1. Experiments were undertaken to examine the kinetics of large ciliate protozoa in the rumen of cattle on sugar-cane diets.2. Three Zebu bulls were fed once daily on a diet of sugar cane and wheat bran. The diurnal patterns of volatile fatty acids and amm0n.a concentrations, and the numbers of protozoa in rumen fluid were determined. The numbers of protozoa re.iched values of 5 x l(r/ml for holotrichs (large ciliates) mainly Isotrichu and Dasytrichu spp and 4 x 105 for smaller protozoa, mainly Entodiniu (small ciliates).3. A method was delieloped which allowed large ciliate protozoa in rumen fluid to be separated from plant material and bacteria ar.d concentrated in a relatively uncontaminated form. Analysis of these protozoa indicated that 1.8 x 10' large ciliates contained 1 mg nitrogen and approximately 32 mg dry matter.4. A labelled preparation consisting tnainly of large ciliates (principally Zsotrichn spp.) was obtained by incubating isolated protozoa in rumen fluid (free of plant materials) containing [14C-methyl]choline and then isolating them by sedimentation and differential centrifugation.5. A portion of the preparation containing labelled protozoa was incubated in vitro with rumen fluid to determine the turnover of "C-labelled metabolites. There was no apparent dilution of the label in the protozoa over a 22 h period.6. A major portion of the preparation containing labelled protozoa was returned to the rumen of each of the donor cattle as a single injection. The specific radioactivity in the large protozoa @Ci/mg N) was monitored frequently for over 30 h, and thereafter daily for a further 12 d. The kinetics of tracer dilution were analyzed to give estimates of the size of the pool of these large ciliates in the rumen (2446 g N), and of their apparent rate of turnover.7. In contrast to thi: slow turnover of the large ciliates, the rate of turnover of the rumen fluid pool (approximately 54 I), esimated from the rate of dilution of polyethylene glycol, was considerably faster. Large ciliates were therefore wlectively retained within the rumen.Involvement of protozoa in the nutrition of ruminants has been studied mainly in animals in which small ciliate protozoa (Entodinia spp.) rather than the large ciliate protozoa (Holotricha spp.) wcre predominant in the population. The smaller protozoa actively engulf bacteria (Coleman, 1975), and do not pass out of the rumen in proportion to their concentration in rumen fluid (Weller & Pilgrim, 1974;Harrison et al. 1979). It has been suggested that these characteristics may reduce nutrient availability to the host animal Bergeii & Yokoyama, 1977) particularly on low-protein diets. Elimination of protozoa from the :umen has increased the growth rates and efficiency of food utilization for live-weight gain (Bird'& Leng, 1978;Bird et al. 1979) indicating that under some circumstances the presence of protozoa in the rumen reduces animal productivity.In cattle given sugar cane diets (Valdez et al. 1977) or grazing some temperate pastures (Clarke, 1965), although th...

The effects of virginiamycin, an agent active against Gram-positive lactic acid-producing bacteria, and NaHCO3 on ruminal and fecal pH, rumen volatile fatty acid proportions, blood metabolites, and milk production and composition were assessed. This study was conducted over 28 d and involved 71 dairy cows that grazed predominantly ryegrass, oats, and clover, and that were fed 10 kg of concentrate pellets/d per head. The pellets contained (per kilogram) no dietary additive, 30 mg of virginiamycin, 20 g of NaHCO3, or 30 mg of virginiamycin and 20 g of NaHCO3 on a DM basis. Ruminal pH tended to be higher in cows fed pellets containing virginiamycin (7.0 vs. 6.9; SED = 0.16). The results of in vitro incubation of ruminal fluid with glucose found the potential for L-lactic acid accumulation in ruminal fluid to be significantly lower in cows fed virginiamycin (15.5 vs. 35.3 mmol/L; SED = 2.98). Cows fed virginiamycin had significantly higher fecal pH (6.72 vs. 6.57; SED = 0.08) and produced more milk (23.94 vs. 23.32 kg/d) and more lactose than those not fed virginiamycin. No effects of NaHCO3 on fecal pH, in vitro potential for L-lactic acid accumulation in ruminal fluid, or milk production were observed, but ruminal pH tended to be higher and ruminal acetate proportion was greater for cows fed NaHCO3. Milk fat and milk protein percentage did not differ significantly as a result of dietary treatment. These data suggest that the inclusion of virginiamycin in the diet will reduce L-lactic acid accumulation in ruminal fluid and increase fecal pH in grazing dairy cattle fed concentrate supplements.

This study investigated the effects in sheep of feed intake and exercise training on (i) the level of glycogen in muscle, and (ii) carcass quality traits including growth rate, carcass weight, fat score, and the ultimate pH of muscle. Merino wethers, 12-months-old and starting body weight 38 kg, were individually penned and housed indoors. The effects of nutrition and exercise were tested for 2 levels of activity (sedentary v. exercised) and 4 levels of feed intake (1, 1.3, 1.5, 2.2 x maintenance) with 8 sheep per group housed individually. Exercise training was for 1 h at 8-9 km/h (approx. 55-65 VO2max), 3 times per week from week 4 to 9 of the experiment. The diet was 20% cereal straw, 26% lupin grain, 53% barley grain, mineral and vitamin premix, and virginiamycin. Animals were slaughtered at an abattoir in week 10. Regular exercise reduced growth rate, carcass weight, and fat score, but did not affect intake. At the highest level of intake, carcass weight was reduced by 0.53 kg and fat depth over the 12th rib (GR fat depth) by 6.3 mm, suggesting that muscle yield was increased. At all sampling times, the level of glycogen in the m. semimembranosis (SM) and m. semitendinosis (ST) increased linearly with increasing feed intake. Regular exercise caused increased glycogen level in SM samples immediately post-slaughter and in the SM, ST, and m. longissimus dorsi (LD) 48 h post-slaughter. The ultimate pH of muscle was reduced as the level of feed intake increased for all muscle groups. Exercise caused a reduction in the ultimate pH of the ST with no change for the SM and LD. The results indicate that glycogen levels in muscle are highly responsive to nutrition and regular exercise. In addition, exercise caused a reduction in subcutaneous fat with no change in feed intake.

An experiment, using a total of 320 Merino ewes, over two successive breeding seasons was conducted to investigate the separate effects of energy-yielding and protein-yielding nutrients on ovulation rate in sheep. The available energy-yielding or protein-yielding nutrients in the blood of sheep fed a maintenance pelleted ration were increased by either intravenous infusions of metabolites (acetate, glucose or acetate + glucose), feeding lupin grain, modification of the pattern of rumen fermentation to increase propionate production using the ionophore, lasalocid, or by feeding of ruminally undegradable protein (formaldehyde-treated casein). All treatments were given for 9 days prior to and including expected time of ovulation. Ovulation rates were measured by laparoscopy. In the first season (the 1984 experiment) when the effects of lupin grain, glucose + acetate and formaldehyde-treated casein were compared, ovulation rates were increased significantly in the group fed lupin (29%, P less than 0.001) and the group infused with glucose + acetate (24%, P less than 0.01). There was an apparent (17%) but statistically non-significant increase in the group fed casein. In comparisons between lupin grain, glucose, acetate, glucose + acetate, formaldehyde-treated casein and lasalocid in the 1985 experiment there were similar significant increases in ovulation rates in the groups fed lupin, and those infused with glucose or glucose + acetate (approximately 25%, P less than 0.001). The increase in the group infused with acetate was lower at 14% (P less than 0.05) and the increases of 7% in the groups fed casein or lasalocid were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Four mature sheep were offered perennial ryegrass (Lolium perenne, cv. S23) silage (885 g dry matter/d) at hourly intervals. The silage was well fermented with a pH of 4.0, a lactic acid content of 139 g/kg dry matter and an organic matter digestibility of 0.766. 5. Lactate appeared to make no direct contribution to glucose flux in the animal, but 0.10 of total lactate was converted to glucose through propionate.6. The results are discussed in relation to overall lactate metabolism, and it is suggested that almost 0.30 of ruminally digested organic matter may be fermented via lactate.Lactic acid is an important intermediate of carbohydrate fermentation in the rumen of grain-fed animals, whilst with animals offered silage it may be as much as 150 g/kg dry matter consumed. The biochemical pathways for the conversion of lactate to acetate, propionate and butyrate are well documented (Wood, 1961 ;Baldwin et al. 1962), but the factors which determine the relative amounts of lactate that are metabolized by the individual pathways are not well understood. Counotte (1981) showed that both bacterial species and rumen pH may influence the relative amounts of the individual volatile fatty acids (VFA) produced. In addition, it has been shown that lactic acid as such may be absorbed from the rumen (Waldo & Schultz, 1956) and could thus contribute to glucose metabolism.It is recognized that the efficient utilization of the end-products of digestion can be significantly influenced by the nature of the VFA produced and absorbed from the rumen in relation to the relative abundance of gluconeogenic (propionate) and non-gluconeogenic (acetate and butyrate) precursors (MacRae & Lobley, 1982). Thus, depending on its metabolic fate in the rumen, lactic acid arising from grass silage may have a significant effect on the overall efficiency of energy utilization in silage diets.The published evidence suggests that acetate or propionate may be the main end-product. Baldwin et al. (1962) studied lactate metabolism using isotope tracer techniques in vitro