An Ounce of Prevention Equals Pounds of
ARS microbiologist Louis Gasbarre (center) and soil scientist Bill Stout
(right) discuss treatment protocols for brown stomach worms in cattle with
dairy farmer Larry Lohr.
This coming spring, Pennsylvania dairy farmer Larry Lohr will treat his cows
just once with a wormer. That should hold them until the end of the grazing
season, when he brings them back in from pasture, says
Agricultural Research Service
parasitologist Lou Gasbarre. Then, Gasbarre recommends one more treatment . . .
just for safe measure.
Even with the extra treatment, it will be three fewer than Lohr gave his
cows in 1996 to battle the brown stomach worm--Ostertagia ostertagi.
This roundworm makes its home in the stomachs of dairy and beef cattle in
temperate regions worldwide. Ostertagia accounts for 80 to 90 percent of
the worm problem in U.S. beef and dairy cattle, costing the industry more than
$2 billion annually. The most common estimates put producer costs at about $20
per animal per year, says Gasbarre, who is with ARS' Immunology and Disease
Resistance Laboratory in Beltsville, Maryland.
Thanks to Gasbarre's recommendation to take a prophylactic approach to the
worm, Lohr's cows kept a 3-pounds-per-day increase in milk production last
summerthat's 6 percent more milkcompared to the same months in 1995
and 1996. And they had "significantly higher body weights," says
Those increases in milk production and body weight also had an environmental
benefit. Nitrogen that went into the increased animal production wasn't
excreted in urine onto the pasture, where a large portion of it would have been
susceptible to leaching into the groundwater.
Lohr is among the first of a growing breed of dairy producers trying to
increase their net income by letting cows feed themselves during the growing
season rather than cut, dry, and store the feed and then serve it to them
later. Since he began pasturing his cows 12 years ago, Lohr says he has had
"real good success. My annual feed costs dropped about $150 per cow."
And it has increased efficiency so much he has been able to increase his herd
from 45 to 100 cows.
When Lohr set up the intensive rotational grazing system, no one advised him
how to keep the brown stomach worm from nibbling into his profits. Although he
routinely treated his cows with a wormer during the grazing season, milk
production increased after the treatments but then dropped again, he says.
Cross-section of one brown stomach worm larva looped inside a gastric gland.
Magnified about 800x.
Lohr suspected that worms might be causing this roller coaster effect. He
mentioned the problem at a meeting at the Pennsylvania State University Center
for Grazing Research and Education, where he represents dairy producers. Fellow
center member, ARS soil scientist Bill Stout, contacted Gasbarre about the
Together, the two scientists applied for and received a grant from the
Sustainable Agriculture Research and Education Program, known as SARE, for a
3-year study of Lohr's farm. Funded by USDA to encourage low-input production,
SARE is administered by the University of Vermont for projects in the
During the 1995 and 1996 grazing seasons, Gasbarre observed Lohr's
operation. He also mixed worm-free calves raised at the Beltsville center in
with Lohr's cows in order to measure infection rates. Lohr has 19 fenced,
1-1/2-acre paddocks on which he rotates the cows daily.
With this scheme, the animals eat the grass when it's most nutritious. But
it also fits into the worm's life cycle perfectly for keeping infectious larvae
at high levels, says Gasbarre.
"The eggs take 10 to 14 days to become infectious after they are passed
in the feces. Normally, cows avoid grazing near feces, where the parasites are
heaviest. But in heavily grazed paddocks, like this farm, cows eat
everything," he says. "There are no tufts left."
With a 19-day rotation, the cows were grazing each paddock shortly after the
eggs that had been deposited in the previous rotation developed into infectious
larvae. The animals kept becoming reinfected until the worms built up to a
critical leveldropping milk production and animal weights.
Gasbarre says some scientists and veterinarians are not convinced that worms
reduce milk production, animal weight, or reproduction in females. They think
cattle have enough immunity to suppress infection.
But the evidence from Lohr's farm belies that notion.
Gasbarre recommended that Lohr treat his cows in the spring right after they
had made their first rotation through all 19 paddocks. That way, any larvae
that survived the winter would be picked up and killed. "The cows act as
big vacuum cleaners," he says.
"They don't pass eggs for 17 to 20 days after they've been infected. By
treating them after 19 days in contaminated paddocks, it kills off the worms
before the eggs can pass out and recontaminate."
And the theory worked, judging by the worm-free calves that Gasbarre mixed
in with Lohr's herd throughout the study.
To estimate the number of brown stomach worms in a pasture, researchers place a
worm-free calf on grass for a measured length of time, then check for parasite
eggs in its feces.
Before treatment, the calves passed the same number of eggs as in the
previous year. By the end of August, only about 10 percent of the calves had
any eggs in their feces at all. And these had only one or two, says Gasbarre.
"Instead of a roller coaster effect," says Lohr, "we've
evened out our milk production."
In 1995, Lohr wormed his cows five times. Last year, under the prophylactic
approach, he wormed them three times. This year, it will drop to two
treatmentsone in the spring, after the first 19-day rotation, and another
at the end of the grazing season.
Lohr will have to continue treating his cows each spring to retard larvae
build-up, Gasbarre says. But pasture levels are so low now that the second
treatment is just for insurance. "It's more expensive to clean up the
problem than to prevent it.
"We don't want the animals to never see a parasite," he adds.
"They need to build up some exposure to stimulate their immune systems.
But you want to keep the exposure below a level where the parasites overwhelm
the immune system."
Gasbarre emphasizes the importance of considering health issues when setting
up animal management programs.
"Lohr would not have gotten to this point if he had been advised to
manage his pastures for parasitesusing prophylaxis," he says.
He recommends that producers treat their animals once, then watch the
weather and give follow-up treatments accordingly.
"The larvae thrive in cool, wet weather. A prolonged dry spell will
slow them down, especially combined with hot weather," says Gasbarre.
As part of the funding for this study, the Northeast SARE review committee
wanted to know how many other producers in the region felt they had a worm
problem and what management practices might be contributing to it. Stout and
Gasbarre developed a questionnaire that was sent to 2,000 livestock
producersfrom Maine to Maryland.
Nearly 800 responded, and the researchers are still analyzing the data.
Preliminary indications are that 40 percent of the respondents didn't know if
worms were a problem on their farm. One-third reported worms to be a moderate
problem, while a little more than one-quarter didn't think they had a worm
problem. Lohr is now among those without a problem.
"It proves the system will work if done properly," he says.
"If farmers have a problem, they should go after an answer."By
AgriculturalResearch Service Information Staff, 6303 Ivy Lane, Greenbelt,
Maryland 20770, phone (301) 344-2861.
Louis C. Gasbarre is at
the USDA-ARS Immunology and Disease
Resistance Laboratory, Bldg. 1002, 10300 Baltimore Ave., Beltsville, MD
20705-2350; phone (301) 504-8509, fax (301) 504-5306.
William L. Stout is at the USDA-ARS
Pasture Systems and
Watershed Management Research Laboratory, Curtin Rd., University Park, PA
16802-3702; phone (814) 863-0947, fax (814) 863-0935.
"An Ounce of Prevention Equals Pounds of Milk" was
published in the January 1998 issue of Agricultural Research magazine. Click
here to see this issue's table of contents.