What’s the deal with milk extender?

How do I know if the semen is in a full-fat milk extender?

The Dynescan is the only instrument capable of measuring the Sustained Motility Lifetime of semen accurately, and it can be used with most extenders. Nonetheless, specific extenders, such as the full-fat milk extender, are known to challenge semen analysis technologies. Thus, it’s crucial to ascertain the type of extender used before presuming that the sample can’t be measured accurately.

How do you know if the semen is in a full-fat milk extender?

Is the semen sex-sorted?  

If the semen is sexed, a full-fat milk extender has not been used.  For sexed semen, the extender is likely to be based on tris hydroxymethyl aminomethane (Tris) buffer with lecithin (with egg-based or synthetic) with added nutrients, because advanced extenders are required to protect the cell walls of the sperm during the sex-sorting process while being optically clean (transparent) to enable efficient sorting.  It is likely the sample looks similar to Figure 1b. Sexed semen is never in milk extender, and you can rely on measurements of the Sustained Motility Lifetime using the Dynescan. 

A. Full fat
A. Full fat
B. NOT full fat
B. NOT full fat

Figure 1: Dynescan images collected in Dyneval Mode for A) Full fat milk extender appearing ‘crowded’ due to the fat droplets and B) an extender that is not full fat milk showing a level of debris that has minimal effect on the measurement.

Does the sample appear white, opaque and ‘milky’ when emptied into a vial?

If so, it is possible it is in a full-fat milk extender.  When a sample is loaded into the Leja slide and viewed down a microscope, the sample will appear ‘crowded’, and it will be difficult to see the spermatozoa due to the presence of fat droplets, as demonstrated in Figure 1A. We apologize that you will not be able to perform reliable measurements of the Sustained Motility Lifetime at this time.  Our scientists in Dyneval are working towards solutions that will enable measurements of the Sustained Motility Lifetime and Motile Cell Concentration in full-fat milk extenders.    We would be delighted if you would continue collecting Dynescan measurements and videos to help us improve and test our new algorithms. We will not charge for these samples if you are on a PAYG subscription.

Have you been advised the sample is in milk extender yet you can see the cells clearly down the microscope?

If so, it is possible the milk extender was skimmed which means the fat droplets have been removed.  In this case, please go ahead performing Dynescan measurements with the confidence that you can rely on the results.

Decades of Research Supporting Science

Dyneval’s unique semen analysis technology is based on 30 years of research into complex fluids. We are working to extend our capabilities through continued research and rigorous testing. We are making strong progress towards developing a solution to measure the Sustained Motility Lifetime of spermatozoa in full-fat milk extenders - a first for the industry.


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