VIII.—The Rôle of Inbreeding in the Development of the Clydesdale Breed of Horses

Abstract

SummaryCoefficients of inbreeding have been calculated for 676 stallions and mares, with the object of studying the part played by inbreeding in the development of the Clydesdale breed of horses. Wright's coefficient of inbreeding was used in this study.It is found that during the early history of the breed very little inbreeding had been practised, and it is suggested that this may be due to the fact that the foundation stock contained many recessive factors for undesirable characters. The first marked rise in the average percentage of inbreeding for the breed occurs during the period 1880–1890, and from that time onwards there is a gradual but constant increase in the breed average, reaching its highest level at 6.25 per cent. for the period 1920–1925.A method is outlined by which a measure can be obtained of the contribution of any particular sire to the graph of the average percentage of inbreeding for the breed. It also measures the degree of concentration of his blood in animals inbred to him and the rate at which his blood is diffused through the breed.