With the use of cooled shipped semen on the rise, breeders want to maximize the effects of this new technology as best they can. However, there are a variety of factors that can affect fertility with cooled semen, said Dickson Varner, DVM, MS, Dipl. ACT, professor in equine reproduction in the College of Veterinary Medicine at Texas A&M University (TAMU), at his presentation at the Bluegrass Equine Reproduction Symposium. The symposium was sponsored by Hagyard-Davidson-McGee Associates veterinary clinic in Lexington, Ky.

Varner said that with stallions being judged primarily on their pedigree, performance record, and conformation, with little consideration being given to semen quality and fertility, the industry might be inadvertently promoting subfertile stallions. There are many factors that affect semen quality and the fertility of the stallion; factors ranging from how the semen is handled and processed to the ability of the semen to withstand cooling, storage, and shipping. Varner discussed several factors in detail, including composition of extender; pH and osmolality (or osmotic pressure) of extender; extender antibiotics; semen dilution ratio; indications and techniques for centrifugation of semen; and selection of shipping containers.

Varner cautions that sperm are quite susceptible to many environmental factors, such as temperature, light, and a variety of common chemicals (i.e. soap and disinfectants).  He recommends keeping the semen warm immediately following collection (35-38°F) until it is mixed with a suitable extender.

Proper preparation of the artificial vagina (AV) is important. Varner recommends the use of sterile HR lubricant or Priority Care lubricant, as opposed to KY jelly for lubricating the artificial vagina, because the KY jelly contains a chlorhexadine base that could jeopordize sperm viability.  He also advises that the volume of AV lubricant be minimized to avoid osmotic- or pH-related damage to the sperm.  Putting a filter in the AV when collecting the semen effectively separates the gel and gel-free portions of the semen, thereby increasing the sperm harvest. Varner suggests using disposable baby bottle liners in the collection receptacle to reduce the risk of chemical or bacterial contamination of the ejaculated semen. In addition, cleaning of the AV prior to collection should be done with hot water only, followed by rinses with deionized water and 70% isopropyl or ethyl alcohol. Use of soaps and disinfectants (i.e. Nolvasan) can permeate the rubber of the AV and damage the semen.  Varner’s preferred AV is the Missouri-model.  He indicates that it is most easily assembled, cleaned, and stored