On Why and How We Developed the Ship-Mate
Have you wondered why your success with shipping chilled semen can be hit or miss? We did and went on a mission to try to find out why.
We carefully followed the instructions provided by the extender suppliers; we checked the sperm under a microscope before and after we added the extender to ensure live and active sperm. Now we were ready to ship, following the instructions supplied with each of a variety of container, we still ended up having a problem. We started recording ambient and sample temperatures when we shipped. We discovered that the ambient temperature could vary dramatically in turn this affected the internal temperature of the sample.
When the outside temperature is 100+ °F (≈ 38 °C) and your package is in the back of a delivery truck that can be 120 °F (≈ 49 °C) or more, a short time later into the cargo hold of an airliner where there is little to no temperature control while parked on the ramp. Now your package makes is next leg on an aircraft flying at 30,000 ft where the outside air temperature is about -30 °F (≈ -34 °C) and you’re relying on the carriers cargo temperature control of your to ma. Now back into a delivery truck to the final destination of course if you ship out of the country the inspector may open the package for inspection removing it from the shipping container and allowing it to warm up. After all this does viable sperm arrive at the destination, you can only hope.
After digging even deeper we found more dangers lurking to foil the uninformed sample taker. How you treat the sperm sample makes a huge difference. Sperm are sensitive to both heat and cold (thermal stress). Short periods of exposure to temperatures just a few degrees above body temperature will usually kill large numbers of sperm. Rapid chilling of semen results in a phenomenon called cold shock that is often manifest by abnormal sperm motility and morphology. To avoid thermal stress, the collection equipment should be between body temperatures 98 °F (≈ 37 °C) and room temperature about 70 °F (≈ 21 °C). The extender, (buffered nutrient solution), you use should follow the temperature guidelines listed above.
We were told to cool the sample slowly to about 41 °F (5 °C). Cool slowly what does that even mean? After more digging we found that damage to the sperm can occur along the cooling process to make a long story short the “cooling slowly” term translates to a cooling rate of 1.25 °F / min. (≈ 0.7 °C / min.) down to 66 °F (≈ 19 °C) then a rate of 0.1 °F / min. (≈ 0.05 °C / min.) to the desired 41 °F (5 °C). This temperature profile just can’t be achieved with a passive box that relies on a cold source and some insulation where the temperature outside box is variable. This temperature profile can be produced using large heavy equipment in the lab, we needed something that is portable that anyone can afford to use.
We assembled a team with a variety of technical expertise and the result is Ship-Mate the semen shipping system that controls the temperature to achieve the profile described above. The correct temperature profile will be maintained regardless of the temperature the shipping box encounters.
Remember the when we talked about the package being opened for inspection. If you had lab equipment to do the cooling optimally before you shipped, when the inspector opens the package the temperature starts to rise and with small amount of fluid the specimen gets to room temperature in just a few minutes. The inspector repackages the shipment and you have a second opportunity to cause cold shock, unless you are using the Ship-Mate to maintain the correct temperature profile.
Now for some technical reasons why your sample may not have arrived in optimum condition.
Why cool semen?
Fresh semen stored at 98 °F (≈ 37 °C) deteriorates rapidly, most raw semen will have no motile sperm after 3 – 4 hours at 98 °F (≈ 37 °C) and 5 – 6 hours at room temperature 71 °F (≈ 22 °C). Cooling the sperm to 41 °F (5 °C) causes a transition in sperm membranes from the liquid crystalline to the gel state. Since damage can arise from these changes why would we want to cool semen? At body temperature spermatozoal metabolism is maximal and at room temperature it is lower. Waste products such as lactic acid and CO2 can increase the acidity causing permanent cellular damage. When the temperature of the sperm cells are reduced, for each 18 °F (≈ 10 °C) reduction, cellular metabolism is reduced by 50%. So when sperm is stored at 41 °F (5 °C) their metabolic needs are only about 10% of what they would be at 98 °F (≈ 37 °C). This lengthen the life of fertile sperm compared to those stored at body or room temperature. Cooling too rapidly however stresses sperm and often causes cellular damage called cold shock. This damage is characterized by an abnormal pattern of swimming (circular or backwards), rapid loss of motility, acrosome damage, plasma membrane damage, reduced metabolism and loss of intracellular components. This cold shock damage can be minimized by including additives to the extender and by careful slow cooling through the temperature zone where the transition from the fluid phase to the solid phase occurs. Once the semen has been collected and examined, it is mixed with a special diluent, (extender), cooled correctly and refrigerated at 40 °F (5 °C). It can be kept for up to 72 hours with excellent viability. Only an actively controlled shipping container can insure the correct temperature profile is maintained.