Discussion

Introduction
There are 2 main purposes for performing ovariectomy in the mare:
1) To moderate unwanted 'oestrus' behaviour traits.
2) To remove a pathological ovary (usually a granulosa-theca cell tumour).

The relevance of the indication for surgery to the surgical method selected is that:
1) To moderate a mare's normal oestrus behaviour requires a bilateral procedure, whereas ovarian pathology is typically unilateral.
2) Pathological ovaries tend to be enlarged, sometimes grossly so.

Possible surgical approaches for ovariectomy are:
1) Colpotomy
2) Flank laparotomy
3) Ventral laparotomy
a) midline
b) paramedian
c) diagonal paramedian
4) Laparoscopy

These definitions are not necessarily mutually exclusive. Laparoscopic techniques have been used to assist ventral laparotomy approaches and, especially in the case of enlarged ovaries, laparoscopic approaches become a flank laparotomy at the point of removal of the organ from the abdomen.

1) Colpotomy:
Colpotomy is an entry to the peritoneal cavity per vaginam, via incisions through the vestibular wall either side of the cervix. It is effectively performed 'blind', with ovaries handled through the incision and removed from their pedicles by means of an ecrasseur. It has the advantages of being performed without general anaesthesia (epidural analgesia is preferred), of providing a reasonably easy access to the ovaries and of being relatively undemanding of specialist equipment and expertise. It has the disadvantages of a lack of full control over asepsis or haemostasis, and leaving open wounds into the peritoneum that are left to heal by second intention, with risk of peritonitis or herniation. It is also unsuitable for enlarged ovaries. The procedure is rarely practised these days, but there remain advocates of its use on pragmatic grounds.

2) Flank laparotomy:
Flank laparotomy is performed on the sedated, standing mare under local infiltration (or paravertebral) regional analgesia. An ipsilateral approach is made through the abdominal muscles behind and centred about the caudal reflection of the costal arch. Ideally a 'grid' approach is used, whereby the internal abdominal oblique and transversus abdominis muscles are divided along the direction of their fibres. This reduces the risk of haemorrhage from muscle wall vessels and facilitates closure, but it also limits the aperture of peritoneal access somewhat and becomes less suitable for bigger ovaries, in which case vertical incisions through all layers remains a practical alternative. Ligation of the ovarian pedicle cannot be performed under direct vision and needs to be performed blind, either by running loop knots tied from the outside of the abdomen, or by use of an ecrasseur, neither of which is without technical difficulty.
The flank laparotomy approach has the advantages of being able to avoid general anaesthesia (although it can also be performed in lateral recumbency if wished) and of providing reasonably direct access to the ovaries. It has the disadvantages of a lack of full control over haemostasis and of being relatively invasive, especially in bilateral procedures or for very large ovaries. The main post operative complication is one of incisional swelling and/or drainage, but this is rarely long-lived.

3) Ventral laparotomy:
Ventral laparotomy has probably been the most commonly used approach to ovariectomy in recent decades. It can be performed through midline, paramedian or diagonal paramedian approaches. A standard midline approach through the caudal linea alba is probably most suitable for bilateral cases or for very large ovaries. The diagonal paramedian approach (running caudomedial craniolateral) is recommended by some for unilateral procedures involving relatively smaller ovaries, because it gives the most direct access to the ovary and its pedicle. Bilateral diagonal paramedian approaches within one surgical procedure can also be used although it extends anaesthesia time. It is difficult to see anything to recommend a normal paramedian approach over one or other of the alternatives.
With any of the ventral laparotomy approaches the goal is to exteriorise the ovary in order for ligation of the pedicle to be performed under visualisation. This is often difficult, requiring steady traction on the relatively short mesovarian attachment. Even when achieved, access to the pedicle is limited by compression against the walls of the laparotomy wound. Haemostasis can be achieved by hand-tied ligatures (usually multiple), a thoraco-abdominal stapling device, a vessel sealing device (Ligasure) or by ecrasseur. With any of these, the immediate retraction of the pedicle back in to the abdomen after transection compromises observation for secure haemostasis. Paradoxically, the procedure is often easier in pathologically enlarged ovaries because their pedicles tend to have been stretched already. However, the vasculature in such cases is often increased in size too, making ligation more difficult. Staplers may still be effective, but possibly surer haemostasis is obtained with a series of overlapping loop sutures.
Ventral laparotomy techniques have the advantage of greater surgical control, albeit with still imperfect surgical access, but the disadvantage of general anaesthesia for what can be a lengthy procedure in all but the most experienced of hands. There is a risk of unseen haemorrhage and also of wound complications, which as a general rule tend to be more problematic with ventral compared to flank incisions.

4) Laparoscopy:
The use of a laparoscopic approach to ovariectomy has increased steadily over the past decade and it is now unequivocally the approach of choice in the author's hospital. It has the advantage of providing excellent surgical access without tension, direct visualisation during haemostasis and the avoidance of general anaesthesia. It can be performed bilaterally within one procedure and is not limited by the size of ovary involved (except that the removal of the dissected ovary requires a proportionately larger final incision). Extra-corporeal or intra-corporeal ligating techniques are available, but secure haemostasis, even for the larger ovaries, can be achieved without any suturing at all, by use of a bipolar vessel sealing device. Laparoscopy has the disadvantage of being relatively demanding of specialist equipment and expertise. The main potential complications are those of flank incision healing and are therefore no greater and probably less than with any of the laparotomy approaches. Intestinal puncture by a trochar and thermal injury from the sealing device are rare, but reported possibilities.

Laparoscopic ovariectomy technique:
This will be described and illustrated with more detail in the presentation, emphasising practical aspects based on experience at the Liphook Equine Hospital. Broadly, the sequence of steps is as follows:

Preparation for surgery
- Starve the mare of solid food for 48 h, but do not withhold water.
- An hour or two before surgery premedicate with broad spectrum antibacterials and nonsteroidal anti-inflammatory drugs (NSAIDs).
- Immediately before surgery empty the bladder.
- Induce standing sedation with an initial dose of detomidine combined with acepromazine and morphine, thereafter continued with a continuous i.v. detomidine drip to effect.
- Perform an initial aseptic preparation of wide areas pre- clipped on one or both flanks
- Regionally infiltrate surgical sites with local anaesthetic solution, including deep muscle layers (using 2" x 18 gauge needles) - at 3 portal sites per flank:
1. Just above level of caudal reflection of the costal arch, midway between it and the cranial point of the tuber coxa (in the case of a normal [i.e. small] ovary this infiltration '2' is made more extensive to allow for its enlargement for ovary retrieval; in the case of large ovaries this infiltration is continued in a line continuous with '3').
2. At approximately the same level as '1', within the last intercostal space.
3. Directly below '1', with a spacing of approximately 8 - 12 cm.
- Complete a final aseptic preparation of the surgical sites.

Surgery:
(In bilateral procedures start with the left side; a surgical assistant is required)
- Introduce a thoracic cannula through the peritoneum and inflate the abdomen with air through negative pressure.
- Introduce a guarded, valved, laparoscopic trochar through portal '1', feeling for a peritoneal 'pop'; point caudal and proximal to avoid the spleen; attach the CO2 line to the ingress tap, connected to a pressure-regulator.
- Insert a 0-degree, 57 cm, rigid endoscope and connect the light source cable and video-camera
- Under visualisation insert Veress needle through portal '2', followed by another guarded trochar to avoid the spleen. Switch the endoscope to this trochar.
- Similarly guide a third trochar into position via portal '3'. Inflate the abdomen with CO2 as necessary (beware: over- inflation will cause discomfort).
- Assess visualisation of the ovary and its pedicle. Gut may need to be displaced, either by manipulation or by gas pressure. Grasp the cranial pole of ovary (usually through portal '1') with grasping forceps and tense the mesovarium (this is often resented temporarily).
- Infiltrate the mesovarium liberally with local anaesthetic solution via a laparoscopic needle introduced usually through portal '3'. Give time for this to take effect!
- For pathologically enlarged GCTs, deflation of haematoma- like cysts via a thoracic cannula at this stage assists later removal.
- Varying endoscope and both instrument portals as necessary, always keeping hold of the ovary in grasping forceps, steadily apply and fire the vessel sealing/transecting device across the ovarian pedicle, from the cranial free border to the proper ligament caudally.
- When the ovary is free, manipulate the instruments such that it is held via portal '1'. Then enlarge portal '1' into a small laparotomy and steadily tease the ovary through it (either directly or within a visceral retrieval bag). In a bilateral procedure it is possible to remove a contra-lateral small-sized ovary from the same side, by passing it across the abdomen with long forceps, behind the small intestinal mesentery and beneath the small colon.
- Close the portals in 2 layers. Close the enlarged laparotomy portal in 4 or 5 layers.

Post operatively:
- Continue broad spectrum antibacterial drugs for 3 - 5 days
- Continue NSAIDs for 5 - 7 days.
- Feed as soon as sedation has worn off and appetite has returned.
- Provide 4 weeks of rest in relative confinement, with walking out for grass frequently.

Complications:
Most mares will show mild abdominal discomfort/mild pyrexia for 12 - 24 h. Incisional swelling and gas crepitus may develop at the laparotomy site, almost always transient and self-limiting. Occasional cellulitic swelling occurs, necessitating prolongation of antibacterial medication. Rarely, incisional discharge may occur, again responsive to management by first principles.