86
Vitamine-A Requirment of Farm Mammals
and McCallum[1938]. Moore and Hallman
[1936] have suggested from their experi
mental evidence that white spotted kidney
in calves may be the result of vitamin A
deficiency.
Ability of bulls and of cows to breed
is not necessarily lost even when they are
completely night blind and have muscular
incoordination. Some evidence of struc
tural changes in the seminiferous tubules
of bulls has been reported by Guilbert
and Hart[1935]. No sperm were found in
the testes of one of their experimental
animals that died of the deficiency. A
young bull became so depleted as to develop
permanent blindness from optic nerve
constriction. Later, when supplied with
adequate vitamin A, this animal became
an active breeder, its semen contained
mobile sperm, and it sired normal offspr
ing, indicating that cessation of sperma
togenesis, which may occur at the height
of the deficiency, is not permanent.
In another experiment of Hart and
Miller [1937] 11 of 17 ewes which at breed
ing time were night blind conceived and 2
had twin foetuses. The depletion was
continued in these 11 cases and all of the
lambs were born dead or died within 24
hours. Thus it may be stated in general
that ability to conceive is affected late in
the deficiency but failure of gestation is a
relatively early manifestation. In hogs
there is some evidence of apparently re
duced prominence of the testicles in defici
ent boars as compared with controls of
the same age. Gestation also fails in this
species and, according to Hughes [1934]
and Hughes, Aubel and Lienhardt [1928],
resorption of the foetuses is common.
Although carotene is the pigment caus
ing the yellow colour in the corpus luteum
this has probably no function in repro
duction. In the heifers studied by Mead
and Regan [1931], which had no roughage
but were supplied with cod liver oil, the
corpus luteum was found to be completely
lacking in pigment. Other animals in the
same group were going through normal
reproduction.
STORAGE AND DEPLETION
While storage of vitamin A under
average condititions is ample for reason
able periods of low intake there are many
conditions in which knowledge of the min
mum requirements is of practical impor
tance. The reserves of vitamin A in the n
born are low. With a given intake the r
of storage depends on the degree of dep
tion and rate of growth, so that maximum
storage occurs in adults of advanced a
The reserves in tissus other than liv
fat and blood serum may be considered
negligible. Semb, Banmann and Steenbo
[1934] found that the blood serum of cattle
contained significant reserves. Guilbert
and Hart [1935] found that in cattle w
livers having 300 to 500 blue units per
the lung and spleen extracts gave negative
tests and the kidneys contained only 1
5 units per g. The reserves in the bo
fat of these animals varied from 7 to
per cent of the total. In normally
animals the reserves in the liver we
largely composed of vitamin A, whereas
the fat carotene predominated. The da
of Guilbert and Hart [1935] showed
withdrawal from storage of 4 to 5 m
daily or obout 9 to 11 γ per kg. liveweigth
and that a daily allowance of carotene
approximating to the minimum require
ment, as defined below, did little
diminish the rate of loss. Thus the int
must be considerably in excess of minimum
requirements to maintain existing reserved
and still greater to provide for storage
depleted animals.
Guilbert and Hart found that about
kg. dry matter from fresh green alfa
would furnish 3.5 to 5.0 g. carotene a
this would be equivalent to the estimated
maximum storage in a very fat aged of
that had had access to green feed
abundance throughout her life. In
case a depleted cow was given about 15
carotene in green alfalfa over a 13-
period. At the end of the period
showed a storage of approximately
rag. or 2.7 per cent of the amount inges