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Bull Semen Parachute

Parachute used by the University of Wisconsin to deliver fresh bull semen to farmers in rural areas, 1944-1947.
(Museum object #1993.7)

Even though nearly 60 percent of all cattle today are born to cows that have never had actual contact with the sire, the high amount of artificial insemination that occurs among dairy cattle in the 21st century would have been unimaginable to the earliest researchers in the field in the 1930s and 1940s. Some of the most significant advances in dairy cow reproduction occurred at the University of Wisconsin-Madison's College of Agricultural and Life Sciences, where researchers achieved herd improvement through the distribution of semen from genetically superior bulls to as many cows as possible. During the early 1940s, the distribution was a race against time, as sperm were viable for only a short time and the demand for deliveries was widespread. One solution researchers developed was to use an airplane and small parachutes like this one to drop fresh bull semen directly to farms with cows in heat.

Prior to the advent of artificial insemination, one bull could father 100 calves the traditional way in what would be considered a very good year. He would be labeled a "plus-proven" sire if the daughters he fathered out-milked their mothers. During the World War II era, there was only roughly one "plus-proven" bull for every four hundred farms, making them exceedingly high in demand. Combined with the fact that cows stayed in estrus (heat) for only a few hours, it is not surprising that successful couplings between these superior bulls and cows would be fewer than ideal.

But through efficient artificial insemination, a high-demand bull could be used to sire thousands of calves over a wider geographical area. One collection of semen - which could contain 10 to 12 million viable sperm - could be successfully divided to service several cows at once. While merely breeding more high-production milk cows would not have raised milk output greatly, combined with other advances in herd management, such as breeding cows who took maximum advantage of their feed, the results have proven to be significant. In 1940, one of the last years not yet largely affected by AI, the average cow produced 4,622 pounds of milk. By 1997, the average dairy cow produced a staggering 16,915 pounds.

While airlifts, such as those provided by the Wisconsin airplane The Flying Bull, did, in theory, greatly increase both the number of farms and cows to which the semen was available, the service was inherently riddled with problems. Even though farmers spread sheets in their yards as targets, pilots that swooped down and dropped the parachuted packages did not necessarily have the greatest aim and rarely hit their mark precisely. In addition, foggy, rainy, or snowy weather could require a complete termination of the mission, leaving disappointed farmers who saw their profits drop significantly without impregnated cows.

Unsatisfied with these realities, researchers at the University of Wisconsin continued to seek a practical extender for semen viability that would lessen the need for immediate deliveries. Biochemist Paul H. Phillips and his graduate assistant Henry Lardy believed chicken egg yolks were promising as well as inexpensive and plentiful. Buffered with phosphate, egg yolks provided all-important nutrients that could extend the lives of the sperm. By November 1948, Phillips and Lardy had perfected their technique, which allowed the sperm to live up to 150 hours under refrigeration. Eventually, liquid nitrogen would be used to freeze the samples, extending the life even further. Having proven incredibly successful, the simple formula devised by Phillips and Lardy is still the most popular extender used today.

[Sources: McCarry, Miles R. "Doing What Comes Artificially" in Invention and Technology Magazine, Summer 1999 (available online at; Cooney, Bob. Stepping Stones to Cloning, Technology Report from the College of Agricultural and Life Sciences, University of Wisconsin-Madison, 1998 (available online at]


Posted on April 19, 2007

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