Agriculture Reference
In-Depth Information
process, resistance to this disease had been lost. Within 2 years the maize breeding
industry was able to remove this susceptibility from their hybrid lines.
Conventional breeding of animals usually involves mating animals that have desir-
able visible traits or established production records. Livestock judging is an established
art in animal science programs. It enables trained persons to select animals for breeding
on the basis of their appearance. In the dairy industry, extensive production records are
kept of each cow during their lifetime. It is easy to select the most productive cows to
mate with a bull from a productive bloodline. Many farms have no bulls, relying
entirely on artificial insemination to upgrade their livestock bloodline.
An unconventional method of reproducing animals has been pioneered by Texas
A & M University. Normal practice consists of freezing semen of productive bulls to
continue their bloodline long after the death of the donor. An unusual animal was ident-
ified in Texas as being naturally resistant to brucellosis, tuberculosis, and salmonellosis.
All of these diseases can be passed to humans by unpasteurized milk, uncooked beef, or
simple contamination. Since this animal was naturally resistant to these diseases, it
could be raised with little or no antibiotics and still produce good beef. The problem
was that this animal was a steer. Steer 86 had been castrated before its unique
genetic makeup was discovered. There was no semen to preserve! It finally died at
the ripe old age of 21 years without producing any offspring.
In 2000 researchers succeeded in cloning steer 86 to produce a young bull named
86 Squared shown in Figure 12.6. 8 It has all the disease-resistant characteristics of steer
86 but will be able to donate semen for insemination of large numbers of cows.
The result will be the preservation and multiplication of this unique genetic makeup.
The long-term goal of the cloning steer 86 project is to reduce or even eliminate depen-
dence on antibiotics for beef production.
In some cases, naturally occurring traits in plants have been discovered that mimic
the traits of transgenic plants. Clearfield rice is an example. Clearfield rice varieties are
Figure 12.6. Angus bull 86 Squared. (Used with permission of Larry Wadsworth, Texas A&M
University.)
Clearfield is a registered trademark of BASF.
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