This thesis gives a complete description of the changes in the ewe-lamb relationship from birth to weaning, and determines those ewe behaviours of greatest importance to lamb survival and growth. Detailed observations on the grooming behaviour of 50 Scottish Blackface ewes illustrated the extent to which grooming behaviour in twin bearing ewes is affected by the birth of the second lamb. Althugh previous experience does not affect grooming behaviour specifically it does affect the ability of primiparous ewes to cope initially with grooming twin lambs. Previous experience does however, strongly affect ewes responses to active lambs, shown in uncooperative movement by primiparous ewes as lambs attempt to suckle. It was also found, using crossbreeding, that although a lamb, such as the Mule, may have a high birthweight and also stand quickly after birth this does not necessarily mean it will also suckle quickly and effectively. The Mule lambs which were intended to be inactive relative to pure Blackface lambs, were not in the event inactive but failed to show appropriate udder-seeking behaviour. It would appear that the initiation of grooming is genetically controlled and that lamb behaviour, particularly lamb activity may influence the further development of grooming. Longer term observations of 73 Scottish Blackface ewes and lambs outdoors in two years showed that the major changes in the ewe-lamb relationship occur at 3 weeks of age. This corresponds to the time of commencement of weaning, or a new phase in the ewe-lamb relationship and is determined by the willingness of the ewe to allow suckling and the subsequent ability of the lamb to adjust its behaviour. The lamb has to learn that it will only be allowed to suckle when the ewe communicates her wilingness by a headup or call signal. These results are discussed in relation to current literature on parent-offspring conflict and weaning theories. Ewe behavioural measures were also shown to influence lamb growth. Estimations of the quality of the ewe-lamb relationship, using measurements such as headup and call frequencies, appear most likely to have an influence on lamb survival and growth. The influence of ewe behaviour, on the lamb and the ewe-lamb relationship, may well be best investigated in the future through the use of an individual ewe 'character' description.

The aim of this project was to isolate a functional BoLA class I gene, to transfect this into L cells and to investigate the possibility of a second BoLa class I locus. Attempts to isolate a functional BoLA class I gene from a cosmid library were unsuccessful, but clones encoding complete BoLA genes were successfully identified from a bacteriophage library. This library was made from animal 10769 which has BoLA type w10/w11 and the genes were identified with a class I cDNA probe, pBoLA-1. These clones were transfected into mouse L cells to look for expression. One of the clones, 19.1, expressed class I molecules when analysed by indirect immunofluorescence on the FACScan and by fluorescence microscopy. The Northern blot analysis confirmed class I transcription products when probed with pBoLA-1. Clone 19.1 was identified as encoding a w11 gene by a microlymphocytotoxicity test. Also in a T cell cytotoxicity assay, Ltk 19.1 cells were killed by alloreactive anti w11 cytotoxic T cell clones but not by anti w10 clones. Nucleotide sequencing of gene encoded in 19.1 demonstrated homology between this and BoLA cDNA clones and HLA. Therefore a functional BoLA class I gene with a BoLA type w11 was isolated and is a stepping stone to many other investigations.

No description available.

Milk production, feed intake, and liveweight records were available on individual animals from a high yielding Holstein-Friesian herd in which selection had been practised on fat plus protein yield using nationally available AI sires. Unlike most other studies, animals were fed <i>ad libitum</i> thus making this data ideal for investigating genetic relationships. In total, the data comprised 475 26-week and 293 38-week (a subset of the 26-week data) lactation records. The relationship between sires and maternal grandsire's transmitting ability (ICC), expressed as a pedigree index (sire ICC + 0.5 maternal grandsire ICC), and offspring performance for milk production traits, feed intake, and gross efficiency (milk energy (MJ)/total intake (MJ)) was investigated. Regressions of fat plus protein yield, fat yield, protein yield, and milk yield, of heifers, on their corresponding pedigree index were not far from the theoretical expectation (for a full lactation) of 1. A genetic increase of 10% in fat plus protein yield of daughters of sires of high genetic merit for fat plus protein yield was accompanied by a genetic increase of 2.0% in feed intake and a 7.9% genetic increase in efficiency. The genetic relationships among milk production, feed intake, feed efficiency and liveweight traits were investigated. Restricted Maximum Likelihood analyses were carried out, fitting an Animal Model, with repeat lactations as an additional random effect. Univariate analyses were done after approximate canonical transformation of the traits. Heritability estimates for fat plus protein yield, feed efficiency and feed intake ranged from 0.45±0.22 to 0.15±0.12, 0.48±0.21 to 0.13±0.09, and 0.52±0.14 to 0.30±0.15, respectively. Genetic correlations between milk production traits and efficiency were generally less than 0.65. Genetic correlations between liveweight traits and efficiency were very high and negative. The results indicate that when selection is on yield, the correlated responses in efficiency may be smaller under <i>ad libitum</i> feeding, compared with published values where cows were fed according to yield. Including liveweight in the selection criterion may give higher responses in efficiency compared to selection on yield alone. In nucleus schemes (based on Multiple Ovulation and Embryo Transfer) it may be worthwhile to include feed intake or efficiency directly in the selection criteria.

The aim of this thesis is to quantify the benefits of selection for resistance to an important sheep disease in Britain. Specific aspects addressed are <i>i</i>) the choice of the specific disease based on economic costs and potential savings from selection, <i>ii)</i> genetic parameters for the disease, such as the heritability <i>(h</i>²) and the relation with production traits, <i>iii)</i> prediction of the response to selection on a trait that is measured in only two classes (healthy or diseased) and depending on environmental factors affecting exposure and prevalence, and <i>iv)</i> modelling of the combined effect of increased genetic resistance and reduced pathogen burden as a result of selection. It is concluded that footrot is a disease of economic importance, with additive genetic variability. Selection for resistance can be effective if based on simple binary scores, especially if animals are scored repeatedly. The response to such selection can be predicted with a newly developed theory for binary traits, which also covers situations when exposure to infection is variable. Selection for resistance is expected to result in animals that can better cope with the disease, in terms of reduced weight loss. A new epidemiological model predicts likely responses to selection, showing a considerable additional decrease in the prevalence of footrot compared to purely genetic predictions. It is concluded that selection for increased resistance to footrot can be expected to be successful in reducing costs of the disease to the British sheep industry.

An increase in the concentration of plasma (PRL) occurs in response to increased daylength in seasonally breeding animals irrespective of whether they are short or long day breeders. In contrast to the wealth of information on the photoperiodic control of PRL secretion in mammals very little information is available in birds. The objective of this thesis is to increase understanding of the photoperiodic control of PRL secretion in birds. The critical daylength (CDL) required to induce PRL secretion in bantam cockerels reared on short days (8h light/day) was between 11 and 12h light/day. Photoperiods of more than 14h of light were maximally photostimulatory. The CDL was dependent on photoperiodic history because in birds reared on 20h light/day transfer to photoperiods of 14h or less resulted in decreased PRL secretion. Transfer from 8h light/day to a single 20h long day and back to short days induced an increase in PRL secretion 20 to 22h after dawn. This increase persisted as a "carry over effect" for 4 days. Changes in ambient temperature or fasting up to 24h did not affect PRL secretion. This eliminated the possibility that photoperiodically induced changes in PRL secretion could be explained by these factors. Prolonged exposure of intact male and female turkeys or bantams to 20h light/day resulted in a depression in plasma PRL. The depression in plasma PRL appeared to be a direct consequence of the development of photorefractoriness and was not the result of a decrease in plasma gonadal steroids due to ageing or the development of reproductive photorefractoriness. This was deduced from the observation that prolonged exposure of castrated bantam cockerels to 20, 18, 16 and 14 but not 12h photoperiods also depressed plasma prolactin indicating the development of photorefractoriness. A 4h increase in photoperiod did not stimulate PRL release in castrates held for a prolonged period on a 16h photoperiod but did so in castrates held on 12h photoperiod. Exposure of photorefractory castrates to short days for 5 weeks dissipated refractoriness and restored the photoperiodic response. The age at which the PRL photoperiodic response first appeared was determined in prepubertal intact male and female bantams reared on 8h light/day. Sexual maturation occurred at 18 to 20 weeks of age. An increase in PRL secretion was observed after photostimulation in both sexes at 4, 8, 12 and 16 weeks.

No description available.

This thesis covers three main areas of research. The first is a longitudinal sero-epidemiological study of a dairy herd which suffered an abortion storm linked to infection with <I>N. caninum</I> during August/September 1995. The main aims were to study the long term antibody response in cattle which have suffered <I>N. caninum</I> associated abortion, and to assess the rates of congenital infection, abortion and repeat abortion on the farm during the subsequent 3 year period. The second area of study investigated <I>Neospora</I> antigens recognised by <I>Neospora</I> antibody positive sera using western blot. Diagnosis of infection with <I>N. caninum</I> depends on detection of anti-<I>N.caninum</I> antibody in serum, but animals which have previously aborted due to neosporosis can become sero-negative by <I>Neospora </I>IFAT and ELISA several months post-abortion. The third area investigates cell mediated immune responses to <I>N. caninum </I>and the antigens involved in induction of T cell responses. <I>N. caninum</I> can induce repeat abortion in some individuals unlike the closely related coccidian parasite <I>Toxoplasma gondii</I> which induces life long protective immunity after primary infection. Cellular immune responses are important in the development of immunity to <I>T.gondii</I> and therefore are likely to be important in preventing repeat abortions in 95% of the cattle which abort due to neosporosis. This study showed that experimental infection of calves with <I>N. caninum</I> NC1 tachyzoites stimulated a cell mediated response detectable in peripheral blood using a simple proliferation assay. This response was characterised by the production of the T cell cytokine IFNγ which is produced by CD4+, CD8+ and natural killer cells and is known to be important for protection against other intracellular parasites.

Studies were conducted using Scottish cashmere goats which were segregated into responsive and non-responsive individuals on the basis of ranked faecal egg count following artificial and natural gastrointestinal nematode infection. These studies demonstrate that caprine responsiveness is a relatively stable and heritable characteristic, largely unaffected by season and mode or site of infection. Initial comparative studies showed does to be considerably more susceptible to mixed artificial <I>teladorsagia circumcincta</I> and <I>Trichostrongylus vitrinus</I> infection than were ewes or worm-naive lambs. This was reflected in distinct differences in mucosal mast cell (MMC) and glouble leukocyte (GL) populations, the does having more GLs but many fewer MMCs than ewes. Theses differences together with the very low sheep mast cell proteinase concentrations recovered from doe tissue suggest that there are important functional differences in the mast cell responses of sheep and goats. The responses of breeding male and female goats were very consistent, with individuals occupying the same position of relative responsiveness while on pasture and after artificial challenge. Differences in the susceptibility of responders and non-responders were apparent in egg count following natural and artificial infection and selection was largely supported by worm burdens recovered after artificial challenge. There was a tendency for enhanced responsiveness to be associated with increased tissue eosinophil and GL numbers though this relationship wasn't very strong. However, responders were able to mount a more rapid and vigorous peripheral eosinophil response than were non-responders suggesting that peripheral eosinophil levels may be indicative of the ability of the host to respond to infection. Analysis of the cellular traffic of the gastric lymph showed that more resistant individuals were responding earlier. Results obtained from the first generation yearlings from the helminth-line showed that under the conditions encountered in these studies increased resistance to gastrointestinal nematode infection in Scottish cashmere goats is a heritable phenomenon with a heritabililty estimate (0.37) similar to those of production traits for which selection has been successful. Over the early stages of the programme selection for enhanced resistance appears to have had no detrimental effect upon productivity.

The main aims of this study were to identify and characterise proteins from <i>T. circumcincta </i>that may induce a protective immune response in the host and to learn more about the biology of the worm. In order to identify possible protective antigens, a complementary DNA (cDNA) library prepared from adult worms was screened with serum from an animal that was protected against a single challenge infection after vaccination with a <i>T. circumcincta </i>protein fraction (S3 TSBP). Forty five immunopositive cDNA clones were identified, of which sixteen had homology to galectin. Of the remaining clones, the majority shared homology with two metabolic enzymes, methylmalonate semialdehyde dehydrogenase and 10-formyltetrahydrofolate dehydrogenase, that have not been characterised in nematodes. A single clone with homology to the antioxidant enzyme, catalase, was also identified. These three enzymes were selected for further investigation on the basis of their roles in nematode metabolism and therefore, their potential as vaccine candidates. Characterisation of <i>T. circumcincta </i>excretory/secretory material (ES) was also performed. L4 and adult worms were cultured <i>in vitro</i> and the proteins released were separated by 1D electrophoresis and analysed by Tandem Liquid Chromatography Mass Spectrometry and N-terminal sequencing. This identified proteins showing similarity to, amongst others, metabolic enzymes, structural components, antioxidants, globin-like proteins and cysteine proteases, present in online databases but not previously characterised in <i>T. circumcincta.</i> This study has identified several novel <i>T. circumcincta </i>proteins that may have potential as future vaccine or drug targets. It has also provided further information regarding the biology of the worm.