It’s spring time and that means the event calendar for our horses is starting to fill up again!
Whether its racing, showing, eventing, pony clubbing or whatever you and your mare get up to, her oestrus cycle and the behavioural changes it brings can get in the way. Even the quietest mares can become a little more moody and snappy when they’re in season, but as well as that it can affect their performance levels. Fortunately, there are ways we can control the oestrus cycle to lessen the effects of oestrus when needs be but also allowing these mares to cycle normally if the time comes for a second career as a broodmare.
One thing to bear in mind is that if your mare has sudden changes in behavior it may not always be hormonal. A full veterinary exam is warranted to rule other possible causes including lameness, back pain, dental problems, gastric ulcers or other issues that may result in behavioral changes.
Racehorses
Firstly, to bring you up to date on the current situation with Altrenogest and the recent positive tests in racehorse, Racing Victoria has released a bulletin to say that based on recent analysis of batches of products containing Altrenogest, they continued to find low levels of the anabolic substances Trenbolone and Trendione. Because of this, there is continued advise to trainers and veterinarians to NOT use products containing Altrenogest for horses planning to race in Victoria. This includes injectable and oral products, although lower levels were reportedly found in oral formulations. As an alternative, Racing Victoria suggest the use of injectable, short acting progesterone for fillies and mares racing in Victoria.
Short acting progesterone can be provided as required. This is usually dosed by giving a once weekly intramuscular injection. It should be done in accordance with the ‘one clear day’ rule of racing and we recommend giving it at least 3 days before racing as some mares can get injection-site reactions.
Altrenogest
In non-racehorses the use of Altrenogest, a synthetic progesterone, is preferred as it more reliably controls the signs of oestrus. Progesterone is the hormone released by the mare when she is maintaining a pregnancy. Altrenogest manipulates the mare’s body into believing she is already in foal and therefore prevents future oestrus cycles.
There are two formulations of Altrenogest available; A daily oral liquid (Ovumate) and a once weekly intramuscular injection (Regu-mate). Both can be used for extended periods of time without effecting ovarian function or future reproductive potential. It can also be used on a “as required” basis where it is given only on the days leading up to a competition in the hopes that oestrus behavior will not disrupt performance on the day. Mares usually will cycle normally soon after removal from treatment.
Caution must be taken when handling Altrenogest as it can be absorbed through the skin. This may affect people with certain medical conditions or women who are or could be pregnant, so gloves should be worn.
Equity Vaccination
GnRH is the hormone responsible for stimulating follicle growth in the ovaries and for triggering the release of these follicles from the ovaries. The Equity vaccine creates an immune response against GnRH which leads to a suppression of these hormones which are essential for producing oestrus. The ovaries are essentially deactivated. The primary vaccination course is two vaccinations 4 weeks apart and oestrus activity should cease approximately 2 weeks after the second injection. It is a highly effective vaccination that may require repeat vaccination every 3-6 months but this varies from mare to mare.
Equity is not without its drawbacks however as it is not advised in mares that are likely to be ever intended for breeding. In one study some young thoroughbred mares vaccinated with Equity never returned to proper cyclicity when the vaccine was stopped.
Ovariectomy
‘Spay’ surgery similar to that we use in dogs and cats is possible with horses however it is a specialized procedure usually done at a referral hospital due to the risks involved with hemorrhage and infection. As a result it is a costly procedure and is mostly only done on horses that have abnormal ovaries with things such as tumors.
If you have any questions regarding your competition mare and the best option for her, or would like a veterinary examination for you mare please give Southwest Equine a call on 0437 380 302.