Oxford Democrat. [volume] (Paris, Me.) 1833-1933, 1920-08-10
AMONG THE FARMERS.
"sPnHD THE PLow."
Animal Husbandry Investigations.

Aulu1ol lAubUouoIy AuV0oGSosAonos
No one problem In connection with
practical breeding OF domestic livestock
is more discussed than the effect Of in
breeding upon the progeny. On the one
hand II has been maintained that In
breeding Is the most pernicious and de.
structive procedure that breeder could
follow. And on the other hand that
without It's powerful aid most of what
the breeder has accomplished could not
have been otherwise gained and that 1t
offers the chief hope for future advance.
When the Maine Agricultural Expert
ment Station began its animal husbandry
the records of registered livestock to de-
termine, II possible, what was the an
swer to this problem. 1t was found that
while inbreeding was much discussed
there was no accurate measure of what
constitutes inbreeding, and that final
judgment was being formed on the basis
of individual Interpretation without any
quantitative measure of comparison.
Among the first contributions of the
many from the station that have proven
of great value to the theory as we'll as
the practice of breeding was an adequate
measure of this much talked of and yet
vague subject. The problem had been
attacked by many investigators, but none
of the published results have reliable
measure of the real intensity of inbreed-
ing. The essential weakness was fail
ure to take account of the composition
OF the generation to which the common
ancestor of an inbred pair belongs. |
In the now generally accepted method
proposed by the Maine Station in 1918
the basic concept of inbreeding is the
narrowing of the network of descent as
result of mating together individuals &C.
netically related to each other. This
means that the number Of potentially
different germ-to-germ lines ("blood
lines') concentrated in q given individ-
ual is fewer In the inbred individual than
in one not inbred. Or stated positively,
the inbred individual possesses fewer
different ancestors in one or more gener-
ations than the maximum number posi-.
BILE.
This means that the two factors for
exact measure are the amount of ances.
trail reduction and the rate of this reduc.
ton. Both of these demands are met If
one takes as the measure of inbreeding
the exact shortage of ancestral iDdividu-
ais In comparison with the maximum
number there might have been.
The prime question of inbreeding,
leading to its exact measurement, is the
question what degree of inbreeding was
involved in the production of a particu.
lar animal. 1t is necessary, therefore, to
start with the individual and work back.
ward into the ancestry rather than to
start back in the ancestry and work
down toward the individual. And this
is the fundamental difference in the
method pointed out by the Maine Sta. |
ton. An individual will have two par.
ents and may have four different grand. |
parents, eight different great-grandpar.
ents, sixteen different great-great-g |
parents, and 80 on until in the twelfth
generation there may theoretically be
total of 4098 different unrelated ances. |
tors. But IL an individual is the product |
of a brother and sister only half that |
number of different ancestors Ia possible |
That is, the coefficient of inbreeding
would be represented by fifty. If the |
brother and sister that were mated were |
in turn the offspring Of brother and sis
ter the coeficient of inbreeding of the
Individual would be ssventy-fve, and IL |
the mating of brother and sister had be- |
gun q generation earlier and been fol- |
lowed through the three generations, the |
of inbreeding of the individual |
would be S75.
This method of measurement of in |
breeding gives rise to the practical rule
that In measuring the degree Of inbreed- |
ing in pedigree 1t is necessary to re- |
gard all different individuals as entirely |
unrelated until the contrary is proved by |
the finding Of a common ancestor. While |
this seems truism there are apparent |
paradoxes that arise in its actual appli
cation. For instance, the coefficient of |
would usually increase some |
what in proportion to the number of
generations considered. For IL in any gen. |
GRAFTON preceding the one considered,
common ancestor to the father and
mother appeared, the number of posi-.
BILE different ancestors becomes progress |
lively decreased as the generations are
backward. Hence the coefi- |
cient of inbreedipg at the fourth gen.
GRAFTON might be 37.5, and by following
backward enough common ancestors
might appear to materially increase the
coefficient. In all events the method is
a strictly qusntitative one for comparing
a like number of generations. From
what has preceded 1t is seen that this
COT fficient would not give an exact quan-
titative measure of the fourth generation |
In one line as compared with the fifth or
a larger number of another
This measurement of the problem has
to do solely with the relationship prob |
lem. And of itself has nothing to do
with the technical side of the gamatic or
zygotic constitution of individuals. 1t
was published by the station In detail in
1918. And elaborate tables extending
up to the tenth generation by which the
of inbreeding could be read
off without the necessity of arithmetical
were also published. While
these books can be found In the hands of
many breeders, and in most Libraries, the
editions of the publications were long
since exhausted and requests for them
are still frequent.
CHAs. D. WOODS, Director.
The Hen of the Walk.
han of the flock of John Reatop.