Vle CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. I

If the heterogeneous sample of mares under survey can be
regarded as representative of the Thoroughbred and Standardbred brood-
mare population of Australia, it seems that approximately only 20% of
empty mares can be expected to ovulate at the beginning of the stud
season in September. The numbers rise steeply through the late spring
and early summer, but the season closes just at the beginning of a
plateau of optimal ovarian activity. A conclusion can be reached that
although the last two months of the four-month breeding season show a
mounting and near-maximal efficiency, the first two months are in a
phase when ovarian activity is merely gaining impetus and when oestrus
may be far from being an infallible forerunner of ovulation.

The period beginning with, and extending some months beyond,
the summer solstice seems to provide the most concentrated ovulatory
activity in these latitudes.

At this point, a plea may be advanced that to eliminate some
of the problems of anocestrus and anovulatory oestrus, the first and
simplest and most logical step would be to sensibly readjust the
official birthdate of the racing horse to allow for at least a greater
proportion of the naturally fertile period to fall within the arbitrary
limits of the official stud season,

Historically it may be argued that it was an unfortunate
administrative expedient when the English Jockey Club undertook in 1833
to alter the birthdate of the Thoroughbred.in the Northern Hemisphere
from the physiologically-fitting, and previously existing, date of
Mayday (c.f. Pond's Kalendar of 17377 to the "artificial™ date of
January 1., This was done to obviate changing the age of a racehorse
during any one year and in any one racing season., In Australia,
geographically situated in the opposite Hemisphere, the official
birthdate was first fixed to the comparable date of July 1. However,
in 1859 this was put back by one month to August 1 where it stands
today.

Mounting awareness that the date of August 1(fixed so long
ago withoui due regard to physiological considerations) may not be the
ideal commencing date for the stud season is resulting in pressure
from at least the Standardbred Breeders' Association of Australia and
New Zealand to still further readjust the existing dates.

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