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    The estimation of genetic and phenotypic parameters for a synthetic lean meat and wool sheep breed : a thesis presented in partial fufilment [i.e. fulfilment] of the requirements for a degree of Master of Agricultural Science at Massey University
    (Massey University, 1989) Southey, Bruce Robert
    A study of the inheritance and interrelationships between wool, growth and carcass traits was carried out as part of the development of a large lean white-faced sire breed. Cross-bred progeny, from three sire breeds (Romney, Dorset, and Border Leicester) mated to Romney ewes, provided information on carcass fatness and composition, liveweight, ultra-sonic backfat depth, fleeceweight and objective measures of fleece characteristics. An overall total a total of 28 sires and 765 progeny were used to collect this information. The analysis of half-sib records was carried out under an assumption of positive assortive mating on ultra-sonic backfat depth. It was considered that any bias, relative to random mating, was minimal due to incomplete assortment, dominance, epistasis and crossbreeding influences. It was assumed that the progeny were only half-sibs in relation to breed, and thus the between-breed component only estimated one-quarter of the between-breed variance. Further, the sires were nested within their respective breeds. The data corrected for the significant non-genetic effects before the variance and covariance components were estimated. In general, the estimates of the Within-breed heritability for the wool and growth traits ranged from 0.1 to 0.6 and were similar to literature values. The carcass estimates were higher than literature values in most cases. The incorporation of the between-breed component resulted in the between-breed heritability being larger in magnitude. This was may of been due to non-additive genetic effects, such as heterosis, in the between-breed component. The ratio of the between-breed genetic variance to the total genetic variance indicated that there was large between-breed variation in liveweight and wool traits and sma1l variation in the carcass traits. The total genetic and total phenotypic correlations presented here suggest that selection for lean growth and wool production can be accomplished by the joint selection of liveweight and greasy fleeceweight. Expected correlated responses in the other traits would include: a)increase liveweight and fleeceweight at all ages, increase ultra-sonic fat depth, GR measurerment, lean content, clean fleeceweight, staple length, mean fibre diameter, clean scoured yield, and b)decrease the carcass C measurement, decrease bone and fat contents, and loose wool bulk. Selection against ultra-sonic backfat depth would result in leaner animals at a constant weight. But the moderately positive correlations with liveweight and fleeceweight would appear to negate the associated advantage of a reduction in carcass fatness.
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    A study of two genetic methods for increasing the performance of sheep in New Zealand : crossbreeding between the Romney, Finnish Landrace and East Friesian : use of number of foetuses scanned as a selection predictor : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Animal Science at Massey University
    (Massey University, 1997) Walker, Georgie J.
    New Zealand's national lamb weaning percentage has been around 100% since 1960 (Walpole, 1995), and as prolificacy is a major determinant of productivity and economic efficiency in sheep production systems (Nitter, 1987 IN: Maria, 1995; Gabina, 1989), the improvement of this trait at a national level is of significant economic importance. The development of more reproductively efficient sheep can be achieved through selection within breeds, by crossbreeding, or by importing new genetic material. This study examines two ways of improving the prolificacy of sheep; by crossbreeding newly imported genetic material with the New Zealand Romney, and by altering the selection methods for prolificacy by using an alternative selection character. The Finnish Landrace and East Friesian are both prolific sheep breeds, and their introduction to New Zealand has provided a potential opportunity to increase prolificacy in New Zealand by crossbreeding them with the current New Zealand sheep population. By assessing their performances under New Zealand environmental and management practices, and in relation to and with current New Zealand sheep, their potential may be predicted. It is important to take advantage of both their additive gene effects and their non-additive genetic interactions (or heterosis) with current New Zealand breeds. The aim should be to achieve an ideal breed composition either as a new composite breed or as regularly reconstituted crossbred stock. The additive and non-additive figures can be used to predict the phenotypic performances for different breed composites by simulating the outcomes of crosses between different ram types made up of different combinations of the breeds with current New Zealand sheep.