In an extensive review of energy metabolism of dairy cows, Agnew and Yan (2000) concluded that high genetic merit cows are capable of partitioning more energy into milk and less into body tissue when compared to low genetic merit cows. The objective of the present study was to use production data for a complete lactation to evaluate the effect of cow genotype on energy partitioning between milk and body tissue.

Holstein-Friesian cattle are the predominant breed of dairy cattle in Northern Ireland. Breeding programmes for the Holstein Friesian have focused on improved milk production with little emphasis on functional traits such as fertility or disease resistance. In contrast Norwegian dairy cattle have been bred via a multi-trait selection procedure and there is evidence that problems associated with disease and fertility have tended to decrease in recent years. It is important, however, to investigate possible differences in efficiency of food use and partitioning of nutrients between the two breeds which may offset the potential advantages of improvements in secondary characteristics. Consequently, the objectives of this experiment were firstly to investigate the effects of breed type on the efficiency of utilization and partitioning of nutrients for milk production and secondly to investigate if there are differences in the energy requirement for maintenance and the efficiency of utilization of ME for lactation (kl) between the two breeds.

The replacement of lost body tissue in modern dairy cows usually takes place later in the same lactation, once milk output begins to decline. Individual cows may not regain all lost body energy in the first lactation leading to a greater deficit to be replenished in the second. This results in carry-over effects from one lactation to the next, on both yield and non-yield traits. The use of random regressions and Fourier series allows modelling of cyclical changes in a trait over seasons (Meyer, 2000) and could be used to model multiple lactation energy balance changes in dairy cows. Parameters of these cyclical functions might then be analysed for relationships with traits of economic importance such as health, fertility and survival. The objectives of this study were 1) to model phenotypic daily milk yield, fresh feed intake, liveweight and condition score using random regression techniques, 2) to combine daily estimates obtained in objective 1) into an overall energy balance for each day of the first three successive lactations, 3) to compare energy balance curves over three lactations and 4) to investigate the feasibility of modelling energy balance in the first three lactations using harmonic analysis.

In Northern Ireland, grazed grass is the main diet offered to dairy cattle throughout the summer months. Whilst the Holstein-Friesian (HF) dairy cow is extremely efficient at converting grass into milk, there is evidence that the incidence of infertility in this breed is increasing (Mayne et al. 2001). This may reflect the fact that the breeding goals for the HF breed have been based primarily on selection for milk production with little emphasis for other traits such as fertility or health. In contrast, Norwegian dairy cattle (NC) have been selected using a multi trait index, with less emphasis on milk production and inclusion of other fertility and health traits. The overall objective of the present study was to evaluate the effect of varying stocking rate at pasture on performance of these two contrasting breeds.

Leptin is involved in the regulation of food intake, energy expenditure and whole body energy balance. In livestock species these processes are important for optimisation of growth, reproduction, lactation and overall health and well-being. Condition score is a useful indicator of energy balance and is highly correlated (-0.84) genetically to commencement of luteal activity (CLA), an endocrine measurement of fertility in dairy cattle (Royal et al., submitted). Circulating leptin levels drop post-partum reflecting changes in energy balance and fat mobilisation. The interval to first ovulation post-partum is phenotypically correlated (0.83) to the interval from parturition to the leptin nadir (Kadokawa et al. 2000), suggesting that a delay in the recovery of leptin secretion postpartum increases the delay to first ovulation. The heritability of circulating leptin concentrations in humans and pigs is high (0.39-0.61; Cameron et al., 2000; Rotimi et al., 1997). If this were also the case in cattle, and postpartum changes were related to concentrations at an early age, then it would be of immense value to the genetic improvement of traits associated with fertility.

Since evidence is present that genetic correlations between start of luteal activity and energy balance, milk yield and live weight exist (Veerkamp et al., 2000), it could be hypothesised that polymorphisms at the leptin gene locus might play a role. The first objective of this study was to associate plasma leptin levels during late pregnancy with genetic differences in the leptin gene. The second objective was to relate these polymorphisms with variations in energy balance, milk production, dry matter intake and fertility.

The initial period of lactation in domestic ruminants is usually characterised by both hyperphagia and negative energy balance (Barber et al, 1997). The factors regulating the hyperphagia of lactation are not well understood. Leptin is a peptide hormone which is secreted by adipocytes, and which acts on a number of neuropeptides and receptors in the hypothalamus to regulate appetite and energy balance (Spiegelman and Flier, 2001). The aim of this study was to investigate the role of leptin in the hyperphagia of lactation in sheep.

Circulating leptin, the obese gene product secreted by adipocytes, is sensitive to short-term (meals, starvation) and long-term (spontaneous food intake, food restriction) changes in energy balance in sheep (Marie et al 2001). The present study aimed to explore relationships between adiposity, adipose tissue from different sites and blood leptin concentrations in rams kept in long days when adiposity is normally high.

Obese protein (OB) also known as leptin serves as a protein signal secreted from adipose tissue and acts on a central nervous system that regulate ingestive behavior and energy balance (Campfield, 2000). The sequence of various leptins from 10 mammalian species was compiled and the 3D structure of human leptin mutant W100E was elucidated (Zhang et al., 1997). We have prepared recombinant leptins of sheep, chicken, cow and pig. Mammalian and chicken leptins are respectively 146 and 145 amino acid containing proteins found in circulation. Leptin in blood is found in both free and bound form; the main binding protein is the extracellular domain (ECD) of leptin receptor (Liu et al., 1997). One of the established functions of leptin, is its attenuating effect on the expression of NPY and other neuropeptides in hypothalamus that subsequently leads to decreased food intake (Campfield, 2000). Therefore it seems logical that blocking leptin receptors that are responsible for transferring it through the blood-brain barrier or for its action in hypothalamus will lead to increase in food intake. Leptin receptor belongs to cytokine receptor superfamily. Its ECD consists of ∷ 800 amino acids but it was suggested that only the cytokine homology subdomain II (CHD) consisting of ∷ 200 amino acids is responsible for binding (Fong et al., 1997). The objective of the present work is to prepare recombinant proteins aimed to block leptin action. We suggest two approaches (a) preparation of leptin antagonists capable of binding but not homodimerizing leptin receptors and (b) subcloning and preparing CHD II of leptin receptor responsible for binding of the hormone.

Forages, such as grass and red clover, are a rich source of n -3 polyunsaturated fatty acids, especially α-linolenic acid (C18:3n -3), and may be used as a method of improving the nutritional value of ruminant products. Silage is an important feed for cattle, therefore, a study was carried out to elucidate the effects of wilting and the use of additives on the fatty acid profile of the resultant silage.

The overall objective of our work is to assess the relative contributions of plant enzymes and rumen microbes to rumen degradation of freshly-ingested herbage. In situ techniques have been used extensively to compare rumen degradation characteristics of feeds, though there remain technical problems associated with microbial contamination of residues after incubation. We hypothesised that techniques to study microbial contamination might also provide insights into microbial colonisation. Our earlier studies (Lee et al., 1999) identified distinctive odd-chain fatty acids that could be used as microbial markers. A dacron bag study was conducted to examine the influence of dacron bag rinsing techniques on DM disappearance and microbial contamination in residues from fresh grass, assessed using odd-chain fatty acids as markers.

The energy feeding systems used for dairy cows recommend that the metabolisable energy (ME) concentration of a feed at maintenance feeding level is calculated from its digestible nutrients. The objective of the present study was to develop equations to calculate the ME concentration from digestibility data for grass silages

Ewe and ram genotype have been shown to have a significant effect on carcass quality. For example, Dawson and Carson (2001) demonstrated that lambs from Bluefaced Leicester X Blackface ewes were of poorer conformation than lambs from the Texel X Blackface, Suffolk X Cheviot or Texel Cheviot ewes while high lean growth index sired lambs had an improved conformation compared with lambs sired by non-recorded rams. Recent work has shown that genotype can have significant effects on the meat quality of lambs from hill sheep systems (Carson et al. 2001). Therefore the aim of the current study was to investigate the effect of ewe and ram genotype from the lowland sector on meat quality.

Systems of lowland sheep production in the UK and Ireland are labour intensive with survey data indicating an average level of labour input of 6.0 to 8.0 hrs/ewe/year (Connolly, 2000). With declining returns from lamb production, management options with reduced labour requirements, such as outdoor lambing, need evaluation. Flock genetics may also influence labour requirements and determine the effectiveness of grass-based lambing systems. Therefore, the aims of current study were firstly to evaluate the effect on lamb output of controlled grass-based lambing systems compared with housing ewes in late pregnancy and lambing indoors and secondly to examine the effect of crossbred ewe genotype and ram breed on lamb output with grass-based and indoor lambing systems.

Best Linear Unbiased Prediction (BLUP) estimates of breeding values (EBVs) for economically relevant traits have been used for selection decisions in the UK Aberdeen Angus (AA) population since the early nineteen nineties. Selection exclusively based on BLUP-EBVs is expected to give higher gains than less accurate selection but can also lead to increased rates of inbreeding (ΔF). Dynamic rules using BLUP-EBVs to maximise genetic merit while DF is constrained to a pre-defined level are currently available (e.g. Grundy et al 1998). They showed that the use of these rules gives higher gains than standard BLUP selection at the same level of ΔF. The objective of this study was to investigate the potential of these procedures for optimising selection decisions in the UK AA population.

Disease resistance is often cited as the major challenge facing animal geneticists, with much effort directed towards finding disease-resistance genes. The PrP gene controlling resistance of sheep to scrapie is such an example. To design effective breeding strategies utilising such genes, it is critical to understand the impact that these genes have upon disease transmission. For example, it has been shown that it is not necessary to make all animals genetically resistant in order to protect the population as a whole from epidemics (MacKenzie and Bishop, 1999). Additionally, concern is often voiced over the possibility of the pathogen co-evolving with the host, reducing the utility of the genes. By combining animal breeding and epidemiology theory, this study derives strategies for using disease resistance genes to control disease transmission, and considers the co-evolution risks with such strategies.

Identity-by-descent (IBD) matrices are used for a number of practical applications, e.g. QTL-detection, marker assisted selection in breeding schemes (MAS), refining of covariances among relatives, and MAS for maintaining genetic variation. The calculation of IBD matrices can be made using Markov Chain Monte Carlo (MCMC). However, this is a computationally expensive method. Therefore, a simple deterministic method (Det) has been developed (Pong-Wong et al., 2001). The objective of this study is to evaluate this deterministic method relative to MCMC for the precision of the matrices and their performance in interval mapping and MAS.

Studies investigating the value of Marker Assisted Selection (MAS) for increasing genetic gain have compared responses from MAS and conventional schemes obtained with standard truncation selection and have ignored rates of inbreeding, DF (e.g. Ruane and Colleau, 1995). On the other hand, research comparing schemes at the same ΔF using optimised selection (Villanueva et al. 1999) has assumed that the effect of the QTL is known without error. This study extends the optimisation methods to include selection on genetic markers rather than on the QTL itself.

Quantitative Trait Loci (QTLs) are chromosomal regions containing genes causing variation in continuous traits. Two alleles are Identical-By-Descent (IBD) if they are copies of the same original allele. For each point on a chromosome, it is possible to predict IBD probabilities among individuals given a pedigree and marker information and use them to map QTLs in farmed species. Pedigree founders can either be assumed unrelated (George et al. 2000) or related through distant common ancestors (Meuwissen and Goddard 2000). The relationship among founders was estimated through simulating the history of a model population. Linking the current population with original ancestors, without a pedigree, is central to the theory of long-term genetic contributions (Bijma 2000). Hence, in the light of this theory, it should be possible to deterministically predict IBD relationships among pedigree founders. A first step towards this objective was predicting inbreeding (F) within each animal at a chromosomal location.

Backcrossing can be used as a tool to introduce new alleles into a population. Having detected an allele of interest in a non-commercial (donor) line, backcrossing methods introduce the allele into a commercial (recipient) population whilst minimising the contribution of the less superior donor genome. Many alleles linked to the desired donor allele are incorporated into the recipient line by a phenomenon called linkage drag. Loci in the region of the target locus may trace back to a common ancestor and become identical by descent (IBD). This leads to a loss of diversity around the target locus. The linkage drag and contributions from ancestral recipient populations mean that the backcross population suffers genetic lag for commercial traits. This study aims to investigate the effect of population size and number of backcross generations on genetic lag, linkage drag and IBD around a target allele reducing back fat found in the Chinese Meishan breed when backcrossed to a commercial Large White population.