The objects of this investigation were to discover the amount of current inbreeding, the extent of any genetic divergence between the beef and dairy types, and whether the breed was dominated by an élite group of herds as for example, in the British Friesian (Robertson, 1953). An extensive investigation by Sewall Wright (1923a), (1923b) and McPhee and Wright (1925), (1926) established that there was at that time little current inbreeding and that genetic divergence between Dairy and Beef Shorthorns was negligible. This work adds to and corroborates their findings and throws some light on breed structure.
The sampling technique in this investigation is based upon Wright (1925). If consisted of noting the number, parents, grandparents and great-grandparents of a randomly selected sample of 128 females registered in Coates’ Herd Book, Vol. 94, 1948. Simple random lines were traced back from each great-grandparent as far as 1900, a toss of a coin deciding whether to record a sire or a dam. The information contained in Coates’ Herd Book made it a simple matter to record in addition the mate of the randomly selected ancestor, thus providing 16 random lines behind the eight great-grandparents.