In intensive animal production, surplusses of nitrogen (N) are polluting the environment. Therefore it is important to compose diets matching the requirements of the animals as close as possible. Untill now mostly apparently digestible N or amino acids (feacal) have been used as criteria. It is also well established that amino acids disappearing from the hindgut do not contribute much to amino acid supply of the animal. Moreover, big differences between ileal digestible amino acids and faecal digestible amino acids are found, depending on the feed composition. Because the amounts of absorbed amino acids is more reflected by the amounts of ileal digestible amino acids than by the amounts of faecal digestible amino acids, contents of the ileal digestible amino acids of the commonly used feed stuffs in the Netherlands have been determined. Diets can now be formulated on contents of ileal digestible amino acids.

The rearing period of replacement stock usually involves two grazing seasons before they calve for the first time and enter the dairy herd. Gastrointestinal nematode infection can affect growth performance in either one of these grazing seasons. However, most investigators concentrated on calves in their first grazing season, partly owing to the fact that clinical disease is rarely observed in older animals. Cows also harbour gastrointestinal nematode infection, and numerous studies were conducted to investigate the effect of anthelmintic treatments on the subsequent milk yield. The result of the latter was a long-standing controversy, some claiming a positive effect, whereas others disputed the (economic) benefit of such treatments. The present paper summarizes the effects of infection on growth performance and milk production and integrates these effects within the context of the rearing period.

Several studies have shown milk protein genetic variants to be associated with manufacturing properties of milk. The main findings were that κ-casein genetic variants affect renneting time of milk and βlactoglobulin genetic variants are associated with casein number (reviewed by Grosclaude, 1988). There are reports also of associations between milk protein genetic variants and milk production traits. Results from these studies indicate that κ-casein genotypes are associated with protein content and βlactoglobulin genotypes are related to fat content (reviewed by Bovenhuis et al., 1992). Therefore, κ-casein and βlactoglobulin genotypes might be of value as selection criteria. The aim of the present study was to quantify the potential effects of selection for κ-casein and β-lactoglobulin genotypes by using stochastic simulation of a closed adult MOET nucleus breeding scheme.

The last ten years have seen a great deal of discussion about the use of animals in education. The aim of this paper will be to summarise current pupil attitudes and perceptions, and to provide an ethical framework within which the use of animals in education can be examined. In many countries the recent years have seen a considerable reduction in the use of animals in school science education (Reiss and Beaney, 1992). Whole animal dissection has become significantly less common within the last decade. It is, for example, now required by none of the Examining Boards in the UK, even for advanced level biology. Part of the reason for such changes has been a shift in the perceptions by many pupils and students, and some teachers, about the appropriateness of the use of animals in schools. Recent work by Roger Lock and Katherine Millett has shown how strong are pupil views against animal experimentation and the use of animals in schools (Lock and Millett, 1992; Millett and Lock, 1992). For instance the majority of 14-15 year-olds disagreed with the statement 'New medicines should be tested on animals before they are taken by humans'. Similarly, the majority of these pupils agreed with the statement 'I think that it is wrong to breed animals that will only be used for dissection'.

During the last ten years the volume of dietary information directed at consumers has increased dramatically. The British Nutrition Foundation (BNF) has become increasingly concerned that the avalanche of sometimes conflicting information is outstripping the ability of many consumers to use it effectively or even comprehend it, and believes that more emphasis should be placed on education rather than information.

The Foundation believes that it is vital to begin education in food and nutrition at school, and that all pupils should receive tuition in this multifaceted subject throughout their school careers.

Earlier studies showed the superiority of NIRS, over fibre measurements, for predicting organic matter digestibility (OMD) in vivo of grass silages. (Barber et al 1990). This system was put into routine use in ADAS in 1989 and after some initial doubts, due to the wider range of the predicted data seen, is now accepted as the best system available for routine use. However, occasional erroneous values were predicted for which there were no obvious explanations, and which resulted in occasional relatively poor repeatability. In common with all NIRS applications it was likely that the sources of the problems contributing to the errors were i) instrumental and environmental noise, ii) sample particle size effects and iii) variable moisture content of the samples. A course of investigation was undertaken with the objective of determining the effects of these on the predicted data.

Due to its slower rate of rumen degradation, molassed sugar beet pulp (MBP) is considered to result in a higher pH in rumen fluid wnen compared with cereals and to be of benefit in diets where maximum fibre digestion is desired (Fahmy et al., 1984). Sodium hydroxide-treatment of MBP, by increasing feed pH may increase the value of MBP still further in these situations. The most common method of processing whole cereal grains is dry rolling. Sodium hydroxide pre-treatment has also been shown to increase the digestibility of whole cereal grains close to thai achieved by dry rolling (Orskov, 1979). Little information is available on the relative effects on rumen fermentation of both processing methods. The objectives of this study were to (1) determine the effects of treating MBP with NaOH and (2) compare the effects of rolfing (R) and S as processing methods for barley and wheat, on rumen fermentation and dry matter (DM) degradability (DMD) in steers offered grass silage.

Methane production by ruminant animals is an important anthropogenic source of methane to the atmosphere and is considered an important source to more accurately estimate and to control. It has been known for some time that, in ruminants, diet type and composition can influence methane production, yet there is little quantitative information for contemporary diets used 1n the UK. Attempts to predict methane production from either diet chemical composition or digestibility have not been successful (Moss and Givens, 1990; Johnson et al., 1991). In order to estimate more accurately the amount of methane produced by a ruminant on a given diet, it is essential to establish whether there are interactions of various substrates with forage and to relate this to the rumen environment. Previous work showing interactions has used mainly hay-based diets (Blaxter and Wainman, 1964); as grass silage is now the major forage in the UK, work with this forage was needed.

Metabolisable energy (ME) and absorbed protein appear to be more efficiently utilised for tissue gain in ruminants fed cereal compared to forage diets but the mechanisms involved are not understood. Forage and cereal diets differ in their pattern of rumen fermentation and hence the relative proportions of absorbed nutrients such as ammonia (NH3) and VFA (Seal et al, 1991). Splanchnic bed metabolism has been demonstrated to extensively modify both the quantity and form of absorbed nutrients (Reynolds et al, 1991) and therefore is an important site for the regulation of nutrient supply to the peripheral tissues. The present study was thus designed to examine the effect of forage versus cereal diet upon splanchnic nutrient metabolism in growing cattle.

The ability of the gut tissues to absorb nutrients and the extent to which these are then metabolised within the gastrointestinal tract plays a central role in regulating the supply of metabolites to the liver and consequently influences the availability of nutrients for hepatic and peripheral tissue use. Energy consumption by the portal drained viscera is extensive and may account for 25% of total body oxygen consumption (Huntington and Reynolds, 1987). Substrates available for oxidative metabolism include volatile fatty acids (VFA) produced in the rumen and large intestine as addition to arterial supply of these nutrients. The aim of this experiment was to investigate the influence of increased propionate availability on metabolism of VFA in the rumen and the gastrointestinal tract.

Recently, we have proposed a new theory of feed intake regulation in ruminants (Ketelaars and Tolkamp, 1992a,b; Tolkamp and Ketelaars, 1992). This theory attributes great significance to the efficiency of metabolizable energy (ME) utilization for feed intake regulation. In brief, we assume that feed intake behaviour of ruminants aims at maximizing the ratio of net energy intake (representing the benefits of feeding) relative to oxygen consumption (representing the metabolic costs of feeding). Starting from this assumption, we have shown that knowledge of the efficiency of ME utilization obtained under conditions of restricted feeding can be used successfully to predict voluntary intake (Tolkamp and Ketelaars, 1992).

If, indeed, voluntary feed intake and the efficiency of ME utilization are so intimately related, the question comes up what the effect of ad lib feeding is on the overall efficiency of ME utilization (total net energy intake, NEI, as a fraction of ME intake, MEI). This paper investigates this question by means of model calculations for growing and lactating cattle according to the UK energy evaluation system.

The accurate detection of oestrus in beef and dairy cows prior to AI or embryo transfer (ET) is essential if optimal pregnancy rates are to be acheived. In dairy cows under normal husbandry conditions only 55% of normally cycling animals are correctly detected in oestrus and inseminated at the appropriate time (Esslemont and Bryant 1976). The use of pedometers, changes in milk yield, milk progesterone and trained sniffer dogs are all methods which can significantly improve the oestrus detection and hence pregnancy rates acheived by AI (Phillips and Schofield, 1988: McLeod, Foulkes, Williams and Weller, 1991; Jezierski, 1988) . However, oestrus detection by visual monitoring is still the most widely used method of detection.

To ensure high pregnancy rates from AI or ET when visual oestrus detection methods are used the form and range of behaviours which cattle perform needs to be understood. There are a wide range of oestrus behaviour patterns displayed both within and between individual cows so deciding on the correct time for AI or ET depends on interpreting the available evidence. This paper reports the behaviour of maiden heifers during natural oestrus and following a pharmacologically induced oestrus (designed to synchronise the time of oestrus for a number of heifers). By understanding the range of oestrus behaviour patterns guidelines can be established for observation methods and the interpretation of oestrus behaviour. This should enable the prediction of the optimum times for AI or ET. A corresponding improvement in the number of pregnancies should be acheived.

Several studies have shown that the level of peri- and post-ovulatory progesterone in ewes can critically influence embryo survival (Ashworth, Sales & Wilmut, 1989; Parr, 1992). However, the effect of altering pre-ovulatory progesterone concentrations in superovulated sheep has not been fully investigated. In view of the inverse relationship between the plasma concentration of progesterone and food intake (McKelvey & Robinson, 1986; Parr, 1992), the present study was carried out to determine the effect of altering feed intake on progesterone concentrations during the pre-ovulatory priming phase and on the subsequent viability of ova collected from superovulated ewes.

Overfeeding during early pregnancy compromises pregnancy establishment and /or embryo survival in a variety of domestic species including sheep, cattle and pigs (reviewed by Robinson, 1990). Embryo survival was reduced in recipient ewes receiving a high as opposed to a low plane of nutrition from embryo transfer on day 5 post-ovulation to day 60 of gestation (McKelvey & Robinson, 1988).Similarly high plane feeding for only 12 days starting on day 2 after mating significantly reduced pregnancy rates at day 60 ( Parr et al .,1987). Although not extensively monitored in either study, peripheral progesterone concentrations were inversely correlated with feed intake. Indeed, the reduction in pregnancy rate in high plane ewes in Parr's study was reversed by progesterone supplementation on days 8-14 after mating.The inhibition of luteolysis and maintenance of adequate progesterone secretion by the corpus luteum is central to the maternal recognition of pregnancy in sheep ( Bazer et al .,1991 ). Progesterone plays a major role in controlling maternal secretion of nutrients, growth factors , immunosuppressive agents .enzymes and steroids required for successful embryo development. It seems likely therefor that the mechanisms underlying nutritionally induced differences in pregnancy rate and embryo survival may operate via changes in progesterone levels which in turn alter the secretory dialogue between the conceptus and its maternal environment.

The potential rate of genetic improvement which can be achieved in sheep through the use of multiple ovulation and embryo transfer (MOET) is limited by the great variation in the response of ewes to superovulation treatments. Factors which have been shown to influence natural ovulation rate in the ewe include season, breed, age and the administration of exogenous gonadotrophins from different sources. The following study was conducted to examine the effects of these factors on the response of ewes to superovulation treatments, with a view to increasing the mean ovulation rate and to concurrently decrease the between-ewe variability.

During the course of 4 experiments a total of 170 ewes (Suffolk and Texel) were treated with 45mg progestagen-impregnated intravaginal pessaries (Chronogest: Intervet Laboratories Ltd.) for a period of 12 days. Sixteen ewes had no further treatment and were used as controls. The remaining 154 ewes, were treated with one of two exogenous gonadotropin preparations on days 10, 11, 12 and 13 of the progestagen treatment period (day 0 = pessary insertion). One group (n = 76) was treated with a porcine pituitary extract (pFSH) and the second (n = 78) with a highly purified ovine FSH (Ovagen: Immuno-Chemical Products).

When semen is frozen ice forms extracellularly, and water is drawn from the cells (Mazur, 1970). Rapid freezing reduces dehydration and causes intracellular ice to form more quickly (Mazur, 1980). Cells frozen rapidly in liquid nitrogen do not survive, suggesting that partial dehydration is necessary for spermatozoa to survive freezing (Fahy et aL, 1984). Watson (1979) suggested that non-penetrating sugars have protective effects on spermatozoa during freezing. The addition of a non-penetrating solute such as raffinose to semen will dehydrate the cells by its osmotic effect.

The object of this study was to investigate the effect of raffinose on cryoinjury of ram spermatozoa.

Experiment 1.Raffinose was added to Tris egg-yolk glycerol buffer (Evans and Maxwell (1987) to concentrations of 0mM, 33mM, 66mM, 99mM, 132mM, 165mM and 198mM raffinose and used to extend (2:1) pooled semen from Cambridge rams.

Factorial experiments with 3 replications were set up to test the effect of raffinose concentration, glycerol concentration, method of packaging of semen, pellet size and cooling rate of straws on the motility and survival of ram semen before and after freezing/thawing.

It has been suggested (Kyriazakis and Emmans, 1992a, b) that the material efficiency with which the pig can retain protein (ep), is directly proportional to the energy:protein ratio of the diet (R), so that ep = k.R. This hypothesis accounts for the finding that the rate of protein deposition can sometimes be increased by increasing the energy supply at a constant rate of protein supply.

It is also possible that the constant of proportionality, k, is a genetic variable, although it was proposed, partly for the sake of simplicity, that there would be no genetic effects on the value of k. To test the propositions: (i) that ep is proportional to R, and (ii) that k does not differ between genotypes, an experiment was designed and carried out on two pig breeds which were expected to be very different from each other.

Enzymic hydrolysis of phytates has been shown to improve the apparent digestibility of phosphorus. Other nutrients bound to phytates may be released during phytate degradation by phytases. Dietary yeast may also improve the availability of phosphorus to pigs by altering gut fermentation patterns.

The objectives of this experiment were (1) to study the effects of phytase on the apparent digestibility of phosphorus and other nutrients associated with phytates, and (2) to determine whether an alteration in fermentation induced by dietary yeast inclusion influenced availability of phosphorus.

Selection for the reduction of carcase fat and the promotion of lean tissue growth has resulted in the production of faster growing, genetically lean breeding females. These animals often have very limited body fat reserves to utilise at times of high nutrient demand, such as during lactation. It is possible that reproductive performance and longevity may be improved as a consequence of alteration of the body composition of the breeding female by nutritional means.

The experiment was designed to investigate the consequences for genetically lean animals of restricting lean tissue growth and promoting fat deposition in the period prior to a maiden service and in gestation using a low protein diet, and minimising fat loss in lactation using a nutrient dense diet (Treatment E) in comparison with feeding a conventional single diet (Treatment C). Two hundred and forty purebred Large White and Landrace gilts were allocated to one of these two nutritional regimes at 6 months of age on the basis of breed, liveweight and backfat. Animals remained on treatment for three parities and growth and performance parameters were monitored.

It is generally considered that increased digesta viscosity is one mode of action by which antinutritional factors such as β-glucans in barley and arabinoxylans in wheat reduce digestibility of nutrients in broilers. The increased viscosity interferes, possibly, with the activity of digestive enzymes and subsequent movement of nutrients prior to absorption, therefore ultimately depressing growth rate and feed conversion. Experimental diets are usually fed for approximately three weeks prior to evaluation of gut viscosity. However viscosity may change considerably during and after this time to a degree which may be influenced by the feeding regime employed. Accordingly, the current series of experiments was designed to identify the pattern of change of gut viscosity as influenced by age of bird (15 to 45 days) and feeding regime when diets based on wheat and barley were offered.