NUTRITION IN RELATION TO REPRODUCTION                 203

content Meigs (43) found that cows were very difficult to get in calf, while con-
trols with a supplement of calcium carbonate gave much better results. Kennedy-
found that animals on a diet deficient in calcium were sterile, although ovula-
tion occurred. The uterus was pale, flaccid and in a state of inactivity. Sim-
monds (44) found, in extensive experiments on rats, that a minimum percentage
of calcium in the ration was necessary for successful reproduction, and that in-
crease above the minimum gave improved reproduction with better condition of
the parents. An interesting observation by Küst is quoted by Frei (45), namely,
that rickets and nymphomania occur together in the same herds. Davidson (46)
has shown that protracted deficiency of calcium in the ration of breeding sows
leads to a very considerable increase in the number of pigs born dead. The effect
is cumulative, becoming more pronounced in the second and third generations.
A salt mixture representing the mineral elements of blood meal, had a marked
effect on the occurrence of œstrus after weaning. Withholding this mixture
delayed the appearance of œstrus. From the composition of the ration, it
is inferred that the effect was due either to potassium or to iron.

Other observations in which the chief deficiencies concerned were probably of
calcium or phosphorus or both, are the following. Rettger, White and Chapman
(47), in an experiment designed to produce contagious abortion in young heifers
by feeding suspensions of cultures of Br. abortus, fed their experimental animals
first on pasteurized milk and later on a ration of corn meal, groundnuts, linseed
oil meal, bran and sodium chloride, with green food only occasionally. No conta-
gious abortion developed, but great difficulty was experienced in breeding, the
control group being even more affected than those fed the cultures. After three
months on a ' well-balanced ration' they came in heat, and were successfully bred.
Kossmag (48) observed that the occurrence of abortions was prevented when a
silica-rich, base-poor diet was replaced by one poor in silica and including sodium
chloride and calcium chloride.

Cotton and Buck (15) state that the abortion rate in a herd numbering over
200, and negative to contagious abortion, was from 5 to 13 per cent. They be-
lieve that some dietetic deficiency must be the cause, although the ration fed
was, in their opinion, adequate. McGilvray (49) also holds the view that mineral
deficiency lowers resistance to abortion disease and increases sterility. This
would be particularly liable to occur in herds stall-fed on restricted rations.
Graves (50) found that foxes reared in captivity failed to breed until the meat in
their ration was reduced and green vegetables were supplied.

Iodine deficiency.—In areas of endemic goitre throughout the world, breeding
difficulties in domestic animals tend to occur (51). It was first shown by Ennis

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