Stallions!

I think I will take a break from the mare side of things and discuss stallion reproduction. Stallions are unique and important in the horse industry because as a male horse matures he can become aggressive towards other horses and humans and he can be harder to keep. Usually stallions are bred because they have won lots of awards on the race track or show ring and mare owners desire foals with their genetic attributes. Male horses that do not have desireable genetic lines are often castrated (gelded) either when they are young or older for aggression purposes or if breeding is not a possibility.

Basic Anatomy

Dr. Janet Roser gives some physical guidelines to a fertile horse. In the article “Is Your Stud a Dud”, which thoroughly discusses all aspects of the breeding soundness exam, she describes physical attributes specifically related to the reproductive organs. Stallions have external testicles and erectile tissue makes up the largest percentage of the penis (there is no bony tissue). I learned interestingly, that the only land mammal with internal testicles is the elephant, just think what an elephant would look like with external testicles! So, back to horses… The penis should be free of lesions and sores and a normal scrotal size for a stallion (dependant on age and time of year) is 9 to 11cm in diameter. Dr. Roser also recommends a rectal palpation of the prostate, ampulia, and seminal vesicles. For many if not all stallions, this would require a set of stocks not in the direct vicinity of any mares and a tranquilizer. A rectal palpation was not preformed on any stallion during a breeding soundness exam at the facility I worked at.

Although the physical characteristics of the reproductive organs are important, Dr. Roser agrees that the stallion must be overall in good physical shape to breed. Some of the things to check for include blindness, lameness or bad conformation. Basically, the horse must be able to mount the mare or phantom (I’ll explain that later) and ejaculate safely. Believe it or not, even though it is a natural process, breeding takes a lot out of a stallion and the breeding technician at the clinic I was at has actually had a horse die while breeding of heart related problems.
Another very essential physical characteristic is presence of libido. This can be detected with a mare that is in heat or a teaser mare. At the farm I was at there were two teaser mares that had their ovaries removed and received shots of estradiol (estrogen) which made them act like they were always in heat and could respond to stallions appropriately. The physical signs of a stallion’s libido are whinnying, nudging, sometimes biting or nipping, pawing and others. Sometime during the teasing, the stallion will “drop” his penis from the prepuce and will be ready to be washed and breed the mare.

Collecting the Stallion

There is a significant population of mare owners who breed with artificial insemination (AI) instead of live cover, which is the “natural” way of breeding. There are certain breed associations, for instance with registered thoroughbreds, that are not allowed to breed using AI. However, if allowed, it is becoming the preferred method of breeding. Its benefits include the reduction of disease and decreased injury to the stallion and mare during the actual breeding process. Stallions must be collected for the purposes of artificial insemination or for semen evaluation. There are two common ways of collecting a stallion. One is letting him tease and mount a tease mare. This involves taping the tale of the mare and making sure she is very calm. It is difficult to collect this way if the stallion likes to bite or thrash his front legs while breeding because this is very uncomfortable for the mare and she will probably not stand long enough for the collection. However, if you do use this method, once the stallion has jumped the mare, an artificial vagina is slipped over the penis before he is able to enter the mare and until he ejaculates.

The second and in my opinion more preferable method of collecting is with the use of a phantom mare. This is a large, padded, block like object that is mounted on an adjustable pole and is built to represent the height and general size of a mare standing to be bred. It is not necessarily intuitive for a stallion to want to breed a phantom and so he must be taught. There was one stallion at my clinic that, upon seeing the phantom, thought it was another stallion and was threatened by it and rushed it and took a bite out of the padding. Anyway, for many stallions (that I have experience with) a teaser is still used to excite the stud and sometimes also to teach a young horse how to jump. Once the horse is excited he is led up to the base of the phantom and will usually mount on instinct. Immediately, when the collector sees that the stallion is on, in the right angle, and it is safe to approach, they grab the penis and guide it into the AV. After this, the stallion will usually ejaculate on his own and dismount.

There is a third way and some veterinarians and stallion owners claim that there is a specific way to teach a stallion this method and it works the best, it is not a commonly held belief. The method is collecting the stallion on the ground, that is, without him mounting anything but standing on all fours. I think this process is more dangerous for the collector and handler because it is circumventing the natural movements of the horse. I think the reasoning behind this is that it does not put as much physical strain on the stallion and some say that it is easier. We did collect one or two stallions like this for a specific client, but in general shied away from it.


So that’s it! The basic procedures for collecting semen from a stallion. There is one aspect I did not mention though and that is the different typed of AV. The two common types are the Missouri and Colorado AVs, named for their state of origin. The Missouri is a soft latex pouch and the semen is deposited into the end of it. The Colorado (I am most familiar with this one) is made of hard fiberglass and has a double latex liner, one which is removable. The ejaculate is collected in a bottle in the end. Both liners have a chamber that is filled with hot water to simulate a mare’s body temperature (<100>

I know it’s a lot of information, so here is an overview of the process to physically evaluate and collect a stallion:
-Check general physical soundness
-Examine external genitalia (penis and testes)
-Rectally palpate internal organs
-Tease stallion to drop
-Wash penis
-Lead stallion to phantom or teaser
-Collect ejaculate with AV once stallion mounted
-Make sure horse dismounts safely



The next process in using and evaluating semen occurs in the lab. There are many checks and steps that the ejaculate will go through depending on what it is being used for. I will go into this at a later time.