Learning of the Variety in Veterinary Medicine: Semen Sorting

I have worked as a laboratory technician in a few instances prior to going to vet school. Being the type to have attention to details makes the methodical tasks within the lab easy for me.


The job I worked right before vet school was at Sexing Technologies. I felt I needed something that would help my knowledge of the production animal side of things. I had already volunteered with a hunter/jumper barn, within small animal clinics, with wildlife, worked at zoos, but I didn’t know much about the dairy industry.

Sexing semen means to separate the sperm that produce female offspring from those that produce male offspring. If you think about natural mating, 50% of the time you will get a female calf, and the other 50% of the time you will get a male. In the dairy industry, females produce the milk and therefore are of higher value to the dairy producer than the male calves. Very few of the male calves get grown up to be breeding studs, and most are raised for veal or slaughtered later for "beef". At Sexing Technologies, I worked on the wet lab side. We would take the semen from the collectors, measure the volume and concentration of the sperm, dilute or concentrate the sample to a specific concentration based on our laboratory protocols, then it would incubate with reagents prior to sorting. The machines used for sorting would pretty well run 24:7, and we worked shifts, day, afternoon or night. I would only sub in on the sorting machines when a sorter was on lunch break. After sorting, you have a tube that is roughly 98% X chromosome sperm, that we would then set to cool prior to loading the sample into straws that then get frozen in liquid nitrogen.


I thought this technology was pretty darn cool. It makes the dairy industry more efficient. Traditional breeding is based on phenotype, which is dictated by genotype. Phenotypes are the things that we can see, as examples: size of the animal, the conformation of the hooks and pins, as well as the number of gallons of milk a dairy cow can produce. These phenotypes are heritable through the parent's genotypes to their offspring. Your prize cow has great conformation and produces several gallons of milk per day, which is much greater than a single calf can consume. You raise her calf, and this replacement heifer gets bred to the best bull, hoping that you can get a likeness of your prize cow in the next generation. This is selective breeding, otherwise known as artificial selection (versus natural selection which occurs in the wild). Mankind has been performing artificial selection on many species, and developed breeds of these species, for thousands of years.


Artificial insemination has been in the dairy industry for over 50 years. The use of sexed semen in the dairy industry has been occurring for the past 30 years. Then, they added genomics. Not genetics, genomics. In genomics, you use the genome of the animal to predict the outcome based on heritable traits. The genome is the DNA sequence (similar to you using your DNA sequenced on Ancestry.com or 23andme.com to find your relatives). Based on the genome of an animal, you can predict whether or not they will make a good cow, or a good bull. Since I was working on the bull side of things, the industry would select a bull calf to raise up to be a breeding bull based on this calf's genome. This essentially skips generations of breeding and waiting for the daughters of those bulls to start producing milk, to see whether or not they are a prized bull. It's a little bit complicated, but essentially, the bull calf has the genetic code to produce daughters that are good milk producers.


One of the problems with artificial selection is inbreeding. Breeds of all species, whether its cattle or dogs, are developed through inbreeding, where relatives are breed together to form offspring with desirable traits. Inbreeding in dairy cattle is one of the causes of infertility in cows. Genomics can help identify which cows and bulls are related, so that dairy producers can get some new genetics into their herds for better fecundity, and ultimately better milk producers.


Whether you consume dairy products or not, this is the reality of the advancement of technology towards safe and sustainable food products for human consumption.

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