Written 2001

In the southern hemisphere, the “Horses’ Birthday” is celebrated by nearly all breeds on the first day of August. The reason for the selection of the first day of August in the southern hemisphere, as opposed to say the first day of January, May or November is that historically, the weather at the commencement of September is just beginning to warm up, prompting mares to commence their oestrus cycle, or ‘come into season’. 

A mare’s oestrus cycle is stimulated by the presence of extended daylight, nature intending that foals be born eleven months later through spring and summer when feed is plentiful so that mares can produce good supplies of nutritious milk.

Therefore, mares successfully bred early in September will produce foals in early August.

The Standardbreds have brought their official ‘birthday’ for foals forward to the first of September, the reason being that changes in global weather patterns have had the effect of delaying the onset of warm weather.  Unlike the Thoroughbred breeders however, Standardbred breeders may use artificial insemination.

Dr. Angus McKinnon, a specialist in equine fertility, spends the majority of his time on Thoroughbred studs.  With Thoroughbreds in Australia producing nearly 18,000 live foals from 27,000 covered mares last year, its production is probably larger than all the other horse breeds combined.  Dr. McKinnon can give many reasons for not bringing the date forward, in fact he gives reasons why it would be preferable the date be brought back to the 1st July.

“The first of August date was devised when nature had to run its course unassisted, however these days, with many commercial breeders using artificial light and hormone injections to induce cycling, mares can conceive earlier in the year,” he explained.

The temptation to breed a mare a little early to get a more mature foal, or cases where mares produce their foals short of the eleven month pregnancy, has created situations where foals are born before the 1st August.   As this means that technically, they turn one year old maybe a few days later, it appears that some of those foals are hidden ‘in the back paddock’ until 1st August before they declare their birth.   This is made apparent by the fact that the Australian Stud Book is advised of a far larger number of foals born on that date compared to the next few days in the season.

Despite the fact that early September is the time in which breeders have the green light to start serving their mares at present, there are factors other than inadequate cycling which lead to the fact that the majority of mares don’t conceive until October or November. A percentage of  mares miss on their first service and cannot be accurately pregnancy tested until 21 days after service.  On some studs, the workload of the stallion (or the stud staff!) can dictate when individual mares are served.

“At the moment, this means that most Thoroughbred foals are  born in September and October, months which are not too hot and when the grass is at its most nutritious,” explained Dr. McKinnon. “If the official ‘date of birth’ was a month later on the 1st September, then it will follow that most foals would be born a month later when heat, flies and dust become a problem,” he said.  Most will still not commence serving until very late August because it will be chilly and wet for newborn foals.

“I think changing the date of the horses’ birthday to 1st September would not make sense,” said Mr. John Digby, the Keeper of the Australian Stud Book.  “With the huge changes in the Thoroughbred breeding industry in recent years, breeders are finding it much easier to get their mares cycling earlier, so we are finding that there is an increase in the numbers of foals being born earlier, not a decrease.”

“It is easier for us to monitor and check covering dates rather than foaling dates,” said Mr. Digby.  He is however, not optimistic that change will take place.  “Despite all the leaps in breeding technology, it is a very traditional industry and there is always a lot of resistance to change,” he added.

Mr. Digby however, did support the Standardbred Association’s change of date to 1st September.  “If the Thoroughbred industry used Artificial Insemination and Embryo Transfer like the Standardbreds, then it would be easy to move the season,” he said.  “When you are serving naturally however, the stallion’s services must be spaced out over the season in order to serve the books of up to and over 100 mares that some of the most popular stallions get.”


  1. just a hello….found your site.

  2. wish I wuz a stallion!

  3. Interesting article from seven years ago I found from URL posted to fB Group RFTTE (Ringers from the Top End) – I would like to know – Do you think this is also valid for the northern half of Australia? Do horses in far northern Australia also foal at the same times even though the seasons are very different?

    • Hi
      The Horse’s Birthday being 1 August is really only applicable for Thoroughbreds (racehorses) and Standardbreds (trotters). They are competing from an early age (as young as two years) and there needed to be a starting date for the age groups.
      With regard to your question, to my knowledge there is no commercial breeding of Thoroughbreds and Standardbreds in far northern Australia, I assume because the grazing land is not conducive.
      The main breeds in the far north would be working breeds such as the hardy stock horses. I think that there would be little attention paid to the ‘official’ breeding season 1 August date and whenever the mare was cycling and able to get in foal would be when they would breed her.
      I hope that helps.
      Cheers Jane

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