Beef and dairy producers who want to control twinning rates may soon get some help. Researchers have identified three regions of the cattle genome that contribute to an increased frequency of double ovulation in the animals.
“Our work has now confirmed the existence of at least one gene on cattle chromosome 19 that affects ovulation rate,” says Brian Kirkpatrick, a University of Wisconsin-Madison animal geneticist who led the study. “We also have strong evidence for genes with similar effects on chromosomes 5 and 7.”
Kirkpatrick, Becky Byla and Keith Gregory published their research in a recent issue of Mammalian Genome. Kirkpatrick and Byla are with the Department of Animal Sciences in the College of Agricultural and Life Sciences. Gregory is now retired from the USDA Meat Animal Research Center in Clay Center, Neb.
The frequency of twinning is typically about 1 percent in beef herds and about 4 percent in dairy herds. Although environmental factors and the age of cows both affect twinning, multiple births are in large measure under the control of genes, according to Kirkpatrick. His goal is to identify genes that increase double ovulation and twinning in cattle.
The research is leading to DNA tests so producers can accelerate the development of herds with a high or low frequency of twinning. Later this summer Kirkpatrick expects to offer producers the first DNA test to detect animals with a high frequency of twinning.
“Our new DNA test specifically identifies the form of chromosome 19 associated with high ovulation rate,” he says. Cows that test positive for that DNA have about a 10 percent chance of producing twins at each birth. The forms of chromosomes 5 and 7 that the researchers identified can increase twinning frequency by a total of another 13 percent.
Kirkpatrick knows that most producers aren”t interested in seeing more twins. Twins often create extra problems for cows during pregnancy and calving. Twin calves are more likely than single calves to be stillborn and weigh less at birth. Therefore, dairy producers might use the DNA test to avoid sires whose daughters are likely to give birth to twins.
But twins can increase profitability for beef producers who have the skills to manage the complications associated with twinning.
The low reproduction rate of beef cattle keeps beef production costs high, according to Kirkpatrick. For each pound of meat produced in a beef or broiler operation, it costs producers about three times as much to maintain breeding cows as breeding hens. A herd of beef cows that consistently bears twin calves could lower production costs by 20 percent or even more.
“Under the right system and with proper management, beef producers are finding that twins can be an advantage,” Kirkpatrick says. “Just how profitable twins might be is something producers need to evaluate based on their particular situation.”
According to statistics from the Wisconsin Department of Agriculture, Trade and Consumer Protection, the number of Wisconsin farms raising beef cattle increased from 10,000 in 1989 to 11,700 in 1999.
Kirkpatrick believes the state”s beef producers may have some advantages over their western counterparts when it comes to managing cows with twins. Producers who palpate or check pregnant cows with ultrasound can detect twins early and be better prepared during calving, he says. While checking for twins may be difficult for ranchers with herds spread over large areas, that”s seldom the case in Wisconsin.
For producers interested in more twins, Kirkpatrick publishes the Twinner Cattle Newsletter. He”s also working with producers to develop a public breed registry for cattle with a high twinning frequency. The North American Twinning Cattle Herdbook will maintain the performance and ancestry records of breed stock and be used to predict the twinning potential of animals, as well as other traits such as birth weight and yearling weight. The herdbook is the beginning of a new composite breed, Kirkpatrick says.
The researchers identified the location of genes associated with twinning by studying cattle from a twinning herd at the USDA Meat and Animal Research Center in Nebraska. The herd is a composite of many breeds, including many dairy cattle. Cows from that herd now bear twins about 50 percent of the time.
Producers who want a herd with a high twinning rate can purchase animals from the USDA herd or from breeders participating in the Twinning Cattle Herdbook. Kirkpatrick”s new DNA test will allow producers to check for the twinning trait in the cattle they buy or in calves produced in their own herds.
Individuals interested in Kirkpatrick”s Twinner Cattle Newsletter or the North American Twinning Cattle Herdbook can write to him at the Department of Animal Sciences, 1675 Observatory Drive, UW-Madison, Madison, WI 53706, e-mail email@example.com
To search for additional genes that increase ovulation, Kirkpatrick will be studying the offspring of a cow he recently leased from an Alberta farm. In her first four natural pregnancies that cow delivered three sets of twins, and quadruplets after her fourth pregnancy. While in Wisconsin she will produce a number of embryos before she”s returned to Canada, he says.
Although Kirkpatrick can improve twinning rate without knowing which genes are involved, he is working toward identifying them. Knowing the actual genes responsible for increasing ovulation will help explain why certain forms of those genes affect twinning.
Because the genomes of mammals are quite similar, Kirkpatrick will turn to the recently sequenced human genome for help in identifying the bovine genes responsible for twinning. He will compare sequences that increase twinning from bovine chromosomes with sequences from the corresponding human chromosome. The known genes on the human chromosome will provide clues to the identity of genes that might increase ovulation in cattle — such as genes that regulate hormone levels.
Kirkpatrick”s research was supported by state funding to the College of Agricultural and Life Sciences, federal grants from the USDA National Research Initiatives program, and Hatch funds from the College of Agricultural and Life Sciences.