The fundamentals of breeding


Equine breeding is a strictly controlled activity requiring regulatory knowledge and technical expertise if it is to be carried out correctly. A few basic principles are set out below.

What you need to know about rules and regulations (example for France)

> To be able to produce offspring of a given breed, the male must be “approved”under the stud book rules of the breed concerned. Depending on the stud book, this approval may be definitive or temporary. Annual accreditation of stallions for public covering was abolished in France in 2008.

For natural covering, any health regulations to be met by breeding stock in order to be “approved” are defined by the stud book rules for each breed.

For artificial covering in France, the State has upheld the mandatory health requirements for the admission of stallions to accredited collection centers.

> Any registered mare (with the exception of French Trotter mares which are “banned from breeding”) may be covered but the designation of her offspring will depend on the applicable stud book rules.                                                                                  


> All equine animals age by one year on January 1st of each year irrespective of their actual date of birth.

> In stud farms, the covering season can begin early in the year (February in the case of racing horse breeds) and continue after mid-September (sport horses).

What you need to know about technical aspects

> Puberty occurs at an age of around 15 to 18 months in both males and females. Therefore, the two sexes must be separated as early as the first winter.

> If you decide to have your entire males castrated, do not do so before the testes have fully descended; this takes place at an age of around 18 months.

> The female has a seasonal reproductive cycle. The length of the cycle is approx. 21 days (but it varies widely from one individual and one season to the next), with alternating periods of estrous phase or heat (when she is receptive to mating) and rejection (when she is unreceptive to mating).

To detect and track these periods, mares must be put in the stocks every 2 days. The test consists in placing the mare behind a partition and bringing in a male. On coming into contact with the male, the female will show signs of either heat or rejection.

Signs of heat

Signs of rejection

Tail raising


Vulval winking

Tail switching


Ears back



> At times of year when the days are short (mid-autumn to early spring), the ovaries of most mares are inactive (resting), so fertilization is impossible. 


> Mares are covered or inseminated when they are in heat, either every day or every two days depending on the technique used, up to the end of their heat phase.

Pregnancy begins with fertilization and ends with foaling. This period lasts about 11 months in horses and 12 months in donkeys, but varies depending on the season: pregnancies that begin in winter are longer than those that begin in spring, and these are longer than those that begin in summer.

> To find out whether a mare is pregnant, the most widely used technique is a rectal ultrasound examination, performed by a veterinary surgeon as of the 15th day after the first time she is seen to reject the stallion.

This is the only technique capable of detecting the presence of twins.                


A twin pregnancy is undesirable since the mare will often abort in around the 7th or 8thmonth. If the pregnancy goes to term, the mare very rarely gives birth to two viable foals.

> The fetus gains most of its birth weight in the last three months of pregnancy, so the mare’s food requirements increase during this period. Her daily food ration must be adapted to her needs throughout pregnancy and until the foal is weaned.

> Most foals are born at night.

The date of full term, the state of the mare’s udder and changes to her body shape are not reliable indicators for predicting when she will foal.

Foaling is imminent when the mare shows sign of slight colic (walking round in circles, sweating, intermittently lying and standing, pawing at the ground, looking at her belly, etc.).

IMAGES  A normal foaling must be fast, i.e. less than half an hour between waters breaking and delivery of the foal. If any complications are suspected, veterinary assistance must be sought immediately.