Modulation of the soleus H-reflex in prone human subjects using galvanic vestibular stimulation.

OBJECTIVES: To determine if vestibular-evoked modulation of the soleus H-reflex can be achieved in a muscle that is not being used for postural support. METHODS: Ten healthy subjects lay prone while the right leg was supported. In this position soleus H-reflex amplitudes were measured with the head facing forward, coupled with ipsilateral monopolar monaural galvanic stimulation (anode or cathode). To evaluate the interval between the onset of the galvanic stimulus and tibial nerve stimulation, the timing was varied between 0 and 200 ms in 20 ms intervals. A two-way ANOVA and student's t-test was performed to compare the mean amplitudes of the test and conditioned H-reflexes. RESULTS: Galvanic stimulation significantly modified the amplitude of the H-reflex in a prone lying subject (P<0.05). Furthermore, the peak inhibitory and facilitatory effect occurred when the galvanic vestibular stimulus was delivered 100 ms prior to the H-reflex stimulus. CONCLUSIONS: The results of this study demonstrate that galvanic stimulation can modulate the excitability of the soleus motoneuron pool when the muscle is not being used posturally. This suggests that in certain situations, it may be possible to use this type of vestibular stimulation to examine the integrity of descending vestibulospinal pathways in prone human subjects.

The effect of muscle length on motor-unit recruitment during isometric plantar flexion in humans.

The triceps surae muscle group, consisting of the mono-articular soleus (SOL) and bi-articular gastrocnemius (GAS) muscles, primarily generates plantar flexor torque. Since the GAS muscle crosses the knee joint, flexion of the knee reduces the length of this muscle, thus limiting its contribution to torque output. However, it is not clearly understood how the central nervous system activates muscles that are at inefficient or non-optimal force-producing lengths. Therefore, the present study was designed to determine the effect of muscle length on motor-unit recruitment in the medial GAS muscle. Single motor-unit activity was recorded from the medial GAS muscle while electromyographic (EMG) activity was recorded from the SOL muscle in nine male subjects. With the ankle angle held constant at 90 degrees, the knee angle was changed from 180 degrees to 90 degrees, corresponding to a long and short GAS muscle length, respectively. Levels of voluntary plantar flexor torque were produced at a rate of 2 Nm.s-1 until motor-unit activity was detected. A total of 229 motor units were recorded, of which 121 and 108 were obtained at the long and short muscle lengths, respectively. At the short length, onset of motor-unit activity occurred at significantly higher levels of plantar flexor torque and SOL EMG. Onset of motor-unit activity occurred at 2.97 +/- 7.78 Nm and 32.14 +/- 10.25 Nm, corresponding to 0.045 +/- 0.075 mV and 0.231 +/- 0.129 mV of SOL EMG in the long and short positions, respectively. No individual GAS motor unit could be recorded at both muscle lengths. Motor units in the shortened GAS muscle may be influenced by peripheral afferents capable of reducing the excitability of the motoneurone pool. This may also reflect a specific inhibition of motor units having shortened, non-optimal fascicle lengths, and they are thereby incapable of contributing to plantar flexor torque.

Magnitude effects of galvanic vestibular stimulation on the trajectory of human gait.

This study examines the contribution of the vestibular system during different magnitudes of galvanic vestibular stimulation (GVS) during human walking. Anodal threshold levels of GVS were determined for right and left sides for each subject. Seven conditions were tested (no stimulation, left and right anode stimulation) at one, two and three times threshold. GVS was delivered to the mastoid processes at first heel contact and continued for the duration of the trial. All subjects responded by deviating towards the anode while walking. In addition, the magnitude of deviation increased as the stimulus intensity increased. Our results demonstrate that the vestibular system is sensitive to GVS intensity changes and responds by altering the magnitude of the response accordingly. These data provide a strong argument in support of a significant role for vestibular information during dynamic tasks.

Comparative pharmacokinetics of fenbendazole in buffalo and cattle.

Swamp buffalo (Bubalus bubalis) and Droughtmaster cattle (Bos indicus x B. taurus), fitted with gastrointestinal cannulae, were dosed intraruminally with fenbendazole at 7.5 mg/kg liveweight, together with a chromium oxide capsule and a pulse dose of NaCoEDTA, to estimate the flow dynamics of the digesta in the rumen and duodenum. The concentrations of fenbendazole (FBZ) metabolites were measured in plasma and duodenal fluid collected over 120 h. In plasma, significantly lower peak concentrations and earlier disappearance of FBZ and its sulphoxide (OFZ) metabolite were observed in buffalo, which considerably reduced systemic availability in comparison with cattle. The availability of OFZ in the duodenal fluid of buffalo was significantly lower, whereas FBZ disposition was similar to that in cattle. The turnover rate of fluid in the rumen was higher in buffalo than in cattle, while the flow parameters for other digesta were similar in the two species. It is concluded that the decreased absorption of drug in buffalo was attributable to the shorter residence time of the dose in the rumen, and probably in the entire gastrointestinal tract. This may reduce the efficacy of treatment and indicate the need for higher dose rates for benzimidazole anthelmintics in buffalo than in cattle.

Resistance of leaf and stem fractions of tropical forage to chewing and passage in cattle.

The voluntary intake (VI) of separated leaf and stem fractions of a grass and legume (Panicum maximum and Lablab purpureus respectively) was determined using Hereford steers fistulated at the rumen and oesophagus. VI of leaf fractions was higher than that of the stem fraction (8.23 v. 3.67 kg/d, P less than 0.001) while that for the legume diets was higher than for the grass diets (6.65 v. 5.22 kg/d, P less than 0.05). The total number of eating chews per day was higher on the leaf than stem fraction (1.6 x 10(4) v. 9.8 x 10(3), P less than 0.05). The mean number of rumination chews (2.4 x 10(4)) was similar (P greater than 0.05) for all four diets. The mean resistance of large particles (LP, i.e. retained on a 1.18 mm sieve during wet sieving) to breakdown (chews per g LP breakdown) during eating was lower for leaf than stem fractions (8.4 v. 23.7) and lower for the grass than legume diets (10.5 v. 21.6). The mean resistance to breakdown of LP by rumination (chews per g LP breakdown) was lower in leaf than in stem fractions (8.2 v. 13.2, P less than 0.01) and higher in grass than in legume (12.5 v. 9.0, P less than 0.05). The resistance of LP to breakdown during rumination was higher than during eating for the grass diets, but was lower for the legume. Fractional passage rates (FPR) of small particles (i.e. passing through a 1.18 mm sieve during wet sieving) from the reticulo-rumen were negatively related to dimensions of particles, with greater ease of outflow for legume than for grass particles of the same length or diameter. When corrected for content of cellulase-indigestible fibre, FPR of small particles of leaf was greater than for small stem particles. It was concluded that VI of tropical forages was associated with the resistance of LP to breakdown by chewing during both eating and rumination and that the patterns of escape of small particles from the reticulo-rumen were only partially explicable in terms of particle dimensions, and that other properties of the particles may be of importance.

Passage and rumination of inert particles varying in size and specific gravity as determined from analysis of faecal appearance using multicompartment models.

Plastic particles of defined length (2, 5 mm) and specific gravity (sp.gr. 1.10, 1.34, 1.77) were administered just before feeding into the reticulo-rumen of four cattle and four swamp buffaloes given a diet predominantly of rice straw ad lib. Simultaneously, doses of ground rice straw marked with Cr and Yb were likewise given. Plastic particles were recovered from faeces for 12 d after dosing, and divided into non-ruminated (NR) and ruminated (R) particles. Excretion data of plastic particles were interpreted using a four-pool model incorporating passage of NR (kp) and R from the reticulo-rumen, post-ruminal passage, rate of chewing (kr) and two lag times. An inverse relationship was found between kr and sp.gr. The kr was higher for 5 mm than that for 2 mm particles. In contrast, kp was greatest for particles of sp.gr. 1.34, with higher kp for 2 mm than for 5 mm particles. Rates of passage and rumination (kp, kr) were higher for buffaloes than for cattle. Rumination time was related to kr, most highly (r2 0.96) with kr of 2 mm, 1.10 sp.gr. particles. Fragmentation of 5 mm particles by rumination tended to increase the rate of passage from the rumen. Ruminal passage rates of Yb and Cr markers were poorly correlated with each other and with kp of any of the plastic markers. Reanalysis of published data from plastic particle studies supported the relationships between sp.gr., size, kp and kr.(ABSTRACT TRUNCATED AT 250 WORDS)

Reticulo-ruminal motility in cattle (Bos indicus) and water buffaloes (Bubalus bubalis) fed a low quality roughage diet.

1. The effect of A and B sequence contractions of the reticulo-rumen on passage rate of digesta was compared in buffaloes and cattle fed low quality rhodes grass. 2. Both species ate the same amount per unit body weight but buffaloes spent 53% more time ruminating than cattle. 3. Buffaloes had fewer A and B sequence contractions each day and the rate of these contractions during eating, ruminating and at rest were slower. 4. A larger pool of fine feed particles in the rumen of buffaloes, generated by extra ruminating activity was associated with the 30% shorter mean residence time of particulate matter in the forestomach compared with cattle. 5. It is concluded that the difference in the number and frequency of contractions between the species was insufficient to affect passage rate of digesta from the stomach.

Rate of passage of corn-canola meal and corn-soybean meal diets through the gastrointestinal tract of broiler and White Leghorn chickens.

The effect of corn-canola meal and corn-soybean meal diets on the form and function of the gastrointestinal tract of broiler (meat-type) and White Leghorn (egg-type) cockerels was measured from 14 to 44 and 14 to 86 days of age or 203 to 1,844 and 115 to 1,777 g of body weight, respectively. Dry weights of the empty crop (P less than .01), gizzard (P less than .001), and ceca (P less than .001) relative to live body weight (g/kg) were lighter in broilers than in Leghorns. Canola meal at 370 g/kg diet was associated with increased (P less than .001) dry weight of the gizzard and jejunum relative to body weight. Soybean meal at 370 g/kg diet was associated with increased (P less than .001) dry weight of the ceca relative to body weight. The lengths, relative to a power of body weight of the duodenum (cm/g.187) and jejunum plus ileum (cm/g.240), were longer (P less than .001) in broilers than in Leghorns. The canola meal diet was associated with an increase (P less than .001) in length of the jejunum plus ileum (cm/g.240) relative to a power of body weight. Mean retention time (MRT) of a particle marker, 103ruthenium phenanthroline, increased with body weight in the entire gastrointestinal tract (P less than .001) and in each of its segments except in the proventriculus, where it was not affected by body weight (P greater than .05), and in the gizzard, where it decreased (P less than .05) with body weight. The MRT, adjusted for body weight in the entire gastrointestinal tract of broilers (338.0 +/- 10.8 min) and Leghorns (359.9 +/- 10.8 min), was similar (P greater than .05) but varied significantly in segments of the gut for both type of chicken and diet. Adjusted MRT was shorter in the crop (P less than .001) and gizzard (P less than .001) and longer in the duodenum (P less than .001) and ileum (P less than .01) of broilers than Leghorns. The soybean meal diet was retained for 2.3 min longer in the duodenum (P less than .001) and 84.2 min longer in the ceca (P less than .001) than the canola meal diet, which accounted for the longer (P less than .001) retention of the soybean meal diet in the entire gastrointestinal tract (388.0 +/- 10.6 vs. 309.8 +/- 10.8 min). Segments of the gastrointestinal tract vary in length, weight, and MRT of digesta with dietary composition and type and body weight of chicken.

Influences of cold exposure on digestion of organic matter, rates of passage of digesta in the gastrointestinal tract, and feeding and rumination behaviour in sheep given four forage diets in the chopped, or ground and pelleted form.

Sixteen sheep, each fitted with cannulas in the rumen and proximal duodenum, were given four diets in the chopped or ground and pelleted form, at fixed intakes at intervals of 2 h. The sheep were closely shorn and exposed to temperatures of 22-25 degrees or 1-4 degrees for four periods of 45 d. Flow of duodenal digesta by reference to the markers CoEDTA and 103Ru-phenanthroline, chewing behaviour and particle size of rumen and duodenal digesta were measured. Apparent digestibility of organic matter (OM) in the gastrointestinal tract was depressed (P less than 0.05) by grinding and pelleting the diet, and by exposure of sheep to cold ambient temperatures. This was attributable to depression (P less than 0.01) by 0.1 of OM digestion in the reticulo-rumen. No effects on intestinal digestion of OM were observed. Cold ambient temperatures did not affect the content, but increased the rate of digestion for pelleted diets but not for chopped diets, of potentially-degradable cell-wall constituents of ground dietary material incubated in nylon-bags in the rumen. Retention times of markers of the particulate and liquid phases of rumen digesta were not significantly (P less than 0.05) affected by ambient temperature, despite significant (P less than 0.001) increases in the rate of contraction of the reticulum. Retention time of 103Ru-phenanthroline in the intestines was not affected by cold exposure. Cold exposure was associated with depression (P less than 0.05) of volatile fatty acids concentration in the rumen and elevated (P less than 0.05)pH. Molar proportions of acetic and isovaleric acid were reduced (P less than 0.01), accompanied by increased (P less than 0.001) proportions of propionic acid during cold exposure. Cold exposure and pelleting of the diets were both associated with reduction in digesta particle size in the rumen. Duodenal particle size was not affected by cold exposure. Pelleting of the diet markedly reduced (P less than 0.001) duration of chewing and number of chews/d during eating and rumination. Cold exposure of sheep resulted in a faster (P less than 0.01) rate of eating of the diets. When allowed to express their voluntary feed consumption during a 10 d period, intakes of chopped diets were increased by 0.13 (P less than 0.01) by cold exposure, in contrast to lack of significant change in sheep given pellets.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of methods for the estimation of the proportion of microbial nitrogen in duodenal digesta, and of correction for microbial contamination in nylon bags incubated in the rumen of sheep.

Four sheep, each fitted with cannulas in the rumen and proximal duodenum, were given two diets (1390 g dry matter (DM)/d) consisting of lucerne (Medicago sativa) pellets (24.2 g nitrogen/kg DM) plus pelleted reed canary grass (Phalaris arundinacea; 14.1 g N/kg DM) or chopped hay (11.8 g N/kg DM) at intervals of 2 h. Flow of duodenal digesta measured by reference to the markers 51Cr-EDTA and 103Ru-phenanthroline indicated a net gain of 5.8-7.5 g non-ammonia-N (NAN) between mouth and duodenum. The proportion of microbial N in duodenal digesta N was estimated using 15N and 35S incorporation into bacteria and digesta. Two methods of analysis for 35S content, the Bird & Fountain (1970; B&F method) and the Mathers & Miller (1980; M&M method), were used. (15NH4)2SO4 and Na2(35)SO4 were infused into the rumen for 3.5 d before and 4.0 d during sampling. A bacterial fraction was prepared from the fluid phases of sampled duodenal digesta and rumen contents by differential centrifugation. In addition, samples of ground canary grass and of lucerne were incubated in nylon bags in the rumen for 3-48 h during the infusion. Each of the 35S analytical methods yielded similar values of 35S content of isolated rumen or duodenal bacteria, but there was more (P less than 0.05) incorporation of 15N into rumen than into duodenal bacteria. Relative to values obtained using the M&M method and 15N incorporation, the B&F method for S analysis yielded higher (P less than 0.05) estimates of microbial content of duodenal digesta from sheep given chopped reed canary grass. 35S activity associated with washed nylon-bag residues increased rapidly with time-period of incubation and was substantially greater (P less than 0.05) when analysed by the B&F method compared with the M&M method. The 35S content (/g DM) of adherent bacteria removed from nylon-bag residues by homogenization in a second experiment varied from 0.65 to 1.88 that of free-living bacteria isolated from rumen fluid by differential centrifugation. The difference in 35S content in digesta and nylon-bag residues as measured using the two analytical methods was considered in relation to 35S-labelled extracellular material postulated to be produced by bacteria adherent to plant residues. Estimates of disappearance of dietary N from nylon bags after correction for microbial contamination indicated a disparity with estimates based on in vivo information.

Some haematological data on pregnant Gurkha women.

In a retrospective survey of 285 pregnancies in Gurkha women living in the New Territories of Hong Kong, the mean values of Haemoglobin, Mean Cell Volume and Mean Cell Haemoglobin Concentration were examined with the aim of establishing basic data.

Effects of cold exposure on feed protein degradation, microbial protein synthesis and transfer of plasma urea to the rumen of sheep.

1. Three diets of barley-canola-seed (Brassica campestris), lucerne (Medicago sativa) or chopped brome-grass (Bromus inermis) were given at intervals of 3 h to closely-shorn Suffolk wethers held at a temperature of 1-5 degree (cold) or 22-24 degree (warm). Apparent digestibility of organic matter (OM) and nitrogen was reduced by 0.08-0.05 and 0.04 units respectively for lucerne and brome-grass diets given to cold-exposed sheep, but no treatment effects on digestibility were observed for the barley-CSM diet. Measurements achieved using infusion of the digesta markers 58Co-EDTA and 103Ru-phenanthroline (103Ru-P) showed that cold exposure depressed apparent OM digestion in the stomach and intestines by 33 and 42 g/d for the lucerne diet, and 13 and 35 g/d for the brome-grass diet respectively. 2. The turnover time (h) of the 103Ru-P marker in the rumen of warm sheep was 38.9 for barley-CSM, 18.4 for lucerne, and 15.6 for brome-grass. In cold-exposed sheep, 103Ru-P turnover time (h) tended to be reduced to 32.3, 12.3 and 15.3 for the three diets, respectively. OM fermentation in the stomach was highly related to 103RU-P turnover time for lucerne and brome-grass diets. 3. Cold exposure increased the escape of dietary N from the abomasum by 0.04 and 0.09 of dietary N intake for sheep given lucerne and brome-grass diets respectively. Dietary N degradation was closely related to 103Ru-P turnover time for lucerne, and to the proportion of large particles in rumen digesta for the brome-grass diet. Estimates of feed N degradation made by use of information on the rate of fermentation of the diet in nylon bags and 103Ru-P turnover time were consistently lower than those observed in vivo for barley-CSM and lucerne diets. Intestinal digestibility of non-ammonia N was not significantly changed by cold exposure. 4. Transfer of urea from plasma to the rumen was 1.4-2.5 g N/d for the barley-CSM and lucerne diets, but the value for brome-grass was 4.5-4.9 g N/d. Cold exposure did not affect urea transfer. The production of ammonia from feed and endogenous protein was approximately 0.66 and 0.47 g N/g N intake of barley-CSM and lucerne diets, with no effect of cold exposure. Cold exposure reduced the value from 0.57 to 0.38 for brome-grass. 5. The results are compared with those obtained previously with pelleted hay, and the importance of large particle breakdown in the prediction of OM and N fermentation using nylon bags is discussed.

Influences of dietary sucrose and urea on transfer of endogenous urea to the rumen of sheep and numbers of epithelial bacteria.

1. The rates of transfer of plasma urea to the rumen of six sheep given brome grass (Bromus inermis) pellets alone or with supplements of sucrose or urea were determined using [14C] urea and 14C-labelled sodium bicarbonate infusions during three periods. 2. The sheep were slaughtered after the third period and samples of rumen epithelium were taken for assessment of numbers of adherent bacteria. 3. Maximum transfer (0.31 g nitrogen/h) of urea ot the rumen was observed for sheep given supplements of 150 g sucrose/d plus 20 g urea/d. Maximum clearance of plasma urea to the rumen (rate of urea transfer to the rumen per unit plasma urea concentration, 5.8 1/h) was observed for sheep given 300 g sucrose/d. 4. Urea clearance to the rumen was negatively related to rumen ammonia concentration; the slope of the relationship was increased with each addition of sucrose to the diet. 5. Numbers of facultative bacteria adherent to the rumen epithelium were increased by urea and sucrose supplements. 6. The results are discussed in relation to a hypothesis which relates the ureolytic capability of the bacteria adherent to the rumen epithelium to the control of the rate of transfer of urea into the rumen.

Metabolic changes in cattle due to the specific effect of the tick, Boophilus microplus.

1. An experiment was designed to provide information on the alterations in body metabolism which would account for the loss of body-weight in cattle due to the specific effect (factors other than reduced food intake) of the tick Boophilus microplus. 2. Two groups of British (Shorthorn x Hereford) and Africander x British calves, each approximately months olds, were used: one group (treated) of each breed was tick-infested and the other (control) was tick-free. Within breeds, calves in the control group were pair-fed to calves in the treated group. 3. In both breeds, the effect of ticks: (a) depressed packed cell volume, serum alkaline phosphatase (EC 3.1.3.1) and amylase (EC 3.2.1.1.) activities, plasma cholesterol and phospholipid levels, serum iron and albumin levels, (b) increased the plasma levels of urea-nitrogen and gamma-globulin (c) increased rectal temperature, water intake, urine volume, urinary and faecal total N, urinary urea-N and alpha-amino acids, the excretion of water, sodium and potassium in the faeces and (d) reduced N balance, N and dry-matter digestibilities. 4. In the British breed, ticks increased the excretion of K with a corresponding decrease in the excretion of Na in the urine and increased the plasma clearance of bromsulphthalein. 5. A second experiment showed that the specific effect of tick infestation increased the flow of organic matter (OM) from the abomasum and the fractional turnover of rumen fluid of Hereford steers. It was also shown that the decrease in OM digestibility in the gastrointestinal tract was largely due to a decrease in OM digestibility in the rumen and that the increased urinary urea excretion and plasma urea concentration was caused by higher production rates of urea despite a tendency for lowered urea degradation in the gastrointestinal tract.

The effects of dietary sucrose and the concentration of plasma urea and rumen ammonia on the degradation of urea in the gastrointestinal tract of cattle.

1. The rates of entry of urea into plasma, of urea degradation in the gastrointestinal tract, and the partition of that degradation between the rumen and post-ruminal tract were determined by use of [14C]urea and NaH14CO3 in Hereford steers receiving hay diets with or without sucrose. The concentrations of plasma urea and rumen ammonia were varied by infusions of urea into the rumen or abomasum. 2. For all diets, plasma urea concentration was related to urea entry rate, to degradation of urea in the whole gastrointestinal tract, and to its degradation in the post-ruminal tract, but the relationship with its degradation in the rumen was poor. 3. Degradation of urea in the rumen was related in a multiple regression in a curvilinear manner in three groups of diets (pasture-hay alone, pasture-hay--lucerne (Medicago sativa) mixtures, diets with sucrose), and negatively to rumen ammonia concentration for pasture-hay diets, and diets with sucrose. 4. Ruminal clearance of urea (rate of urea degradation per plasma urea concentration) was negatively related to the rumen ammonia concentration for steers given diets with sucrose, of pasture-hay with or without urea infusions. Provision of sucrose in the diet significantly increased clearance. 5. Enhanced urea degradation in the rumen associated with dietary sucrose supplements accounted for 0.4 of additional microbial N synthesis in the rumen. 6. The partition of transfer of urea to the rumen via saliva and through the rumen wall is discussed.

Transfer of urea from the blood to the rumen of sheep.

1. The rate of transfer of plasma urea-nitrogen to rumen ammonia was measured by infusion of 15NH4Cl and [15N]urea into sheep given brome grass (Bromus inermis) or lucerne (Medicago sativa) pellets. Urea was infused into the rumen or abomasum of two sheep given brome grass in order to increase the concentration of rumen ammonia. 2. From 6.2 to 9.8 g/d of plasma urea-N were transferred to the rumen of sheep given brome grass pellets and a measurement of 1.3 g nitrogen/d was obtained for a sheep given lucerne pellets. When urea was infused into the rumen of sheep given brome grass pellets the transfer was only 2.8--3.7 g N/d. 3. There was a significant negative correlation between the rate of transfer of plasma urea-N to the rumen and the concentration of rumen ammonia.

Quantitative aspects of the transformations of sulphur in sheep.

1. [35S]sulphate was used to obtain quantitative estimates of the transfer of sulphur between the blood, rumen and postruminal tract of four sheep given brome grass (Bromus inermis) pellets or lucerne (Medicago sativa) pellets at the rate of 33 or 66 g/h. Sodium sulphate (0-4 g S/d) was infused into the rumen or abomasum of sheep given brome grass during four periods of 19 d and was not infused into the sheep during a subsequent period in which lucerne was given. The flow of sulphide, sulphate, microbial S and non-microbial organic S from the abomasum was estimated using 103Ru and 51Cr. 2. The concentration of inorganic sulphate in serum was increased to maximum values of 35-46 mg S/l by infusion of sulphate into the rumen or abomasum. The rate of irreversible loss of serum sulphate and rumen sulphide was positively related to the amount of sulphate infused. 3. Reabsorption of sulphate by the kidney reached a maximum of 0.69-1.1 mmol sulphate/l glomerular filtrate. 4. The transfer of sulphate from blood to the rumen was related to the concentration of inorganic sulphate in serum, attaining maximum values of 133 (+/- 13) mg S/d for sheep given brome grass plus sulphate, and 127-159 mg S/d for sheep given lucerne. 5. Bacteria derived 0.52-0.67 of organic S from rumen sulphide in sheep given brome grass, and approximately 0.45 of bacterial organic S was derived from sulphide for sheep given lucerne. Protozoa derived approximately 0.90 of organic S from bacteria. 6. It was estimated that endogenous organic S contributed 300-340 mg S/d to the rumen, and that 0.24-0.45 of S digested in the rumen was derived from endogenous sources.