The Art of Manufacturing Bull Semen

Day in and day out, you grab your tweezers, open the tank, pluck out an A.I. semen straw and place it in the water bath (or wrap it in a paper towel and put it in your pocket). But, did you ever think what it took to get that A.I. straw to your tank? As Glen Gilbert, Genex Vice President of Production, explains, it all starts in the factory …

A bull basically has a sperm factory that never takes a break. It constantly produces sperm 24 hours a day, seven days a week. It does not take time off for holidays or bad weather, although weather can impact how the factory performs. A bull’s health, his body condition, nutritional status, age and his environment can impact the factory too.

The Semen Assembly Line

The “assembly line” production process takes about 10 weeks to produce a sperm capable of fertilizing an egg. It’s a complex process in which cells divide to reduce their chromosomes (amount of DNA) by half, dramatically change their shape and grow a tail capable of motion. Any imperfection in the process, such as breaks in the strands of DNA, results in a defective sperm that won’t be fertile.

Semen production is a 10-week "assembly line" process.



A Climate Controlled Factory
The thermostat in the factory is set to maintain the temperature at 4 degrees below body temperature. If the factory runs hotter, the sperm is defective. To help ensure quality sperm, males are equipped with a sophisticated “air conditioner” that works to maintain the proper temperature. Features of that air conditioner include a large number of sweat glands along the surface of the bull’s scrotum, the ability to raise or lower the factory depending on the outside temperature and a system where warm arteriole blood coming from the body is cooled at the top of the scrotum by cooler blood returning from the testis. In over-conditioned bulls, fat deposits in the top of the scrotum interfere with this cooling mechanism and result in a factory that is too warm.

Of course, things such as hot summer temperatures or illness with fever can overwhelm the factory’s cooling capacity and result in defective sperm too. Even brief heat blasts lasting only a few days can impair normal semen production for several months. In other words, a bull with “good quality” semen one day can have a change in quality the following day.


The sperm factory has a sophisticated
"air conditioner" to maintain proper temps.

Sperm Quality Characteristics

Sperm need to be able to swim, have an adequate energy supply, be able to move up through the uterus into the oviduct, attach to the lining of the oviduct and wait for a signal from the female that her ova will soon be passing by. Then, the sperm needs to have enough energy to pull away from the lining of the oviduct by becoming hyper-motile, possess the necessary membrane structure that can attach to the ova and have the enzymes necessary to digest its way through the covering of the egg. Finally, the sperm needs to have the right complement of DNA that will combine with the ova’s DNA to create an embryo. Once inside, its DNA must be fully functional and not have any lethal genetic defects.


For effective cattle artificial insemination,
sperm need to be able to swim.

Every bull will produce some sperm that have flaws. Some sperm can’t swim. Some don’t have adequate energy stored. Some have faulty membranes, and some don’t have properly packaged DNA. Any one of these flaws causes that individual sperm to be useless. However, as long as enough of the entire population has the necessary traits, a bull’s semen will be fertile when deposited at the right time and the right place in a female’s reproductive tract.

Collectively these necessary physical characteristics of a population of sperm are referred to as “semen quality.” Each collection arriving in a Genex laboratory is screened to ensure it has sufficient numbers of sperm with those quality characteristics. If an ejaculate does not have adequate quality, it ends up outside in the dumpster.

Production Protocols

Collections that pass the initial screening tests proceed to the next steps - adding preservation media and freezing. Following the protocols precisely for preservation and freezing is important in order to yield an adequate number of normal sperm per straw after freezing and because each part of the process (preservation media, how its added, ratio of semen to extension media, rate of temp change, etc.) can influence others.

Quality Control Commitment

From the time a bull leaves his stall to go to the collection arena until his semen comes out of the freezer no less than 56 distinct steps are carefully carried out and monitored. Throughout the process, Genex production staff work by the motto, “If there’s any doubt, throw it out.”



At Genex, sperm quality is checked again and again.
Staff follow a "if there's any doubt, throw it out" motto.

That motto and the laboratory staff’s work doesn’t end when the semen is frozen in liquid nitrogen. Instead, straws from each batch are thawed and again inspected in the laboratory to ensure an adequate number of quality sperm survived the freezing process.



The batches that are deemed “good quality” are sent off to Genex reps around the country who deliver the semen straws to your farm. So tomorrow, while that A.I. semen straw is thawing in warm water for at least 40 seconds (or in your pocket for 2-3 minutes), think about what it took to get that straw to your tank.