. Comparison
of this oil with the U.S.P. reference oil
permitted expression of these values as
I.U., namely 18 to 27 I.U. per kg. body-
weight daily. The most recent observations
of the same group of workers [Guilbert,
Howell and Hart, 1940] have shown that
the requirements of the horse can be
calculated on a basis similar to that used
for sheep, cattle and swine; the daily re
quirement per kg. bodyweight for horses
was found to be about 5 γ vitamin A or 20
to 30 γ carotene. The table in which these
results are summarized is reproduced
below.
At least 5 to 10 times this minimum
level is recommended in practice. Signi
ficant storage occurred within a few
months with this dose, but the milk of cows
was low in vitamin A potency. Fraps,
Copeland and Treichler [1934] consider