THE INHERITANCE OF PRODUCTIVITY IN FARM

                                       LIVE STOCK

                   III. BREEDING FOR EGG-PRODUCTION

                                  A. W. GREENWOOD

         (Institute of Animal Genetics, University of Edinburgh).

Discussing the future possibilities for increasing egg-production in poultry,
Jull [ 1 ] has stated that progress largely depends upon the poultry-breeder's
ability to control heredity. Further, he suggests that " heredity can be con-
trolled and directed best only when the knowledge of poultry-breeders develops
sufficiently to enable them to select breeding stock that will transmit to their
offspring the most desirable qualities. Selection is the keynote in the programme
of future development."

Selection without an exact knowledge of the mode of hereditary transmission
of desirable qualities, but with a belief that they are transmissible from parent
to offspring, has been the basis of all breeding practices in the past. It has been
responsible, together with improvements in husbandry, for the tremendous in-
crease in the production records of our modern domesticated breeds when com-
pared with the ancestral types from which they have sprung. Such advance
bears witness to the importance of heredity.

In attempting to assess the possible value of the science of genetics to the
cause of increased fecundity in poultry, we should begin by considering the results
that are now obtainable when selection along certain definite lines is practised.
An examination of the production figures at egg-laying contests testified to the
skill of the intelligent breeder in developing highly fecund strains of birds. His
methods of selection, however, when improved flocks are dealt with lead to negli-
gible progress over a fairly long period of time. This has been demonstrated by
Dunn [ 2 ] from an analysis of egg-laying contest figures in America. Over a
period of nine years he found that there was little material change in average
egg-production. This is very significant. Since only a small percentage of a
flock of birds is rigorously selected by certain standards for participation in egg-
laying trials, it follows that the results obtained represent practically the highest
individual performances possible with the methods of selection now used by
breeders. The production of the flock as a whole, however, usually falls far short
of these individual records, and perhaps the most pressing question to be faced
from the economic stand-point is that of devising a means of raising the figure
for average production, even in the most improved flocks.

The problem of improving egg-yield by breeding has been the incentive
to much scientific work, which has taken the form of analytical attempts to
define and measure the desirable qualities that a hen should possess in order

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