D. Bilateral ovariectomy
The ovaries can be removed:
Under general anaesthesia via a ventral abdominal midline incision or a
Para inguinal approach
a standing flank laparoscopy, laparotomy or by colpotomy.
The standing laparoscopy is now most commonly practiced in our area.
Hooper et al. (16) found that after bilateral ovariectomy, 35% of the mare continued
to show oestrous behaviour after surgery. Kim and Hendrickson showed 78% client
satisfaction in mares with bilateral ovariectomy as a treatment for behavioural
problems. The most common source of dissatisfaction for owners of patients with
behavioural problems was the lack of behavioural change after surgery, including
continued signs of oestrous behaviour. Ovariectomy offers the advantage of being a
potentially permanent solution to a cycle-related behaviour problem but there are
significant disadvantages as well. The procedure is relatively expensive, though
when compared to repeated hormonal treatments, the cost may in fact be
comparable. There are also risks associated with the surgical procedure. (16,17) The
permanency of the procedure can also be a significant disadvantage as all
possibilities for future reproduction are eliminated. It is important to note that, if the
performance problem is truly related to oestrus, removing the ovaries may not solve
the problem as mares can continue to display oestrous behaviour. It is possible that
estradiol is of adrenal origin since sexual steroids are also produced by the adrenal
cortex in response to ACTH. Therefore, this option should be weighed carefully
before proceeding with ovariectomy. One way of evaluating the potential
effectiveness of ovariectomy for a behavioural problem is to evaluate the mare’s
behaviour during either a natural (i.e., seasonal) or induced anovulatory state (e.g.
down regulation with a GnRH agonist); if the problem is not resolved or at least
significantly improved during the anovulatory state, it is unlikely ovariectomy will be
any more efficacious.
CONCLUSIONS:
If a behaviour or performance problem in a mare is defined as an oestrous cyclerelated problem, oestrus suppression methods can be considered. There is not such
a thing as a perfect method to suppress oestrous in the mare, so advantages and
potential disadvantages should be weighed for each individual animal, owner and
trainer.
References:
1. Freedman LJ, Garcia MC, Ginther OJ. Influence of photoperiod and ovaries on seasonal reproductive activity in mares. Biol
Reprod 1979; 20 :567–74.
2. Ginther OJ. Folliculogenesis during the transitional period and early ovulatory season in mares. J Reprod Fertil 1990 ;
90:311–20.
3. Ginther OJ. Occurrence of anestrus, estrus, diestrus, and ovulation over a 12-month period in mares. Am J Vet Res 1974 ;
35:1173–9.
4. HartPJ,SquiresEL,ImelKJ,NettTM.Seasonalvariationin hypothalamic content of gonadotropin- releasing hormone (GnRH),
pituitary receptors for GnRH, and pituitary con- tent of luteinizing hormone and follicle-stimulating hormone in the mare. Biol
Reprod 1984; 30:1055–62.
5. Asa CS, Goldfoot DA, Garcia MC, Ginther OJ. Sexual behavior in ovariectomized and seasonally anovulatory pony mares
(Equus caballus). Horm Behav 1980; 14:46–54.
6. Asa CS, Goldfoot DA, Carcia MC, Ginther OJ. Dexamethasone suppression of sexual behavior in the ovariectomized mare.
Horm Behav 1980; 14:55–64.
7. Crowell–Davis SL. Sexual behavior of mares. Horm Behav 2007; 52 :12–17.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
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