Animal breeding / by A.L. Hagedoorn.

  • Hagedoorn, Arend L. (Arend Lourens), 1880-1953.
Date:
[1939]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Animal breeding / by A.L. Hagedoorn. Source: Wellcome Collection.

    155/410 (page 121)
    In-breeding and Out-crossing 121 are plastic, and capable of being changed by selection. This is only true insofar as some potential variability (impurity) still remains in them, and it should be the aim of the breeders of all economically important breeds, to reduce this potential vari¬ ability as much as possible. When, during the process of selec¬ tion, a breed becomes fixed for a genotype of its own, it becomes less plastic and more and more fixed, and when this has hap¬ pened, only cross-breeding would help in bringing back the desired variability necessary to improve some quality which had become fixed as a result of in-breeding while our attention was given to some more obviously important quality. Just as we should give enough attention to all the possibly important qualities of any breed, we should especially avoid giving too much attention to really irrelevant qualities. If we give our attention to such unimportant things as colour-mark¬ ings, shape of the backline, or set of the tail, we only make selection for really valuable qualities more difficult, as we restrict our choice to only part of the really best animals in our herds. In our most important animals, it is necessary to use in¬ breeding with great caution. The best thing we can do is to select our male breeding-stock with scrupulous care, according to the quality of their offspring. In-breeding sires with their own daughters greatly helps to recognize those sires which are impure (heterozygous) for factors which we want all our animals to have, and it gives us a chance to eliminate such sires together with all their get. As soon as we come to know a few very good sires which have such a make-up that all their offspring are valuable, we must employ these sires as far as possible to the exclusion of less valuable or even of untried young sires. Artificial insemination may be of very great help in doing this. The use of in-breeding in selection makes it necessary to avoid the use of any but the very best breeding stock available. No one should ever be led to use faulty animals in an in-breeding programme. Most faults are recessive, and it is obvious that if in a certain generation all animals are aa it is never possible to get factor A back into the group without cross-breeding. It is easy when in-breeding to get certain faults fixed in the group, because the material becomes homozygous for genes affecting the quality. Just as it is impossible to get animals hav¬ ing A when in a certain generation all the members of an in-