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Your Mare and Foal

Mares - Overview of reproductive physiology


Mares breed in the longer day length of the year. Large breed mares cycle each 21 days while ponies often take 23 days. Mares stay in season 3 to 7 days depending on the stage of their season. Mares generally ovulate when they have a 35 to 45mm follicle.


Veterinarians use a transrectal ultrasound to determine the best time to breed the mare and this procedure is often called a follicle test. Factors such as follicle size, follicle softness, follicle shape and endometrial oedema indicate the proximity to ovulation.


A typical breeding cycle breeding using cooled semen consists of:


  • Follicle tests to determine where the mare is in her oestrus cycle and how long to ovulation. Generally mares are examined each second day then daily as ovulation approaches

  • An endometrial swab to culture for bacteria if required 

  • Ovuplant or chorulon are often given to induce ovulation within an average of 41 or 36 hours respectively 

  • Post breeding examination to detect ovulation(s) and to determine whether the uterus is normal 

  • Post breeding treatments may be required if the uterus is inflamed or contains excessive fluid 

  • Problem breeders may require various treatments to help them establish pregnancy 

  • Pregnancy diagnosis needs to be carried out 14 or 15 days from ovulation. It is important to examine mares prior to day 16 so twin pregnancies can be effectively managed 

  • Follow up pregnancy tests at 25 and 45 days 

  • Problem breeders may require a uterine biopsy and another endometrial swab for bacterial culture 

Birth of your Foal 


Many foals will stand within 30 minutes of birth and suckle within 60 minutes. Generally foals are considered abnormal if they do not stand within 2 hours of birth and/or don’t suckle within 2 hours of birth.


The first milk from the mare is called colostrum and foals need to absorb the antibiodies (IgG) from the colostrums. The IgG from the colostrum enables the foal's immune system to function properly. We recommend that all foals are IgG tested at 8 to 12 hours after birth to ensure they have absorbed the IgG in the colostrum. A plasma transfusion is recommended for foals that fail to absorb IgG/colostrum.


Worming Your  Foal


The worming of foals and young horses is very important. Immature lungs and digestive systems are easily damaged by migrating worms, and a worm burden that may not cause a problem in an adult horse, can easily block the gut of a foal. Ascarids are the most dangerous worms in young horses as they are such large worms and can quickly develop into huge populations in the horse. These Ascarid worms can cause damage to the lungs and the liver. 


It is recommended that a foal be wormed from six weeks of age.  A product such as Equimax Elevation can safely be used in foals and young horses. Equimax Elevation will protect your young horse from Ascarids as well as other worms. The first worming of your foal should be at six weeks old and then every three months until they are two years old. 


One your foal reaches two years of age you can then place them on a yearly rotational worming program. At Dynamik Stallions we use Strategy T during one year and Eraquell/Equimax program during year two. 


Worming your Pregnant Mare


Your mare can be safely wormed with a product such as Equimax Elevation during her pregnancy. It is important that your pregnant mare be wormed again, two weeks before her expected foaling date. When you worm your foal at six weeks of age, the mare should also be done.  


Vaccinating Your Pregnant Mare 


It is recommended that pregnant mares are vaccinated with a Strangles/Tetanus Vaccine such as Equivac 2in1 no less than two weeks before foaling. 


Some vets recommend that maiden mares are vaccinated against Equine Herpesvirus (EHV). 


Vaccinating Your Foal 


At 12 weeks of age ....... Vaccination against Strangles/ Tetanus … Equivac 2in1 

At 14 weeks of age ….... Vaccination against Strangles …… Equivac S 

At 16 weeks of age ….... Vaccination against Strangles / Tetanus … Equivac 2in1 

At 16 months of age …..Vaccination against Strangles / Tetanus … Equivac 2in1 


For Ongoing Protection 


Strangles Equivac S ….. every 12 months 

Tetanus Equivac T or Equivac 1in2 …. Every 4 – 5 years 


If you have any concerns about your mare and foal and their worming and vaccination regime then please contact your veterinarian. If your mare or foal has suffered any ill health during the pregnancy or post foaling, then please check with your veterinarian before administering the vaccination or wormer. 


Information courtsey of Baldivis Vet Hospital

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