408
ABSTRACTS
Carotene (or vitamin-A) deficiency and some common unsoundness in
horses. EDWARDS, J. T. (J. Roy. Army Vety. Cor., 9, 1, 1 and ibid. 9, 2,
60.)
THIS article, which is well illustrated, contains an excellent review of the literature
on vitamin-A deficiencies in animals and the possible relationship of this deficiency
and some of the common unsoundnesses, e.g., shivering, stringhalt, partial para-
plegia, roaring, impaired vision and sterility in horses, as suggested by Mitchell, has
been stressed.
The tissue changes in animals suffering from carotene deficiency are caused by
a degeneration in the body cells generally, characterised by keratinization of the epi-
thelium, demyelinization in the nervous tissue, and probably loss in function of cells
in other organs such as the liver, spleen and kidney. In the various species the changes
are exhibited clinically by manifestations that are differently localized. Thus, for
example, in the less severe forms, in the pig and the dog, the most prominent symptoms
are ordinarily those of nervous incoordination, in the sheep those of urinary calculi;
in the fowl and ox those of xerophthalmia. But in severe cases all symptoms may
appear. Sterility is a very common sequel even in mild cases. Symptoms related to
changes in the respiratory and alimentary tract are common. All the changes seen in
other animals in vitamin-A deficiency arise in fowls almost simultaneously and are des-
cribed under nutritional roup in fowls. The occurrence of pasty eyes in ducklings
illustrates rather typically some of the effects produced upon the offspring when the
diet of the mother has been deficient in vitamin-A. It is likely that some of the defects
which in ignorance are spoken of as constitutional are probably as much due to the
effects of prenatal nutrition as to true heredity, e.g., deficient growth of embryonic
intestinal tissue in the developing chick in the absence of vitamin-B 1 , in the mother
and the defective development of embryonic nerve tissue as a result of maternal defi-
ciency of vitamin-A. There is the well-known cumulative effect of malnutrition, the
effects of which in experimental animals have been found to extend to at least three
or four generations.
Hemeralopia or night blindness, which is an inability to see in dim light, is a com-
mon early symptom of vitamin-A deficiency in some species, such as human beings,
cows and sheep. Its prevalence during the war among army horses, and camels in
Persia and rarely mules has been described. It was believed that it was caused through
exhaustion of the sensibility of the retina by the glare of the sun. Recent studies have
shown that in the absence of vitamin-A, the retina is unable to synthesize a substance
called visual purple (rhodopsin) which is bleached by strong light and the absence of
which causes this condition. Some cases of night blindness may probably be coupled
with a slight degree of optic nerve degeneration in adult cows, a condition from which
the animals recover completely after ingestion; of adequate vitamin-A. In the con-
genitally blind calves, however, the degeneration of the optic nerve would have pro-
gressed to a stage beyond repair. In such cases the pupils become widely dilated
and a rather characteristic greenish, instead of the normal yellowish, colour is thrown
from the retina on looking through the cornea with the animal facing the light or better
with the help of an ophthalmoscope. Clouding of the cornea appeared in the later
stages of the deficiency.