The objectives of this thesis were to i) determine the energy expenditure of draught oxen performing common farm operations, ii) establish the relationships between work on intake and digestibility of feeds by draught oxen, iii) investigate the effect of body condition before work and live weight losses during work on work output, and iv) investigate the implications of heat stress on draught oxen in semi-arid areas. The ultimate aim of this study was to generate information necessary for the design of feeding and working strategies for draught animals in semi-arid areas. To meet these objectives four experiments were conducted at the ICRISAT Sahelian centre, with the collaboration of the International Livestock Centre for Africa. In the first experiment the Oxylog, a portable breath by breath gas analyser, was used on 7 animals to determine their standing metabolic rate, their energy cost of walking on soils of different consistencies, and their efficiency of doing work, i.e. ploughing and carting. The average standing metabolic rate of animals was 487 (± 10.6) kJ/kg LW<SUP>0.75</SUP>. The consistency of the soil on which animals were working had a marked effect on their energy cost of walking which was 1.59 (±0.069), 2.15 (±0.084) and 1.0 (±0.10) J/m/kg live weight on unploughed land, ploughed land and laterite tracks, respectively. The efficiency of ploughing sandy soils was 0.32 and was not significantly different from the efficiency of carting with different loads. The efficiency of doing work was not influenced by the type of work performed, the draught force exerted or the walking speed. In the second experiment intake of millet stover, water intake, live weight, plasma concentrations of T3, T4 and urea-nitrogen were measured on 18 animals that worked for 0, 2 or 4 h/day in sequence during three 3-week experimental periods. In addition to these variables, the digestibility and rate of passage of feeds through the digestive tract were measured during the third experiment on 12 animals working either 0, 2.5 or 5 h/day in sequence during three 2-week experimental periods. In the fourth experiment feed intake was measured on 18 animals of different body condition that worked 4 days a week for 7 weeks. The absence of effect of work on intake of millet stover was consistent during these experiments. The efficiency of utilisation of eaten roughages and the rate of passage of the digesta in the gastro-intestinal tract were not influenced by work either. This suggests that the nutrient supply from intake of roughages by working oxen and bulls is unlikely to be sufficient to compensate for the extra energy expended during work. Feed intake was however significantly affected by the quality of the millet stover fed and by the body condition of the animal.

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This thesis comprises a collection of 39 research papers divided into three groups. The first group is entitled 'Statistical Methods, including variance component estimation with general application'. The second group report on 'Application of statistical methods to animal breeding studies'. The last group 'Experimental Studies' reports on studies on animal breeding data in beef and dairy cattle. The major theme of Group I is variance component estimation and the introduction of a method, now known as REML (Residual Maximum Likelihood) that unifies the area. The method was introduced for the analysis of incomplete block designs with unequal block size but was found to have important applications in the analysis of groups of trials, time-series, multivariate data and detecting outliers. The work on variance components has applications to animal breeding and is discussed in Group II. Papers discuss efficient designs for estimation of genetic parameters, including heritability, maternal and multivariate genetic parameters. These designs can lead to substantial reductions in the variances of the parameters over classical designs. It is shown that REML can be applied in certain circumstances when there is selection of animals. Links between variance estimation and best linear unbiased prediction are explored. Methods of prediction, estimation of genetic parameters and optimal designs are given for non-normal data. The last group includes reports on the comparison of breeds and cross-breeding in beef cattle in Zambia. Other studies include estimating the genetic relationship between beef can dairy characters in british Friesian cattle. The validity of models used in dairy sire evaluation are investigated including the heterogenity of heritability of milk yield at different levels of production and a novel method for taking account of environmental variation within herds.

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This thesis reports on an investigation of the association between muscularity and meat quality in Scottish Blackface (SBF) and Texel (TEX) lambs, and the in vivo assessments of these traits using X-ray computed tomography (CT) with a view to their possible inclusion in breeding programmes. The objectives of this work were: (i) to develop comprehensive in vivo assessments of muscularity using spiral CT scans; (ii) examine the relationship of the new muscularity indices with carcass and eating quality; (iii) explore the associations among CT assessments of carcass composition, muscularity and muscle density, and (iv) investigate the possibility of limiting the antagonism between selection for reduced fatness and maintaining eating quality by introducing a CT predictor of intramuscular fat (IMF) as an additional selection criterion for the breeding programmes using CT. The calculation of muscularity indices requires the measurement of the muscle mass and skeletal dimension of the regions of interest. Priority was given to the hind leg (HL) and lumbar region (LR), where high priced cuts are located. The utilisation of new novel imaging technology called spiral CT scanning, which captures detailed information on any specific region, was explored. An algorithm to automatically segment the spiral CT scans (SCTS), and procedures to assess the real dimensions of skeletal structures, were developed. Compared to previous CT m uscularity measurements, the accuracy was much higher with the new index in the HL (correlations with equivalent indices bases on dissection of 0.89 vs 0.51). The accurate measurement of femur length by CT used in the calculation of the new HL index made an important contribution to the higher accuracy of the index. The improvement in accuracy was smaller for the LR (0.55 vs 0.44). The association of CT muscularity indices and carcass traits by dissection in both breeds showed that improved muscularity is not phenotypically correlated with detrimental effects on other carcass quality traits. The correlation coefficients, after adjusting for carcass weight, were positive with meat yield and low and negative, or close to zero, with fatness. This is particularly relevant for the terminal sire breeds, in which the economically important traits included in breeding programmes tend to be carcass composition traits. In the case of SBF, the CT muscularity indices provide an opportunity to improve carcass conformation, a trait included in current breeding objectives. Differences in muscularity of the HL and LR, assessed by the CT muscularity indices, and eating quality were investigated between sexes (ram vs ewe lambs), breeds (SBF vs TEX) and progeny of high- and low-muscularity sires (HM, LM). TEX lambs had 16% greater muscularity than SBF in both regions, whilst differences between sire groups were 4%. Ewe lambs had slightly higher values of muscularity for the F1L than rams but no difference was found for the LR. Meat from SBF lambs was more tender, and had stronger lamb flavour and higher overall liking scores than TEX meat. Sex had a weak influence with ram lambs having a stronger abnormal flavour and lower overall liking in the LR only. No significant differences in meat eating quality were found between HM- and LM-sired lambs, suggesting that improved muscularity would not have unfavourable effects on sensory traits. Genetic parameters for the CT muscularity indices, predictions of carcass muscle and fat weights and CT muscle density were estimated. The estimates of heritabilities of the CT muscularity indices showed they were at least moderately heritable (from 0.38 to 0.92) in both breeds. CT muscle density, measured in the LR, had a moderate to high heritability in both breeds, and strong negative genetic and phenotypic associations with IMF and carcass fat weight. Little association was found between muscularity indices and CT muscle density, implying that improved muscularity would not have a negative effect on CT muscle density. These results suggest, overall, that the effect of selection for improved muscularity of sheep is likely to be favourable for carcass quality and neutral with respect to meat eating quality. Because of the strong phenotypic and genetic associations with IMF, CT muscle density may be a promising selection tool to counteract possible negative effects of decreasing fatness on IMF and therefore eating quality. The inclusion of CT muscle density as a selection criterion allowed more favourable genetic responses in IMF, without further unfavourable increases in carcass fat weight or detrimental effects on leanness. Because increased economic values for IMF led to different expected gains in IMF and other traits in the breeding goal, the definition of the specific values depends on the desired gains in all traits by the industry. Positive returns for the industry from using CT muscle density at the second stage of selection can be obtained for all economic values included in this simulation. The economic benefits were maximised when the proportions of ram lambs CT scanned were 0.15.

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Considerable variation in pre-laying behaviour of domestic hens <I>(Gallus gallus domesticus)</I> is observed within individuals, between individuals and between different husbandry systems. The contributions of internal and external factors to this variation were considered. The main internal factors considered related to lag and position of eggs in sequences. The duration of the sitting phase and the total time spent in the nest box was related to lag. The duration of pre-laying behaviour was longer for the first egg of a sequence than for the other eggs. This was mainly due to a longer searching phase in which hens performed more nest examinations. The duration of the sitting phase was longer for the last egg of a sequence than for other eggs; this may have been related to a longer lag found for the last egg. A series of experiments was conducted to investigate the performance of pre-laying behaviour while altering the availability of food and motivation to feed. Hens always interrupted their pre-laying behaviour in order to feed when food was presented. Length of deprivation did not influence the duration of feeding or pre-laying behaviour, that is, even "satiated" hens stopped their pre-laying behaviour and fed. However, the delay in oviposition was found to be greater when food was presented in the later, rather than the earlier, stages of pre-laying behaviour. The duration of pre-laying behaviour and of the searching phase was longer if hens were food deprived than if food was available. External factors examined included the effects of conditions that facilitate searching and nesting behaviour on pre-laying behaviour. Hens provided with an unlittered nest box showed an extended pre-laying behaviour and searching phase, more searching behaviour and nest examinations and more nest entries of a shorter duration than when provided with a littered nest box. Providing an exploratory walkway to facilitate searching behaviour resulted in the searching phase starting earlier than expected, and in the occurrence of more searching behaviour and nest examinations during this time.