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Physiological changes in rumen fermentation during acidosis induction and its control using a multivalent polyclonal antibody preparation (PAP) were studied in a completely randomized experiment using 12 crossbred heifers (452 [+ or -] 20 kg of BW). Treatments were control (CTR) or PAP. The acidosis induction protocol consisted of 3 periods: 3 mo of 100% rescue hay fed for ad libitum intake, 10 d (from d 1 to 10 of the experiment) of adaptation to the treatment (100% forage feeding + 10 mL/d of PAP top-dressed to the treatment group), and 5 d (from d 11 to 15 of the experiment) of transition, which consisted of increasing the concentrate (16.5% CP) 2.5 kg/d up to 12.5 kg/d while maintaining ad libitum intake of fescue and providing 10 mL/d of PAP to the treated heifers. Concentrate feeding of 12.5 kg/d was maintained until heifers developed acidosis (from d 16 to 22 of the experiment). When an animal was considered acidotic, it was changed to a 50:50 forage:concentrate diet, monitored for 4 d, and removed from the experiment. Samples of ruminal fluid were collected before and 6 h after feeding to determine pH, VFA, lactate, protozoa counts, and DNA extraction for quantitative real-time PCR and denaturing gradient gel electrophoresis analyses. Only samples collected during adaptation to the treatment, at 3 and 1 d before acidosis, on the acidosis clay, and at 1 and 4 d after acidosis were analyzed. Differences were declared at P < 0.05. Heifers (83% for CTR, and 50% for PAP) entered into acidosis 5.25 [+ or -] 0.17 d after the beginning of the transition. The fermentation profile of animals with acidosis was similar between treatments. From 3 d before acidosis to acidosis day, decreases in pH and in acetate-to-propionate ratio and increases in total VFA, butyrate, and entodiniomorph counts were observed. However, the greatest concentrations of Streptococcus boris and Megasphaera elsdenii (79 [+ or -] 54 and 104 [+ or -] 73 ng of DNA/mL of ruminal fluid, respectively) and a decrease in DMI (10.6 vs. 6.46 kg, respectively) were recorded 1 d after acidosis. Compared with CTR heifers, heifers fed PAP had greater pH before feeding on d 6 (6.70 vs. 6.11), 8 (6.54 vs. 5.95), and 9 (7.26 vs. 6.59) after the beginning of the feeding challenge. Heifers fed PAP tended to have greater total VFA concentrations than CTR (124 and 114 [+ or -] 4.0 mM, respectively). These results indicate that PAP may be effective in controlling acidosis of heifers during a rapid transition to a high-concentrate diet. Key words: acidosis, antibody, microbial profile, rumen fermentation

Recent advances in chromatographic identification of CLA isomers, combined with interest in their possible properties in promoting human health (e.g., cancer prevention, decreased atherosclerosis, improved immune response) and animal performance (e.g., body composition, regulation of milk fat synthesis, milk production), has renewed interest in biohydrogenation and its regulation in the rumen. Conventional pathways ofbiohydrogenation traditionally ignored minor fatty acid intermediates, which led to the persistence of oversimplified pathways over the decades. Recent work is now being directed toward accounting for all possible trans-18:1 and CLA products formed, including the discovery of novel bioactive intermediates. Modern microbial genetics and molecular phylogenetic techniques for identifying and classifying microorganisms by their small-subunit rRNA gene sequences have advanced knowledge of the role and contribution of specific microbial species in the process of biohydrogenation. With new insights into the pathways of biohydrogenation now available, several attempts have been made at modeling the pathway to predict ruminal flows of unsaturated fatty acids and biohydrogenation intermediates across a range of ruminal conditions. After a brief historical account of major past accomplishments documenting biohydrogenation, this review summarizes recent advances in 4 major areas of biohydrogenation: the microorganisms involved, identification of intermediates, the biochemistry of key enzymes, and the development and testing of mathematical models to predict biohydrogenation outcomes. Key words: biohydrogenation, rumen, microorganism, conjugated linoleic acid, modeling

The objective of this study was to understand the effects of fumarate addition on methane (C[H.sub.4]) and VFA production in the rumen through a meta-analysis of its effects on ruminal batch cultures. Because the reduction of fumarate to succinate can draw electrons away from ruminal methanogenesis, fumarate has been studied as a potential feed additive to decrease C[H.sub.4] production in ruminants. The average decrease in C[H.sub.4] in batch cultures was of 0.037 [micro]mol/ [micro]mol of added fumarate, which is considerably lower than 0.25 [micro]mol/[micro]mol, the decrease predicted from the stoichiometry of the reactions involved. One reason that fumarate was not effective at decreasing C[H.sub.4] in batch cultures was that only an average of 48% of added fumarate appeared to be converted to propionate. Secondly, the incorporation of reducing equivalents in the conversion of fumarate to propionate was almost entirely offset by their release from an average of 20% of added fumarate that appeared to be converted to ace tate. Thermodynamic calculations indicated that the conversion of added fumarate to both propionate and acetate was feasible. Fumarate appears to be more effective in decreasing C[H.sub.4] production and increasing propionate in continuous culture than in batch culture. This suggests that microbial adaptation to fumarate metabolism can be important. Variation in populations of fumarate-reducers, methanogens, and protozoa could all be involved. Fumarate supplementation for an extended period may result in the amplification of otherwise small populations of fumarate-reducers. Addition of some of these organisms may be helpful to improve fumarate conversion to propionate. Strategies based on enhancing the rumen's capacity to convert fumarate to propionate by maintaining a low fumarate concentration have been effective. Thermodynamic considerations should be taken into account when designing strategies for C[H.sub.4] abatement through the addition of external electron acceptors. Key words: fermentation, fumarate, meta-analysis, methane, rumen

Research findings reveal that the hyper-ammonia-producing bacteria vary very widely in the rumen of sheep and this diverse range of bacteria produce different rates of ruminal ammonia production depending on the substrates involved.

A ruminal simulation device (Rusitec) was used to compare the effects of Saccharomyces cerevisiae strains NCYC 240, NCYC 694, NCYC 1026, NCYC 1088, and Yea-Sacc (a commercial product containing S. cerevisiae) on ruminal fermentation. S. cerevisiae NCYC 240, NCYC 1088, NCYC 1026, and NCYC 694 were grown on malt extract at 30 [degrees] C in aerated fed-batch culture and harvested along with spent growth medium by freeze-drying. Each vessel received daily 20 g of a basal diet consisting of hay, barley, molasses, fishmeal, and a minerals/vitamins mixture at 500, 299.5, 100, 91, and 9.5 g/kg of DM, respectively. Yeast preparations (500 mg/d) were added along with the feed. S. cerevisiae NCYC 240, NCYC 1026, and Yea-Sacc stimulated total and cellulolytic bacterial numbers, whereas S. cerevisiae NCYC 694 and NCYC 1088 had no effect on the numbers of bacteria. The effects of S. cerevisiae NCYC 240, NCYC 1026, and Yea-Sacc on ruminal fermentation were further investigated in vivo-using ruminally cannulated sheep fed 1.5 kg/d of the diet used in Rusitec, supplemented with 2 g/d of yeast culture. All treatments tended to stimulate total and cellulolytic bacterial numbers. However, the stimulation was only statistically significant for S. cerevisiae NCYC 1026 with total bacterial numbers and S. cerevisiae NCYC 240 with cellulolytic bacteria (P < .05). Increased bacterial numbers were associated with an increase in the rate of straw degradation in the rumen and a non-significant (P > .05) increase in the excretion of purine derivatives in the urine, measured as an index of microbial nitrogen leaving the rumen. Thus, differences exist between strains of S. cerevisiae in their ability to modify the rumen bacterial population. Key Words: Ruminants, Rumen Fermentation, Yeasts, Saccharomyces cerevisiae, Probiotics

Present methods for manipulating ruminal fermentation that involve microbial biotechnology include dietary ionophores, antibiotics, and microbial feed additives. Developments in recombinant DNA technology mean that future methods will have a much wider scope. It has been suggested that genetically engineered ruminal microorganisms will be used in future to improve ruminal fermentation. Several technical objectives must be achieved before that will be possible. First, methods for inserting foreign or modified genes into ruminal microorganisms and ensuring their efficient expression must be developed. Broad host range plasmids and transposons have been used successfully to introduce new DNA into ruminal bacteria, as have shuttle vectors constructed as chimeras of plasmids from ruminal species and Escherichia coli. Although so far only antibiotic resistance markers have been transferred, the prospects for introducing other genes into selected ruminal bacteria are excellent. Second, the expression of the gene products(s) should be known to be nutritionally useful in vivo. A few examples of this type of benefit have been demonstrated, and many more proposed, including polysaccharidases for improving fiber digestion, methods for improving the amino acid composition of ruminal bacteria, and breakdown of plant toxins. Third, the difficulty that has been examined least, yet may prove most difficult to overcome, is that mechanisms have to be found for introducing and maintaining the new strain in the mixed ruminal population. Factors governing the survival of new strains in vivo are ill-understood, and attempts to select in favor of added new organisms have so far been unsuccessful. Because of the last obstacle, it may be advantageous, at least in the short term, to use nonruminal organisms, such as Saccharomyces cerevisiae, rather than indigenous ruminal species as a vehicle for implementing the benefits of recombinant DNA technology to ruminal fermentation. Yeast is already in widespread use as a feed additive, so no enrichment is necessary; and its genetics are already well known. Alternatively, adding particular enzymes to the diet may achieve some of the objectives described above, with the advantage that the manipulation could be achieved without the release of a recombinant microorganism.

Ammonia binding properties of glycocomponent and the toxicity of saponin components of Yucca shidigera affect ammonia metabolism and reduce ammonia concentration by inhibiting proteolysis in vitro. Microbial production and protein flow of rumen are increased with the injection of saponins into the animal to reduce the ciliate protozoan effect.

Studies on Trypticase peptides revealed that their reaction with acetic anhydride, succinic anhydride or maleic anhydride prevented their breakdown into ammonia by rumen microorganisms. This inhibition was measured at an average of 89% after 12 hours of incubation in vitro. All three reactions resulted in similer inhibitions. Acetylation was seen to provide protection to dipeptides comprising lysine and methionine derived from degradation. The best protective shield was achieved by combining lysine and methionine to form N-epsilon-methionyl lysine.