Animal Health Care -
BIO "Animals, People, and Biotechnology." Washington, D.C.:
Biotechnology Industry Organization, 1992.
New Health Products for Farm Animals
Animal diseases cost U.S. agriculture $17 billion each year, according
to the Congress Office of Technology Assessment. To help prevent
these losses, animal scientists are using biotechnology to develop an
array of products to diagnose, treat, and prevent disease in farm
An area where animal biotechnology has already had a profound impact
is diagnostic testing. Many animal diseases are difficult to
diagnose. A veterinarian often has to wait hours or days for
laboratory results to confirm a diagnosis. In the meantime, the
veterinarian must either withhold treatment or risk using an
Using biotechnology, scientists are developing fast, accurate
diagnostic tests for many of the most common farm animal diseases. In
some cases, a veterinarian can conduct the diagnostic tests right on
the farm and immediately start the best therapy.
Many of these new tests use
monoclonal antibodies. Antibodies are
proteins an animal's immune system produces in response to invasion by
bacteria, viruses, or parasites. Each kind of antibody binds
specifically with a characteristic part of a particular kind of
Scientists make monoclonal antibodies by fusing two kinds of cells.
One is an immune system cell that produces antibodies, which bind to
part of a particular disease-causing microbe; the other is a cancer
cell. The cell that results from the fusion inherits from the immune
system cell the ability to produce antibodies, and from the cancer
cell the ability to reproduce indefinitely.
This new hybrid cell, or hybridoma, acts as an antibody factory. The
antibodies are called monoclonal because they are produced by
identical "clones" of the original hybridoma - all will bind with the
identifying structure on the surface of the microbe in question.
One application of monoclonal antibodies is as a test for brucellosis
in cattle. This bacterial disease often causes cows to abort
pregnancies, and it can be spread to farmers and people who drink milk
from infected cows.
Vaccines protect pregnant animals from abortion, but vaccinated cows
may become carriers of the disease. Conventional diagnostic tests
cannot distinguish between the disease-causing microbe and the
vaccine, which is made from the microbe. Thus, these tests cannot
help the farmer determine which animals are carriers of the disease
and which are not.
But diagnostic tests using monoclonal antibodies are so specific, they
distinguish between cattle that carry the disease-causing bacterium
and those that carry only the vaccine. With the aid of these new
tests, farmers can isolate carriers to prevent the spread of
Diagnostic tests are not just for diseases. A monoclonal antibody
test to detect pregnancy in animals is so simple that a farmer can
read the test right on the farm.
Monoclonal antibodies are also used in a test to detect a disease
called scours in piglets and calves. Scours is a bacterial disease of
newborn animals that causes diarrhea. Many of the afflicted animals
die of dehydration. By providing quick, accurate diagnosis, the
monoclonal antibody test for scours permits immediate administration
of therapy. The therapy for scours in calves is also based on
monoclonal antibodies. Infected calves are fed monoclonal antibodies
that coat the offending bacteria, preventing the microbes from causing
Some other therapies for animal diseases are based on recombinant
DNA technology. Genetic engineering allows scientists to insert
one or more new genes into an animal, plant, or microbial cell. In
developing treatments for an animal disease, for instance, an animal
gene is inserted into a microbe or an animal cell that can be grown in
a laboratory culture. The inserted gene is one that produces a
natural disease-fighting protein. The microbes or animal cells become
minute factories, producing large quantities of the therapeutic
For example, genetic engineering is used to produce interferons and
interleukin-2, natural proteins that fight viruses. Veterinarians
long have used antibiotics against bacterial diseases, but they have
had few drugs to treat viral infections. Interferons and
interleukin-2 not only kill viruses directly, they also stimulate the
animal's immune system, improving the immune system's ability to fight
One target of research regarding interferons and interleukin-2 is
shipping fever, a disease of cattle caused by several viruses
infecting an animal simultaneously. Although the animal's immune
system normally keeps the viruses in check, outbreaks of the disease
may result from stress during transport to feedlots or market.
Shipping fever costs the beef industry more than $250 million a year.
Injections of interferons or interleukin-2 before shipping may help to
augment the cattle's natural immunity and prevent shipping fever.
Better Vaccines to Prevent Disease
In addition to producing new diagnostic tests and therapeutic
proteins, animal scientists are using biotechnology to develop
vaccines to prevent disease. A safe, effective vaccine for swine
pseudorabies, a fatal herpes-virus, is already in use. An advantage
of the swine pseudorabies vaccine, and other vaccines made through recombinant
DNA technology, is that they use only a small portion of the
original microbe. Conventional vaccines use killed or weakened forms
of the disease-causing microbe. Sometimes, when the microbes are not
completely killed or sufficiently weakened, a conventional vaccine may
cause the disease it was supposed to prevent. Disease-causing genes
are not included in the genetically engineered vaccines. Therefore,
the recombinant vaccines build up the body's immunity without the risk
of causing disease.
Another advantage of recombinant vaccines is the speed with which they
can be developed. "Conventional vaccine development can take 20 or 30
years, maybe even 100 years," says Karen Jacobsen, D.V.M., University
of Georgia College of Veterinary Medicine. "This is one reason why we
don't have vaccines for a lot of animal diseases today. "
Recombinant vaccines are being developed for foot-and-mouth disease, a
highly contagious viral disease that infects cattle, sheep, and other
animals. Although this disease has been eradicated in North America,
it still causes substantial livestock productivity losses elsewhere,
particularly in developing countries. Infected herds must be
slaughtered, and contaminated ranches must be left idle for months to
prevent new outbreaks of the disease.
Conventional foot-and-mouth vaccines are made by weakening the virus
that causes the disease. These vaccines sometimes revert to the
virulent state, and they have caused outbreaks of the disease in
Europe. The foot-and-mouth vaccine made with biotechnology cannot
cause the disease because, as in other biotech vaccines, the
disease-causing genes have been removed. The biotech vaccine does not
need to be kept cold and, therefore, can be used in developing
In addition to being used in treating swine pseudorabies and
foot-and-mouth disease, recombinant
DNA technology is being used to develop vaccines against dozens of
livestock and poultry diseases, such as scours and a variety of
respiratory disorders. Some vaccines may be injected into eggs so
that chickens are immunized before they hatch.
Most vaccines protect against viral or bacterial infections, but using
genetic engineering, researchers in New Zealand and Australia have
developed a vaccine against a parasitic disease. Farmers must destroy
the meat from sheep infested with a species of tapeworm common in
those two countries. The new vaccine, which protects sheep from the
tapeworm, may save farmers millions of dollars annually.
Proteins for Animal Nutrition
Natural proteins called somatotropins, or growth hormones, help
animals convert feed into muscle or milk. Using recombinant
DNA technology, scientists have been able to develop bacteria that
produce commercial quantities of somatotropins. They have found that
administering small additional amounts of these proteins to animals
helps to increase the animals' efficiency of feed conversion, thereby
saving the farmer money.
Porcine somatotropin (PST) may help improve human health, as well as
lower the farmer's cost of production. PST improves feed efficiency
in hogs by 15 to 20 percent. It also reduces fat deposition, allowing
PST-treated hogs to provide consumers with leaner cuts of pork. The
ability to produce lean pork has enormous implications for improving
human health by reducing dietary fat and cholesterol.
Another growth protein, bovine somatotropin (BST), is being
administered to make dairy cows more efficient, thereby lowering the
dairy farmer's costs. Regular administration of small amounts of BST
increases a cow's milk yield by 10 to 25 percent. Although feed
intake also increases, this feed increase is proportionately less than
the increase in milk production. Studies indicate that BST can
improve the milk-to-feed ratio by 5 to 15 percent.
Extensive laboratory testing has shown that the meat and milk of
treated animals contain no more PST or BST than the meat or milk from
untreated animals. Other tests have shown that these proteins do not
act on the human body, and therefore, they are safe to eat.
Nevertheless, the use of BST remains controversial. Testing is under
way to make sure that animals are not adversely affected by treatment
Another protein that can be administered to animals to increase feed
efficiency is called growth hormone releasing factor (GHRF). While
not a growth protein itself, GHRF causes the animal to increase
production of growth proteins.
Improved Animal Breeds
Long before anyone knew about genes or DNA, people were selectively
breeding animals to produce desirable traits, such as strength, feed
efficiency, and disease resistance. Selective breeding is a crude
technology, because each cross between two animals mixes hundreds of
thousands of genes, both desirable and undesirable. Recombinant
DNA technology is now making it possible for scientists to breed
animals with great precision. One or more new genes can be inserted
into an animal embryo without disturbing the rest of the animal's
genes. The resulting animal with the new gene or genes is referred to
as a transgenic animal.
Despite the differences in technique, the scientist using recombinant
DNA has the same objectives as the selective breeder: improving
efficiency, disease resistance, and other desirable traits. But recombinant
DNA provides a wider array of possible new traits, since
recombinant techniques allow animal scientists to insert genes not
only from the same or closely related species, but also from distantly
related animals, plants, and even microbes.
One possible application of gene transfer in animals is to develop
dairy cows that produce more nutritious milk. Bottle feeding human
infants with cow's milk is not an ideal substitute for breast feeding,
because cow's milk differs from human milk in some important
components. Scientists are looking for ways to transfer genes into
dairy cows that will enable the cows to produce milk that more closely
resembles human milk.
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