Poor animal performance associated with low digestibility silages results partly from the reduced nutrient yield per unit intake, but also from the associated lower intakes which were presumed to be a consequence of rumen fill effects. Legume silages have a lower average digestibility than grass silages, and yet often have higher intake characteristics. The objective of this work was to compare rumen fill and rumen particle size distribution for animals fed grass silage or legume silage-based diets.

The intake potential of silage is determined by the intrinsic characteristics of parent herbage, e.g. plant species, cell wall content and digestibility. Measured intake may, however, be markedly reduced due to modifications of carbohydrate and N fractions during ensilage, and therefore the relationship between digestibility and intake has been weaker for ensiled than dried forages. Increased proteolysis and extent of fermentation have generally decreased silage DM intake (SDMI). However, correlations between fermentation characteristics and SDMI reported in literature are generally weak, particularly those based on individual cows data. In addition to D-value (g DOM/kg DM) and fermentation quality, SDMI is also influenced by DM content, amount and type of concentrates fed, production level and stage of lactation. Gordon et al. (1998) measured SDMI under standardized conditions in cattle and developed straight NIRS calibrations for the prediction of SDMI. The purpose of this study was to develop a SDMI index describing the relative intake potential using available data based on mean treatment digestibility, fermentation characteristics and SDMI values.

Study of short-term feeding behaviour (STFB) could improve the understanding of variation in daily intake in dairy cows. STFB is generally measured in short bouts (e.g. visits to feeders) that are clustered in larger bouts (or meals). The value of bout analysis depends strongly on the choice of an appropriate bout. Before bouts can be grouped into meals, a meal criterion (MC, that is: the longest non-feeding interval accepted as part of a meal) must be estimated. Tolkamp and Kyriazakis (1999) criticised existing methods and recently developed a new technique to estimate meal criteria. These log-normal models were developed on basis of the idea that eating bouts end when animals are satiated (i.e., in a state of low feeding motivation) (Tolkamp and Kyriazakis, 1999). This implies that feed consumption during the relevant eating bout will result in a gradual increase in satiety. This will be associated with an increase in the probability of cows ending a bout. In this study we will analyse whether meals are a more biologically relevant unit of STFB than the short feeding bouts (i.e. visits) that are routinely recorded.

While the shear property of grasses is considered to be an indicator of the resistance to physical breakdown of ingested particles, few effects on intake or retention time of digesta have been observed with ryegrasses differing in shear breaking load (Inoué et al. 1994). The aim of this study was to examine the effects of ingestive mastication on the differences of shear properties of ryegrass at two stages of maturity and two chop lengths.

Protein breakdown in the rumen often leads to excessive ammonia production and inefficient use of dietary protein by ruminants (Wallace et al., 1997). Attention has for many years focussed on the proteolytic activity of ruminal microorganisms (Wallace et al., 1997). The wide variety of proteolytic species and proteolytic enzymes and their between-animal variability has made the task of decreasing microbial proteolytic activity difficult (Falconer & Wallace 1999). Much less attention has been paid to the contribution of proteinases originating from the feed. In particular, grass cells contain vacuoles harbouring broad spectrum proteinases which are known to be responsible for protein breakdown in the silo (Wetherall et al., 1995). Theodorou et al. (1996) proposed that much of the rapid release of ammonia in grazing animals might be initiated by the action of plant, rather than microbial, proteinases. The present study was undertaken to compare the proteolytic activities of fresh grass and ruminal microorganisms and to evaluate their likely contributions to ammonia production in the rumen.

Tail-biting is a behavioural vice with important welfare, economic and carcass quality implications observed in growing pigs. Fraser (1987) proposed that mineral deficiencies in the diet may be related to tail-biting while Beattie et al (1996) found that tail-biting did not occur in intensive housing when pigs had access to a rooting substrate. This study compared the effects on pig performance and behaviour of increased dietary salt concentration with a negative control (standard diet, no rooting substrate) and a positive control (standard diet, rooting substrate provided).

The resource requirements, such as feeding space, of pigs housed in large groups are poorly understood. The feed intake requirement may be unaffected by group size, but the ability to gain access to the feeders may be influenced by the changed social environment. The observation of pigs feeding may stimulate others to feed also. In large groups, the number of pigs attempting to feed simultaneously could lead to increased competition for access to the feeders (Spoolder et al., 1999). Consequently, the suitability of two feeder space requirements, derived from UK recommendations, for pigs housed at different groups sizes was investigated.

Post-weaning ‘growth check’ due to low feed intakes continues to pose a problem for commercial producers. It may be possible to improve feed intake by weaned pigs through manipulating the way in which feed is presented to them. The objective of this study was to assess the influence of five different commercially-available feeders on the performance and behaviour of weaned pigs.

The current energy rationing system in the U.K., the metabolisable energy (ME) system (AFRC, 1993) takes no account of the partitioning of increments of ME intake (MEI) between milk energy output (E1) and body tissue (Eg). However, recent work at this Institute, Agnew et al., 1999, has shown that the response in E1 to increasing MEI complies to the law of diminishing returns, while the converse response is obtained for Eg. Rationing cows for economic milk production requires a full understanding of the dietary and animal factors which influence this partitioning. The objective of this study was to examine the effect of one animal factor, stage of lactation, on the partitioning of increments and decrements of MEI between E1 and Eg.

Significant increases in genetic merit for milk production in the UK dairy herd have led to high and persistent milk yields becoming relatively common. Data relating this level of performance to the extent of the energy deficit in early lactation, possible impact on milk quality and the contribution of mobilised energy to milk production are relatively scarce. The aim of this study was to compare lactational performance in high- (HYC) and average- (AYC) yielding cows and to reconcile changes in body status (liveweight and condition score) of HYC with associated measurements of energy depletion and repletion.

Earlier work showed that red clover silage has considerable potential for milk production (e.g. Thomas et al., 1985), though low digestibility and difficulties ensiling clovers were seen as problems that needed to be addressed. Advances in legume breeding and conservation technology as well as a renewed emphasis on extensive organic production systems within Agenda 2000 meant that it was timely to reconsider the potential of legume silages for milk production.

Meeting the greater nutrient requirements of high genetic merit dairy cows in grassland based systems provides a very real challenge. This study examines the performance of high genetic merit animals, managed on four contrasting grassland based systems of milk production, including both the winter and summer periods.

The UK dairy industry has entered a period of rapid increase in cow genetic merit. Feeding and management during the rearing period will influence the extent to which the genetic merit of these animals is realised. Current systems for rearing dairy herd replacements are based on research undertaken in the 1960's and 1970's with animals of lower genetic merit. High genetic merit Holstein Friesian animals have an increased live weight and frame size at maturity compared with their medium merit contemporaries, which may have implications for the optimum weight at first calving. The aim of this study was to determine the effect of rearing regime, in terms of diet offered and target calving weight, on first lactation performance of high genetic merit heifers over a range of milk production systems.

Recent studies have reported a substantial increase in the incidence of reproductive cycle problems in modern dairy cows (Opsomer et al., 1998; Royal et al., 1999). This increase is often attributed to the ever-increasing metabolic demands placed upon these cows by continually increasing milk yields. In this study we have monitored a variety of metabolic parameters in lactating dairy cows and related these to reproductive function in an attempt to establish metabolic predictors of impending reproductive failure.

Fertility of UK dairy cows is at an all time low (Royal et al., 2000). Genetic improvements through direct selection is minimal since parameters can only be measured in the mature female and generally have low heritability (h2 < 0.1). It may be possible to overcome these genetic limitations with the use of an indirect selection criterion. Whilst commencement of luteal activity might prove a valuable genetic indicator of female fertility (Darwash et al., 1997), a major step forward would be the identification of a highly heritable trait in the male that is measurable in early life and genetically correlated to a measurement of female fertility. The physiological control of reproduction is by the same gonadotrophic hormones in both sexes (Land, 1973), and Haley et al. (1989) reported that the underlying variation in gonadotrophin response to GnRH is controlled by the same genes in both sexes. High heritabilities (0.4–0.55) for the response to GnRH have been reported in ram lambs (Haley et al., 1989) and beef bulls (Mackinnon et al., 1991). The objective of this study was to estimate the genetic variation in a number of parameters associated with the LH response to a GnRH challenge in pre-pubertal Holstein-Friesian (H/F) heifers.

Genetic parameters of mastitis are required in genetic selection for mastitis resistance. Excluding cows that are culled at an early stage of lactation due to mastitis from genetic parameter estimation may introduce culling bias. The use of linear models, suitable for continuous traits, is inappropriate for analysis of mastitis records because it is recorded as an all or none (binary) trait. Here, a Bayesian-threshold model with Markov chain Monte Carlo (MCMC) techniques was used to analyze mastitis data. The objective was to estimate genetic parameters of mastitis in first and all-lactation cows using complete or incomplete records on disease.

Infection by nematode parasites is an almost-inevitable consequence of sheep grazing improved pasture. Susceptible classes of sheep include growing lambs and ewes during the period of physiological stress caused by gestation and lactation. Nematode infections in lambs are well documented, less well documented is the decrease in resistance in ewes during the periparuturient period. The consequent elevation in faecal egg counts, the periparturient rise (PPR), leads to pasture infestation by worm eggs (Morris et al., 1998) - thus serving as a trigger for the subsequent epidemic in the lambs. Alternative control strategies to complement anthelmintics are continually being sought, with genetic selection of resistant animals a promising option (Woolaston, 1992). Unlike resistance in lambs, relatively little information exists on the genetic control of the PPR in ewes. The aim of this study is to quantify, and estimate the heritability of, the PPR in Blackface ewes grazing improved pasture and facing a natural mixed, nematode challenge.

In animal production significant losses occur due to parasitism (Coop et al. 1985). The classic means of treating animals against parasites is with anthelminthic drugs. However, the recent years resistance to anthelminthic drugs has become a major problem in many countries. Novel ways of overcoming the problem of nematode parasites have been proposed. One of them is breeding for resistance to parasites (Bishop and Stear, 1999). The aim of this study was to estimate the genetic parameters needed to devise strategies to breed against nematode parasites. Faecal egg counts (FECs) are used as the indicator trait of resistance to parasites.

Lactating sows will respond to increasing dietary lysine during lactation providing that energy does not become limiting. In a recent experiment Sauber et al. (1998) demonstrated that fat genotypes readily mobilised fat to make up for inadequate nutrient intake in lactation whereas lean genotypes mobilised protein. The aim of this experiment was to investigate whether fat versus lean animals of similar genetic merit were equally able to utilise diets varying in lysine content. The animals used in this experiment were of a high lean genotype and had been allowed to express their natural variation for fatness during rearing and gestation.

Testing different pig genotypes on a single diet may constrain protein and lipid deposition or reduce the efficiency of nutrient utilisation by under- or over-supply of nutrients. If the ranking of genotypes is dependent on the diet used when performance testing animals, then genotype-specific nutritional regimes may be required by breeding companies to identify animals of high genetic merit and by producers to realise the benefits obtained by genetic improvement programmes. In the Edinburgh lean growth project, divergently selected lines for efficiency of lean growth (LFC), for rate of lean growth with animals performance tested on ad-libitum (LGA) or restricted (LGS) feeding or for daily food intake (DFI) have been established with seven generations of selection in a Large White population (Cameron, 1994). The selection lines provide an experimental resource to estimate the genotype with nutrition interaction for protein and lipid deposition rates as differences between selection lines will relate to the selection strategy since the lines were derived from the one base population.