EQUINE | Notice
during early gestation began in May of the 2016
breeding season and June of 2017 breeding season.
The highest number of abortions occurred in March
of both years, and the last abortions occurred in July
of 2017 (2016 breeding season) and May of 2018
(2017 breeding season). Abortions were categorized
into infectious (2016= 55% and 2017= 38%) and non-
infectious causes (2016= 45% and 2017= 62%). with umbilical cord torsion (2016= 3.9% and 2017=
7.9%), fetal stress (2016= 1.8% and 2017= 2.0%),
placental “cervical pole” necrosis (2016= 0.5% and
2017= 0.4%), twin pregnancy (2016= 0% and 2017=
0.6%), miscellaneous causes (hydrops, tissue necrosis
of unknown etiology, and maternal stress and disease;
2016= 1.2% and 2017= 2.0%), and abortion of
undetermined cause (2016= 14.9% and 2017= 27.5%).
Infectious causes of fetal death were attributed to
bacterial, viral, fungal, and unidentified (presumably
bacterial) agents that resulted in placentitis and/or
systemic infections. Placentitis was the most common
cause of infectious disease and was identified in
280 cases (24.6%) in 2016 and 102 cases (20.2%) in
2017. Approximately 5% of abortions each year were
attributed to ascending placental infections through
the mare’s cervix by bacteria such as Streptococcus
zooepidemicus and Escherichia coli. Nocardioform/
mucoid placentitis was diagnosed in 145 (12.7%) and 27
(5.3%) cases during 2016 and 2017, respectfully. Three
cases of mycotic placentitis were diagnosed in 2016,
and one case was diagnosed in 2017. Placentitis due
to unidentified agents occurred in 79 (6.9%) cases in
2016 and 47 (9.3%) cases during 2017. Agents were not
identified, presumably, due to the use of antimicrobial
therapy, chronic resolved infections, or overgrowth
by environmental organisms. Leptospiral abortion or
perinatal death was identified in five cases (0.4%)
during 2016 and 11 cases (2.2%) in 2017. Abortion
due to fetal bacterial septicemia or pneumonia was
diagnosed in 4.4% of cases in 2016 and 1.6% of cases
in 2017. Equine herpesvirus 1 was the only viral agent
identified in fetuses over the two-year period, and it
was responsible for 16 (1.4%) abortions or perinatal
deaths in the 2016 breeding season and 10 (2.0%) in
the 2017 breeding season. Abortion of undetermined cause occurs quite regularly
and is frustrating to both clients and diagnosticians.
Based on the human and veterinary literature, many of
these occur due to physiologic abnormalities (e.g. fetal
cardiovascular disease, hypoxia), stress and disease
in the pregnant mare, autoimmune disorders, genetic
irregularities, environmental exposures, and endocrine
abnormalities; all of which cannot be easily assessed or
tested for in the aborted fetoplacental units. A diagnosis
of abortion of undetermined etiology isn’t completely
without value, because infectious diseases and other
possible causes of abortion storms can be readily ruled
out.
In conclusion, equine abortion remains to be
unfortunately common. Both infectious and non-
infectious causes are frequently responsible. Evaluation
of the aborted fetoplacental unit by your local
veterinary diagnostic laboratory can aid in determining
the cause of abortion, help to monitor and track known
abortifacients, and identify new and possibly emerging
causes of abortion.
CONTACT:
Alan Loynachan, DVM, PhD
[email protected]
(859) 257-8283
University of Kentucky Veterinary Diagnostic Laboratory
Lexington, KY
Non-infectious causes of abortion are considered
sporadic events. They included abortion associated
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• Equine Health Update •