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A 15-year-old Friesian mare presented for routine pre-breeding examination on farm. The mare was in good physical condition with a body condition score 6/9, was ambulatory, with normal vital signs and external genitalia. While no behavioural changes had been noted by the owner, regular oestrus cycling had not been observed in the mare despite it being the time of year when normal cyclicity of mares is expected.
A transrectal ultrasound revealed an enlarged right ovary measuring 15cm x 15cm in diameter, with a central anechoic structure surrounded by hyperechoic multi-cystic parenchyma of ‘honeycomb’ appearance. The mare’s left ovary was very small in size, measuring 3-4cm in diameter, with small <0.5cm follicles (inactive).
The trans-rectal ultrasound findings were consistent with either a granulosa cell tumour (GCT) or an anovulatory haemorrhagic follicle. The surrounding multi-cystic appearance of the right ovary and the small size of the left ovary were consistent with GCT. The options to pursue further diagnostics such as collection of serum blood for measurement of hormone GCT panel or waiting and scheduling a re-check in 2-3 months’ time were discussed with the mare’s owner, and the latter option was chosen.
A follow-up trans rectal palpation and ultrasound examination three months later revealed further enlargement of the right ovary, measuring 18cm x 18cm in diameter, with small inactive left ovary.
Management
After discussion with the mare’s owner, an ovariectomy was recommended. In preparation for surgery the mare’s diet was tapered down over two days with the last 12 hours consisting of handfuls of hay every four hours. The procedure was subsequently performed under standing sedation through a right flank approach with laparoscope assistance.
Immediately prior to surgery, a 14g 15cm long term IV catheter was placed in the left jugular vein. The mare was sedated with detomidine hydrochloride 0.01mg/kg and butorphanol tartrate 0.01mg/kg analgesia was provided as required.
Pre-operative anti-inflammatory of flunixin meglumine 1.1mg/kg IV BID was commenced, along with ceftiofur 2.2mg/kg IV BID antibiotics, and omeprazole 4mg/kg PO SID gastroprotectant.
The mare’s right flank was clipped and the skin aseptically prepared for surgery. Local infiltration of mepivacaine was instilled in a vertical line midway between the last rib and the tuber coxae. A laparoscopic portal was made dorsal to the internal oblique muscle and a 12mm trocar and cannula inserted via a 15mm skin incision through the musculature to the abdomen.
The trocar was replaced with a 10mm diameter, 35cm long, 30-degree laparoscope. Insufflation of the abdomen with carbon dioxide was initiated until 12mmHg pressure. The right ovary was visualised. Additional laparoscopic portals were made distal to the primary portal for instrumentation access.
Approximately 30ml of mepivacaine was infiltrated into the ovarian pedicle using a long laparoscopic needle. A vessel sealing device (ValleyLab Force Triad) with a 10cm diameter laparoscopic handpiece was used to ligate and divide the ovarian pedicle while grasping the ovary edge with laparoscopic forceps.
The flank incision was expanded by connecting the laparoscopic portals and blunt dissection of the musculature in a ‘grid’ pattern which allowed exteriorisation of the ovary. A three-layer closure of the flank incision was performed using absorbable suture for the muscle and subcutaneous tissue, and non-absorbable suture for the skin (Figure 1).
A tie-over bandage was applied to cover the flank incision. A five-litre IV fluid bolus of Hartmanns solution was given to the mare post-surgery and a total of four litres of electrolyte and mineral oil solution was also administered via nasogastric tube. The mare recovered from sedation well, and was transferred to a hospital stall, wet feed was reintroduced and the mare’s comfort closely monitored.
The gross findings of the ovary were consistent with GCT (Figure 2.), with a large cystic central area containing serosanguinous fluid and multi-cystic peripheral parenchyma.
Outcome
The mare remained comfortable following the procedure, and was continued on antibiotics, anti-inflammatories and gastroprotectant for three days post-surgery before being released back into the care of her owners.
The owner was instructed to confine the mare to a small pen for 14 days. On day 10 post-surgery, serous drainage from the distal end of the surgical site was noted by the mare’s owner. Follow-up examination revealed the presence of a fluid pocket at the distal end of the incision.
The distal two skin sutures were removed, and the pocket was drained of approximately 10ml of serosanguinous fluid. The owner was instructed to commence sulfadiazine and trimethroprim paste 25ml PO BID and to provide local wound care.
The wound drainage resolved in five days after which the remainder of the sutures were removed. The owner was instructed to confine the mare to a small yard area for a further 14 days after which a transition back to regular pasture could be undertaken. Ridden exercise of the mare commenced eight weeks post-surgery, and the horse is in good health.
Discussion
Abnormalities of the mare ovary are uncommon. The most common abnormality is granulosa cell tumours (GCTs) associated with behavioural changes that can include stallion-like behaviour, persistent oestrus signs, anoestrous, and performance related issues such as refusing jumps, and colic.
Diagnosis is confirmed with characteristic ultrasound findings (enlarged multi-cystic ovary) and serum hormone profile (elevated inhibin, testosterone, anti-mullerian hormone, with low progesterone). Ovariectomy is the treatment of choice, and the prognosis is usually excellent given the majority of GCTs are locally invasive and rarely metastasise.
Most affected ovaries can be removed via a flank approach; however large tumours may require a ventral midline approach under general anaesthesia. Haemorrhagic anovulatory transitional follicles may have similar ultrasonographic appearance to GCTs but can be differentiated by repeated ultrasound examinations combined with hormonal profiling.
References:
1. A Review of Equine Standing Laparoscopic Ovariectomy. February 2008. Journal of Equine Veterinary Science 28(2):105-111. Monika Lee and Dean A Hendrickson DVM MS.
2. Granulosa cell tumours in the mare: A review of 52 cases. September 2015. Equine Veterinary Education 28(2):75-82. C. E. Sherlock, K. Lott-Ellis, A. Bergren, J. M. Withers, D. Fews, T. S. Mair.
Dr James Brown BVSc MS Grad. Dipl. Ag. Ec
Mount Barker Veterinary Hospital, WA
Dr Brown graduated from Melbourne University in 1998 and went on to work on the Flemington racetrack and in the thoroughbred stud scene around Melbourne. He and his wife Theresa, also a veterinarian, moved to the USA in 2004.
Dr Brown completed specialty training in Equine Reproduction (three years in California) and Equine Surgery (three years in Virginia), making him one of just a handful of specialists in the world that is double boarded in Equine Specialty training (he is a Diplomate of both the American College of Theriogenologists and the American College of Veterinary Surgeons).
Dr Brown worked at Virginia Tech for a further 11 years as a faculty surgeon and gained extensive experience in all soft tissue, colic, reproductive and orthopaedic surgeries.
He then moved to Texas and played an integral role in establishing the new veterinary school teaching program for Texas Tech University.
Dr Brown and his family purchased Mount Barker Veterinary Hospital when they moved back to Australia in 2023.
