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    A study of some aspects of growth and reproduction in two inbred lines of mice and their crosses : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Massey University of Manawatu
    (Massey University, 1964) Lawson, R A S
    The mating of closely related individuals is generally believed to result in inferior offspring. Recognition of this danger has been suggested as the reason for evolution of human social customs. However, historical researches suggest that inbreeding unavoidably occurred in small, isolated, ancient communities, and marriage of close relatives was encouraged in the Egyptian, Greek and Hebrew civilisations (Zirkle, 1952). Inbreeding is likely to have occurred in the isolated flocks of nomads, but it is probable that inbreeding depression, as such, was not recognised until the eighteenth century when the early livestock improvers are reputed to have found that the fertility of their animals deteriorated with continued inbreeding. Hybrid vigour from cross breeding plants was described by Koelreuter (1766) and confirmed by later botanists., .After much detailed work, Darwin (1876) concluded: " •••cross fertilisation is generally beneficial and self fertilisation injurious." and that (a) Mechanisms exist widely for the avoidance of inbreeding. (b) Inbreeding has effects likely to incur selective disadvantages. No suitable hypothesis could account for the usually deleterious effects of inbreeding, or the reverse phenomenon of hybrid vigour until the rediscovery of Mendel's work in 1900. The effects of inbreeding can now be explained in terms of the dominance and recessiveness of genes. (Falconer, 1960). The aim of experiments reported in this thesis was to study growth, reproduction and mortality in two inbred lines of mice, derived from common ancestors, to find if differences between them had arisen during inbreeding. Reciprocal crosses and matings of the F1 progeny of these crosses were made to find if hybridisation of the parent lines led to improvements of these charact­eristics. This study was suggested by Drs. D.S.. Flux, M.F. McDonald and R.E. Munford to whom the author is indebted for advice and guidance. The author also wishes to acknowledge the assistance of Mr. E. Ormsby in histological preparations, of Mr. P .S. Dale in photomicrography, and of Mr. C. Muir who drew some of the figures reproduced in this thesis. Thanks are also due to the staff of the University Library for their efforts in obtaining literature. [From Preface]
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    Coefficients of inbreeding and relationship among pedigree Jersey bulls used in artificial breeding or in natural mating in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the Victoria University of Wellington, Massey College
    (Massey University, 1962) Hamilton, C O
    Since 1950, when the New Zealand Dairy Board assumed responsibility for the commercial development of Artificial Breeding, there has been a tremendous increase in Artificial Breeding usage. Whereas in 1950,0.2% of the total cow population was artificially inseminated, the corresponding figure for 1960 was 26%. In any Artificial Breeding scheme there are dangers of inbreeding through the use of a limited number of sires, and if the young sires selected for the scheme are largely the sons of the best sires already in the scheme, then the dangers of inbreeding are increased. Inbreeding to high levels is undesirable because it generally reduces the mean level of all characters closely connected with fitness in animals and leads in consequence to loss of general vigour and fertility. Since most characters of economic value in demestic animals are aspects of vigour or fertility, inbreeding is generally deleterious. The genetic basis of this inbreeding degeneration is not completely clear. Another harmful effect of inbreeding is the possibility that it may fix undesirable genes in the homozygous state.
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    Inbreeding and population structure studies in the New Zealand Angus breed : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1977) Cheong, Weng Keong
    The breed structure and genetic history of the New Zealand pedigree Angus breed were analysed by Robertson and Asker's (1951) modification of the Wright-McPhee (1925) pedigree sampling method. The pattern of the breed structure obtained is generally similar to that found in other studies, but it is both diffuse and dynamic owing to the present rapid expansion of the breed. There are changes taking place in the herd composition of the major breeders' herds and many new herds have yet to find their level in the structure. Considerable emphasis has been placed on the use of imported animals in the development of the breed. Of all herds registering in Volume 61 of the herd book, 20.5% used imported sires, and the percentage of genes in the breed in 1966/67 derived from animals imported since 1863 was 85.4. The most important herd in 1969 has a genetic contribution to the breed of 21.9 per cent:, while the contributions of the four next most important herds were 8.72, 8.7, 4.7 and 3.7 per cent. In the four-generation pedigrees from which these figures were derived, the contribution of imported animals was 42.4%. The relationship between herd size and importance of the herd was considered. Herd duration was also discussed, in so far as it relates to improvement of the breed. The animal with the highest relationship to the breed was Blackleg (11.65% in the 1900 pedigree sample). But overall, the most important animal over the period 1900-1966/67 was Lancer of Advie. Of the 33 sires and 9 dams whose direct relationships are 3.0% or more in any of the 8 sample years, 19 sires and 3 dams were imported. The total inbreeding in 1966/67 (base year 1863) was 1.80%. This comprised 0.09% current inbreeding, 0.95% long-term inbreeding, and 0.76% strain inbreeding. The index of subdivision calculated from the non-current and long-term inbreeding is 1.79, indicating that there is only a slight tendency towards family formation in the breed. The effective generation length is approximately 5.6 years. About 50-56% of the animals in the 1966/67 sample were sired by bulls 4 years old or younger, while about 38% are from dams 4 years or younger. It is unlikely that there is much genetic variation between herds. This is because bulls from major breeders' herds are used widely throughout the breed while about 80 percent of sires and 37 per cent of dams are bred in herds other than the one in which they were used.