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.

    540/578 page 518
    518 ANIMAL GENETICS the mechanisms by which genetically resistant animals cope with disease to permit identification of such animals. This has been done with respect to pullorum disease in the fowl. In a series of studies too long to be reviewed here, it was found that the chicks most resistant to Salmonella pullorum have superior con¬ trol of the processes that maintain their body temperatures. The degree of such control can be measured by determining (from the average of several readings) how quickly the chicks can raise their temperatures from about 102° F. (when they hatch) up to the 105° to 107° F. that is normal at ten days of age. The differences among them in that ability are evident by six days after hatching. Chicks most efficient in making the transition are most resistant to pullorum. For one thing they respond to infection, as do other animals, by run¬ ning their temperatures up to fever heat, and maintain that high temperature better than susceptible chicks. That in turn is believed to accelerate the production of antibodies and other mechanisms for defence, such as phagocytosis, or the ingestion of invading organisms by cells specially assigned that task. This tale has all been told else¬ where (Hütt, 1958). To test the feasibility of using such an indicator of resistance and of breeding resistant stock in birds not infected, selection to dif¬ ferentiate two lines was carried out for two generations. One strain was bred for high temperatures, and the other for low ones. As a result, in the first generation, average temperature during the first six days in the low-temperature line was 105.54° F., or 0.42° F. lower than in the high-temperature line. In the next generation the dif¬ ference was 0.59° F. When chicks of the two lines were tested by oral inoculation with a standard dose of S. pullorum, those of the high-temperature strain were consistently more resistant than chicks of the low-temperature line. Results in two of these trials are shown in Fig. 22-5. While it seems clear that, by using the early indicator of resist¬ ance, it is feasible to raise the genetic resistance of fowls to pullorum disease, and to do so without exposing them, that procedure is not likely to be followed because the extensive programs to eradicate S. pullorum have succeeded so well (in some parts of the world) that the disease is no longer considered serious. One wonders, how¬ ever, whether or not similar indicators might be found, if sought, that would identify chicks resistant or susceptible to leucosis, or calves which would be resistant or susceptible to mastitis after they get old enough to have it. Such an indicator might possibly be found in blood antigens, the proteins of blood serum, or, perhaps, in association with some enzyme.
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