COMMON REASONS MARES ABORT EARLY IN PREGNANCY ARE.
( EED – early embryonic death)
(1). Ascending infection
(2). Chromosomally abnormal embryo
(3). Iatrogenic causes ( man made causes)
(4). Fever or Heat Stress
(6). Nutritional stress
(7). Other severe stresses
(8). Abortogenic Viruses eg EVA, EIA
The first two reasons are by far the most common cause of losses. UNLIKELY CAUSES:
(1a). Hormone imbalances particularly progesterone.
(3a). Bacterial Infection via the blood stream ( haematogenous spread).
There is a expected normal rate of loss of up to 5% between 16day and 28day scans and
another 5% between 28day and 45days scans. Losses after this time are more common
late in pregnancy after 5 months. Older mares are going to be over represented in these
losses whereas young mares don’t often lose pregnancies. Repeated losses in mares are of
much more significant than a single resorption.
(1). Ascending Infection:
ie infection via the cervix and is the result of poor or damaged anatomy of the external
part of the reproductive tract. Poor vulval shape, damaged perineal body, damaged
cervix, damaged vestivaginal area (eg scar tissue through length of vagina from previous
foaling). Except for extreme vaginal scarring these can be repaired surgically. Older
mares or mares with a history of difficult recent foalings are more likely to be affected.
(2). Chromosomal abnormality in the foetus :
is a chance thing and can be the cause of EED in any aged mare although old mares are
more likely to have defective eggs hence either won’t conceive or to suffer EED.
(3). Iatrogenic Causes:
This referrs to man made causes eg giving PG or oxytocin injections to the wrong mare
by mistake, giving cortisone to pregnant mares for some allergic condition, giving
organic phospate containing dewormers.
(4). Pyrexia or Heat Stress:
A common problem in studs with strangles running through young mares. They develop a
fever (pyrexia) and lose pregnancies. If mares recently bred are affected by diseases such
as strangles it is important to give temperature lowering (NSAID drugs )as well as
antibiotics. This seems only to occur in early pregnancies as mares heavy in foal with
strangles seem much more likely to carry foals to term. High ambient temperatures are
know to cause early pregnancy looses in cattle. This has not been written up in horses but
I believe I have experienced this in tropical Australia where pregnancy losses were
greater than 13% up to 45 days. (5). Endotoxaemia
Endotoxins stimulate the release of PG from the mares uterus. Mares producing
endotoxins are in a life threatening situation as a result of gram negative infections such
as might occur with acute diarrhorea, colitis, or travel sickness. These mares are unlikely
to maintain pregnancy but anti-endotoxic doses of Finadine (0.25mg/kg) are normally
part of disease treatment anyway. (6). Nutritional Stress
Unlike cattle mares which become severely nutritionally deprived tend to lose
pregnancies to help maintain their own weight. Interestingly enough cattle seem to starve
to death and still maintain pregnancy. (7). Severe Stresses
Severe prolonged cortisone producing stresses cause early and late pregnancy losses. (8). Abortigenic Viruses
Make sure EHVI vaccinations are up to date Unlikely causes of early pregnancy losses:
(1a) Hormone Imbalances:
Ovarian produced progesterone in required for early pregnancy up to about 70 days
where the foetal placental unit takes over the production of progestagens. Progesterone
levels rise after secondary ovulations caused by the development of endometrial cups at
about 35 days. Low progesterones have long been accused of causing early abortions.
The fact is that after mares abort they all have low progesterone but it is unlikely that the
low progesterone was the cause of abortion. The exception might be if the wrong mare
was accidently given PG or a mare was given PG at a negative first scan which turned out
to be positive.
To maintain pregnancy progesterone only has to be greater than 1ng/ml and goes up to
about 15ng/ml depending at what time of the day the progesterone is measured.
However we all still tend to use progesterone in chronically early aborting mares even if
it is only to keep the client happy. Depo injections of progesterone eg Depolutein,
Hydroxy P 500, Farlutal Depo, Proluton Depot on their own have been shown not to
supply sufficient progesterone to maintain pregnancy in ovarectomised mares even when
such injections were used every day. (Angus McKinnon). Pregnancy was maintained in
ovarectomised mares using half recommended daily doses of Regumate. In any case
neither is probably warranted.
Mares which have recently been bred and develop short term painfully conditions such as
foot abscesses or lacerations in spite of stud personell concern go in foal at the normal
expeted rates and mares early in foal don’t seem to abort. Needless to say pain alleviating
drugs such as NSAIDS would be indicated anyway. (3a) Haematogenous Spread Bacteria
Bacteria rarely primarily invade the uterus or foetus via the bloodstream although
severely septicaemic mares might lose pregnancies as from endotoxaemic causes as
described. COMMON CAUSES OF ABORTION IN LATE GESTATION:
(1). Ascending Bacterial Infection
(2). Abortigenic Viruses eg EHV1, EVA, EIA
(1). Ascending Bacterial Infection
Mostly due to poor anatomy especially vulval conformation. More common in old mares
with a sway back conformation. As they get pendulous in the belly the anus is pulled
forward and the vulva becomes more horizontal.
Action: Make sure the vulva is Caslicked sufficiently. Pourets procedure may be
indicated if vulval closure still not sufficient.
We tend to treat all chronically aborting mares from 5 months gestation with broad
spectrum antibiotics either injectible or oral for the first three days of each month to
there are not so many mares per stud but these tend to be more valuable and there are more staff and for that matter more veterinarians. High risk mares are ultrasounded at the beginning of each month and evidence of placental thickening or placental separation is assessed. If such changes are found the mares are then confined and treated intensively with penicillin and gentamycin, finadine, and uterine calming agents such as Regumate or Clenbuterol ( Ventipulmin).
EXTERNAL PARASITES Winter is the season when external parasites rear their ugly head. This is when sheep are held in closer confinement and parasites are easily spread among penmates. External parasites that affect sheep are classified in three general groups: lice, keds and mites. There are many species of lice that can infect sheep. Lice species are divided into two generally classific
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