ABSTRACTS 177
persistency may, however, be overdone since the moult occurs each fall. If the hen is so
persistent as to interfere with or delay moulting, production may not be normal when re-
sumed.
Rate of production is expressed as the percentage of days on which eggs were pro-
duced. Gross rate permits confusion of non-pausing birds possessing low intensity with
pausing birds possessing high intensity. " Net rate " excludes the days during pauses.
Clutch size, or the number of eggs layed on successive days before one day is missed, has
been used to indicate the rate of production, but it does not appear to the authors as a
basis for successful estimation of this rate.
Viability includes the number of chicks hatched from a given number of eggs, the
proportions of these chicks raised to maturity and the mortality of the laying birds.
There is good evidence to show that mortality up to the end of the first laying year is
partly genetic. The selection of longer-lived strains will result in greater viability. In
selecting against diseases the breeder should select breeding birds from those families
which are most free of the diseases and not from survivors of less free families.
For measuring flock production the hen-lay average and the average of the records
of surviving birds are not preferred to the production index of the Kimber Poultry Breed-
ing Farm. This is a quotient of total eggs layed by a group over the original number of
pullets in the group. The prevalence of non-productive or non-viable birds in the flock
can best be shown by the Kimber production index since both a high mortality rate and
intensive culling reduces the number of pullets after laying has begun. This index is
therefore decreased.
A direct correlation exists between body size and egg size, yet the producers of large
eggs seldom have a high rate. The authors refer to Hayes as saying that egg size involves
one dominant gene for small-eggs and two dominant genes for large eggs. Egg colour
is apparently controlled by several pairs of genes, some of them acting cumulatively
to produce darker shades, others acting as inhibitors of colour. Shell thickness is probably
dependent on a complexity of hereditary factors. Diet, however, is very important in
this respect. A considerable number of genes seem to be involved in albumen quality.
Hatehability, it is suggested, is controlled by a single gene, although the authors report
that some workers question this. Six or more lethal genes are known, however, to cause
embryonic death in poultry.
[J. N. W.]
A study of nicking in Jersey cattle. L. A. JOHNSON, J. W. BARTLETT
AND LYNN COPELAND (1940). J. Dairy Sci. 23, 709.
N ICKING is generally used in reference to the production of superior progeny
from certain matings. Outcross, linebred and inbred matings are used by breeders
in the hope of purifying or intensifying good qualities. If one such mating is superior it is
said to ' nick '. An unanswered question in this connection, however, is : " Will a bull
proved to transmit high producing capacity in one herd be equally successful in another
herd where a different family blood line exists ? "
In co-operation with the American Jersey Cattle Club a study was made to determine
whether or not differences may appear in the producing capacity of various matings.
Bulls were selected which had at least two groups of six daughters, of which each group of
daughters was out of dams by one sire. All records were converted to a three times a
day, 365 day, mature basis. Total fat production was used as a basis of comparison as
milk and fat percentage are inherited separately and total fat is a product of the two.
The authors conclude that if nicking is not evident in the mating of a bull with two
or three groups of daughters from dams sired by one bull for each group it must not be
assumed that nicking will not arise with a different group of daughters. Furthermore,
nicking may arise from a group of dams transmitting more producing capacity to their
daughters than their own records show.
A bull may nick better with one group of daughters than another and still nick satis-
factorily with both. It is also recognised that six cases are too few for as satisfactory a
comparison as is possible from a larger number of cases. With a small number of cases,
therefore, results may be obtained which would not hold should the number of cases be in-
creased. Environment is also of great importance.