The Smyth line chicken serves as a biomedical model for the human disease vitiligo. In the chicken, this condition results in white feathers and a disruption of the retinal pigmented epithelium of the eye, which can lead to visual impairment. The expressivity of this amelanosis is highly variable and does not follow single gene inheritance patterns. This dissertation addresses genetic and endocrinological factors which affect either the melanocyte or the immune system and their effect on the incidence, onset time and severity of the amelanosis. Techniques utilized in this dissertation to investigate amelanotic inheritance included genetic outcrosses, backcrosses and selection criteria. The administration routes of the treatments on this work included IM and IV injections, implantation of silastic tubing and mini-osmotic pumps and incorporation into the feed. Birds were monitored for immune system response, serum glucose levels and rate of gain as well as the development of both feather amelanosis and visual impairment. Treatments were performed on embryos, chicks, juveniles and adult Smyth and control line individuals. The results indicate that the variability in the Smyth line amelanosis can be explained by many physiological and genetic factors. An increase in pigmentation intensity will increase the incidence and severity of amelanosis in the offspring. Corticosterone and testosterone administration resulted in a significant depression in the incidence and severity of amelanosis. One haplotype (EA-B/101) at the major histocompatibility locus of the chicken, exhibits a significantly higher incidence and severity of amelanosis and visual impairment. Several of the flocks in these trials exhibited a significant sex effect (females $>$ males) in amelanotic incidence. It is concluded that the amelanotic variability in the Smyth line is due to individual physiological differences between birds due to sex, environment, health and genetics. It is apparent that any condition which yields a generalized suppression of the immune response will result in a decreased incidence of amelanosis.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7717 |
| Date | 01 January 1990 |
| Creators | Boyle, Milton Lorimer |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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