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♦ Extending Semen for Optimal Pregnancies
♦ Extending Semen for Optimal Pregnancies


Historically GENEX and its predecessor organizations have used a homogenized whole milk media as a semen extender. In some of our laboratories milk extender has been used for more than 50 years. Semen extended in milk does present challenges in evaluating the post-thaw viability of sperm cells. However the superior pregnancy results historically achieved with milk-extended semen outweigh the difficulties of post-thaw microscopic examination.

“If we wanted our product to look the best under the microscope, we would use a different extender,” states the GENEX Vice President of Production. “But we have chosen to use the extender that provides the most pregnancies.”

Evaluation Challenges for Untrained Eye
Under ideal conditions semen extended in milk is difficult to evaluate. Unlike most egg yolk based extenders, the optical clarity of milk extender is poor because of the fat droplets. Light passing through the sample is reflected and refracted making the observation of individual sperm difficult. The thickness of the sample being evaluated is critical in order to obtain repeatable results. If the sample is too thick, the optical distance from the top of the sample to the bottom (distance from the bottom of the cover slip to the top of the slide) will be too great and sperm will be impossible to visualize. At the same time, a sample that is too small will not have adequate depth, and sperm will appear immobile because they are stuck to the slide or cover slip. Each of these cases would lead the evaluator to conclude the number (percentage) of sperm moving in a straight line is very low.

GENEX Quality Check
Each collection of GENEX semen is evaluated after freezing to ensure it contains an adequate number of viable sperm cells to result in a high percentage of pregnancies. It goes without saying that semen is a perishable product whose quality can diminish after it is initially frozen and evaluated if it is not kept at temperatures below –130°C.

Field Research Reveals Optimal Choice
GENEX research comparing semen extended in egg yolk media to milk shows that evaluators typically rate semen extended in egg yolk media higher than milk. In addition, sperm cells incubated in an egg yolk extension media for extended periods of time after thawing will almost always continue to exhibit motility long after the milk extended sperm have stopped movement. As a result one would expect egg yolk extended semen to achieve greater pregnancy rates. However, GENEX field research based on hundreds of thousands of inseminations shows semen extended in milk achieves equal or superior results compared to semen extended in an egg yolk media.

Published Research on Conception Advantage
An article published on extenders points out a unique positive property of milk extender: it gets cows pregnant. The Journal of Theriogenology article, Comparison of two processing systems for bull semen with regards to post-thaw motility and nonreturn rates, authored by E. Kommisrud et al. (Volume 45, no. 8 June 1996: pp1515-1521) compared a skim milk extender with 5% egg yolk to a commercial all egg yolk tris extender for a total of 197 ejaculates from 45 sires and 41,445 inseminations. Although percent motility was not different between these two extenders, fertility did differ significantly. The extender comprising primarily milk with a small amount of egg yolk was superior to the extender with only egg yolk. Milk-extended semen received a 60-day non-return rate of 73.1%, while semen processed with the egg yolk tris extender achieved 71.9%.

“At GENEX, we are proud of the quality of semen we provide,” adds the GENEX Vice President of Production. “Using milk media as a semen extender is one more way this cooperative helps members and customers achieve pregnancies on the farm or ranch.”