The Y chromosomes of cattle have more genes and are more active than the Y chromosomes of other primates, according to Penn State researchers.
Understanding this discovery may help biologists better understand how cattle and other mammals evolved, as well as help animal breeders and farmers better maintain and enhance fertility in the cattle industry, said Wansheng Liu, associate professor of animal genomics, Penn State.
"Low fertility is a big problem for the dairy and beef industry," Liu said. "In the past 60 years, we paid more attention to milk, or beef production as a sign of herd success, but, even as milk production goes up, the animal's fertility goes down, which means it's time to pay more attention to male fertility now."
The researchers identified 1,274 genes in the male specific region of the bovine Y chromosome, compared to the 31 to 78 genes associated in the Y chromosomes of various primates. They also identified 375 novel noncoding gene families on the bovine Y chromosome, which are predominantly expressed in different stages of the testis.
The researchers analyzed the expression of the entire Y-linked genes as the bull aged, beginning soon after the bull's birth, during puberty and then again after the bull matured.
With this information, Liu said researchers can begin to understand the Y chromosome variation among male lineages in a cattle breed, and how genetic isolation and lineage-specific evolution resulted in the unique structure of the bovine Y chromosome.
"And, also, we can better understand how we can maintain genetic diversity in males," Liu said.
While most animal breeders and farmers select bulls based on physical characteristics, such as the size of the testis, researchers say understanding genetic diversity may give farmers another tool for managing their herds to improve male fertility.
The lineage of most of the bulls in current Holstein herds, for example, can be traced back over a hundred years to just a few bulls, Liu said.
While the potential impact of a limited number of bulls on fertility and the surviving of the breed as not been investigated, Liu said the findings of the bovine Y chromosome study is a significant contribution to the completion of the bovine genome project to further understanding of strategic breeding decisions.