Agriculture Reference
In-Depth Information
This holds potential for reducing antibiotic use in milk-producing cows. Current
research on cows is directed toward reducing methane emission from their digestive
tract and the production of naturally low-fat milk.
Sheep have been produced to make pharmaceutical proteins. A transgenic ewe,
Tracy, produced a human protein called a-antitrypsin. This is a potential treatment
for cystic fibrosis. Unfortunately, she died in 1997. The first cloned animal was
Dolly, made from cells of Tracy. Another transgenic sheep was produced in 1996,
resulting in a small but significant increase in wool weight.
18
This was not enough
of an increase to warrant adoption by farmers but shows the potential.
Swine have received much attention because of their potential to grow organs for
transplant to humans. Some programs are concentrating on environmental effects of
large swine fattening farms. A major problem with large swine farms is that they
produce a lot of manure. This manure tends to be high in phosphorus. When this
manure is applied to crop fields, the phosphorus builds up and eventually leaches
into streams, an environmental hazard. A transgenic swine, dubbed Enviropig, has
been developed to reduce contamination from manure. Genes were inserted to enable
the swine to digest phytate, thereby eliminating the need to add phytase to their
rations and reducing phosphorus excretion by 60 percent.
19
By digesting phytase, the
animals have improved digestion and increased weight gain.
Another transgenic swine has been produced that makes increased amounts of
insulin-like growth factor I (IGF-I).
20
Production of more IGF-I stimulates muscle
production and results in a less fat, more lean animal. This extra lean animal was
worth an extra $6 at market prices in 2004.
Goats have also been the focus of transgenic modification. Most attention has been
focused on the production of pharmaceuticals such as malaria antigens and monoclonal
antibodies useful against cancer and AIDS (acquired immunodeficiency syndrome).
One unique application is the insertion of genes in a goat to produce spider fibers via
the milk.
21
Spider silk is extremely strong and flexible but cannot be manufactured
in large quantities. Unlike silk worms, spiders are not social creatures and tend to eat
each other when raised in groups. The transgenic goats produce spider fibers in their
milk, serving as a source of large quantities of spider fibers.
Transgenic fish have been developed in several countries. Research for development
of common carp is underway in Canada, rainbow trout in China, and striped bass and
various shellfish in Israel.
22
Many of these fish have an increased level of growth
hormone resulting in larger sized fish with increased feed conversion efficiency. A
major problem with moving these transgenic fish into production is the danger of
escapes. Some fish production facilities are basically cages in open water. Others are
raised in ponds adjacent to rivers and lakes. The risk of escape, and competition with
wild species, is great and little is known about their potential for multiplication in the wild.
12.7
FUTURE OF TRANSGENIC ANIMALS
At the current stage of development, the widespread use of transgenic animals in farm
production appears unlikely for many years. Their use has been adopted most readily in
applications where they are confined and where the products do not enter the food chain.
