Introduction To Reproduction In Horses

The mating of a stallion and mare should be easy, right? It can be if you learn 1 secret – the necessity of observing the horses and recording these observations accurately.  Accurate records reveal subtle patterns in mating behavior that can help in getting the mare to accept the stallion.  

There are 2 types of breeding: natural and artificial.  I have a series of images of my elder statesman gelding who was castrated late in life and continued to show good natural mating behavior, especially when turned out with his new girlfriend.  This is called pasture breeding and it is the way nature intended it to occur.  In breeding operations where only natural breeding is allowed yet a maximum return on effort is required for business, the stallion and mare are held by handlers trained in this very specific type of horsemanship.  I will discuss this as my training before vet school was on a Thoroughbred farm where hand breeding was the only way allowed.

Artificial breeding details are beyond the scope of this website as the complexities are nuanced and detailed.  However artificial breeding includes: 1) collection of the stallion either on a mare or a dummy mount, 2) the artificial insemination of the mare by a veterinarian, 3) the freezing or cooling of semen for shipment to other farms far away, 4) the collection of fertilized eggs and transfer of these ovums into recipient mares.  

Complicating things include shy or aggressive mating behavior, venereal diseases, systemic viral diseases, acquired reproductive tract infections, attrition or damaged sperm and eggs, twin fetus development, birth canal damage and abortion (pre-term and full term).  I’ll do what I can to touch on these topics but this subject could be a whole website.  In my 12 years of full vet practice I have seen all of these topics and I will have several stories to illustrate them all.

Mating Behavior Of Horses

The mating behavior of horses is based on one stallion per herd of mares. In addition, the mares start cycling with increasing daylight (spring) and stop cycling as daylight decreases (fall).

read more

Stallion Testicles

The purpose of the testicles is to make and store sperm as they mature from infertile immature sperm formed in the testicle and move up the epididymis into the secondary reproductive organs where the semen is created. Because they are temperature sensitive and will die if warmed to body temperature, the testicles in mammals remain outside the body to keep the sperm’s temperature below body temperature.

read more

The Estrous Cycle Of The Mare

The mare has a seasonally poly-estrous breeding cycle. It is seasonal because it occurs during increasing daylight (spring) and does not occur with decreasing daylight (fall and winter). It is poly-estrous because they become receptive to mating (in heat) for about 6 days and then become unreceptive to breeding (out of heat) for about 15 days for a cycle of 21 days.

read more