Forum—New Ways for an Ancient Science
Long before the world knew of science in the modern sense, there was
husbandry--the scientific control and management of a specified branch of
farming--at least in the production of livestock.
Remains of domesticated cattle dating to 6,500 years B.C. have been found in
Turkey, but some experts say domestication of cattle may reach back 100
centuries. And wherever there are domesticated livestock, there is someone
who's worrying and thinking and planning to improve those animals'
That's because, for the livestock producer, reproduction means paydays.
Whether the end commodity is meat or milk--or muscle power for the farm--all
the hard work and tender care ultimately come to naught if the herd doesn't
For a function that animals have long been doing naturally, breeding can be
remarkably fraught with difficulties. Big bulls can mean big, strapping
calves--but that can also translate to calving difficulty.
And though twin calves would appear to be a double payoff, more than a third
of calvings involving twins need human assistance for a successful outcome,
compared with only 15 to 20 percent of single-calf births. According to
Agricultural Research Service scientists
at the U.S. Meat Animal Research Center at Clay Center, Nebraska, cows carrying
multiple calves may take longer to rebreed under typical production systems.
That's because the fetuses don't leave enough room in the cow's body cavity for
a full stomach of the normal low-energy diet needed to attain the physical
condition to rebreed quickly.
To improve the livestock breeding odds for agricultural producers, ARS
scientists have been pushing the edges of scientific knowledge for years.
One of their most remarkable advances of recent times was development of
technology at Beltsville, Maryland, that makes it possible to sort livestock
sperm based on their chromosomal content--X versus Y. Y-chromosome sperm result
in male offspring, while X-chromosome sperm promote females.
Why would farmers care about gender, as long as their herds get bigger?
For the dairy farmer, milk's the thing--and a cow that delivers a male calf
has paid for her year of feed and veterinary care with an animal that's not
going to contribute a drop to the dairy's milk output. Beef farmers, on the
other hand, are more likely to want male calves because, pound for pound, males
grow faster than females on the same amount of feed.
Recently, ARS scientists at Beltsville announced advances in the
cryopreservation of pig embryos--a major step forward in making swine with
important genetic traits available to breeders worldwide.
The meat industry has been routinely cryopreserving embryos of various
livestock species--especially cattle--since the mid-1980s. But conventional
freezing methods won't work for pig embryos, which are extremely sensitive to
slow cooling below temperatures around 59oF. As they cool, pig
embryos undergo physiological and structural changes that leave them incapable
of normal development.
So ARS scientists are using a rapid cooling process called vitrification
that is thought to outrace the damaging effects of slow cooling. They have
increased the cryopreserved pig embryo survival rate to more than 80 percent in
the laboratory. [See "Vitrification Keeps Pig Embryos Viable,"
Agricultural Research, March 1998, pp. 19-20.]
Up-to-date information is crucial for helping producers get the best results
from their livestock breeding efforts. That's why ARS scientists at Beltsville
recently doubled the frequency of their reports evaluating dairy breeding
animals. The reports show which have outstanding milk yield, milk composition,
and other valuable traits. That's vital news for farmers as well as businesses
specializing in artificial insemination and embryo transfer. Thanks to this
increased reporting from ARS, dairy farmers can now pinpoint the best bulls and
calves 3 months sooner.
At Clay Center, ARS scientists have reported findings from a 4-year study
that indicate cattle producers can pay particular attention to birthing ease
when selecting breeding animals, without giving up larger calves later on. In
the study, calving assistance was required 24 percent less frequently among
young cows selected on the basis of ancestral records for calving ease dating
back to 1978. One good indicator of calving ease: lower birth weights of
calves. But while the average birth weight of calves born to easy-calving
2-year-olds was 6.6 pounds lighter than calves from unselected breeding lines,
yearling weight wasn't affected, the scientists report.
As the past year's headlines about Dolly, the cloned Scottish sheep, have
proved, advances in reproductive technology are big news. ARS scientists
nationwide are working hard to turn their reproductive research advances into
"news you can use" for America's livestock producers.
Caird E. Rexroad, Jr.
Associate Deputy Administrator
Animal Production, Product Value, and Safety
"Forum" was published in the July
1998 issue of Agricultural Research magazine. Click here to see this
issue's table of contents.