The Principles of Breeding | Page 7

of the room, and
one day was found opposite a rabbit hutch apparently begging the
rabbits to come and play."
If even in such minute particulars as these, hereditary transmission may
be distinctly seen, it becomes the breeder to look closely to the "like"
which he wishes to see reproduced. Judicious selection is indispensable
to success in breeding, and this should have regard to every
particular--general appearance, length of limb, shape of carcass,
development of chest; if in cattle, the size, shape and position of udder,
thickness of skin, "touch," length and texture of hair, docility, &c., &c.;
if in horses, their adaptation to any special excellence depending on
form, or temperament, or nervous energy.
Not only should care be taken to avoid structural defects, but especially
to secure freedom from hereditary diseases, as both defects and
diseases appear to be more easily transmissible than desirable qualities.
There is often no obvious peculiarity of structure, or appearance,
indicating the possession of diseases or defects which are transmissible,
and so, special care and continued acquaintance are necessary in order
to be assured of their absence in breeding animals; but such a tendency
although invisible or inappreciable to cursory observation, must still,
judging from its effects, have as real and certain an existence, as any
peculiarity of form or color.
Every one who believes that a disease may be hereditary at all, must
admit that certain individuals possess certain tendencies which render
them especially liable to certain diseases, as consumption or scrofula;
yet it is not easy to say precisely in what this predisposition consists. It
seems probable, however, that it may be due either to some want of
harmony between different organs, some faulty formation or
combination of parts, or to some peculiar physical or chemical
condition of the blood or tissues; and that this altered state, constituting
the inherent congenital tendency to the disease, is duly transmitted
from parent to offspring like any other quality more readily apparent to
observation.

Hereditary diseases exhibit certain eminently characteristic phenomena,
which a late writer[2] enumerates as follows:
1. "They are transmitted by the male as well as by the female parent,
and are doubly severe in the offspring of parents both of which are
affected by them.
2. They develop themselves not only in the immediate progeny of one
affected by them, but also in many subsequent generations.
3. They do not, however, always appear in each generation in the same
form; one disease is sometimes substituted for another, analogous to it,
and this again after some generations becomes changed into that to
which the breed was originally liable--as phthisis (consumption) and
dysentery. Thus, a stock of cattle previously subject to phthisis,
sometimes become affected for several generations with dysentery to
the exclusion of phthisis, but by and by, dysentery disappears to give
place to phthisis.
4. Hereditary diseases occur to a certain extent independently of
external circumstances; appearing under all sorts of management, and
being little affected by changes of locality, separation from diseased
stock, or such causes as modify the production of non-hereditary
diseases.
5. They are, however, most certainly and speedily developed in
circumstances inimical to general good health, and often occur at
certain, so called, critical periods of life, when unusual demands on the
vital powers take place.
6. They show a striking tendency to modify and absorb into themselves
all extraneous diseases; for example, in an animal of consumptive
constitution, pneumonia seldom runs its ordinary course, and when
arrested, often passes into consumption.
7. Hereditary diseases are less effectually treated by ordinary remedies
than other diseases. Thus, although an attack of phthisis, rheumatism or
opthalmia may be subdued, and the patient put out of pain and danger,

the tendency to the disease will still remain and be greatly aggravated
by each attack.
In horses and neat cattle, hereditary diseases do not usually show
themselves at birth, and sometimes the tendency remains latent for
many years, perhaps through one or two generations and afterwards
breaks out with all its former severity."
The diseases which are found to be hereditary in horses are scrofula,
rheumatism, rickets, chronic cough, roaring, ophthalmia or
inflammation of the eye,--grease or scratches, bone spavin, curb, &c.
Indeed, Youatt says, "there is scarcely a malady to which the horse is
subject, that is not hereditary. Contracted feet, curb, spavin, roaring,
thick wind, blindness, notoriously descend from the sire or dam to the
foal."
The diseases which are found hereditary in neat cattle are scrofula,
consumption, dysentery, diarrhea, rheumatism and malignant tumors.
Neat cattle being less exposed to the exciting causes of disease, and less
liable to be overtasked or exposed to violent changes of temperature, or
otherwise put in jeopardy, their diseases are not so numerous, and what
they have are less violent than in the horse, and