Report on the Agricultural Experiment Stations, 1953 Page: 7

LIVESTOCK PRODUCTION AFFECTED BY ANIMAL DISEASES 7
A high fertilization rate among so-called infertile heifers, is believed
to be caused by a subsequent high embryonic death rate (54.1
percent) during the first month of pregnancy, according to the Pennsylvania
station. Genital abnormalities occurred in only 13.5 percent
of the heifers studied and did not appear to be a significant cause of
breeding failures.
Comparative studies at the Mississippi station on the genital organs
or normal and difficult breeding dairy cows revealed that the latter
had larger ovaries by weight and more acid cervical and vaginal mucus
than did the former. Of the difficult breeding animals, 63.5 percent
had infections in various parts of the genital system and 28.8 percent
had obstructions that would mechanically interfere with spermatozoa
and ova transport in the female tract. The uterine mucosa and cotyledons
were so seriously eroded in 25 percent of the difficult breeding
animals that normal fetal attachment could not occur. This suggests
that impaired fertility may have been due to failure of attachment of
the embryo rather than failure of fertilization.
Stilbestrol has frequently been recommended and used as a treatment
for shy breeders. However, the Tennessee station was unable to
determine ovulation in 21 cows treated with stilbestrol and examined
post morten 24 hours later. The South Dakota station reported easier
labor for cows at time of parturition when the hormone relaxin was
injected just prior to calving. At the Illinois station cows were bred
in a normal manner and then were separated into three groups. One
group received injections of epinephrine and another oxytocin in an
effort to speed the transport of spermatozoa to the site of fertilization.
The third group was untreated. The conception rate in each
of the two groups injected with hormones was significantly higher
than that of the untreated group.
The Wisconsin station observed that the uterus is much more resistant
to infection by bacteria near the period of estrus, when the estrogenic
hormone is predominant in the endocrine fluids of the body.
This apparently is a protective device to prevent bacterial invasion
of the reproductive tract prior to breeding.
Vitamin A deficiencies
Studies at the Oklahoma station indicate that vitamin A deficiency
is most likely to occur in beef calves during the first few weeks after
birth if their dams have been on low vitamin A ration for some time.
Unthriftiness, diarrhea, blindness, and secondary infection were common
among the calves. A biopsy technique, developed at the Oklahoma
station, was used to determine the liver stores of vitamin A
and carotene in cows and calves. These were compared with the
blood and milk levels and with health of animals. Pregnant cows
on low carotene rations were able to maintain themselves for long
periods on their liver stores, but their calves soon showed serious lack
of vitamin A unless the cows were provided a ration adequate in
carotene immediately after calving. These findings should aid in
avoiding losses caused by inadequate nutrition under conditions where
cows are wintered on dry grass low in carotene (provitamin A) and
calve in the spring, especially following drought.
At the Colorado station it has been found that the native range
grasses in the eastern dryland area of the State supply enough carotene