The ancient medical maxim primum non nocere (first, do no harm)1 comes to mind when reflecting on the more than 10 years that veterinarians have been using intrauterine glass balls (ie, marbles) for estrus suppression in mares. Although these devices were initially thought to be innocuous, a spate of recent reports2–6 has documented the potential for deleterious reproductive consequences associated with their use. In light of these reports, rethinking the use of these devices seems prudent, particularly because they are intended to address a behavioral issue (ie, the real or perceived adverse effects of estrus on
Objective—To determine whether performance of transvaginal ultrasound-guided follicle aspiration (TVUFA) repeatedly in mares adversely affects their fertility.
Design—Historical prospective study.
Animals—23 mares that had never undergone TVUFA and 59 mares that had undergone TVUFA on 1 to 11 occasions.
Procedure—Mares were classified into 4 groups according to the number of TVUFA procedures previously performed on the ovary in which ovulation occurred at the time of insemination as follows: group 1, 0 TVUFAs (control group, n = 23 mares); group 2, 1 or 2 TVUFAs (40 mare-cycles); group 3, 3 or 4 TVUFAs (21 mare-cycles); and group 4, 5 to 11 TVUFAs (13 mare-cycles). Each ovary and its associated number of TVUFAs were considered separately; therefore, some of the mares that underwent TVUFA were represented in > 1 group (1 mare was included in group 2 twice [once for each ovary]), and the sample size in groups 2, 3, and 4 was denoted as mare-cycles. Fertility was assessed as pregnancy rates in cycles in which mares were inseminated with fresh or cooled semen from 1 fertile stallion.
Results—There were no significant differences in pregnancy rates among groups 1, 2, 3, and 4 (83%, 90%, 81%, and 85%, respectively).
Conclusions and Clinical Relevance—Results indicated that repeated performance of TVUFA (as many as 11 times) had no detectable adverse effect on fertility in mares. This finding is clinically important for situations when TVUFA is performed on fertile mares, whether for oocyte collection or other purposes.
Objective—To determine whether IM administration of exogenous oxytocin twice daily on days 7 to 14 after ovulation blocks luteolysis and causes prolonged function of corpora lutea (CL) in mares.
Procedures—Beginning on the day of ovulation (day 0), jugular blood samples were collected every other day until day 40 for determination of progesterone concentration. On day 7, mares (n = 6/group) were treated with saline (0.9% NaCl) solution (control group) or oxytocin. Beginning on day 7, control mares received 3 mL of sterile saline solution every 12 hours, IM, and oxytocin-treated mares received 60 units of oxytocin every 12 hours, IM, through day 14. Mares were considered to have prolonged CL function if progesterone concentration remained > 1.0 ng/mL continuously through day 30.
Results—The proportion of mares with prolonged CL function was significantly higher in the oxytocin-treated group (6/6), compared with the control group (0/6). All control mares underwent luteolysis by day 16, at which time their progesterone concentrations were < 1.0 ng/mL. In contrast, all 6 oxytocin-treated mares maintained progesterone concentrations > 1.0 ng/mL continuously through day 30.
Conclusions and Clinical Relevance—IM administration of 60 units of oxytocin twice daily on days 7 to 14 after ovulation was an efficacious method of inhibiting luteolysis and extending CL function in mares. Disrupting luteolysis by administering exogenous oxytocin during diestrus appears to be a plausible and practical method of long-term suppression of estrus in mares.
Objective—To determine the effect on fertility of
large-volume uterine lavage with lactated Ringer’s
solution (LRS) performed immediately prior to insemination
Design—Prospective randomized controlled study.
Procedure—Control mares (n = 10) were inseminated
with 1 billion (estimated before cooling) progressively
motile spermatozoa that had been cooled in a
passive cooling unit for 24 hours. Mares (n = 10) in
the treatment group were inseminated with 1 billion
progressively motile spermatozoa (cooled as
described for control mares) immediately after uterine
lavage with 4 L of sterile LRS.
Results—There were no significant differences in
pregnancy rates or size of the embryonic vesicle on
days 12, 13, and 14 after ovulation between control
and treated mares.
Conclusions and Clinical Relevance—Results indicate
that uterine lavage with LRS can be performed immediately
prior to insemination without adversely affecting
fertility in mares. This is clinically important, because
insemination may be necessary when a mare has
inflammation-associated fluid (detectable ultrasonographically)
in the uterus; removal of the fluid is desirable,
because it adversely affects spermatozoal motility
and fertility. This situation typically arises when mares
require rebreeding after they have developed persistent
mating-induced endometritis or are inseminated multiple
times in a 24-hour period (during the period of physiologic
mating-induced inflammation), which is a common
practice when using cooled or frozen-thawed
semen. (J Am Vet Med Assoc 2003;222:1108–1110)
A 2-year-old Quarter Horse filly was retired from race training in the fall of 2012 in preparation for breeding in 2013. To hasten the onset of seasonal ovulatory activity, the filly was exposed to an artificial long-day photoperiod (16 h of light/d) beginning December 1, 2012. On January 25, 2013 (day 0), transrectal palpation and ultrasonography were performed to assess the status of the filly's reproductive tract. Examination revealed the left ovary was small (length, 31 mm; width, 12 mm; height, 23 mm), firm, and devoid of follicular activity. In contrast, the right ovary was considerably larger (diameter, approx
Objective—To determine the incidence, ultrasonographic
characteristics, and risk factors associated
with embryonic development characterized by formation
of an embryonic vesicle without an embryo in
Animals—159 pregnant mares.
Procedure—From 1994 to 1998, mares between 11
and 40 days after ovulation with normal and abnormal
embryonic development were examined ultrasonographically,
and characteristics of each conceptus
Results—The incidence of abnormal embryonic
development in mares characterized by formation of
an embryonic vesicle without an embryo was 7/159
(4.4%) during the 5 breeding seasons. Age and breed
of mare or type of semen used did not differ for
mares with normal and abnormal embryonic development.
The percentage of mares in which the conceptus
was undersized during ≥ 1 examination was significantly
higher for mares with abnormal conceptuses
(5/7), compared with mares with normal conceptuses
(2/147; 1.4%). The percentage of examinations
during which the conceptus was undersized was significantly
higher for abnormal conceptuses (12/27;
44.4%), compared with normal conceptuses (4/448;
Conclusion and Clinical Relevance—To diagnose
an embryonic vesicle without an embryo, mares
should be examined by use of transrectal ultrasonography
on day 25 after ovulation. When an embryo cannot
be identified at that time, mares should be reexamined
at intervals of 1 to 3 days until day 30.
Because undersized conceptuses are more likely to
be abnormal, development of undersized conceptuses
should be monitored closely. (J Am Vet Med Assoc
A 6-year-old Arabian mare was bred by a stallion 2 times with an interval of 2 days between breedings. Transrectal ultrasonography performed 21 days after the second breeding revealed a single embryonic vesicle (30 mm in diameter) at the base of the left uterine horn. The mare subsequently gave birth to a healthy male foal 351 days after the second breeding.
Fetal membranes were expelled approximately 1 hour after parturition. The fetal membranes were examined the following day to ensure they were complete (ie, all membranes had been expelled) and for evidence of abnormalities. During evaluation of the fetal