Milk output has been manipulated by dietary methods for many years, however the underlying mechanisms for changes in milk composition are as yet unclear. In an attempt to further understand these mechanisms we have compared the mammary uptake of metabolites on two isoenergetic diets with different protein levels expected to provide different amounts of amino acid to the mammary gland.

Early- to mid-lactation Friesian cows were used to examine the effect of increased dietary protein supply on the supply of metabolites to and uptake by the mammary gland in relation to milk protein synthesis. Two barley based concentrates were formulated to contain 20.8 (Cl) or 29.1 (C2) g N/kg DM, using fishmeal (Provimi 66, high UDP) as the supplementary protein and fed with grass silage (28.3 g N/kg DM) at a total dry matter intake of 17 kg/day. In Experiment 1 these diets were fed at 50:50 (concentrate:silage) to four lactating cows fitted with rumen and duodenal cannulae in a simple crossover design.

With the failure of current nutritional schemes for dairy ruminants to predict yields of milk and milk components, and perceptions of milk's nutritional value following recommendations to reduce dietary fat intake, an integrated approach to feeding and metabolism needs to be developed. Such a system must therefore be ‘metabolite’ based.

An ability to predict changes in milk constituent output in response to alterations in nutrition requires, in the first instance, the identification of specific precursors for milk component synthesis in the lactating mammary gland. Arteriovenous differences across the mammary gland indicate that blood free amino acids (AA) are either taken-up by the gland in excess, equal to, or in insufficient amounts compared to their output in milk (1). Isotope labelling experiments have indicated that, in addition to AA free in blood, the mammary gland utilises a substantial amount of AA derived from constitutive mammary gland protein breakdown (2). The present experiment was designed to investigate the AA precursors and kinetics of milk protein synthesis and to confirm and extend the latter observations.

Previous studies have shown a low efficiency of utilisation of urea treated whole crop wheat (UWCW) when offered as the sole forage to dairy cows (Hill and Leaver 1990). The poor efficiency of utilisation of metabolisable energy could possibly be influenced by the level and quality (the balance in QFN, SFN, and UN) of protein intake by the cow.

To investigate the effect of level and quality of protein intake on the digestibility of UWCW fed ad libitum to lactating cows, an experiment was carried out using three concentrate sources based upon molassed sugar beet pulp pellets (Diet A), soya bean meal (Diet B) and fishmeal (Diet C). A concurrent experiment was implemented to analyse the degradation characteristics of UWCW using sheep.

Six multiparous mid to late lactation Holstein Friesian cows were allocated to two 3x3 latin squares. Each cow was housed in an individual pen and fed UWCW ad libitum once daily and concentrate twice daily. Individual DM intakes of forage, milk production, liveweight and faecal output were estimated for each diet. The degradability trial used the methodology of Paine et al (1982).

Consumer demand for leaner beef necessitates a reduction in the fat content of a major proportion of the beef carcasses currently produced. It is generally accepted that reducing the plane of nutrition of beef cattle reduces fat content. However the effects on growth rate and overall efficiency of production are also important. The effects of reducing energy intake on performance and carcass composition may be influenced by the nature of the change in energy intake. An experiment has been carried out to examine the effects of reducing energy intake, either by increasing forage: concentrate ratio (F:C) in the diet or reducing dry matter intake at constant F:C.

Thirty-six Friesian (F), Limousin x F and Belgian Blue x F 12-month old steers which were initially 368 kg, and which had been reared under uniform management and nutrition were used. They were purchased from dairy farms during October and November at approximately 10 days old, were aritifically reared and were at pasture from April until October. After a three week acclimatization period they were divided into blocks according to breed and live weight and allocated to the three treatments at random with each block. The three treatments were a complete diet consisting of 0.67 grass silage (719 g digestible organic matter and 144 g crude protein/kg DM; 82 g ammonia N/kg total N) and 0.33 concentrates (0.9 rolled barley and 0.1 soyabean meal) offered (1) ad libitum or (2) at 0.8 of ad libitum intake.

Balancing the rate of nitrogen and energy yielding substrates to rumen micro-organisms has been proposed in order to maximise the capture of rumen degradable nitrogen and to optimise microbial growth rate and efficiency (Johnson 1976). Current systems for diet formulation of ruminants are based upon the extent of fermentation of organic matter or carbohydrate fractions and the supply of rumen degradable and undegradable protein (ARC 1984, Webster, Dewhurst and Waters 1988). Little attention has been paid to the effect of the rate of supply of energy and nitrogen to rumen microorganisms in-vivo. The objectives of the current experiments were to formulate diets that had similar daily degradation of nitrogen and energy yielding components but varied in the rate of energy and nitrogen release based upon in-situ degradation characteristics of the raw ingredients, and to monitor the effect of these diets on rumen fermentation and microbial growth.

Over the course of the last 40 years or so increasingly reliable procedures have been developed for multiple ovulation, embryo recovery and embryo transfer, initially for cattle (see review of Woolliams and Wilmut, 1989) and, more recently, for small ruminants (McKelvey and Robinson, 1986). During this time a number of applications have been proposed or practised. These include uses in (i) within-breed genetic improvement programmes, (ii) the import and export of genetic material (offering potential advantages in economy, animal welfare and disease control), (iii) accelerating breed substitution by multiplication of newly introduced breeds and (iv) conservation of genetic material (by freezing embryos) from valuable individual animals, or from rare or endangered breeds or species. Additionally, there are several new ‘reproductive’ procedures available or being developed for use in animal production (eg. in vitro fertilisation, embryo sexing, cloning, gene transfer) which hinge on the use of embryo transfer. These are discussed in detail by Woolliams and Wilmut (1989) and in the following two papers. The aim of this paper is to examine the first of the applications listed above - the use of multiple ovulation and embryo transfer (MOET) in within-breed genetic improvement programmes.

Molecular genetic manipulation can now be used to produce pharmaceutical proteins in the milk of farm animals. In the longer term this technology will be used to modify aspects of animal production, but it is not clear how many manipulations will be useful nor when such applications will become practicable. Improvements are required in all four aspects of an effective scheme for either gene transfer or targeting: it must be possible 1). to make the change, 2). to regulate expression of the gene in the desired manner, 3). to identify genes that are able to have a significant effect and 4). to disseminate the change into the target population.

There is only one method that has been used to transfer a gene in livestock and this depends upon injection of a few hundred copies of the gene into a nucleus in the early embryo. It is believed that integration occurs because the act of injecting fluid causes breakages in chromosomes and that the repair mechanisms sometimes include injected DNA. There are serious implications.

The propagation of genes from farm animals of superior genetic merit is presently most rapidly achieved by superovulation and embryo transfer. Although these procedures increase the number of offspring from superior females, genetic uniformity and predictability are not guaranteed because of the diversity introduced by genetic recombination at meiosis. To overcome this problem, techniques that generate identical embryos from a single founder have been devised. Embryo splitting and blastomeres separation represented the first approaches to embryo multiplication, but both these techniques are severely limited by the very small clone size which rarely exceeds two offspring. Nuclear transplantation has the potential to produce far larger number of identical embryos but is technically more difficult and involves three separate procedures. Firstly, a source of nuclei, or so called caryoplasts, in an appropriate undifferentiate state is required. Secondly, a supply of enucleated host cells or cytoplasts is essential for the support of the transplanted nucleus.

Dietary energy is the major factor influencing the cost of pig feed and consequently pig meat production. Therefore, precise estimation of the energy value of feedstuffs is particularly important. The 1991 Braude Scholarship was used to finance a visit to a number of research establishments based in the Netherlands, Denmark, Germany, Switzerland and France to compare their systems of energy evaluation, to investigate the energy-yielding ingredients included in pig diets in these countries and to learn of current research concerning these areas, specifically on the digestibility of fats.

Satisfactory levels of performance and improved carcass and meat eating quality in growing pigs fed high levels of sugar beet pulp (SBP) have been recently demonstrated by Kay et al. (1990) and Longland et al. (1991). One of the main advantages from feeding SBP was a reduction in carcass fatness and increased returns from improved grading. The objective of this work was to determine whether these benefits could be sustained to heavier finishing weights and to compare differences in the response to SBP as a source of readily fermentable non-starch polysaccharides (NSP) and to oat feed (OF), a cereal by-product high in insoluble NSP, which is less easily degraded.

One of the potential advantages of choice feeding is that it could remove the need to formulate and manufacture complete diets for pigs. The simplest and most attractive option would be where pigs could select an adequate diet from basic raw feed ingredients offered separately. However, intrinsic differences in the composition of feed ingredients, particularly naturally occurring antinutritional and toxic factors, may influence selection, nutrient intake and performance. The aim of this study was to determine whether growing pigs could select an adequate diet when offered an unrestricted choice between a cereal and a protein supplement.

A theory of diet selection (Kyriazakis, 1989), which is supported by the results of a series of experiments, proposes that growing pigs, given a choice between a low and a high protein food, will select a diet that meets their protein requirements and avoids, at least to a certain extent, excess protein intake. It is important to test whether the rules that appear to underlie the diet selection of pigs persist when one, or both, of the foods given as a choice contain an anti-nutritive factor. A rapeseed meal of high glucosinolate content, was chosen as the protein source to test the above hypothesis. The objective of the experiment wad thus to investigate the rules that may underlie the diet selection of pigs when they are given a choice between two foods that differ in their protein content (a low and a high) and the inclusion level of rapeseed meal.

Pigs are believed to posses a strong motivation to perform exploratory behaviour, which include a range of activities such as walking, orientation towards stimuli and direct investigation. Under free-ranging conditions these activities often occur in connection with foraging (Stolba and Wood-Gush, 1989). In ad libitum fed young growing pigs the provision of straw has been found to stimulate various behaviours involving direct investigation of the straw (e.g. Fraser et al., 1990; McKinnon et at., 1989). As it is assumed that growing pigs under such ad libitum conditions ingest sufficient nutrients, it is often assumed that the straw directed behaviour is unrelated to feeding motivation. However, individual pigs offered single diets may not be able to meet their nutritional requirements (Kyriazakis et al., 1990), and this may have behavioural consequences. For example, the straw directed behaviour observed in growing pigs may be a reflection of unfulfilled nutritional demands and in fact represent appetetive foraging. The aim of the present experiment was to assess the extent to which the exploratory activity of growing pigs is affected by limitations in nutrient intake (specifically the crude protein content of the food).

An Increasing amount of data are being generated on the digestible amino acid content of feedstuffs. Progress towards formulations based on digestible amino acids rather than total values is promising. A wider variety of feedstuffs may feature in feed formulations along with greater use of crystalline amino acids when more confidence can be placed on their digestible amino acid values. However crystalline amino acids are often assumed to be 100 per cent digestible. This study was designed to assess the digestible value of crystalline L-tryptophan in young pig diets.

Heat treated cereals whether steamed and flaked or extruded are widely used in pig starter diets despite the dearth of experimental information to support the view that cooking of cereals improves their utilisation by young pigs or improves growth performance of weaned pigs.

McCone et al. (1991) showed that micronisation and flaking of cereals had no beneficial effect on pig performance. The objective in the present trial was to evaluate extruded and steamed-flaked wheat and steamed-flaked maize in diets for pigs immediately after weaning.

The quantification of the relationship between feed composition and the efficiency of protein utilisation is a critical step in any model intended to predict the responses of an animal to its diet as rates of protein and lipid retention. Current descriptions of this relationship propose that the efficiency of protein utilisation (ep) is constant and independent of energy supply (Stranks et al, 1988), that ep is a function of protein intake only (ARC, 1981) or that it is a complicated function of the supply of energy at constant protein intake (Fuller and Crofts, 1977). The objective of the two experiments described here, was to define the form of the relationship between feed composition and ep, by using suitable experimental designs.

Little is known about how creep-feeding influences later growth rate in pigs. In previous studies, creep-food consumption has been measured by limiting access to food to allow the time spent feeding by individuals to be measured, however there are problems with this approach. Competition for the feeder may result in inaccurate measurement since some piglets may not have the opportunity to feed. Also, piglets will have less opportunity to learn about the food source by observing others. The approach used in the current experiment gave all piglets access to creep-food at the same time, allowing the piglets to feed normally. Any synchronisation in feeding activity that might affect food consumption was possible. Five litters of Large White X Landrace piglets were offered a home-mix starter diet from 10 days of age. A mark and capture technique was employed. The inert marker (Microtracer RF-Ni; Guinness Chemicals Ltd.) was mixed with the diet (30 g/tonne) that was fed to the piglets. The microtracer was a ferro-magnetic alloy powder of minute particle size (25,000 parts/gramme), that resisted dissolution in the gastrointestinal tract and was easily recovered from a faeces-water slurry using a magnetic ‘wand’. Faeces were collected from piglets at 18 days of age. Piglets were weaned at 21 days and were randomly allocated to one of four types of weaner pen, where they remained for 4 weeks. Weaned piglets were fed the starter diet ad lib for 7 days after which they were fed a standard weaner diet. On average 1.9 g (dry matter weight) of faeces were collected from each piglet. The number of particles retrieved from faecal samples (mean = 5.4, range = 0 - 39), and the proportion of iron particles per gramme of dried faeces was calculated for each piglet that was sampled, as an estimate of creep-feed intake. There was a large variation among piglets in creep-feed intake but no significant difference between litters. Females consumed more creep-feed than males (p < 0.001, t-test) (Fig. 1), but experienced the same growth check as males post-weaning. There was no relationship between weight gain post-weaning and creep-feed intake. It was concluded that creep-food consumption, measured using this method, did not influence weight gain post-weaning. This method may be used in association with other methods of measuring creep-food consumption, such as measuring lime-spent at the feeder, to give a more accurate estimate of individual creep-food consumption.

Although ciliate protozoa make up 50 % of the total microbial biomass of the rumen and play an active part in the degradation of feed, some authors have shown that animal performance is sometimes improved if they are eliminated. We have been working on a research project to determine the effect of the presence of certain genera of protozoa on digestion in ruminants.

Birth is associated with dramatic changes in nutrient supply and environmental conditions, and survival of the newborn animal is highly related to its ability to withstand stress and to develop quickly major physiological functions such as nutrition and thermoregulation. In pigs, susceptibility to hypothermia and to hypoglycemia are usually reported as major factors involved in neonatal mortality. Low energy stores, lack of brown fat and poor insulation largely contribute to the limited thermoregulatory response of the newborn pig but thermogenic capacities are developping quickly over the first 48 hours of life. Postnatal hypoglycemia is mainly due to the impairment of gluconeogenesis during the first hours of life in starved piglets (Pegorier et al.,1985) in relation with the low ability of the piglets for hepatic fatty acid oxidation.

Our research program consists in studying the biochemical and physiological characteristics of myofibers during genesis, differentiation and growth of skeletal muscle in the pig. The objective is to be able to turn muscle differentiation into characteristics that are good for meat quality and consistent with a high level of growth performance. Our experimental work comprises three main topics: (1) description of myofiber differentiation and growth during fetal and postnatal periods; (2) investigation of factors affecting muscle differentiation and growth and (3) study of relationships between muscle histochemlcal traits and meat quality.