Part One of a Two Part Series – Jonathan Lombardo, DVM
One of the most significant developments in the area of equine reproduction is the use of cooled transported semen in the breeding of mares. This technology allows the mare owner to utilize superior genetics, and to breed to a stallion which may be in a distant location. This has benefited the horse industry greatly in recent years, and resulted in a consistent improvement in the quality of foals produced nationwide.
It is helpful to know the process by which the stallion is collected and the semen prepared and transported prior to the actual insemination. The semen must first be obtained from the stallion by performing a collection. This involves the use of an artificial vagina (AV), a device which is designed to provide the necessary stimulation to cause ejaculation. The AV also contains a plastic liner which directs the semen into a collection vessel. The collection procedure also makes use of a phantom, or breeding dummy, which the stallion mounts in the same manner as he would an actual mare. Stallion collection requires a skilled stallion handler as well as an individual who will handle the AV. These individuals are well trained to perform the procedure safely and efficiently. The actual collection procedure happens in the following manner. The stallion is led into the collection area and allowed to develop and erection. The penis is washed with warm water and a soft cloth. Once he is sufficiently aroused, he is allowed to mount the breeding phantom, and his penis is directed into the artificial vagina. Ejaculation is confirmed by observing tail flagging and urethral pulsations. Once he has ejaculated, he dismounts the phantom and is led from the area. The AV, which now contains the semen, is taken to the laboratory, where the semen is processed. A microscope is used to determine the percentage of spermatozoa (sperm) which are swimming actively (progressively motile). The sperm are also assessed to be sure that they are of normal shape (morphology.) The concentration of spermatozoa in the semen is measured. This data is then used to determine how the semen should be prepared for transport.
Research has shown that the effective insemination dose to breed a mare is 500 million progressively motile sperm. The transported semen should have a concentration of 20 to 50 million sperm per milliliter. The transported semen should contain a minimum of three parts extender to one part semen. Extender is a product, usually prepared from skim milk, which is added to the semen to help keep the sperm alive from the time they are collected until they are inseminated into the mare. Using the motility and concentration data, the correct amount of extender is added to the appropriate amount of semen to provide 500 million motile sperm at a concentration of 20 to 50 million sperm per milliliter. The processed semen is placed into either a syringe or a plastic bag, sealed, and placed in a semen transport container. This container is basically a Styrofoam cooler, containing an ice pack, which chills the semen and keeps it at the optimal temperature to allow it to survive until it is placed into the mare. A document detailing the stallion name, date of collection, and other information about the semen is placed within the box. The container is closed, labeled and shipped overnight to the mare owner.
Upon its arrival, the semen is examined under a microscope to determine how well the sperm survived transport. The semen information is checked to be sure the shipment is from the correct stallion. The mare’s tail is wrapped, and her perineal area cleansed. A pipette, which resembles a long straw, is placed through the mare’s cervix, and the semen injected into her uterus. She is given a drug to cause ovulation, and she is examined later to verify that ovulation has occurred in a timely manner. In a future issue, we’ll discuss the breeding management of the mare.
Dr. Lombardo is an equine veterinarian based in Red Wing, Minnesota. He may be contacted at Dr.Lombardo@EquusDVM.com or telephone (651) 755–6515.