Animal genetics / Frederick B. Hutt.

  • Frederick Hutt
Date:
[1964]
Catalogue details

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

Credit: Animal genetics / Frederick B. Hutt. Source: Wellcome Collection.

    535/578 page 513
    GENETIC RESISTANCE TO DISEASE 513 trois, found the proportions (per cent) resistant in the two groups to be as follows: Unselected Selected controls , Resistant $ $ X unselected $ $ 71 33 s Resistant ^ ^ X untested daughters of resistant $ ç 83 31 It would seem that genetic ability to resist intestinal parasites in sheep and goats could be utilized to great advantage. The pheno- thiazine and other drugs on which chief reliance has been placed for controlling worms in these species do not kill all the worms, but merely reduce them to a number that the animal can tolerate with¬ out becoming unthrifty. Who can assure us that the survivors will not multiply and eventually produce races resistant to such drugs, just as the houseflies did with DDT? Trypanosomes carried by tsetse flies are a serious threat to the production of cattle in many parts of Africa, but some breeds are so resistant to trypanosomiasis that they have a special value in areas where the flies abound. West African Shorthorns and the N'Damas, which originated in French Guinea, have proven to be more resist¬ ant to these protozoan blood parasites than breeds from areas where the flies are not prevalent. In Nigeria, Chandler (1958) found the N'Damas to be resistant to two species of trypanosomes and, within those species, to strains of different geographic origins. Such a gen¬ eral resistance could make the N'Damas useful over wide areas where the tsetse fly is common. Other protozoan parasites to which genetic resistance is known include coccidia of the genus Eimeria, which are ubiquitous para¬ sites of fowls. The feasibility of breeding strains highly resistant, and of doing so in a few generations of selection, was demonstrated by Rosenberg and others. Crosses of the resistant lines with unse¬ lected stock showed that, as with most genetic resistance to other diseases, resistance to coccidiosis is a quantitative character. Resistance to External Parasites Animals differ genetically not only in resistance to internal para¬ sites, but to those on the outside as well. Resistance to blood-sucking arthropod parasites of one kind or another is vitally important in the many parts of the world where insects and ticks act as vectors, i.e., carriers of pathogenic protozoa, Rickettsia, and other organisms. Diseases thus transmitted include the yellow fever and malaria of man, and trypanosomiasis, anaplasmosis, and piroplasmosis (one
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