Breed structure in the pedigree Ayrshire cattle population in Great Britain

Abstract

Ayrshire Cattle Herd Booksfor the years 1927, 1946 and 1947 were examined to study the breed structure. Extended pedigrees of a sample of registered females showed that more than half their genes had come from eight herds. Most of the genetic contribution of these herds comes through the bulls they breed.Herds were divided into: breeders' herds (a), breeders' herds (b), multipliers' herds (i), multipliers' herds (ii), and herds registering males only. The function and numerical importance of each group is shown. The position of any one herd in the breed hierarchy is unstable. Changes in the extent of specialization of herd function between 1927 and 1946 are described.The Ayrshire breed structure is discussed in the light of its implications on the effective size (N) of the population and on the selection of bulls for breeding.