Op/Ed: Should In-Foal Mares Be Declared?

Following on from my piece a fortnight ago regarding the question of whether breathing operations should have to be formally declared, it is perhaps worth having a similar discussion about the common question of whether it should have to be declared when fillies/mares are in foal whilst still racing.

It is a debate that arises every season, and, in common with the breathing operation debate, the fact that the public generally doesn't hear that a filly/mare is in foal until after they win means that the general perception is that being pregnant is a major performance enhancer for the fairer sex. However, this tendency very much raises the possibility that confirmation bias is skewing the reality.

There are various logical theories behind why some fillies/mares seem to improve during the 120-day period (as per the rules in Ireland and Great Britain) that they are permitted to race whilst in foal. The abolition of the oestrus cycle and the associated behavioral changes that are part of coming in and out of season is one factor, as is the calming effect of the hormone progesterone which is produced during pregnancy. However, there is little rock-solid scientific evidence that being pregnant enhances racing performance in fillies/mares, which is what makes further study of the subject so important to establish the truth of the matter.

In common with the breathing operation question, the in-foal declaration question isn't straightforward. While the old saying goes “one can't be a little bit pregnant,” defining when a filly/mare is in foal isn't as easy as one might think. With modern stallions being expected to cover large numbers of mares, many mares being older and less fertile, as well as it generally not being an exact science, veterinary data suggests that only approximately 65% of individual coverings results in a pregnancy. Thus, many mares fail to go in foal after one covering and are covered on multiple occasions in the hope of achieving a pregnancy. For this reason, it would be unsatisfactory and inaccurate to presume a filly/mare to be in foal after they have been covered. So, what would be an appropriate time to report a filly/mare as being in foal?

For the benefit of those that are unfamiliar with the process, here is how it tends to play out. After a filly/mare is covered by the stallion, they will generally be scanned around 15 days later to assess whether they are pregnant or not. Even if they appear to be pregnant at that stage, it isn't uncommon for pregnancies to be lost in the days that follow, so some breeders opt to have them scanned again between 25 and 30 days in search of a heartbeat in the developing pregnancy, which should be visible at that stage if all is well. Even if all is well at that stage, pregnancies can still be lost in the weeks and months after that. To quantify the risks, veterinary data suggests that approximately 7% of mares that were confirmed pregnant at 15 days lose the pregnancy in the subsequent 30 day and another 8% lose their pregnancy between that point and the expected date of foaling.

One obvious challenge that the above facts present with the real-time collection of this sort of data, is that not every breeder is inclined towards scanning their filly/mare more than once. If a pregnancy is confirmed at 15 days, some will opt not to check the pregnancy for a heartbeat or thereafter. So, with it perhaps being unreasonable to expect breeders to incur the cost of having their mare scanned against their will, those that are in favor of pregnancy being declarable have to weigh up whether a 15% rate of loss of pregnancies that were confirmed at 15 days is an acceptable margin of statistical error.

Thus, the problems with collecting this sort of data in real time are clear. Both from a practical and statistical point of view, there are challenges in finding a method that would ensure the collection of data that could be trusted as being accurate. However, that doesn't mean that this is a lost cause, as there is still a way that existing data could be used to draw informed conclusions as to the significance of a filly/mare being in foal with regard to their racing performance.

The last covering date and foaling date for every mare/foal that is registered is officially recorded as a matter of course by Weatherbys. Using that data in conjunction with racing form databases, it would be possible to establish with 100% certainty a substantial sample of mares that raced whilst in foal and evaluate how they performed on the racecourse during that time relative to how they performed whilst not in foal.

It would be time consuming, but such a research project would make for a very worthwhile study that should surely appeal to someone in the world of academics, as it would promise to once and for all establish whether being in foal is a statistically significant performance enhancer for fillies/mares. If the historic data did indeed suggest that it had a significant impact, then the tricky discussion of the best method to collect such data in real time can recommence.

Feedback: Kevin Blake at @kevinblake2011 (or [email protected]).

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