Female hormones in microgram amounts[1] accelerate fattening of cattle
and sheep. Before this method can be used on animals for human
consumption, however, it must be determined that no possible human
injury can result from any residue. With chemical tests the measurement
of such tiny amounts was impossible. Even with radioactive carbon-14,
doses of hormone 1000 times normal dosage were required before the
hormones in the flesh were measurable.
Fig. 4—Future high-producing milk cows may be selected as calves,
because of the measured activity of their thyroid glands. A minute
amount of iodine-131 is fed and within minutes has concentrated in the
thyroid. High concentration means high thyroid activity, which in older
animals means high milk production.
[Illustration: Iodine-131 fed ... concentrates in thyroid.]
Recently an isotope of hydrogen (tritium or H³) was linked to hormones,
and these were fed in normal amounts to cattle. Tests 90 days afterward
showed less than one part per billion in the meat, a big step toward
cheaper fattening of meat animals with hormones.
The use of tranquilizers has been proposed for reducing the customary
loss of weight in cattle being shipped to market. These chemicals, also,
are used in such minute quantities that residues could not be detected
except with radioactive tracers. Tritium can now be used by health
officials to study the effects of tranquilizers.