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The hereditary defects: congenital dropsy of cattle and atresia ani of swine Irwin, Robert Edward Thomas

Abstract

Two hereditary defects, Congenital Dropsy of cattle and Atresia of swine, are investigated. The introduction makes reference to the evolutionary significance of lethal and sub-lethal characters and compares it to the importance of such factors to the practical breeding of livestock. Some reviews published on the hereditary defects of farm animals are listed. Part one is concerned with the congenital dropsy defect which was observed and studied in the Ubyssey herd of registered Ayrshire dairy cattle owned and bred by the University of British Columbia. The history of the herd and the breeding practices employed since the herd's foundation are outlined. A single-factor recessive genetic hypothesis to account for the occurrence of the ten defective calves is formulated and tested. Genetic analyses of the pedigrees of 153 of the 501 calves born in the herd up to September 30, 1951 indicated the average theoretical probability of the defect occuring to be 0.0853. A test for the ''goodness of fit'' was applied and showed that the sample studied fits the hypothesis. The etiology and pathogenesis of the defect are investigated under a working immunogenetic hypothesis based on the two assumptions: l) that the defect, congenital dropsy, is the counterpart of the hereditary disease of new-born infants, Erythroblastosis fetalis; 2) that the Rhesus isoimmunization theory which serves to explain the familial incidence of the disease in humans may be adapted to the genetics of cattle populations. The immunogenetic studies undertaken to test this hypothesis are described and an explanation of the results, aberrant to the hypothesis, is offered. Part two deals with a more complex hereditary defect. Atresia ani of swine. The literature is reviewed. The histories and pedigrees of three abnormal litters born in a local herd of registered Yorkshire swine are presented. Two explanations of the possible mode of inheritance of the defect are put forward and tested on the sample available for study. The recommendations made to the breeder which would enable him to rid his particular herd of breeding stock of the defect are quoted. The conclusion is a brief discussion of the problems confronting the breeder of registered livestock in whose herds or flocks a hereditary defect occurs. The appendices include explanations of the methods used to calculate the coefficients of inbreeding and of probability. The chi-square test for ''goodness of fit” is outlined. The procedures for the serological reactions employed in the immunogenetic study of cattle are also presented.

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