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Breeding Bulls Can't Take the Heat

FOR THREE MONTHS EACH YEAR DURING BANGLADESH’S HOT SEASON, the nation’s artificial insemination industry ships out a bunch of blanks. That’s because the sperm collected from bulls is often so heat-damaged that it doesn’t support life well.

“The temperature in the testes only rises about two degrees Celsius. It doesn’t take much at all,” explains John Parrish, a professor of animal science who studies male fertility problems in dairy and beef cattle.

With funding from CALS’ Babcock Institute, Parrish established a collaboration with National Bull Stud, Bangladesh’s federal artificial insemination institution, to test a hypothesis he’d been examining for a number of years: that heat damage, which affects the shape of sperm cells, can be measured.

In Bangladesh, National Bull Stud employees collected semen from a set of dairy bulls during hot and cool seasons. They then stained the sperm cells, took pictures of them under a microscope and e-mailed them to Parrish in Wisconsin for analysis. “We found significant changes in the shape of the sperm in those animals (between the hot and cool seasons),” says Parrish, who added hundreds of lines of code to an off-the-shelf software program to get the sperm-cell coordinates he needed. “It’s only very slightly different; there’s no way you could see it with
your eye.”

Although Parrish originally set out to answer a basic scientific question, his work could end up benefiting Bangladesh’s dairy industry. That’s because a small percentage of bulls are able to maintain their fertility during the hot season. “We can use this test to look for bulls that are not affected by the heat,” says Parrish. “Those should be the parents of the next generation.”

Similarly, the test could be used to monitor when heat-affected bulls recover their virility after the hot season ends. “The idea is to test semen and say, ‘Now it’s okay to ship out.’