Explanation Of Gene Action As Related To Physiological

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Wyatt: I would llke to ask Dr. Lush how you proceed in the case of
mortality in chickens, for example. How do you go about finding one of
these populations that you can use for a tester? How do you know how far
this population is above the threshold and so forth?
Lush: I expect there are some in the room that can answer that better
than I. Maybe some of you think you haven't much difficulty in finding a
population with low vitality!
Seriously, the vitality must be above a certain minimum to keep them
going, does it not? You could not have a tester population in which all
died off before reproduction. They must have a certain amount of vitality
to keep them going.
Incidentally, you do not need a tester strain badly, as long as the
mortality in the stock you are trying to improve is much above thirty per
cent. Then mass selection and progeny testing can give about as much help
as you can use. Even when you get the mortallty below thirty per cent,
progeny testing and family or sib-testlng can help quite a bit until you get
mortality on down toward _wenty or even fifteen. _hen the effectiveness of
these begins to taper out. It does not_go completely to zero, but progeny
tests and slb-tests diminish fast in their effectiveness when your mortality
falls much below twenty per cent. Hence, I would not worry much about finding
a tester stock until the mortality in my own stock was down under fifteen.
If I ever got it under ten, then I would just about have to find a tester
stock with high mortality.
How I would find it, I am not sure. Maybe, if I did not have it in
my own flock, my neighbors might sell me a stock which was low enough in
vitality.
Wyatt: Well, if you are going to measure this tester Just by the incidence
of mortality in the tester, say that that is below the threshold,
_hy can't you just measure the incidence of mortality in the flock you are