Breeding Cycle of Events

Below are the material activities which occur on particular dates during the stud year:


1st January is every Thoroughbred’s birthday! Mares should, ideally, be at the place of foaling one month beforehand. Blood tests and swabs can be taken – see below. Early foals start to arrive.


15th February and the covering season starts, for which all mares require up to date passports, flu/tetanus vaccinations and, for mares foaling away from home, a vaccination record against equine herpes virus abortion (EHV 1 & 4 vaccines). Also required are a negative EVA certificate, a negative Coggins test for EIA (Swamp fever) and a negative endometrial swab for Pseudomonas, Klebsiella & CEM, all taken on or after 1st January of the current year. Mares from France, Germany & Italy or any ‘high risk’ mares may also be subject to secondary testing.

Foaling will be well under way for mares covered early the previous year. Just before mares go to be covered, the vet will take a further clitoral swab to ensure the mare is clean (free from infection); this is often faxed directly to the stud where the mare is to be covered.


Some think late February/early March is the optimum time for a foal to be born. Once safely delivered, the mare & foal should be examined by a vet, the foal’s IgG level tested, and the mare’s milk and colostrum checked.

During the first 24 hours after giving birth, the mare produces thick milk called colostrum.  Colostrum is very important because it is rich in antibodies, protein, and calories.  The mare transfers her antibodies to the foal primarily through colostrum, rather than through the placenta like humans; these antibodies protect the foal against environmental disease.  These proteins are also called Immunoglobulins (IgG).

The birth of foals must be notified within 30 days of their birth to Weatherbys being the custodians of the General Stud Book

Reference: The Care of Newborn Foals by Dr. Tracie Hill Hulse, DVM

Merlin - The Teaser!

Some mares will be covered on their foal heat, i.e., when they come into season very soon after foaling, but this is often not satisfactory and generally they come back into season within a month of foaling and are ready to be covered. Occasionally mares require a little help and are given prostaglandin (PG) to speed up the process.

Thanks to scanning technology, a vet can see exactly when a mare is ready to be covered and can be “walked in” to the stud where the selected stallion stands. Ovulation can be checked 48 hours later either by a vet or by a lack of interest from the mare in a teaser.

At 16 days a conceptus can be seen on the vet’s screen – should there be two, the vet will squeeze one to ensure a single pregnancy.


Foals will still be arriving and mares still being covered. Any that did not conceive the first time will return to the stallion and the later producers will be covered for the first time.

Foals can now be blood sampled and micro chipped as soon as required after birth but it is often done at about a month old. Weatherbys issue veterinary practices with microchips which are implanted into the foal’s neck and at the same time the vet will make a note of the foal’s colouring, marks, whorls, etc. The paperwork and blood sample are sent to the Animal Health Trust in Newmarket for DNA sampling and then passed on to Weatherbys.

​At 28 days post covering, the vet should be able to detect a heart beat in the growing foetus.

It is a good idea to start making Stud Book Returns to Weatherbys as the foals arrive. The final date for submission of completed paperwork (Stud Book Return Form and Covering Certificate) to benefit from the most economical registration fee is 31st July and there is a tremendous rush then. Early registration reveals any discrepancies in the paperwork in time to sort them out before the due date. This process can be completed online.


Late foals arrive and mares will often be brought back into season (short cycled) artificially to get them in foal again as soon as possible.

Representatives from the major auction houses, Tattersalls, Doncaster & Goffs, come to inspect the yearlings that will be offered for sale in the autumn.


Hopefully a quiet time with all horses turned out to grass. Foals may have their first ‘flu/tetanus vac at 4/5 months old.


Yearlings selected for Doncaster Bloodstock’s St. Leger sale in late August will start their sales preparation.

Mares covered in February will require their first vaccine against abortion caused by equine herpes virus (5 months). The mares subsequently receive two more vaccinations at 7 and 9 months of pregnancy.

Weaning will have started for early foals who are now 6 months old.

The forms for any foals not yet registered should be returned to Weatherbys by the 31st. This process can now be completed online.


Yearling preparation starts for those selected for October sales.

Weaning time for most February foals.

Doncaster St. Leger Sales.

First vaccinations for March covered mares.

All Southern Hemisphere horses have their birthdays.


Weaning continues for March foals.

Tattersalls (Ireland) Yearling Sales.

Mares must be tested for pregnancy at the end of the month and a vet’s certificate obtained for any who are barren.

For those mares who have lost their pregnancy there is no obligation to pay the nomination fee for the stallion if 1st October terms have been agreed.

Any more vaccinations against abortion for mares covered in April.

Second vaccinations now due for those started in July.


Payment is due for nominations (see above).

Goffs Yearling Sales.

Tattersalls Yearling Sales.

Weaning of April foals.

On the sale of a thoroughbred there is a requirement to inform Weatherbys of the change of ownership


Foal sales at Goffs and Tattersalls.

Time to start considering suitable sires for following year.

Broodmare sales at Goffs.


Broodmare sales at Tattersalls.

Final flu/tetanus booster for foals.

On any stud, routine worming programmes and foot care are carried out all year round, as and when necessary.

Contact Details

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+44 (0)1327 855 513 / 855 660


Charlock Stud – Abthorpe – Towcester – Northamptonshire – NN12 8TW – UK