Studies of the Australian Illawarra Shorthorn breed of dairy cattle. II.* Genetic analysis

Abstract

A genetic analysis of the Australian Illawarra Shorthorn breed of dairy cattle has shown that the most important herd in 1973 made a genetic contribution to the breed of 29.5% and the next most important herd contributed 27.9%. The 12 most important herds combined contributed 70.5%.

The sire with the highest relationship to the breed was 'Jean's Monarch of Blacklands' with direct relationships of 3.5, 4.0, 7.5 and 10.9% to the 1938, 1949,1960 and 1973 samples respectively. 'Sunny View Little Princess 30th' was the dam with the highest relationship to the breed with direct relationships of 0.5 and 8.6% to the 1960 and 1973 samples respectively.

From 1930 to 1973 inbreeding increased a total of 7.6%. This comprised 1.6% current inbreeding and 6.0% non-current inbreeding. Strain inbreeding was at its maximum in the 1949 sample (2.02%) but had disappeared by 1973.

The effective generation length was 5.23 years. Of animals in the 1973 sample, 72% were sired by bulls 5 years old or younger, while 50% of animals were from dams 4 years old or younger. It is shown that the bull requirements of the breed could be met by the progeny of performance-recorded animals.

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*Part I, Aust. J. Agric. Res., 28: 1107 (1977).