The influence of importations on the New Zealand pedigree Jersey breed and the level of inbreeding, 1895-1950 : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science of the University of New Zealand
Of the 1,845,000 dairy cows in milk in New Zealand in January 1950, 85% were either purebred or grade Jersey cattle (A & P Statistics 1950). With the exception of the Island of Jersey no other country has such a predominance of this breed and it is of interest to both the animal husbandman and the geneticist, to trace not only the growth of the breed in this country but also the changes in its structure during the last half century. There is at present no authoritative information available relating to the breeding methods employed by New Zealand dairy farmers and the lack of comprehensive records of performance in the Jersey breed as a whole makes it unlikely that the selection policies of the last fifty years will ever be adequately presented. The dependence of the more popular breeders on the importations during the present century is, however, generally recognised but no attempt has yet been made to measure the influence of these much popularised animals on the breed as a whole. If imported animals differ in their genotype from New Zealand-bred animals, then a general preference for the former or their descendents should gradually change the average genotype of the breed. That such a preference exists is suggested by Fahimuddin (1952). He found that the Jersey breed was divided into strata and that the herds using imported sires were in the upper and the most important strata. There is no way of calculating whether imported and New Zealand-bred animals do differ genetically, but estimates of the proportion of the genes in the breed as a whole for which imported animals are ultimately responsible are of interest for several reasons.