Bull's Y chromosome may aid herd fertility

Bull's Y chromosome may aid herd fertility

*Krissa Welshans holds a bachelor's degree in animal science from Michigan State University and a master's degree in public policy from New England College. Welshans has long been involved in agriculture and has worked with numerous agricultural groups, including the Animal Agriculture Alliance.

PENNSYLVANIA State University researchers have discovered that the Y chromosome of cattle have more genes and are more active than the Y chromosomes of other primates.

The finding 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, Wansheng Liu, associate professor of animal genomics, said.

"Low fertility is a big problem for the dairy and beef industry," Liu explained. "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, whereas various primates have 31-78 genes associated in the Y chromosomes.

They also found that the genes in the bovine Y chromosome were much more transcriptionally active compared to other mammals. Transcription is the first step of gene expression when DNA is copied. In this process, the cell produces messenger RNA that copies the genetic information from the cell nucleus to serve as a template for protein synthesis.

In addition to the 1,274 genes that take part in coding proteins, the researchers also identified 375 novel non-coding gene families on the bovine Y chromosome that are predominantly expressed in different stages of the testis.

According to Liu, most researchers believed that the Y chromosome of cattle would be similar to the Y chromosome of other mammals, which does not have a large number of genes and is considered mostly transcriptionally inactive. Liu said the Y chromosome, which was once similar to the X chromosome, evolved predominantly for testis development and male fertility.

Currently, the gene content and transcription pattern of the bovine Y chromosome is the only non-primate Y chromosome that researchers have studied in depth, according to Liu.

"These findings directly contradict the traditional view that the Y is largely heterochromatic with a paucity of genes and transcription activity," said the researchers, who released their findings in the current online issue of Proceedings of the National Academy of Sciences.

The X and Y sex chromosomes in most mammals began to diverge after 160 million years of evolution. However, Liu said genetic isolation and lineage-specific evolution resulted in the unique structure of the bovine Y chromosome, which determines the gene content and transcriptional activity of the Y chromosome among cattle.

With little knowledge of the roles the Y chromosome genes play in fertility, most animal breeders and farmers select bulls based on physical characteristics, such as the size of the testis. Because the Y chromosome is present in males only, the Y-linked testis genes that govern male fertility are passed directly through the male line.

Liu hopes understanding genetic diversity may give farmers another tool for managing their herds to improve male fertility. As an example, Liu pointed out that the lineage of most of the bulls in current Holstein herds can be traced back more than 100 years to just a few bulls.

The potential impact of a limited number of bulls on fertility and the survival of the breed has not been investigated.

"We can begin to understand the Y chromosome variation among male lineages in a cattle breed, and also, we can better understand how we can maintain genetic diversity in males, particularly in a breed, such as Holsteins, that has been extensively selected and is almost all based on artificial insemination in reproduction," Liu said.

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. They analyzed complimentary DNA from the bull testis. Complimentary DNA is a form of DNA that is synthesized from a messenger RNA template.

"The bovine genome sequence was published in 2009," Liu said. "As that genome sequence was from a female, the findings of the bovine Y chromosome study are a significant contribution to the completion of the bovine — male and female — genome project."

 

Drylot cow production

North Dakota State University researchers are studying drylot versus pasture cow/calf beef production systems and found that drylot beef cow production can be a viable alternative for producers.

The researchers are in the middle of a six-year study that compares drylot and pasture cow/calf beef production systems.

"We are conducting this study because pasture and rangeland for grazing beef cattle are diminishing in some parts of the county due to drought, land taken out of pasture and hayland for more profitable crop production, labor shortages and other factors," said Vern Anderson, animal scientist at the North Dakota State Research Extension Center in Carrington, N.D., who is leading the research.

Preliminary results of the study suggest that spring-calving beef cows can be managed in a drylot system, but careful herd management and integration with crop production are needed for competitive biological performance and economics.

For the drylot system part of the study, the researchers confine cow/calf pairs to a feedlot pen during the summer until crop residue is available for cows to graze in the fall. The drylot calves are weaned at that time. Pasture calves are weaned in late October, and cows graze the native grasses until about Dec. 1, when they are returned to wintering pens.

Lactating drylot cows are fed a variety of feeds, with rations balanced to meet or exceed requirements. Feeds used include crop residues (corn stover, wheat, barley and pea straws) and multiple co-products (distillers grains, wheat midds, barley hulls and others), plus some corn silage and grass hay. The two groups of cows are wintered in separate pens but are fed the same basic ration.

The study found that the drylot calves were 46 lb. lighter than pasture calves that were weaned in late September. Creep grazing can improve calf gains and reduce creep feed consumption. Steers from the two groups were equal in weight when sent to market on the same day after feedlot finishing."

Key findings from the study so far include:

* Cow weight varied more in drylot cows during the year and from year to year.

* Pregnancy rates were similar for both groups of cows after three years of the study.

* More drylot cows were assisted at birth than pasture cows (14% versus 5%).

* Feed costs were higher for drylot cows during lactation compared with cows on pasture — $1.72 versus $1.00 per head per day, respectively — but drylot cows spent fewer days on high-cost diets.

The researchers reported the following findings related to cost:

* Annual feed costs were $519 per cow for drylot cows and $457 per cow for pasture cows. Extending crop aftermath grazing can reduce drylot cow feed costs and distribute manure.

* Creep feed costs were $84 per calf for drylot calves and $101 for pasture calves, which consume creep feed for more than four weeks longer than the drylot calves.

* Manure from drylot cows was valued at $60 per head for nitrogen, phosphorus and potassium fertilizer.

"The net annual production cost was $580 per cow for drylot and $557 for pasture cows," Anderson said. "The drylot cost equates to $43-per-acre pasture rent, with six acres per cow for the six-month grazing period from late May to early December. The crop enterprise gets paid for stover and other feeds, enhancing crop/livestock integration."

The weaning weight in late September was 571 lb. for drylot calves and 617 lb. for pasture calves. Considering the costs of production, this equates to $1.02/lb. of drylot calf and 79 cents/lb. for pasture calves weaned in late October at 707 lb.

"The critical factors for drylot production are providing the right nutrition at the right time to keep feed costs down," Anderson said. "This means sourcing low-cost or high-nutrient density feeds at competitive prices. Feed quality is critical, especially from calving to the end of the breeding season as drylot cows perform based on what is placed in the bunk."

Volume:85 Issue:33

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