A common cause of infertility in mares is persistent mating-induced endometritis. Semen initiates an inflammatory response in the uterus. Normally this is of little consequence, usually subsiding without treatment. However, about 15% of mares still have fluid present in the uterus 24 hours after mating.
If the inflammation has not resolved by the time the fertilised egg reaches the uterus the pregnancy is unlikely to get established.
Factors that affect the ability of the uterus to remove inflammatory fluid include poor conformation, failure of the cervix to dilate, and abnormalities of uterine contractility.
In problem mares, oxytocin may be used to promote drainage of inflammatory fluid, and intrauterine antibiotics are frequently used.
What about anti-inflammatory drugs? Some studies have shown corticosteroids have been shown to have a beneficial effect, giving improved pregnancy rates. However there are concerns over the effects of a prolonged course of corticosteroid on the function of the pituitary gland or the ovaries, and the risk of laminitis.
Research in the Equine Reproduction Laboratory of Colorado State University, by Dr Ryan Ferris and Dr Patrick McCue,1 studied the effect of daily corticosteroid treatment during oestrus. Eighteen normal quarter horse mares were divided at random into three groups, which received dexamethasone (0.05mg/kg twice daily by intravenous injection); prednisolone (0.5mg/kg orally twice daily) or a placebo
Ferris and McCue found that dexamethasone-treated mares had less marked uterine oedema. The surge in luteinising hormone (LH) that would be expected around the time of ovulation was suppressed, and the mares often did not ovulate. The ovulation rate was 40% (2/5) for mares treated with dexamethasone, compared with 66% (4/6) for prednisolone and 100% (6/6) for the placebo.
The mares' blood cortisol was suppressed significantly more by dexamethasone than by either prednisolone or the placebo.
The researchers suggest that dexamethasone treatment for persistent mating-induced endometritis should be limited to only 1-2 days - and the use of lower doses should be considered to avoid possible adverse effects on reproductive function.
Another approach is to use non-steroidal anti-inflammatories. A study at the Centre for Artificial Insemination and Embryo Transfer at the University of Veterinary Sciences, Vienna, Austria, suggested that non-steroidal anti-inflammatories might be useful for treating mares with PMIE.
Dr Horst Rojer and Dr Christine Aurich studied mares that had failed to conceive the previous year and had shown signs of persistent mating-induced endometritis.
Eight mares in the treatment group were treated with oral vedaprofen (initial dose of 2mg/kg followed by 1mg/kg twice daily). Treatment started one day before the first insemination and continued until one day after ovulation. A control group of nine mares received no vedaprofen. All mares were given oxytocin three times daily.
The researchers found no significant difference between the two groups in the number of mares that had fluid in the uterus on the day after ovulation. Both the treated and untreated groups showed increased inflammatory cells in the uterine mucosa the day after ovulation compared to the day before ovulation.
There was a significant difference in pregnancy rate between groups. Only two of nine mares in the control group were confirmed in foal, compared with seven of eight in the treatment group.
Reporting their work in Reproduction in Domestic Animals, Rojer and Aurich suggest that non-steroidal anti-inflammatories may improve fertility in mares with persistent mating-induced endometritis. A follow-up study will be performed to investigate in more detail the effect of NSAIDs on the inflammatory reaction in the endometrium in mares with PMIE.
The effects of dexamethasone and prednisolone on pituitary and ovarian function in the mare.
RA Ferris, PM McCue
Equine Vet J (2010) 42, 438- 443
Treatment of persistent mating-induced endometritis in mares with the non-steroidal anti-inflammatory drug vedaprofen.
H Rojer, C Aurich
Reproduction in Domestic Animals (2010) Jan 14. (E pub ahead of print)