Since automated gas production equipment became available (Cone et al., 1996), there is an increasing interest in this technique. The gas production technique is not only widely used in reasearch programms, but is also used as a routine feed evaluation technique and will soon be used in feed evaluation systems, as the gas production technique potentially can replace the nylon bag technique. Although many investigators use the technique, the interpretation of the gas production profiles is still difficult (Cone et al., 1997). The gas production caused by the fermentation of carbon hydrates is well understood and described (Beuvink and Spoelstra, 1992). Since, the gas production caused by fermentation of protein is not the same as that of carbon hydrates, comparing the gas production data of feedstuffs, differing largely in protein content, may lead to misinterpretation of the results. The aim of this study was to investigate the influence of protein fermentation of gas production profiles.

The aim of using any in vitro method is to obtain a good description of the nutritional value of forages as they are fed, which in most cases is on a fresh basis. The in vitro gas production technique has the potential to characterise fermentation pattern of the carbohydrate fractions of forages, and has been used extensively with forage material that has been dried and ground through a 1mm screen. The objective of the present study was to compare the fermentation patterns of fresh and dry forage.

The gas production (GP) technique has been developed to assess dynamics of ruminant digestion. Relationships have been observed between a feed's GP profile and in vivo parameters such as digestibility (Khazaal et al., 1993), feed intake and growth rate (Blümmel and Ørskov, 1993), and in situ degradability (Sileshi et al., 1997). However, there are few studies which relate GP data to the in vivo pattern of rumen fermentation (in terms of the rate of pH decline 2 h post-feeding and the mean rumen pH, concentration of total VFA and molar proportion of individual VFA). The object of this experiment was to determine whether such a relationship existed between a feed's GP profile and the pattern of rumen fermentation observed in animals fed that feed.

During ensilage readily fermentable organic matter (OM) is fermented to lactic acid and short chain volatile fatty acids (VFA). These acids provide little energy as ATP for rumen microbial growth and are essentially absorbed intact. The UK metabolisable protein system defined the energy available for microbial growth, termed fermentable metabolisable energy (FME), as the proportion of metabolisable energy (ME) in a diet/feed less the ME in oil and fermentation acids. The aim was to establish if fermentation acids yield direct gas production resulting from microbial fermentation. Grass silage was simulated using grass hay (GH; containing no fermentation acids) with additions of individual fermentation acids in solution.

GH (~2 kg) was oven-dried overnight at 100°C, nulled (1 mm screen) and then sieved (25 μm screen). 0.5 g GH was weighed into 250 ml Duran bottles according to the treatments; 1) GH + anaerobic incubation mixture (AIM, 85/15 v/v anaerobic medium and strained rumen fluid) + ~5 ml distilled water; 2) GH + AIM + ~5 ml fermentation acid solution (100 mg DL-lactic acid (LA)/10 ml, 30 mg acetic acid (AA)/10 ml or 20 mg n-butyric acid (BA)/10 ml) (equivalent to 100, 30 and 20 mg/g GH dry matter (DM) for LA, AA and BA respectively); 3) anaerobic medium (85 ml) + 15 ml clarified rumen fluid + ~5 ml fermentation acid (as treatment (2)).

There is contradictory evidence regarding the effect on the gas production (GP) profile of a feed if the incubation medium is shaken during the fermentation. In experiments conducted by Theodorou et al. (personal communication), there was no effect of shaking on the rate of gas production (when the medium was shaken after a recording). However, when buffer solutions (containing no substrate) were continually shaken, there was an effect on the volume of gas produced (Rymer et ai., 1998). The objectives of this experiment were therefore to determine whether die time of shaking affected the GP profile, and whether there was any significant difference between laboratories in this observation.

Sugars and starch are used as fermentable metabolisable energy (FME) sources in ruminants. Compared with starch, sugars are associated with increased microbial protein supply to the animal when both types of carbohydrates are supplemented to the basal forage diet (Chamberlain et al., 1993). However different sugars respond differently which is associated to differences in their rates of fermentation. Knowledge of the fermentation kinetics of these FME sources is very helpful to synchronize energy and protein supply to the rumen. Limited data are available on the comparative rates of fermentation of starches and sugars. This experiment was conducted to determine fermentation kinetics of selected starch and sugars by measuring gas production, volatile fatty acids (VFA) production and protozoa changes in the fermentation medium

It was observed by Gurung et al. (1996) that Nepalese farmers’ perceptions of the nutritive value of grasses was poorly related to in situ estimates of DM degradability. Recording the gas production (GP) profile of a feed is another method which is used to predict the nutritive value of ruminant feeds. However, many factors affect the GP profile of a feed, of which the source of rumen inoculum is an important one. There were therefore two objectives to this experiment. One was to determine whether the GP profile of the grasses studied by Gurung et al. (1996) was associated with the farmers’ perceived assessment of nutritive value. The other objective was to compare the GP profiles obtained with rumen inocula taken from sheep and buffalo.

The experiment was conducted using a range of forages with accurately predetermined OMD values (ADAS) to compare rumen liquor (RL) and faeces (FA) as sources of inocula in the pressure transducer technique (PTT) (Theodorou et al., 1994). Gas production results were examined in relation to OMD determined in vitro (PTT, Tilley and Terry) and in vivo.

The gas production (GP) technique has previously been used to estimate the gas volume (fermentable energy (FE)) of compound feed ingredients for ruminants (Newbold et al., 1996). It was shown that the FE content of feed mixtures was represented by the combination of the total gas from the incubation of the individual feeds. However this additivity might not be consistent throughout the incubation period. The objectives were to test whether 1. other GP parameters give better estimates of FE for simple mixtures and are they additive; 2. whether organic matter apparently degraded in the rumen (OMADR) explain differences in GP; and 3. to find out if there are any other better measures than OMADR for estimating FE.

The use of a syringe (manual method) to measure gas production is time consuming and inaccurate. In addition the time taken prevents frequent measurements and therefore does not allow gas production kinetics to be fully described. According to Boyle's Law, gas volume corrected for temperature, is directly related to pressure. A simple, semi-automatic system recording of gas pressure and equations to estimate volume, was therefore developed.

Data for this work came from a study which compared rumen liquor and faeces as sources of inoculum using the method of Theodorou et al. (1994). Six substrates (wheat straw, hay, soyabean meal, wheat starch, maize starch, and potato residue) were utilized. Gas pressure readings (observations = 1187) were measured using a hand-held pressure transducer with an LED readout. Interfaced to a computer using a Mini-Pod 300 (AD converter). MS-Visual Basic (Microsoft) was used to convert the mini-pod readings and automatically enter them into an Excel spreadsheet. Gas volume was measured using a syringe to remove the gas produced until the readout indicated zero.

When analysing the fermentative breakdown of cell wall material in plants it is important to realize that it is not homogeneous. The cell walls are composed of different cell wall types which can differ in both their breakdown characteristics and composition. In this experiment in vitro cumulative gas production (Theodorou et al., 1994) was measured to study breakdown characteristics of cell walls from hulls and endosperm of soya beans.

Because high quality forages are scarce and expensive, most Mediterranean countries traditionally follow a “barley-beef” system. Within a few weeks after switching to a dry feed diet, the progressively weaned calf is able to digest its diet as efficiently as adult ruminants (Anderson, 1987; Lalles and Poncet, 1990). Assuming that in high concentrate diet enough energy is available, the level and degradability of protein may influence the amount and quality of AA supplied to the duodenum and total nitrogen excretion in faeces and urine. The objective of this experiment was to study the effect of crude protein and degradability level on performance and rumen fermentation in weaned crossbreed beef heifers from 100 to 230 kg body weight fed with high concentrate rations.

Beneficial effects of inoculants on the nutritive value of well-preserved grass silage for beef cattle have been described (Keady and Steen, 1994). Less information is available on the efficacy of inoculants when untreated grass is preserved badly. The first objective of this study was to determine the effect of one inoculant under such conditions. Since an improvement in nutritive value of silage may be hidden when supplementary concentrates are offered, the second objective of this study was to determine the interaction between silage additive treatment and concentrate supplementation on the nutritive value of the resulting diets.

There is increasing consumer resistance to feeding antibiotic performance enhancers to beef cattle which has created interest in the use of yeast cultures as an alternative. Yeast cultures such as Diamond V ‘XP’ (Rumenco) are produced by growing selected yeast strains (on a semi-solid medium under stressed conditions) which are then dried. Yeast cultures are now used in a considerable number of North American beef feed lots. The objective of this work was to evaluate the effect of feeding ‘XP’ Yeast to finishing beef cattle on a typical UK grass silage-based diet.

The efficiency of dietary nitrogen use on ruminants fed on forage is poor and this may be largely attributed to an asynchrony between the supply of energy and nitrogen to the rumen microbes, resulting in poor microbial protein synthesis and a low efficiency of utilisation of absorbed amino acid (AA). One of the main factors contributing to the latter is the efficiency of absorption of AA from the small intestine and it has been concluded that a value of 0.75 is appropriate across a range of diets (MacRae and Reeds, 1980). However, it is uncertain how this value may vary on grass silage diets and what effect additional rumen undegradable protein may exert. The objective of this experiment was to measure body nitrogen utilisation and AA absorption from the small intestine in steers fed on grass silage or supplemented with fishmeal.

Due to the high growth potential of bulls compared cross steers and the reduced price of concentrate feeds, there is a gradual move towards feeding continental and bulls from the suckler herd on all concentrate diets from weaning to slaughter at 12 to 15 months of age. The objective of this study was to determine the effects of diet type and slaughter weight on animal growth and feed conversion efficiency.

It has been suggested that cattle have a greater ability to digest fibrous feeds and a lower ability to digest non-fibrous feeds than sheep (Mc Donald et al., 1995). This statement applies mainly to forages and few direct comparisons have been conducted using concentrate ingredients. The digestibility of concentrate ingredients may be influenced by the level of consumption since an increase in intake of a complete diet resulted in a decrease in digestibility (El Khidir and Vestergaard Thomsen, 1983). The aims of this study were (a) to determine the effect of level of consumption by cattle and (b) to examine the effect of animal species (sheep and cattle) on the digestibility of concentrate ingredients.

Manipulation of amino acids (AA) supply to the duodenum is constrained in ruminants by insufficient knowledge on the AA profile of undegradable protein. There is evidence that rumen degradability and intestinal digestibility of individual AA may differ from that of nitrogen (N) or total AA (TAA) (Erasmus et al., 1994, O'Mara et al., 1997) although differences in intestinal digestibility are probably of relevance only in roughage and overheated feeds (Van Straalen et al., 1997). The objective of this experiment was to provide more information about the relative influence of rumen degradation and intestinal digestion on the AA profile of the absorbed fraction of four protein sources commonly used in beef cattle rationing.

Values of ammonia concentration in rumen liquid have been used as an index of nitrogen requirements of rumen microflora even though ammonia requirements seem to depend on the type of diet. Cellulollitic flora mainly use ammonia as N source, while bacteria that ferment non-structural carbohydrates use either ammonia or protein nitrogen. The aim of this experiment was to establish the minimum concentration of ammonia to optimise microbial synthesis in the rumen of steers fed concentrate-based diets.

Studies in the use of the purine derivatives technique in ruminants have been stimulated by the possible use of this technique as an estimator of the rumen microbial-N supplied to the host animal. The recovery factor influences the estimation of the total purines absorbed and therefore the microbial-N supply. The relationship between exogenous purine input and urinary excretion and recovery has been studied using cattle maintained with the intragastric infusion technique (Orskov et al., 1979). The urinary recovery of exogenous purines has been estimated to be 0.77-0.85 (Chen et al., 1990a, Verbic et al., 1990), and this relationship has been assumed to be applicable to normal feeding situations. To our knowledge there is no data to support or reject this approach. This study examined the urinary recovery of exogenous allantoin input in steers under normal feeding conditions.