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.

    533/578 page 511
    FIG. 22—3. Mortality from all causes (from 42 to 500 days of age) in 27 annual flocks of three strains of White Leghorns at Cornell University. In the two strains, С and K, which were bred for resistance to leucosis and other dis¬ eases, mortality gradually declined to about one-quarter of the original level, or lower, but it remained high in the strain selected for susceptibility to leucosis. Birds of all three strains were intermingled every year from hatching to the end of the test. Fluctuations from year to year have been smoothed out by the use of three-year moving averages except for the terminal points. Breaks in the curves in 1942 mark initiation of more severe exposure to leucosis. Following a high incidence of that disease in 1959, mortality from neoplasms of any kind in the Susceptible strain fell in 1960 and 1961 to about two per cent, and showed thus that in those two years the flocks had apparently escaped exposure to leucosis. (From data of F. B. Hütt and R. K. Cole, Cornell University.) exposure. Another problem is that the breeders must combine the genetic resistance to leucosis with some eight or ten other traits of economic importance, such as egg production, egg size, etc. The feasibility of doing this has been demonstrated. One advantage of breeding for resistance to leucosis is that the indispensable pedigreeing of chicks and the records of their fate and performance can also be used to detect families susceptible to dis¬ ease of any kind; hence, breeding for resistance to leucosis is really equivalent to breeding for superior viability. The effects of such selection at Cornell University are shown in Fig. 22-3, in which viability of two resistant strains is compared with that of a third which was deliberately selected for susceptibility to leucosis.
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image