Chinese Pigs Provide Insight to U.S. Swine Reproduction
Geneticist Gary Rohrer examines
Meishan pigs at the ARS Roman
L. Hruska U.S. Meat Animal
Research Center in Clay
Some say the animal is so cute. Others say it is the funniest-looking
thing they've ever seen. Either way, scientists in the United States
were delighted to obtain some for research in the late 1980s.
They are the Meishan (pronounced MAY-shawn) pigs of southern
China. They were always known for their large litters (15-16 piglets
compared to 10-12 for U.S. sows). Researchers from various countries
wanted to find out why this occurred.
The first Meishan pigs (and a few other Chinese-bred pigs)
were brought to the United States in 1989. After being quarantined in
Florida, they were delivered to ARS'
Roman L. Hruska U.S. Meat Animal Research Center (MARC) in Clay Center,
Nebraska; the University of Illinois; and Iowa State University.
Initially, researchers were interested only in the females;
male Meishans were brought along simply to help produce more females,
says MARC animal physiologist Joe Ford. Scientists hypothesized that
elevated levels of follicle-stimulating hormone (FSH) in Meishan females
were the cause of their large litters. But the researchers found that
FSH levels in Meishan females were similar to those in U.S. females,
says Gary Rohrer, a geneticist at MARC.
| After further study, they found
that Meishan females begin puberty in only 60 days, much earlier than
other pigs. They also ovulate more eggs per cycle and have a greater uterine
capacity to deliver more live piglets.
Eventually the researchers started studying the males
and learned some interesting facts about their reproductive organs,
too. The first important finding was that Meishan boars have five to
seven times more FSH in their blood than U.S. boars have, but their
testes were 40 percent smaller than those of U.S. boars.
The small size reflects the finding that Meishan boars
have fewer Sertoli cellsthe cells that develop spermin their
testes. So, fewer Sertoli cells means less sperm and, curiously, more
FSH. But how this mechanism relates to litter size or to other reproductive
traits is still under study.
ARS researchers also found that a gene (or genes) on the
X-chromosome affects the size of Meishans' testes, whereas in rodents,
testis size is more affected by the genes on the Y-chromosome.
Scientists like the fact that Meishans provide a new and
different model to investigate swine sperm production. Ford says that
since 75 percent of newborn pigs in the United States are produced through
artificial insemination, finding ways to improve sperm production is
important to improving the efficiency of U.S. pork production.
Pork products from Meishans taste as good as those from
conventional breeds, but Meishan meat has more fat. Ford says his laboratory
is using the Meishans only as an experimental model to compare to other
breeds of pigs. They are not very useful for crossbreeding, but their
unusual characteristics help scientists study biological processes in
traditional pigs.By David Elstein, Agricultural
Research Service Information Staff.
This research is part of Food Animal Production, an
ARS National Program (#101) described on the World Wide Web at http://www.nps.ars.usda.gov.
Ford and Gary A. Rohrer
are in the USDA-ARS Roman L. Hruska U.S.
Meat Animal Research Center, P.O. Box 166, Clay Center, NE 68933-0166;
phone (402) 762-4184 [Ford], (402) 762-4365 [Rohrer], fax (402) 762-4382
[Ford], (402) 762-4390 [Rohrer].
"Chinese Pigs Provide Insight to U.S. Swine Reproduction" was published in the November 2002 issue of Agricultural Research magazine.