Week 1: Genetics

Basic Genetics

·       Every living organism has DNA that composes genes. The genes control everything about the organism from how it looks to its biochemical processes. The environment also plays a role on how these genes are expressed. For more information check out the following page:

☀https://ghr.nlm.nih.gov/primer/basics/dna

Dairy Cow selective Genetics

·       For years dairy cows have mostly been selecting for milk production. With selecting for milk production there has been a decrease in fertility [1].

·       In the past 10 years there has been a sharp decline in fertility among Holsteins.

·       In 2013 German Holsteins-Friesians averaged only 2.7 lactations before they were slaughtered due to infertility. It was the same case for Red Holsteins with only 2.8 average lactations before slaughter [1].

·       Extensive research in the field of genetics is being done to pin point the exact gene(s) attributing to the dramatic drop in fertility [1].

Polled Genetics and Research

·       In the United States an estimated 80% of all dairy calves are dehorned. Only 25% of beef calves are dehorned. Dehorning is done to protect both animals and producers [2].

·       This is because a far greater number of beef cattle are what is considered polled or “hornless”

·       To traditionally introduce this polled trait into the dairy industry through cross breeding of different breeds would cause a reduction in milk production. New research is being done to introduce a polled gene without effecting milk production [2].

·       Genetic analysis has identified the genes responsible for the polled trait. This trait was introduced by somatic cell nuclear transfer and resulted in five live calves from two separate genetic backgrounds. At birth horn buds were not detectable. A PCR genetic analysis was performed and genetically confirmed that two of the calves were homozygous for the polled gene. At ten months of age when this study was published the calves were still phenotypically polled [2].

·       This research is establishing a possible alternative to creating polled dairy cows without out loosing milk production. Theoretically if you only alter the one gene needed to create a polled animal there should not be a loss in milk production[2].

References 2. Carlson, Daniel F., Cheryl A. Lancto, Bin Zang, Eui-Soo Kim, Mark Walton, David Oldeschulte, Christopher Seabury, Tad S. Sonstegard, and Scott C. Fahrenkrug. "Production of hornless dairy cattle from genome-edited cell lines." Nature Biotechnology 34.5 (2016): 479-81. Web.
 * 1) Müller, M., Rothammer, S., Seichter, D., Russ, I., Hinrichs, D., Tetens, J., . . . Medugorac, I. (2017). Genome-wide mapping of 10 calving and fertility traits in Holstein dairy cattle with special regard to chromosome 18. Journal of Dairy Science, 100(3), 1987-2006. doi:10.3168/jds.2016-11506