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Rachel Greene
Mary Pendergast
Biology 1010
9 February 2016
Artificial Selection in Dairy Cows
Across the globe people are producing more and more offspring. Due to this there is a
growing demand on agriculture for the most efficient crops and animals to supply the population
with food. Scientists have worked for many years trying to artificially select specific traits that
would be beneficial for the growing demands. However, as history has shown by selecting
positive traits you may also be selecting for negative ones. They have found this to be the case
in dairy cows. By increasing the milk production they have also selected for a trait regarding
infertility problems. In trying to fix the demand problems they have created more. Without an
increase in the cow population due to infertility they will soon run out of dairy cattle to select
from making the original trait they were trying to select for insignificant.
Artificial selection did not start in dairy cows but rather corn. It began thousands of years
ago without anyone realizing what they were doing. In artificial selection two adults are breed
together that posses the desirable trait. From their offspring, the ones with the most desirable
trait are chosen to breed with another generation to have a higher chance of the desired trait. It is
similar to Charles Darwin’s theory of natural selection in that a species changes over time
adapting traits that would be best for the environment around them. Unlike natural selection
however humans are influencing the trait instead of nature and habitat. Due to artificial selection
there is a decrease in the variability of a species. Variability is important in a species for
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survival. It works like an insurance policy assuring that with variability there will be a decrease
in mutations and also can allow species to adapt to change over time.
Long before Darwin’s time however, farmers used artificial selection without knowing.
Naturally, farmers wanted their crops and animals to have the best traits possible. They would
breed their best livestock together or use the best crops. Artificial selection was the cause of the
potato famine in Ireland. Farmers wanted the biggest, most effective potatoes so they kept
breeding the same plants that had the characteristics they wanted. Since all of the plants had the
same genetic material and there was very little variability, one airborne fungus was able to kill
off all of the plants. If people had not controlled the selection of the potatoes there would have
been more variability thus allowing some of the plants to survive. This unfortunate circumstance
may happen today with dairy cows becoming infertile due to the selection of increased milk
production.
To select traits for a higher milk yield in dairy cows, you must first look at the bulls. Due
to technological advances semen is widely available online from many different countries to
artificially insemination cows for the higher milk yield trait. This means that one bull’s semen
can produce many offspring all across the globe. This can cause the same problems that
happened with the potato famine. Since one bull can produce many offspring due to artificial
insemination genetic variety is very low. Also this makes it more likely that inbreeding will
occur often in the dairy cattle population. When there is a reduction in genetic variability there is
usually an increase in recessive traits that would not normally be so prevalent. In the case of the
dairy cattle it is causing more infertility in the population.
A recent study done by the Agricultural Research Service’s Animal and Natural
Resources Institute and the University of Minnesota suggest “there may be a genetic connection
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between increased milk yields and reduced fertility.” They were specifically focused on the
Holstein cows that naturally have higher milk yields. The University of Minnesota had cattle
that were never exposed to breeding practices today allowing an insight to what cows were like
before selective-breeding practices. They found that almost as much as 30 percent of the genetic
makeup in cows today has been influenced from current breeding practices. Although changes
can occur randomly as in the case of natural selection, it is very rare for a large change like this
one to be related to anything else besides artificial selection. The scientists in the study observed
“many of the genes and chromosome regions associated with milk yield were also related to
lowered fertility rate, supporting their hypothesis of a genetic link between the two traits.”
Artificial selection in dairy cattle has been very beneficial so far allowing milk
production to double over the past 50 years however it is starting to cause problems that must be
taken into account now before it is too late. Scientists need to find a way to allow milk
production to increase while also having high fertility rates. To do this they will need to increase
the genetic variability in the cows.
Thomas Malthus came up with a theory on the relationship between population and
agriculture. He states that the population increases geometrically (1, 2, 4, 16, 32) while
agriculture only increases arithmetically (1, 2, 3, 4). Therefore he purposed that if the population
was not controlled than death and famine are inevitable. Even though his ideas may not be
supported today due to the increase in technology with things like artificial selection and
insemination that allow us to produce more food than normal, I believe he still has an important
point. As we have discussed due to artificial selection we are now facing infertility problems in
dairy cattle. So no matter how much we try to influence various things like agriculture to help
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our species survive if we do not try to control the population to keep up with the demands of
food then we could be facing a mass famine.
I choose the topic of artificial selection because I am very interested in the technological
advantages we have come up with over time that have allowed our species to continue and live
longer. I think it is amazing how far we have come with artificial selection in agriculture getting
many different plants just from one in the case of the wild mustard. Due to selective breeding of
the wild mustard plant we were able to get many different vegetables like cabbage, kale, and
broccoli. The most amazing advancement so far is corn however. It has been selectively breed
for thousands of years now and originated from a grass called teosinte and has now evolved into
a tall plant that produces large stalks of corn with big kernels. I agree with Malthus’ theories
however, I believe the population needs to have a plan set in place for how many children
families can have. Even with new technologies I believe we need to think about the impact we
all have on the planet and with an increase in the population it can hurt the ecosystem over all.
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Works Cited
"Artificial Selection at Work." Learner.org. Web. 10 Apr. 2011.
<http://www.learner.org/courses/essential/life/session5/closer1.html>.
"Breeding and Genetic Change in the Holstein Genome." United States Department of
Agriculture. Oct. 2009. Web. 10 Apr. 2011.
<http://www.ars.usda.gov/is/AR/archive/oct09/genome1009.pdf>.
Brotherstone, S., and M. Goddard. "Artificial Selection and Maintenance of Genetic Variance in
the Global Dairy Cow Population." Pub Med Central. 7 July 2005. Web. 10 Apr. 2011.
<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1569519/>.
Flori, Laurence, Sebastien Fritz, and Florence Jaffrezic. "The Genome Response to Artificial
Selection: A Case Study in Dairy Cattle." PLoS ONE: The Genome Response to Artificial
Selection: A Case Study in Dairy Cattle. Web. 09 Apr. 2011.
<http://www.plosone.org/article/info:doi/10.1371/journal.pone.0006595>.
Mader, Sylvia S. "Darwin and Evolution." Concepts of Biology. Dubuque, IA: McGraw-Hill,
2009. 242-61. Print.
Mader, Sylvia S. "Speciation and Evolution." Concepts of Biology. Dubuque, IA: McGraw-Hill,
2009. 262-81. Print.