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This thesis reports on an investigation of seasonal changes in tissue levels in Scottish Blackface hill ewes throughout their reproductive lifetime. X-ray computed tomography (CT) scanning was used to produce accurate estimates of total body weights of muscle, carcass fat and internal fat. Seasonal tissue changes, estimated from CT measurements, were then investigated during one annual cycle, in ewes producing different numbers of lambs. Carcass fat (subcutaneous and inter­muscular) and internal fat depots were depleted during pregnancy and early lactation and repleted from mid-lactation to mating the next year. Muscle was mobilised only when fat reserves were severely depleted. Genetic parameters were estimated for fat (carcass and internal) and muscle weights during the first production cycle of ewes (at pre-mating, pre-lambing, mid-lactation, weaning and pre-mating the following year), and for total tissue weight loss (pre-mating to mid-lactation) and weight gain (mid-­lactation to pre-mating). Heritabilities were moderate to large for most traits except total tissue weight gain of fat and muscle, which showed little genetic variation. Genetic and phenotypic correlations with lamb production traits were then investigated. Muscle weight in the ewe throughout the production cycle, and internal fat weight at events before lambing, tended to be positively correlated with number of lambs born and total weaning weight of lambs. No clear relationships were apparent between total carcass fat weight and lamb production traits. Moderate to large genetic correlations were estimated between weight loss from each tissue and total weights of lambs reared to mid-lactation or weaning. Changes in tissue levels were modelled over the reproductive lifetime of ewes using random regression, and genetic and phenotypic parameters estimated at different time-points. Heritabilities were moderate to high for each tissue and were highest during mating for fat weights, and during the dry period and at lambing for muscle weights. Tissue levels in the ewe were affected by the number of lambs produced in the current and previous years and this effect increased as ewes aged. Correlations were estimated for ewe tissue weights throughout their reproductive lifetime (modelled using random regression) with total weights and growth rates of lambs produced. Genetic correlations with lamb growth traits were moderate to large and positive for muscle weights throughout the productive lifetime of the ewe, and small to moderate and positive for internal fat weights. The findings from these analyses have implications for hill sheep breeding programmes. To achieve the aims of increasing litter weights at weaning whilst improving carcass quality, it may be preferable to increase muscle weight in the ewe flock, decrease carcass fat weight and maintain, rather than reduce, internal fat.

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The overall aim of this thesis is to explore quantitative genetic aspects of carcass and meat quality traits in sheep and consider the utilization of such information in breeding programmes. The focus is to breed for improved lamb meat quality. This thesis investigated the use of <i>in vivo</i> composition traits to predict meat quality. Additionally, it investigated potential opportunities for genetically improving meat and carcass quality by using <i>in vivo </i>predictor traits and quantitative trait loci (QTL). Data for carcass composition and meat quality was collected over four years from a Blackface population. Within this population, a double backcrossed design created nine half-sib families, for QTL detection. Carcass composition was measured using <i>in vivo</i> computed tomography (CT) on equal number of males and females per year. This thesis provided considerable novel information of the genetic control of meat quality traits in sheep. In particular, three main contributions are (i) the quantification of heritabilities for a wide range of meat quality traits, (ii) genetic relationships between traits measured <i>in vivo</i>, such as CT-muscle density, and many of the meat quality traits, and (iii) QTL for a wide range of traits. Thus, selection to improve meat quality in sheep is possible, in principle, and this thesis provided tools which may pave the way towards implementation in practical breeding programmes. In particular, the use of CT-muscle density may be a means of making broad improvements in the perceived quality of sheep meat, and QTL that have been detected that, after independent validation, may allow improvement of specific meat quality attributes and alteration of the fatty acid profile.

The phasing out of popular chemical nematicides has led to increasing difficulties in plant parasitic nematode management, in particular the newly emerged root-knot nematode (RKN) Meloidogyne minor. Infestation by this nematode results in stunted development of turf-grass and consequently the appearance of chlorosis. This damage is largely the result of the nematodes invasive endoparasitic life-cycle. Although M. minor has been found in potato crops, its appearance is steadily increasing in sports amenity sites. Initially this study investigated the population dynamics of plant parasitic nematodes (PPN) on sports amenity sites in the UK and Ireland. The investigation suggests that PPN ecology within these Isles is somewhat different to what is observed in the USA. The availability of a turf naturally resistant to key pest M. minor, was investigated leading to the suggestion that the propensity to adopt USGA specification and trends may not be appropriate for our more temperate climate which appears to be a factor in the proliferation of M. minor and other genera. The study progressed to exploring the effects of natural nematicidial compounds, such as biostimulants and plant extracts on turf development, plant resistance and PPN control. The key trend to emerge from the data was that of hyper-vari"lbility, a trend also reflected in the current available literature. However the potential for a plant based nematicide could not be ruled out; the data indicated promising in vitro effects on PPN mobility follOWing treatment with natural plant extracts, but the need for further exploration is apparent. Overall the investigations outlined in this study indicate that PPN management within sports amenities will no longer be as straightforward as applying a quick-fix nematiticide . Further study is most ardently warranted and it would be suggested that successful control of PPN within sports amenities will involve a relatively complex program incorporating observation of PPN ecology, lessening of external stress opposed to turf and careful selection and application of approved nematicidal products.

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The price obtained for lamb carcass has a direct effect on the profitability of a sheep and hence market requirements should be directly reflected in the objective of any breeding program for sheep. Despite their importance, market requirements are often assumed rather than known and market prices are not always used to form the objective. Moreover, although carcass shape affects commercial value, it has not been directly considered in current breeding programs. The aims of this study were (i) to establish the requirements of the current and likely future markets for lamb (ii) to develop methods of incorporating measures of carcass shape into selection programs and (iii) to develop methods for calculating economic values for selection objectives. A case study was conducted to establish current and likely future markets for lamb. Questionnaires were sent to the largest lamb retailers and abattoirs in the UK. Current markets generally required a carcass of weight 16-21kg, conformation E-R and fat score 2 or 3L. The forecast for future requirements was not clear, although both abattoirs and retailers desired carcasses that fitted a narrower range of quality specifications and foresaw increasing demand for heavier carcasses (above 21kg) to supply bone -less products. This suggests that a two market scenario, one for medium sized lambs to supply bone-in cuts, and the other for heavier, lean carcasses to supply bone-less lamb, could develop in the long term. Carcass shape is quantified commercially using a conformation score. However, the assessment is subjective and confounded with fatness and hence an objective assessment of muscularity is undoubtedly preferable. five measures of muscularity (three for the <i>M. longissimus thoracis et lumborum</i> (LTL) muscle, one for the hind leg and one for the whole carcass) were derived from carcass dissection data for 100 Suffolk, 40 Texel and 20 Charollais lambs. Changes with growth, relationships with tissue composition and lean distribution, as well as the relationships between the different muscularity measures were investigated. Higher muscularity at a given live weight was generally associated with higher lean to bone ratio and carcass lean content. Associations with fat content were either non-significant or negative. Relationships with lean distribution were also non-significant. Correlations between muscularity measures in different regions were low in Suffolk and Charollais lambs but higher for the Texels. This suggested that more than one measure would be required, particularly for Suffolk and Charollais lambs, if the muscularity of a carcass was to be described effectively. The results of this study provide the information needed to develop new selection indices that include measures of carcass shape and are well suited to produce sires with progeny that will meet the requirements of current markets for lamb, and those likely in the future.

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