ABSTRACT
Genetics and livestock production. F. W. DRY (1938). Department of
Science & Industrial Research, New Zealand, Bulletin No. 64.
Introduction.—Genetics is the science of the internal factors that direct development.
It deals with the control from within, as contrasted with influence from without. A
horse is caused to be bay instead of black by an inborn factor handed down from at least
one parent. A blue-eyed man has eyes of that colour because he has received from both
parents something which determines that eye colour instead of brown. Moreover, if
your children have eyes destined, through inherited make-up, to be blue, blue they will
remain in any conditions in which children are raised.
On the other hand, as is obvious at sight, a young pig may receive any sort of prize-
winning, profitmaking genetic endowment, but let the air-supply be cut off for a very
short time and there is no fulfilment of that bright promise. A pig may inherit a capacity
for rapid growth, but without material suitable in quantity and composition supplied
through the mouth he does not grow.
In one sense we may call the inborn supreme. Equally may we argue that food and
surroundings are all-important. That which comes from within and that which comes
from without are both vital, and your personal preference will lead you to exalt genetics
more than nutrition, or the converse.
Thus early is it well to emphasize how perpetually and tantalizingly genetic and non-
genetic forces interact ? It is often very difficult to apportion credit and blame. The
disentangling of what is inherited and what is imposed from the outside is often far from
easy, and this is a difficulty of which livestock research workers are perhaps more acutely
aware than pure scientists.
Genetics is the science which seeks to explain the resemblances and differences be-
tween related individuals. One polled bull sires nothing but polled calves. Another
polled bull sires some horned calves. This is an example of a simple problem in the
genetics of livestock. Although many breeding problems are less clear-cut and more
complicated, it is well to put the position in perspective by acknowledging that our study
of heredity means in practice the study of the modes of inheritance of minor differences.
Calves, of sorts, we take for granted, and heifers that give some milk ; but to get
much milk from many animals we have to win it. One way of doing this, on the relative
importance of which it is seemly to be hesitant in staking a claim, is to explore and exploit
the mechanism of heredity.
Can genetics help livestock breeding ?
In matters of detail, genetics, as yet, can do little for the livestock breeder.
Things
have not proved as simple as was hoped just after the rebirth of Mendelism at the begin-
ning of the century. In due course will be set forth, convincingly enough, the limitations
to the application of present-day genetics to livestock breeding.
In matters of principle, on the other hand, genetics can speak with helpful autho-
rity. Especially can guidance be offered on broad breeding plans ?
The risks and possible gains of inbreeding can be assessed, and the value of pedigree
is exposed to dispassionate judgment in terms of genetic units instead of blue blood.
Bateson, the pioneer British geneticist, said in 1900 : ' The exact determination of
the laws of heredity will probably work more change in man's outlook on the world, and
in his power over Nature, than any other advance in natural knowledge that can be fore-
seen.' Some twenty years later Crew underlined, as the chief service of genetics to the
breeder, the introduction into breeding practices of a new point of view. This new view-
point, he said, must have far more beneficial effects than could any new method of breed-
ing that might be devised. Since then the worth of the new outlook has been stressed
repeatedly by eminent men, geneticists interested in livestock, or animal husbandmen
interested in genetics.
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