Estimates of digesta passage through specific segments of the alimentary tract are a vital component of modelling approaches which attempt to quantitatively partition digestive processes in equines. This study reports results from three studies where digesta passage of Chromium (Cr) mordanted feeds was determined in the caecum of ponies.

Caecal outflow rates were determined during three in vivo apparent digestibility studies conducted using three caecally-fistulated ponies as described by Moore-Colyer et al, (1999) for studies 1 and 2; and McLean et al, (1999) for study 3. Pony basal diets consisted of unmolassed sugar beet pulp (USBP), hay cubes (HC) or a 2:1 mix of oat hulls:naked oats (OHNO) in study 1; a 1:1 mix of USBP:HC (USHC) in study 2 and either 100% HC or one of 3 diets consisting of a 1:1 HC:barley mix where the barley was either rolled (RBHC), micronised (MBHC) or extruded (EBHC) in study 3.

A wide range of roughage foodstuffs is available for feeding to horses. Considerable variation exists in the quality of these feeds in terms of nutrient composition and freedom from dust, fungal and bacterial contamination and infestation by mites. Many horse-owners are now feeding forages such as haylage and baled silage to horses as opposed to hay. However, limited information is available regarding the effect of chop length on digestibility and thus the feeding value of chopped or long-cut silage to horses. More information on fodder type and preparation could help to provide the basis for improvements in the practical guidelines and recommendations for those involved with the production and feeding of forages to horses.

The consequences of chewing during eating and rumination of ingesta on the reduction of feed particles has been studied extensively in ruminants (Kennedy, 1984). These studies have lead to the development of the concept of critical size, that is the minimum reduction of feed particle size to allow passage from the rumen. However, feed particle size ingested seems to have little effect on reduction of particles to critical size as a result of chewing and rumination to facilitate passage from the rumen (Faichney, 1990). In the horse once feed has passed the cardiac sphincter into the stomach, no post ingestive mastication can occur. This may be an important component in the apparent reduction in the digestibility of energy substrates in the horse compared to the ruminant. The study reported here examines the relative particle size distributions of faeces of horses and sheep given identical diets.

In the United Kingdom, a range of distillery by-products is available and may have a useful role in the formulation of equine rations. Pagan and Jackson (1991) investigated the ingestive behaviour of horses offered dried distillery by-products at differing rates of inclusion in the diet in a choice-preference study and concluded that they could be offered to 0.2 of the diet DM without adversely affecting ingestion rate. The aim of the study was to investigate the ingestive behaviour of horses offered the various distillery by-products as part of the concentrate component of the diet.

Ten horses were used in the experiment. Five horses (three years of age or under; mean age 1.6 years) and five horses (pregnant mares; mean age 13.2 years) were allocated to two 5 x 5 latin squares. The horses were housed individually, bedded on straw and were offered rations of hay (7.5 kg DM/day) and concentrate (1.8 kg DM/day) at 0700 and 1600 hours.

Inoculants containing lactic acid bacteria, added to herbage at time of cutting, aid the natural process of fermentation to produce lactic acid during ensilage. This lowers the pH and preserves the silage. It is also claimed that enzyme additives break down polysaccharides in plant cell walls, releasing fermentable sugar to stimulate fermentation and increase the digestibility of the silage. This study was carried out to investigate the effects of inoculants and enzymes on silage fermentation characteristics and gas production during in vitro fermentation.

A second cut of perennial ryegrass (Lolium perenne) was mown, chopped to 2 – 4 cm lengths, divided into aliquots and treated at a rate of 10 ml kg-1. The treatments were: 1) control (water), 2) inoculant (Pediococcus pentosaceus, Lactobacillus plantarum and Propionibacter jensenii at 1.6 x 105 cells g-1 herbage) 3) enzyme (xylanase, β-glucanase and amylase, applied at a rate of 0.001 g kg-1 herbage) and 4) inoculant + enzyme.

Tree legume forages plays an important role in livestock nutrition in many parts of the tropics. One of the commonly used tree species is leucaena. However, the recent infestation of Leucaena leucocephala by the pest Heteropsylla cubana calls for alternative sources of legume forages. Abdulrazak et al. (1997) for instance, showed that Gliricidia sepium could be an alternative, and indicated the need to identify more promising species. Prosopis Juliflora (prosopis) grows in many parts of the tropics, including the arid and semi arid areas of Kenya. The objective of this study is to evaluate the nutritional value of prosopis fruits (pods with seeds) and leaves as ruminant feed.

In a previous study in Reading (altitude 66 m) (Mauricio et al., 1997) the lag phase was greater when cow faeces was used as a source of microorganisms in the in vitro gas production technique instead of rumen liquor when twelve temperate forages were fermented for 96 h. In the Reading study faeces and rumen liquor were obtained from a cow fed grass silage and concentrate (60:40). The present study was done in Piracicaba, Brazil-BR (altitude 780 m) which has a tropical climate. Using the same forages as in Mauricio et al. (1998), the study examined whether the same differences between faeces and rumen liquor would occur in a tropical environment. In addition, the opportunity was taken to develop an equation relating pressure and volume for the semi-automated pressure transducer technique and compare it with the equation developed in UK by Mauricio et al. (1998).

Mauricio et al.(1997) reported that faeces as an inoculum in the gas production produced similar results to rumen liquor in terms of total gas production and OM digestibility but a greater initial lag phase was observed. Where a mathematical description is to be used to develop the gas production profiles an accurate description of the lag phase (the period prior to degradation during which multiplication and attachment of the micro-organisms occur) must be obtained. For this to be achieved when a large number of samples are to be examined, measurement of gas production has to be achieved rapidly; this is possible using a semi-automated technique (Mauricio et al., 1998). This study evaluated the effect of recording gas production using a manual (syringe) technique, with a standard 3 h interval, and at 1h and 3 h intervals using a semi-automated system.

The semi-automated Reading Pressure Technique (RPT, Mauricio et al. 1998) combines gas production profiles and both rate and extent of degradation to evaluate feedstuffs in vitro. The simplicity, low initial cost and high capacity of the system (75 treatments with 4 replicates plus controls can be examined per run) allow it to be widely applied. However, and in common with many other in vitro systems, little information had been generated regarding either its sensitivity or precision. This paper describes how pure substrates were used to identify the minimum amount of fermentable material required to develop distinct degradation profiles. Substitution techniques examined whether changes in degradability at either the mono- or polysaccharide level could be detected and quantified, and replication of these studies provided data regarding precision of the system.

A major criticism of in vitro gas systems is that measurement of nutritionally wasteful products (i.e. CH4 and CO2, either directly from fermentation or indirectly from neutralization of VFA by the bicarbonate buffer) provides little useful information. However, as VFA and gas production are inversely related to microbial biomass yield for any given unit of substrate degraded, it has been suggested (e.g. Getachew et al., 1998) that an estimate of fermentation efficiency or partitioning factor (PF) can be obtained by relating gas production (ml) to the extent of degradation (mg). This study examined the relationship between in vitro DOMD, gas release and PF values using data obtained from an assessment of four maize silages.

The use of small ruminants, such as sheep, in metabolism studies is more convenient as handling problems are reduced and their maintenance costs are lower, in comparison with cattle. However in vivo digestibility estimates obtained at maintenance are known to differ between these two species. With the increased use of in vitro gas production techniques, to evaluate ruminant feedingstuffs, it is of great importance to identify whether the species from which the rumen fluid inoculum is obtained has a significant influence on the results obtained.

Rumen fluid samples were obtained from a non-lactating Holstein cow (C) and six wether sheep (S) offered the same diet (80 % tropical grass and 20 % dairy concentrate) and prepared so as to have similar dry matter (DM) contents and therefore potentially the microbial mass. Nine substrates (two tropical grasses 1-2, tropical alfalfa 3, barley straw 4, and five temperate grasses 5-9) were examined.

The treatment of straw with sodium hydroxide in order to upgrade its nutritive value and to increase the utilisation of its energy by ruminants has been widely employed in many parts of the world. The aim of the experiment was to assess the fibrolytic activity of the anaerobic fungi in vitro using either untreated or NaOH treated barley straw.

Anaerobic fungi were isolated from the rumen of a sheep fed with a diet of hay and lucerne pellets using medium C based on that described by Davies et al. (1993) and as modified by Rezaeian (1996). The Isolates were inoculated into two series of culture media containing either sodium hydroxide treated (TS) or untreated milled straw (US). Five replicate cultures were prepared and incubated at 39 °C over a period of 12 days. The dry matter loss of the substrates and changes in pH of the medium cultures were measured.

Lead from car exhausts persists on roadside verges, and ruminants grazing close to a busy road are likely to consume contaminated herbage. However, cattle can detect lead on herbage when it is at concentrations of 170 mg Pb/kg DM or above and have been observed to avoid grazing pasture with 304 and 462 mg Pb/kg DM (Strojan and Phillips, 1997). Herbage 7.5 m from a busy dual carriageway has been recorded with 454 mg Pb/kg DM (Motto et al., 1970).

The avoidance of lead-contaminated herbage may be the result of low digestibility of the leadcontaminated herbage, so the digestion rate of samples of herbage from the experiments of Strojan and Phillips (1997), referred to in the Introduction, was determined by the gas production technique (Menke and Steingass, 1988). Using 15 and 10 replicates/treatment from two experiments where lead acetate was sprayed onto cut (Experiment 1) and grazed (Experiment 2) herbage, 200 mg DM of each herbage sample was incubated in sheep rumen liquor in syringe pipettes.

Food eaten by a ruminant firstly undergoes microbial fermentation within the rumen. Nutritionally important characteristics of the food are the rate and extent of fermentation of its carbohydrate fraction, which can both be estimated using the in vitro gas production technique. The single greatest source of uncontrolled variation in any in vitro rumen fermentation system is the rumen fluid; curves produced from gas production data were influenced significantly by the variation in microbial activity between days (Menke and Steingass, 1988; Beuvink et al, 1992). A more reliable measure of rumen fluid activity is needed. The objective of this study was to determine whether the frequency of sampling of rumen fluid affected the microbial activity and subsequent fermentation.

Herrero et al. (1996) found that NIRS was able to calibrate and cross-validate the static values of gas produced from the incubation of Kikuyu grass using manual in vitro gas production. However, the fermentation kinetic coefficients were not calibrated satisfactorily by NIRS. The aim of this study was to investigate the potential of NIRS as a means of predicting fermentation and the France et al. (1993) model parameters obtained from the automated in vitro gas production experiments for a range of concentrate feeds.

Thirty-eight milled (1 mm) samples representing three typical concentrate feed types were scanned over the infra-red region covering 1100 to 2300 nm using an NIRS systems 6500 spectrometer. Optical data recorded as log 1/Reflectance were transformed to their standard normal variates and detrended values (SNV-D).

The assessment of protein degradability in the rumen is a complex process. The infinite combination of interaction between the rumen microbial population and the nature of the protein fed to the animal makes the estimation of ruminal protein degradability very arduous. At present the in situ technique is the most popular means of predicting ruminal nitrogen (N) degradation. However this procedure is slow, expensive and relies on the use of numerous surgically prepared animals. A number of studies (Assoumani et al., 1992; Aufrère and Cartailler, 1988) have shown that the use of in vitro methods using proteases can predict with reasonable accuracy the extent of protein degradation. The objective of this experiment was to examine the possibility of replacing the in situ technique with an in vitro procedure based on the use of the ficin protease to predict the extent of N degradation.

Assessing the availability of a feed in the rumen is an important element of its characterisation. In the Metabolisable Protein system, it is assumed that all starch is available in the rumen, although clearly this is not the case. However, estimating the amount of starch that is apparently fermented in the rumen is difficult, expensive and cannot be routinely undertaken. The objective of this experiment was to determine whether the in vitro gas production technique could be used as a means of predicting the amount of starch that apparently disappears in the rumen (STA ADR).

Four Holstein cows, each fitted with a rumen and duodenal cannula, were used. They were fed one of four diets in a 4x4 latin square design. The diets consisted of grass silage (GS), molassed sugarbeet feed (MSBF), fishmeal (FM) and minerals (MIN). They were also supplemented with either wheat (WHT) or maize (MZE).

Biotin is a prosthetic group for a number of enzymes involved in carboxylation reactions. Biotin deficiency has been associated with poor growth of integumental tissues by currently unknown mechanisms. Pyruvate carboxylase is a biotin-dependent enzyme which has an important anaplerotic role in intermediary metabolism, catalysing the formation of oxaloacetate from pyruvate and bicarbonate. It thus provides oxaloacetate for gluconeogenesis and replenishes Krebs cycle intermediates. Biotin deficiency may reduce pyruvate carboxylase activity and so oxaloacetate production. Malate is a Krebs cycle intermediate which can convert to oxaloacetate and reduce demand for oxaloacetate generated by pyruvate carboxylase. The aims of the study were to determine (a) the effect of biotin supplementation of the medium on hair follicle viability and pyruvate carboxylase activity and (b) the response to supplementation of the culture medium with malate.

Apoptosis is a physiologically active process whereby cells die in a programmed manner (Stenn et al 1993). Growth of hair occurs as a consequence of proliferation and differentiation of the epidermal cells in the bulb of the hair follicles. Reduction of hair growth or loss of follicle viability may arise from reduction in proliferation, and also from apoptosis of epidermal hair shaft-forming cells. Increases in apoptosis have been associated with reduction in expression of the apoptosis inhibitor bcl2 (Lindner et al 1997). Previous studies (Tahmasbi et al 1998) have shown that biotin deficiency reduced the viability of mohair follicles and thymidine uptake in vitro. The aim of this work was to investigate the presence of apoptosis and bcl2 in follicles which maintained growth or were quiescent following culture in media unsupplemented or supplemented with biotin.

Many of the anabolic effects of growth hormone (GH), including promotion of lean tissue growth, are mediated by the actions of insulin-like growth factor-1 (IGF-1) (Gluckman et al, 1987). It is known that the response of hepatic IGF-1 synthesis to GH may be modulated by alterations in levels of feeding or changes in protein supply (Pell et al, 1993). The aim of the current study was to develop an in vitro model to characterise interactions between amino acid supply and GH on hepatic IGF-1 release in ruminants.

Ovine hepatocyes were prepared by a modification of a published method (Luo et al, 1992) from the median lobe of livers removed immediately after slaughter from sheep killed at a local abattoir. Free amino acid concentrations in test media were 5x, 1x and 0.2x physiological concentrations based upon in vivo ovine portal venous blood data (Lobley et al, 1995).