Artificial insemination of dairy cattle is a common practice in the developing world that can improve farmer incomes and food security by yielding more productive breeds. Generally, the semen used for artificial insemination is stored and transported in liquid nitrogen, which maintains the semen at the mind-blowingly low temperature of -196⁰ C.
Most developed world bovine inseminators are taught to never remove semen straws from liquid nitrogen for more than eight seconds, unless they are being thawed for immediate usage. Some practice a five second rule, and the most seasoned professionals practice a three second rule.
These rules are drilled into inseminators’ heads because even very short exposures to ambient temperatures can cause large temperature fluctuations within the straws. And while these fluctuations often are not large enough to thaw the straws’ contents, they do cause cumulative and irreversible damage that makes the semen less fertile.
While following the three, five or eight second rule does a great job of avoiding exposure-induced damage, the rules are not well followed in the developing world and are even commonly unheeded in developed world. One study estimates that poor handling in the United States accounts for a 9% decrease in semen fertility. The problem is likely worse in the developing world—primarily because training is less rigorous—meaning that inadvertent mishandling of semen causes a large number of pregnancies to be missed, and that can have devastating consequences for farmers and artificial insemination programs alike.
In an effort to improve bovine artificial insemination conception rates in the developing world, IV Lab’s Artificial Insemination project aims to develop technology that protects frozen semen from exposure-induced damage. Our focus is on improving existing canisters that hold an inseminator’s semen inventory, the equipment at the top of the poor handling “most wanted” list. When an inseminator removes the improved canister from liquid nitrogen to pluck a straw for use, the added technical features will protect the remaining semen inventory from exposure-induced damage.
So how will we know if we are addressing the problem as we design the device? The first step is to measure exposure-induced damage by subjecting semen straws to poor handling practices and quantifying damage to the semen. We can then test our device and measure the improvement.
While thermal damage affects many aspects of sperm biology, it commonly manifests in the form of ruptured membranes, the most sensitive of which surrounds the acrosome. The acrosome sits at the head of a sperm cell and contains enzymes that allow the sperm to fuse with an egg. When we used fluorescent stains to visualize the acrosomes of semen exposed to poor handling practices, we saw structural abnormalities that were a result of acrosome membrane damage.
We measured the percentage of intact acrosomes of frozen semen subjected to repeated ambient temperature exposures using existing equipment. The results support our hypothesis that increased temperature exposure correlate with increased damage, as seen below.
We suspect that the fertility of some of these samples is much worse than the plot implies as the method we used to assess acrosome damage was relatively coarse. We are repeating similar experiments with more sophisticated methods that look at several other features of sperm biology. The basis for one experiment is shown below.
We are confident that exposure-induced damage is an important problem, and now we have a means to measure it and the added protection our technology provides. In an upcoming post we will describe the features and performance of our leading designs.