A technique involving the measurement of the gas production from the microbial fermentation of a specified substrate in sealed conditions has recently been proposed as a method of assessing the fermentation kinetics of tropical feeds (Theodorou et al, 1992). In this technique the feed under test is the sole source of nutrients to the microbes and therefore it is possible that the nutrient release profile may have an influence on the microbial population leading to a modified gas production profile. The objective of this study was to investigate the effect of previous microbial experience on gas production.

One gram air dried feed samples were placed with 95 ml of modified van Soest media and 5 ml of strained rumen liquor in 150 ml serum bottles and sealed under anaerobic conditions. The rumen liquor was obtained from fistulated yearling wethers fed a maintenance diet of 0.9 good hay: 0.1 commercial 16% CP compound feed). Four replicates of fish meal (FM) and eight of spring barley grain (SPB) were set up together with control blanks.

Gossypol ﹛2,2'-bi(8-Formyl-l,6,7 trihydroxy-5-isopropyl-3-methyl naphthalene)﹜ is a toxic polyphenolic factor indigenous to the cotton plant. Concentrations of free gossypol contained in such feed stuffs as whole cottonseed (WCS) vary considerably. WCS is fed widely to animals. Free gossypol is extractable with aceton-water (70:30) and is toxic to monogastric animals. Bound gossypol has been considered relatively non-toxic. Calhoun et al (1991) has demonstrated there was extensive binding of free gossypol in ruminant digestive system. But they did not support the suggestion that bound gossypol is released during digestion in the small intestine. The present experiment examined the effect of gossypol on the rumen microbial degradation of grass hay (GH) under CBC. In sacco rumen digestion was also conducted to examine DM, CP and ADF digestibilities of grass hay and whole cottonseed at 48 h.

In vitro forage-digestion techniques, such as Tilley & Terry (1963) and the recent Pressure Transducer Technique (PTT) of Theodorou et al (1992), rely on rumen-fistulated animals to provide the microbial inoculum. The present study aimed to minimise reliance on rumen-fistulated animals by using the vessel or effluent fluids from the in vitro rumen simulation technique (RUSITEC) of Czerkawski & Breckenridge (1977) as sources of inocula for assessing rate of fermentation of forages using the PTT. A previous study (Owen et al 1991) demonstrated the feasibility of using RUSITEC effluent as a source of micro-organisms for the Tilley and Terry (1963) technique.

Cattle fed forage based diets often absorb a high proportion of dietary N as ammonia (NH3N) and this must be detoxified in the liver to urea. It has been suggested that this process utilises both energy and amino acids and may contribute to the lower efficiency of utilisation of dietary nitrogen and energy observed in forage fed ruminants (Fitch et al, 1989). However it is not known to what extent ammonia conversion to urea requires simultaneous deamination of amino acids. We report an experiment which examined hepatic nitrogen and energy metabolism at two different rates of NH3 arrival at the liver, in response an infusion of arginine to increase urea cycle flux. Arginine stimulates the hepatic synthesis of N-acetyl glutamate which is an activator of carbamoyl-phosphate synthase, the rate limiting step of the urea cycle (Meijer et al, 1990).

Some recent studies (Frutos et al., 1992) comparing Spanish sheep breeds have indicate possible differences between breeds in the digestive diet utilization. The aim of this experiment was to compare the activity of microbies in the rumens of Churra and Merino sheep which were kept in the same environment and received the same diets. The pH and ammonia nitrogen (NH3-N) concentration in rumen liquor were also determined in all animals.

The experiment was conducted with 5 mature Churra sheep (47.2 ± 2.74 kg live weight (LW)) and 5 mature Merino sheep (45.0 ± 0.91 kg LW), which had been fitted with a rumen cannula of 35 mm diameter 4 months before the start of the experiment. All animals were housed in individual pens and had free access to water and mineral blocks. The animals received alfalfa hay at maintenance level through the experimental period, which was distributed in two equal amounts at 10:00 and 18:00 h.

Yeast culture (YC) based on Saccharomyces cerevisiae has been reported to stimulate bacterial activity within the rumen, leading to increases in ruminal fibre digestion and microbial protein flow from the rumen (Wallace and Newbold, 1992). Dawson (1987) suggested that S. cerevisiae might grow in the rumen. Newbold et al (1990) found no evidence for the growth of S. cerevisiae in the rumen of sheep when the numbers of live yeast in the rumen were measured at various times after a diet contain YC had been consumed. The current experiment was designed to investigate further the possibility that S. cerevisiae grows in the rumen and to establish the importance of viable yeast cells in the action of YC in the rumen.

Developed models to estimate rumen microbial yield from the urinary excretion of purine derivatives fail to account for a complete absorbed purines (Chen et al., 1990a, Balcells et al., 1991). Ruminal degradation of purine derivatives recycled via saliva has been suggested as a possible explanation after detecting the presence of allantoin and uric acid in the sheep saliva (Chen et al. 1990b). However, it is not known to what extent these losses may be affected by dietary induced variations in saliva flow (Kay, 1966).

This paper reports preliminary results of an experiment designed to study the effect of diet processing and blood allantoin concentration on the rate of purine derivatives losses through salivary secretion.

Diurnal variation in the yield of microbial protein from the rumen may limit the use of urinary purine derivatives (PD) to estimate microbial protein yield from the rumen when assessed using spot samples. Chen, Grubic, Ørskov and Osuji (1992) found only small differences in the urinary PD excretion in young steers, and even less variation when PD excretion was estimated as a ratio to urinary creatinine. Lactating dairy cows have a much higher feed intake than steers and as a consequence may exhibit greater diurnal variation in urinary PD excretion. An examination of data from three experiments was undertaken to assess the effects of diurnal variation in rumen microbial protein yield on urinary PD excretion.

Utilization of cereal straws by ruminants is limited by low digestibility and intake. One solution is to supplement with rapidly fermentable carbohydrates (RFC), usually as starchy cereal grains. In restricted feeding experiments with roughages supplemented with RFC in the form of cereal grain concentrates, a slight increase in ruminal microbial protein (MP) synthetic efficiency has been observed with low, but a decline in efficiency at higher levels of supplementation (eg. Chen et al. 1992b). Huque (1991) noted that supplementation with low levels of starch improved straw intake and rumen digesta outflow rate. We have observed increased digesta flow rates to be associated with greater MP synthesis and yield per unit of digestible organic matter (DOM) (Chen et al. 1992a).

The efficiency of conversion of Metabolisable Energy into live weight gain by growing sheep may be improved by the partial substitution of fibrous diets with barley. This effect is associated with a reduction in the ratio of acetate to propionate in rumen fluid. Previous studies (Galbraith et al. 1988, 1989) have investigated responses of lambs to combinations of molassed sugar beet feed (MSBF) and barley and found a ratio of 0·75:0·25 MSBF:barley to be as effective as 0·25:0·75 when the diets were ground and pelleted.The incorporation of the yeast culture product, Yea-sacc, has been associated with increases in the concentrations of propionate in the rumen and variable growth responses in ruminants. The objectives of the present study were to investigate diets for finishing lambs which differed in the ratios of pelleted shreds of MSBF and barley and the effects of supplementation with Yea-sacc on growth, rumen metabolites and the physical properties of the diets.

It is now well established that the height of the sward grazed by sheep has a large effect on their performance (Hodgson, Mackie and Parker, 1986). However, there is a scarce of information about the rumen fermentation in sheep grazing at different sward heights. The aim of this experiment was to study the effect of sward height (4 vs 6 cm) on the rumen fermentation in Merino sheep which were continuously maintained on the pasture.

The study was carried out on a continuously stocked pasture in August 1992. Twenty mature Merino sheep were used to obtain two different sward heights: 4 cm (low; LSH) and 6 cm (high; HSH). Sward height was measured twice weekly using a swardstick and was controlled by the addition and removal of sheep. Herbage mass was of 633 and 1397 kg of dry matter (DM)/Ha for the LSH and HSH paddocks, respectively.

After calving, milk secretion in dairy cows increases rapidly, but the slower rate of increase in feed intake by the cow can lead to a substantial negative energy balance in the animal. Consequently, body tissues, comprising principally of adipose tissue are mobilised and this energy contribution is accounted for in calculating the feeding regime of the animal. In contrast, the extent of body protein mobilisation is considered to be much less but the potential contribution of such to the animal's protein requirements for milk synthesis are neither recognised or exploited in most of the feeding systems used in Europe, including the Swiss ‘APD’ system. The objective of this study was to examine the effect of reducing the calculated supply of absorbed protein on the secretion of milk and milk constituents and whole body energy and nitrogen metabolism in order to quantify any possible contribution of body protein to the nutrition of early lactation cows.

Polyphenolics are a common group of anti-nutritional factors, which occur in many browse plants found in the tropics. They have been implicated in the poor performance of ruminants. Detrimental effects could occur in the rumen or, if phenolics or their metabolites escape degradation, in the intestines or animal tissues. Most published reports have concentrated on examining the effect of feeding plant material containing anti-nutritional factors or the effects of administration of plant extracts containing a mixture of possible anti-nutritional compounds. We have adopted an alternative approach by investigating the metabolism of individual phenolic compounds rather than broad groups. For our initial studies the flavonol glycoside rutin (a monomeric unit of many condensed tannins) and gallic acid (monomeric unit of many hydrolysable tannins) were chosen as models to study the fate of these compounds in the rumen environment.

All samples were analysed for phenolics by HPLC (Spectra Physics Focus System) using a diode-array detector (220-900nm) and a 250 × 4mm column packed with ODS Hypersil, CIS. Samples run on this system were eluted with a linear gradient of 2% glacial acetic acid(A) and methanol(B), 100% A - 100% B in 30-60 min, the gradient run time depending on the type of sample being analysed. Sample peaks were identified using their retention time, maximum absorbances and peak spectra relative to known phenolic standards. All samples containing phenolics were extracted in 100% methanol by homogenization (Polytron AG Kinematic, Switzerland) at 13,500 rpm for 2 × 90 sec. The homogenate was then centrifuged at 1·000g for 10 min. The resulting supernatant was analysed for phenolics by HPLC.

It has been reported (Castlejon and Leaver 1990, Hill and Leaver 1991) that when offered as the sole forage intakes of urea treated whole crop cereals (UWCC) were high. However energy output in milk and liveweight change was less than expected from calculations of energy intake.

The level of crude protein (CP) in UWCC is high, typically in the range 200-300 g CP/kg DM. It has been suggested that a non-synchronous supply of available energy and rapidly available nitrogen to the rumen microorganisms was responsible for the low efficiency of utilization reported.

The work described here was carried out to determine whether the utilization of diets containing UWCC could be improved by increasing the supply of readily available carbohydrates to the rumen micro-organisms.

The use of South American camelids, as producers of fine fibres, has been proposed as a means of agricultural diversification. Relatively little is known however, of their nutrition and digestive ability under U.K. conditions. The present study was undertaken to determine if South American camelids (llama x guanaco) differ from sheep in terms of the voluntary intake and digestibility of contrasting forages.

Two chaffed ryegrass hays of high (A) and low (B) nutritive value were fed ad libitum to six animals of each species for two periods of 22 days in a cross-over design.

The provision of grain supplements to ruminants provide extra fermentable organic matter for the rumen microbial biomass, but often results in a lower whole efficient of ruminal digestion (Obara et al., 1991; Weakley et al., 1983). The present study was conducted to evaluate the effect of different basal diets on rumen degradability of several feedstuffs.

Ruminal digestion of three feedstuffs - soybean meal (SBM), lucerne hay (LH) and barley straw (BS) - was determined by in saccomethod according a 2 × 3 factorial design defined by 2 basal diets - lucerne hay (H) or lucerne hay plus barley (40:60; HB) - and three churra ewes fitted with ruminal cannula.

Recently has been shown that allantoin or total purine derivatives excretion in urine are strongly related to the amount of purines reaching the small intestine (Chen et al., 1990; Balcells et al., 1992) and as consequence purine derivative output is propouse to be used as an index of microbial protein flow to small intestine.

Because energy and rumen degradable protein supplies are the main factors affecting rumen microbial growth, the effect of changes in rumen degradable protein supplies at different levels of ME intake on urinary excretion of purine derivatives was studied in this work.

Provision of additional trace elements to cattle at grass by means of free-access mineral mixtures, feed blocks or molassed liquid feeds results in both wide variation and unpredictable individual intakes. Frequently, more than one trace element may be required and sometimes, for example, animals may individually receive combinations of selenium (by injection or rumen bolus), copper (by injection or as copper oxide needles) and cobalt (by rumen bolus or vitamin B12 injection).

This communication describes the use of a multi-trace element/vitamin bolus system (“Alltrace”, Agrimin Ltd.) in situations where dietary selenium intakes were very low over extended periods. The bolus is a dietary supplement composed of normal trace element salts such are used in mineral mixtures, vitamin sources and copper oxide powder. It is in the form of a compressed cylinder (2·5 cm diameter × 7·5 cm length) coated, apart from one exposed end, with an impervious polymer. Two boluses, by a process of solution and mutual erosion in the reticulum, release nutrients at mean rates (estimated by the use of rumen-fistulated cows) over about 240 days of 2 mg Se and 9 iu vitamin E with (mg/day) Cu 138, Mn 71, Zn 113, Co 2,1 2·1 with (lu/day) vitamin A 4644 and vitamin D 929. An end weight is included to increase the overall density. This disperses to leave no permanent residue in the rumen.

Dacron bag measurements (in-situ) to determine protein degradability of feedstuffs are often used as the “reference method” when comparing laboratory procedures. The model commonly adopted for interpreting data from “in-situ” dacron bag studies is that proposed by Ørskov & McDonald (1979) which is described by the asymptotic equation p = a + b (1-eα) where p is the proportion of material degraded after time t and a, b and c are constants. This model was later extended to deal with the presence of lag times and describes the instantly degradable soluble fraction (‘a’ in the above equation), and a fraction, ‘b’ which is degraded more slowly at an exponential rate V. A knowledge of the rumen fractional rate of outflow (k) for the feedstuff is also necessary to estimate effective degradability (ED). The value of ‘a’ (also referred to as the wash value) forms a major proportion of ED calculations. ED = a + (bc/(c+k)) as it is assumed to be wholly degradable.

Twenty-four steers of low iodine (I) status were selected from a group of 40 of similar weight and type. Changes in plasma inorganic iodide (PII) levels in steers treated with I were examined in a randomised block experiment (Part 1 below). Relationships between PII, plasma total I (TOTI) and thyroxine (T4) levels were examined also (Part 2 below).

The trial began after a pre-treatment blood sampling (Pre) on Day 1. Selected steers (4 groups of 6 each) were assigned at random to individual stalls. Treatments were: C = no I supplement; D = a daily oral drench of 10 mg I (as potassium iodide)/100 kg liveweight (LW) on Days 1 to 7 inclusive; F = one application of 70 mg I (as Tincture of l)/100 kg LW to the flank fold on Day 1; L = intramuscular injection (1.1 ml/100 kg LW) of an oil-based iodine preparation (Lipiodol; 400 mg l/ml)) on Day 1.