Fat is often fed to dairy cows as a means of increasing dietary energy concentration; however feeding fat often reduces feed intake. For many fat supplements this can be due to negative effects on rumen digestion, however feeding rumen inert fat and post ruminal infusions of fat can also depress intake although the mechanism by which this happens is not clear. The effect of fat on intake may also be influenced by stage of lactation as in early lactation fatty acid levels in the blood can be elevated. The aim of the present study was to investigate the effects of fat infusion into the abomasum on dry matter (DM) intake, milk production and metabolism of splanchnic tissues (portal drained viscera (PDV) and liver) in early and mid lactation cows.

The very long chain n-3 fatty acids eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6) are metabolised to certain prostaglandins and thromboxanes which are thought to reduce platelet aggregation and to possess important anti-atherothrombotic properties. The major source of C20:5 and C22:6 in dairy cow diets are fish oils, but the efficiency of uptake of these fatty acids into milk fat is low (Storry et al, 1969; Hagmeister et al, 1988). The aim of this experiment was to investigate the extent of uptake of EPA and DHA into milk fat in high yielding dairy cows.

Identification of genetically unique populations is a key aim in the study of livestock breed diversity (Hall and Bradley, 1995). In this study random sampling techniques were used to test the significance of genetic distances between European cattle breeds, and to analyse the stability of breed relationships.

There is evidence that selection for milk yield alone in dairy cattle leads to a deterioration in fertility (e.g. Hoekstra et al., 1994) and health (e.g. Uribe et al., 1995). Genetic selection to improve health and fertility traits should be considered for reasons of both welfare and profitability. The aims of this study were to estimate genetic parameters for health disorders and measures of fertility in Holstein Friesian cattle and to estimate correlations between these traits and 305 day milk yield.

Mastitis remains a costly health problem to dairy farmers despite a significant reduction in both clinical and sub-clinical mastitis over the last 25 years. This reduction has been due predominantly to the success of management control programmes. The continuing losses have raised the interest in breeding as a means to reduce mastitis incidence. Somatic Cell Counts (SCC) have been used since 1977 as an indirect means of monitoring mastitis within dairy herds. Since 1991 an optional individual cell count service has been offered by Milk Recording Organisations in the UK. The result is that 0.80 of recorded cows have SCC records. The Animal Data Centre has analysed the SCC data to establish genetic parameters and produced preliminary evaluations on bulls and cows (Mrode et al, 1996). As a forerunner to launching SCC evaluations it is important to determine whether SCC evaluations in the UK agree with similar evaluations overseas.

Over the past 10 years, dairy breeding in the United Kingdom has switched from British Friesian to the North American type Holstein. Many of the bulls entering progeny testing in the UK in that period were sourced from overseas bull mothers, especially from the US. The aim of this study was to compare current predictions of the genetic merit of those bulls, using pedigree information, with the performance of their UK daughters.

Wray and Thompson (1990) described the relationship between genetic contributions and the rate of inbreeding and this work was extended by Woolliams and Thompson (1994) to interpret genetic response in terms of genetic contributions. By using these relationships Meuwissen (1997) developed an algorithm for obtaining optimum selection decisions at a given (discrete) generation and level of inbreeding by maximising a function of accumulated gain corrected for squared contributions. Here we extend this method for optimising populations with overlapping generation structure and maximising response at a given rate rather than level of inbreeding. Three modifications to the afore mentioned model are presented: an augmented numerator relationship matrix which has not been corrected for reduced Mendelian variance with inbreeding, the consideration of committed future contributions beyond the next cohort derived from the lifetime breeding profile of the population, and a constraint to achieve the desired rate of inbreeding.

A significant relationship between the ESR gene and litter size has been reported for a range of Meishan synthetic and Large White lines (Rothschild et al., 1995). The effect of one copy of the positive (B) allele in a European 50% Chinese Meishan synthetic (L93) was estimated as +0.79 pigs born alive per litter in the first parity (Southwood et al, 1995). It is therefore of interest to incorporate the positive allele into a comercial parent gilt, the growing performance and soundness of these animals also being of importance. The objective of this trial was to evaluate the effect of the ESR gene on growth and performance traits in a commercial type background.

Information on the sensitivity of genotypes to different nutritional inputs is important to the pig industry to ensure the feeding of appropriate diets. Testing genotypes on a single diet may constrain potential growth, defined by an animal's genotype, by under-supplying nutrients or may reduce the efficiency of nutrient utilisation by over-supplying nutrients. The current study examined the relationship between selection strategy and the sensitivity of genotypes to different nutritional inputs.

A delay in the onset of puberty in gilts with intensive selection for efficient lean growth would have substantial implications for pig breeding programmes due to later first parity matings. Therefore the current study determined the responses in gilt traits at puberty to selection for components of efficient lean growth rate.

Until recently, to enable accurate recording of feed intake, pigs were kept in individual pens. The advent of electronic feeders has allowed accurate records of feed intake and feeding patterns in group housing which is more similar to that found in the production environment. The objectives of this study were to estimate genetic parameters for these feeding pattern traits and their correlations with production traits to show potential benefits in selection.

Responses in muscle fibre characteristics of pigs, due to selection for lean growth, would be of concern to the pig breeding industry, if there were also associated changes in meat and eating quality. The present study evaluated the responses in muscle fibre characteristics to selection for components of efficient lean growth.

Embryo mortality is a major cause of reproductive loss in all the farm species (Bolet, 1986). Losses of a total litter by embryo mortality account for about 15% of all services but may be substantially higher in the summer months, particularly in outdoor systems (Love et al., 1993). There has been interest in the use of gonadotrophin releasing hormone (GnRH) in cows and sheep, both on the day of service and 12 days after, to improve pregnancy rates (see review by Peters 1996) with 10 -12% improvements being reported. The mechanisms of maternal recognition of pregnancy are different between pigs and ruminants, however, a pilot study was carried out to determine whether GnRH might have similar effects in the pig.

Embryo culture or manipulation can severely influence fetal development resulting in increased gestation length and unusually large offspring (Walker et al, 1996). The aim of this study was to compare the effect of transferring in vivo or in vitro produced bovine embryos on gestation length, calf sex, birth weight and calving ease.

Embryonic loss between day 8 and 16 after insemination is a major cause of reproductive wastage in cattle. Plane of nutrition in the peri-ovulatory period is inversely related to both systemic progesterone and embryo survival in pigs and sheep. The objective of this study was to investigate the effect of short-term changes in plane of nutrition during the peri-ovulatory period on systemic progesterone and on embryo survival in cattle.

In beef suckler cows, the prolonged interval from calving to first ovulation (post-partum interval, PPI) is due to failure of ovulation of dominant follicles. It appears that a combination of poor body condition, maternal calf-bond and suckling act to suppress the LH pulse frequency necessary for ovulation. A combination of calf isolation and once-a-day suckling can significantly shorten the PPI, but the first ovulation generally occurs without overt oestrus and the subsequent cycle is short (8 to 11 days) due to lack of progesterone priming. The aim of this study was to examine the effects of progesterone or progesterone and oestradiol in conjunction with calf isolation on the interval to first ovulation, incidence of overt oestrus at first ovulation and length of the subsequent interovulatory interval.

Suckling cows following milk extraction has been found to increase total milk yield (Bar-Peled et al, 1995; Margerison et al, 1995) and allows calves to be reared by suckling. These restricted suckling systems are common in developing countries and have been applied in developed countries (Boden and Leaver, 1994; Sandoval and Leaver, 1995). There are few long term studies of restricted suckling which include milk yield, milk composition and calf development. The objective of this experiment was to study the effect of restricted suckling on lactation, reproduction and calf development in Colombia.

An earlier study at Langhill (Veerkamp et al, 1995) showed that selection for yield in dairy cows increases body tissue mobilisation during lactation, since high genetic merit animals had a lower average condition score (CS) compared with low genetic merit animals. However, in this study no diet effect for condition score and no interaction between diet and genetic merit was found. The reasons for this might have been that average condition scores during lactation were analysed, and therefore the objective of this study was to evaluate the effects of genotype and diet during lactation using weekly observations.

Performance characteristics of high genetic merit cows on different feeding systems are not only important to establish the biological and economic consequences of current genetic selection practices, but can be used also to establish ‘standards’ which will be helpful to people who want to develop breeding, management or feeding strategies for high genetic merit cows. Whereas the performance of high and average genetic merit cows on two different feeding systems has been presented before (Veerkamp et al. 1995), the aim of this study is to define if some of the advantages of high genetic merit cows persist throughout the first three lactations of a cow's lifetime.

Supporting the higher milk yields of high genetic merit cows requires an increased supply of nutrients to the animal. In grass silage based production systems this is achieved by either offering additional concentrates or by improving the quality of the silage. However, the relationship between silage quality and the response to concentrate supplementation has not been defined for high merit animals. It might be expected that as level of concentrate supplementation increases, the quality of the silage offered will become less important. This study was undertaken to define the responses of high merit dairy cows to a range of concentrate levels given in addition to two contrasting silage types.