ABSTRACTS
253
To its offspring, as we know, the animal hands on only half its complement factors,
but to different children it passes on an assortment of assortments of half its genes, a half
which varies from one germ cell to another. We thus have the chance to see the effects
of genes hidden in the parent. This illustrates why we can learn more from a collection
of offspring of a breeding animal about its genetic worth than by measuring its own
merits. Arresting examples of the success of progeny testing are to be found in success-
ful poultry breeding. Then breeding animals of both sexes were selected on the egg-
laying performances of their daughters, and in two years production was nearly doubled,
and remained at that high level. Great results have also been obtained in breeding for
production in dairy cattle. One limitation of progeny testing as we here observe, is the
simple fact that it takes time.
In recent research in Russia (Moisseiev) rams were judged on their success in siring
offspring of good size. A high correlation was demonstrated between live weight at
weaning and live weight at a year or fourteen months. By thus evaluating the rams
early, a few weeks before the ewes were due to be mated again, a breeding season was
saved.
A bull may raise production when mated with poor-yielding cows and lower it with
high-yielding cows. And a bull may lower butterfat when given excellent cows and still
be very good—far above the average of the breed—for factors for butterfat production.
The better the dams, the harder is it to judge the worth of the sire, and a random
sample of the population is inferior for testing to dams chosen for low production. Poor-
laying fowls have sometimes been purposely used. Warwick and Copeland have suggest-
ed that the same might be done in dairy cattle.
More than the progeny test.—Knowledge of detail is a help also in making progeny
testing more accurate. In progeny testing in poultry for egg production mere total
number of eggs has not been considered enough, but a watch has been kept for early
sexual maturity, high intensity, lack of winter pause, non-broodiness, persistency, egg
size, and hatchability. Knowledge of detail is a help, an essential preliminary sometimes
in breeding experiments to ascertain whether a character is inherited, and, if it is, its
mode of inheritance. We may remember, simplifying the position, and simplifying it
very much, that there is hairiness that can be recognized at birth, and there is hairiness
that appears after birth, and the inheritance of the two must in large measure be studied
separately.
To establish that a character is strongly inherited, or weakly inherited—easily in-
fluenced, that is, by non-genetic forces—may be a substantial project. This is a field in
which statistical studies may be important to bring out that a character is inherited
sometimes revealing its mode of inheritance, from an analysis of the characterization of
related animals.
Usually the position is less simple, but by the analysis of breeding records or
by planned breeding experiments the manner of inheritance can be ascertained broadly.
Often it will become clear that the mode of inheritance is multifactorial, and that in large
measure you will get what you breed for, but with some disappointments in animals
falling short of the ideal if this be an extreme condition, or flying high and flying low if the
desired condition be an intermediate one, like thickness of fat on the back of the pig.
Again, although precise genetic analysis is not achieved, it may become apparent
that the factors concerned are dominant rather than recessive, or conversely. Dominance
can be taken advantage of in crosses as with Astrachan curl in Karakul sheep. If a
character results from recessive factors, eschew out-crosses with especial care.
One more physiological line of great import to livestock breeders is artificial insemi-
nation. By this device, which of late has been brought much to the notice of breeders,
we may depend upon it that the fruits of research in the genetics of livestock will be
garnered with increasing speed.
The organized measuring of the merits of dairy bulls by statistical analysis is a
project of national importance. It would be of further help if we could form some
judgement of the breeding worth of a bull by determining what his milking performance
would have been if he had been a cow. Various European workers have made contri-
butions which bear on this problem. They have looked for correlations between
certain characters in the cow and milk yield. One investigator, to take but a single
example, reports a high correlation between the abundance of sweat glands and milk