348
ABSTRACTS
Pigs, horses, and poultry may be dosed with the drug mixed with the food material.
The sheep must be dosed by the use of a simple speculum and fingers or forceps. It is
not advisable to dose a dam approaching parturition, although the drug does not appear
to exert an advderse effect upon pregnant animals.
A list of 31 important, references is appended to the article. [ G. D. B.]
Vitamin-A deficiency and requirements of farm mammals. G. H. HART
(1940). Nutr. Abst. & Rev. 10, 261
T HE subject of vitamin A deficiency and requirements of cattle, horses, sheep and pigs
for vitamin A have been reviewed under several heads, viz. symptoms of vitamin
A deficiency in cattle, horses, pigs and sheep, its effect on reproduction, storage
and depletion, minimum requirements of vitamin A, loss of carotene during
preparation and storage of fodder, and relation of carotenoids in the food to
the colour of milk and body fat. Dealing with the symptoms of vitamin
A
deficiency, it is shown that the state of maturity, lactation, gestation, development,
production, and rate of growth, all influence the onset of vitamin A deficiency
symptoms. Eye lesions are the first characteristic and visible symptom of vitamin
A deficiency and these lesions vary from profuse lachrymation and slight clouding
of the cornea to extensive keratitis, ulceration of the cornea, loss of the aqueous
humour, lens opacity and shrinking of eyeballs with complete and permanent blindness.
Practically all the adult cows show night blindness without corneal lesions. Cows that
are deficient only during the early months of pregnancy may give birth to permanently
blind, but otherwise normal calves. In calves, deprived of carotene, permanent blindness
was produced and this is presumed, to occur only in young animals because mature cows
have the optic canal fully developed and calcified. Vitamin A deficiency may affect
epithelial structures of the body as well as the peripheral nerves and the central nervous
system.
The respiratory tract is commonly affected and pneumonia is usually the ter-
minal condition, causing death. In horses, roaring, stringhalt, navicular disease and
bony exostoses are considered to be manifestations of vitamin A deficiency as well as Ca
and P imbalance. In Finland, Klemola showed that faulty hoofs in the army horses
were due to vitamin A deficiency. In pigs, besides paralysis, other symptoms due to
vitamin A deficiency are loss of appetite, cessation of growth, impairment of vision
in daylight, abnormal gait and convulsive fits leading to nervous collapse. Pneumonia
is of course, the cause of death. These conditions are corrected if 0.5-2 per cent cod liver
oil were incorporated in the feed. In sheep, night blindness is common and in some cases
permanent defective vision in semi-darkness results, irrespective of subsequent vitamin A
intake or storage. In aged ewes, night blindness did not manifest itself before 22 months
had elapsed. As in cattle, vitamin A reserve was used up more rapidly during the first
year than subsequently. As urinary calculi are more common in sheep than in any other
farm species, efforts were also made to trace its etiology to vitamin A deficiency, but
no definite proof was obtained. Reproduction is adversely affected ; 25 to 30 cows calving
at the height of vitamin A deficiency brought forth calves which were weak, had severe
diarrhoea and died in 1 to 5 days. Cessation of spermatogenesis in bulls, which also occurs
at the height of the deficiency, is not permanent. Again, with ewes it was found that
the ability to conceive is affected late in the deficiency but failure of gestation is a relatively
early manifestation.
Coming to the question of storage and depletion, it has been found that the reserves
of vitamin A in the newborn are low ; indications are also there to show that pregnant
mother on high vitamin A intake is unable to supply vitamin A to the foetus much faster
than it is utilized. Maximum storage occurs in adults of advanced age. Liver is the
main seat of reserve, although the reserve in blood stream is also significant. To main-
tain existing reserves, the intake must considerably be in excess of minimum requirements
and still greater to provide for storage in depleted animals. In mammals 20 to 30 Y
per kg. body weight constitute the daily requirement of carotene and 4.6 to 6.1 Y of
vitamin A. In practice, at least 5 to 10 times this minimum level is recommended.
Artificially dried hays, generally speaking, are high in carotene content than field
cured hay. The loss of carotene in alfalfa fodder prepared by vacuum drying is negligible;