SELECTED ARTICLE
VITAMIN A DEFICIENCY AND REQUIREMENTS OF FARM MAMMAL
By GEORGE H. HART, Division of animal Husbandry, University of California, Davi
(Reprinted from Nutrition Abstracts & Reviews, Vol. 10, No. 2, October 1940)
INTRODUCTION
VITAMIN A is essential for herbivorous
animals but their food contains little or
none. The riddle was not completely
solved for nearly 20 years after MaCollum
and Davis [1913] discovered the fat solu-
ble vitamins, though it early became
apparent that green plants also possessed
vitamin A activity. Steenbock and his
co-workers [1919; 1920; 1921] found a
close correlation between the amount of
yellow pigment in roots, maize, leaves and
peas and their power to cure rats deprived
of vitamin A. He offered the fruitful
suggestion [1919] that vitamin A might be
a leuco-form of a carotenoid pigment.
Coward [1923], too, found that vitamin A
activity was associated with the lipochro-
mes in fruits and flowers and concluded
that wherever carotene is found vitamin A
may be expected to be present.
The significance of the observations of
Steenbock and his co-workers, and of
Coward was obvious, but they did not bear
fruit for some years. The early attempt
of Drummond [1919, 2] to ascertain
whether pure carotene could be subs-
tituted for vitamin A miscarried, as caro-
tene was unstable in the solvent, ethyl
oleate, he happened to employ. Further,
Steenbock, Sell and Buell [1921] could not
discover any relationship between vitamin
A potency and pigmentation in butter, cod
liver oil or egg yolk.
In 1928, however, Euler, Euler and Hell-
strom [1928] proved that carotene cured
rats suffering from advanced vitamin A
deficiency and believed that it was as effec-
tive as vitamin A. The matter was finally
settled by Moore [1929] who showed that
carotene was converted into vitamin A in
the animal body and stored in the liver.
The chemical relationship between vitamin
A and carotene was believed by Karn
and co-workers [1931] to be such that two
molecules of vitamin A were formed from
the division of the symmetrical molecules
of ß-carotene with the addition of H 2 O
this fission and hydrolysis presumab
occurring in the body with the assistance
of an enzyme.
In cattle, according to Moore [1932]
only part of the carotene absorbed
changed into vitamin A, much being store
in the body fat. The proportions store
and converted vary with the breed of cattle
and this accounts for differences in the
depth of colour in their body fat and mil
Preformed vitamin A has not bes
found in plant tissues but active carote
noids are present in all green plants, pur
kins, sweet potatoes and carrots. Seed
except yellow maize and palm kernel
are relatively free and the amounts pr
sent are inadequate for the nutrition
animals. Active carotenoids other tha
ß-carotene which occur in plants are α- an
γ-carotene and cryptoxanthin, the la
being the biologically active pigment
yellow maize. According to Kuhn, Broc
mann, Scheunert and Schieblich [1933]
ß-carotene has twice the biological
activity of α- or γ-carotene, but the
observation has never been confirme
and the relative value of cryptoxanthin
also unknown. Kacrer and Schlien
[1934] obtained principally ß-carotene
from grasses, spinach and nettles, and
carotene from plant sources including
alfalfa was found by Smith and Milne
[193±] to have a high melting point and to
be optically inactive, indicating that the
ß-form predominated. ß-carotene is use
as the international standard for vitamin
A, and the vitamin A potency of the usu
forage plants can, therefore, be deduces
with reasonable accuracy from the amount
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