Genetics / by H. Kalmus ; in collaboration with Lettice M. Crump.

  • Hans Kalmus
Date:
1948
Catalogue details

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

Credit: Genetics / by H. Kalmus ; in collaboration with Lettice M. Crump. Source: Wellcome Collection.

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    fat production because they mature and grow fat early. These are best fed abundantly and slaughtered early; slow maturing strains kept on a low diet produce more lean and less fat. In sheep also environmental and genetical factors must be combined to produce good mutton or good wool, and use is also made of differential growth in this species. It is not generally known that the fine texture of the wool of the Merino sheep is not only controlled by the inherited characters of the breed, but is also due to partial starvation. The methods of improving livestock will to a great extent depend on the fertility of the species concerned. In poultry and in pigs, where the progeny are numerous and reproduc tion is fast, it is possible to start and breed from scratch by buying eggs or boars and sows. In cattle, sheep and horses, however, which normally produce one offspring only in a season, improvement of stock can as a rule not be effected by replacement by a new stock. These species are usually graded up—that is, the available females, for instance, scrub cows or some low-producing stock of ewes, are fertilized by a bull or a ram of high quality. This is now more easily possible than it used to be because of the greatly improved technique of artificial insemination, as it is of course much cheaper and easier to transport the sperm from the breeding males over great distances than to transport the animals themselves, and a much greater number of females can be served than by the natural mating process. This latter ad vantage, however, differs greatly in the three species. If the grading-up process is continued on the female off spring over several generations animals are obtained which are almost as good as the pure-bred stock and also breed fairly true. If the animals are living under hard conditions a graded-up stock may even be superior to the pure race in that particular environment. Apart from grading up and from inbreeding, organized
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