Research Focuses on Lost Genetic Diversity

Intense genetic selection can have an unintended side effect -- the loss of genetic diversity.

There is one cattle breed, in particular -- Holstein -- that Chad Dechow and Wansheng Liu, researchers in Penn State's College of Agricultural Sciences, believe needs a bit of help on the genetic diversity front. Thanks to their research, calves recently born at Penn State may help to reintroduce valuable genetic variance.

"If all cows were genetically identical to each other, then there would be no opportunity to select for cows with improved performance," said Dechow, associate professor of dairy cattle genetics in the college's Department of Animal Science. "Little to no genetic diversity makes cattle more susceptible to disease and vulnerable to environmental changes."

And, because Holsteins -- known for their distinctive black-and-white markings -- produce more milk than any other dairy breed, their health and well-being is important to humans' health and well-being.

"Milk is important for good health," said Liu, associate professor of animal genomics. "The efficient production of milk from healthy and fertile cows improves society because we can obtain milk at a reasonable cost and still be confident that farmers are maintaining high levels of animal welfare."

Though the Holstein breed dates back 2,000 years to the Netherlands, these cattle are relatively new to America -- the first Holsteins were brought to the country in the mid-1850s by a Massachusetts breeder named Winthrop Chenery. He bought a cow from a Dutch ship owner who had used it to provide milk for his crew. It wasn't long before Chenery was importing Holsteins from Holland because of their exceptional milk production.

Dechow and Liu wanted to know more about the breed's history, so in 2014, they teamed with graduate student Xiang-Peng Yue to trace the ancestry of Holsteins in America. Through this research, they learned that nearly all male Holsteins alive today can be traced back to two bulls from the 1960s: Pawnee Farm Arlinda Chief and Round-Oak Rag Apple Elevation.

"Artificial insemination was really beginning to take off in the 1960s," Dechow said. "Today, three-quarters of Holsteins result from artificial insemination. Even those born from a 'natural mating' usually have a grandfather that was an artificial insemination bull. The widespread use of artificial insemination is what allowed these two bulls to have such a large impact."

There is one additional bull from the 1960s that still appears in the male lineage of a handful of sires -- a bull born at Penn State named Penstate Ivanhoe Star. He and Pawnee Farm Arlinda Chief share a common male ancestor born in 1890 called Paul De Kol.

While these bulls were responsible for many offspring in the country, they were not the only bulls used for breeding during that era. In fact, thousands of sires from that era have descendants through female lineages. However, over the course of time, the other sires' lines failed to thrive for several reasons. Penstate Ivanhoe Star is an example.

"He carried two lethal genetic recessives. Once those defects were discovered, many of his male descendants were removed from the population so that the defects would not be propagated so widely," said Liu, a leading authority on bovine Y-chromosome variations.

This narrowing of the genetic base is not a good thing for Holsteins because it leads to inbreeding, which has the potential to cause genetic defects, poor health and poor milk production.

The researchers then set out on what they thought would be a difficult task -- finding descendants of other lineages that existed in the 1960s. Their first call was to the National Animal Germplasm Program in Fort Collins, Colorado, a repository under the United States Department of Agriculture that collects reproductive samples from agriculturally important species. Dechow, who serves as the dairy species chair for the program, thought it would be a good place to start.

And, he was right -- as luck would have it, the repository recently had procured semen from two lost Holstein lineages from the University of Minnesota and ABS Global. The samples were used to fertilize a dozen embryos from genetically elite Holstein females owned by one of the nation's largest dairy genetics companies -- Select Sires Inc. Embryos from the first lineage were implanted in surrogate heifers at Penn State's dairy farm last summer.

The first group of bouncing baby bovines -- three males and three females -- were born in April, all healthy and full of spunk. Their growth and health is being tracked by animal science doctoral student Han Longfei to determine how they compare to calves from other lineages. An additional 10 calves from the second lost lineage are expected to make their appearance later this year.

With the calves are, from left, Chad Dechow, associate professor of dairy cattle genetics; Lydia Hardie, postdoctoral scholar; and Han Longfei, doctoral student. Image: Amy Duke

"After several years of planning, seeing those first calves was exciting," Dechow said. "The team really didn't know what they would look like, and the first calf's white face with white eyelashes was the first thing that we noticed. Of course, how they look is the least important aspect of the project, and what we really hope is that the lost genetic diversity they represent eventually will be reintroduced to the Holstein population."

Liu agreed, adding, "We are very happy to see the calves and bring back these lost lines. These calves will further advance our research in cattle genetics, and with that knowledge we can continue to improve genetic diversity, the health of Holsteins and milk production."

Dechow and Liu thanked partners on the project, including Penn State's College of Agricultural Sciences, the National Animal Germplasm Program, Trans Ova (which produced the embryos), Select Sires Inc., the University of Minnesota and ABS Global. Perhaps the most important partners, Dechow noted, are the management team and employees at the Penn State dairy farm who care for the calves every day.

"Many people and companies have provided resources to help resurrect these lineages, so it really has been a broad-based industry effort that we believe will enhance the breed's diversity and make dairy breeders better stewards of our genetic resources," Dechow said.

http://news.psu.edu/story/467412/2017/05/08/research/recovering-lost-genetic-diversity-holsteins-focus-professors