Figure 22 shows how animals differ in their retention of orally
administered zinc-65, as revealed by a whole body counter. It is
apparent that counters can be used to determine the differences in the
metabolism of different animal species used for research. Standard data
developed in this way can serve to reduce error that may occur if
results from one species are used for interpretation of data for another
species, such as man.
A University of Illinois project to breed meat animals with a high
lean-to-fat ratio has been aided by whole body counters. The tendency to
deposit fat seems to be inherited, and breeding stock with low fat
content can be selected, using “muscle-seeking” potassium-40 to show the
proportion of muscle in each potential parent. The Illinois counter is
unique in being large enough to examine an adult steer (Figure 23). A
similar counter at Cornell University has been used to study animals
infested with internal parasites, comparing them with parasite-free
animals. The counter revealed that a positive relationship exists
between the level of parasite infestation and loss of iron-59-labeled
blood from the digestive tract. The possibility of using this method to
evaluate parasite-killing drugs is being considered. The Cornell counter
is kept clean by covering the animals with plastic sheeting. The same
counter also can serve human patients, who are positioned in a wheeled
hospital stretcher. (See Figure 1D.)