Quantitative effects of defaunation on rumen fermentation and digestion in sheep

Foraging behaviour, digestion and growth performance of sheep grazing on dried vetch pasture cropped under conservation agriculture

This study aimed to investigate the replacement value of half time grazing of wheat stubbles by vetch, which had been cropped under the context of conservation agriculture (CA). Three grazing treatments were evaluated on Barbarine lambs (initial BW 18 ± 1.42 kg). Treatment 1 consists of 6-hr grazing on dried vetch only (V). For treatment 2, the sheep were grazing 3 hr on wheat stubbles in morning and 3 hr on dried vetch in the afternoon (VWS). Treatment 3 consists of 6-hr grazing of wheat stubbles only (WS). At grain maturity stage, biomass yield of vetch averaged 7 tons DM/ha allowing a grazing period of 2 consecutive months. Along this period, vetch conserved its pods indehiscent. Biomass and nutritive value of vetch and wheat stubbles were decreasing from the start to the end of the grazing period. Residual biomass was higher in vetch and wheat stubble assigned to treatment VWS. WS lambs spent more time on walking and standing, while V and VWS lambs allocated more time on biomass uptake. The DM, OM and CP intakes were higher in animal grazing vetch alone or combined to wheat stubble. Rumen fermentation parameters (pH, ammonia nitrogen concentration and protozoa count) were not affected (p > .05) by any of the three treatments. The average daily gain of lambs on V and VWS lambs was three times greater (p < .05) than that of WS lambs (164, 152 and 49.5 g respectively). Cold carcass yield averaged 444, 428 and 388 g/ kg for lambs assigned to V, VWS and WS treatments respectively. It is concluded that grazing vetch alone or combined with WS increased substantially the growth performance and carcass yield of lambs compared with WS grazing only. Therefore, dried vetch grazing could be a solution to make possible mulching and biomass uptake by sheep under the context of CA.

Effects of Isotricha, Dasytricha, Entodinium, and total fauna on ruminal fermentation and duodenal flow in wethers fed different diets

The objective was to measure rumen fermentation and duodenal flow of amino acids and nonammonia N components in five groups of five ruminally and duodenally cannulated wethers that were fauna-free, or inoculated with the ciliate protozoa genera of Isotricha, Dasytricha, Entodinium, or a normal population (total) of fauna. They were used in two 25-d periods and fed a haycrop-based diet in the first period and a corn silage-based diet in the second period. Feces, duodenal digesta, and rumen contents were sampled in each period and analyzed. The number of Entodinium in wethers containing the Entodinium monofauna was higher than the total protozoa numbers, including Entodinium, in wethers containing total fauna population. The type of diet or fauna did not affect total volatile fatty acid concentrations in rumen fluid. The ammonia N concentration in rumen fluid was higher in wethers containing total fauna (25 mg/100 ml) than in fauna-free wethers fed the two diets (18 and 12 mg/ 100 ml). In comparison with the respective fauna-free wethers, the concentration of ammonia in wethers containing Entodinium was higher when fed the corn silage diet, but not different when fed the haycrop diet. Ruminal presence of total fauna or Entodinium decreased the nonammonia N by 16 and 17%, and total amino acid flows from the stomach by 20 and 19%, respectively. Flow of bacteria N was decreased in wethers fed the two diets when Entodinium or total fauna were present in the rumen. The presence of Isotricha resulted in higher flow of bacteria N in wethers fed the haycrop diet, but the presence of Dasytricha resulted in higher bacteria N flow in wethers fed the corn silage diet. Entodinium was the most detrimental of ciliate protozoa species concerning protein nutrition of the host ruminant.

Manipulation of microbial activity in the rumen

Different methods of optimizing feed conversion into nutrients in the rumen are now available to scientists. But the rumen must be considered as an integrated system and this makes it difficult to rationalize manipulation. The observed result of any treatment is a combination of several interactive reactions. Any change to one component of the system has several uncontrolled effects on other components. The positive effects aimed for are sometimes associated with undesirable effects. Numerous chemical additives have been studied during the last two decades among which ionophore antibiotics represent the most important group. The interest of non-ionophore antibiotics, methane inhibitors, and compounds inhibiting proteases or deaminases, has also been considered during the last years. The observed effects of these chemical additives on animals, and their possible mode of action on rumen microbes and on animal metabolism, are discussed. However, the risks of the presence of residues in meat and milk are questioned by consumers. Microbial activity in the rumen can be altered by feeding animals with large amounts of certain food constituents (fats, starch) or minerals (buffer substances). The responses in the rumen to these dietary conditions are analyzed in terms of the digestive effects on plant cell wall degradation and microbial protein synthesis. Modification of the rumen microbial population is now considered as a possible approach to rumen manipulation by scientists. The effects on digestion of the elimination of ciliate protozoa (defaunation) are presented. The feasibility of these objectives, from a practical standpoint, is discussed. Finally, there is an overview of the effects of the addition of live yeasts (Saccharomyces cerevisciae), or fungi (Aspergillus orizae), used as probiotics. A possible mode of action of probiotics on the rumen ecosystem is suggested.

Balancing carbohydrates and proteins for optimum rumen microbial yield

Establishing conditions under which rumen fermentation will be optimized requires an understanding of the nutrient requirements of the mixed microbial population. The major nutrients required by rumen microbes are carbohydrates and proteins, but the most suitable sources and quantities needed to support maximum growth have not been determined. Digestion of proteins results in the production of peptides, which can accumulate in the rumen. Peptides are further hydrolyzed to amino acids, some of which are deaminated, producing ammonia. Although peptides, amino acids, and ammonia all may individually serve as sources of N for various microbes, the total population achieves the highest growth rate on mixtures of all three sources. In a somewhat analogous manner, carbohydrates are digested by exoenzymes to oligosaccharides that are available for crossfeeding by the mixed microbial population. Based on data from both in vitro and in vivo studies, there is general agreement that rate of digestion of carbohydrates is the major factor controlling the energy available for microbial growth; in addition, rate of digestion of total carbohydrate is directly related to proportion of starches, pectins, and sugars. Proteins affect both total fermentation and production of microbial DM per unit of carbohydrate fermented. It appears that the quantity of ruminally available protein needed to optimize microbial growth may, under some conditions, be as high as 14 to 15% of diet DM.

Effect of defaunation on protein and fibre digestion in sheep fed on ammonia-treated straw-based diets with or without maize

Using a defaunating method which preserved bacteria and fungi in the rumen, the effect of protozoa on protein and fibre digestion was studied in six adult wethers in relation to the nature of the diet. Sheep were given daily, 42 g dry matter (DM)/kg metabolic body-weight (W0.75), one of two isonitrogenous diets: one contained ammonia-treated wheat straw as the only energy source (diet S) and the other was supplemented with maize grain pellets (diet SM). Mean daily intakes (g/d) of nitrogen, neutral-detergent fibre and acid-detergent fibre were respectively 22, 573 and 373 for diet S and 23, 450 and 334 for diet SM. Elimination of protozoa increased duodenal non-ammonia-nitrogen flow. This result was mainly due to an increase in microbial protein flow and, to a lesser extent, to a higher dietary protein flow. Defaunation markedly increased the efficiency of microbial protein synthesis. Maize-grain supplementation had a net positive effect on this variable in defaunated sheep, but not in faunated sheep. Cell-wall carbohydrates were less well digested in the defaunated rumen, and the negative effect of defaunation was greatest with the diet SM. Intestinal fibre digestion increased in the defaunated sheep especially in those fed on diet SM, but not enough to compensate for the decrease in rumen digestion.

Effects of centrifugation speed and freezing on composition of ruminal bacterial samples collected from defaunated sheep

Triplicate ruminal samples from four rumen-cannulated defaunated sheep (50 kg BW) were used in a completely randomized design experiment with a 2 x 3 factorial arrangement of treatments to test effects of two pretreatments (fresh vs. freezing) and three centrifugation speeds (4640 x g for 30 min; 9820 x g for 20 min; 25,900 x g for 20 min) or quantity of ruminal bacteria harvested and composition of ruminal bacterial samples. There were no differences among centrifugation speeds on quantity of ruminal bacterial harvested, organic matter, total N, RNA, and diaminopimelic acid concentrations (% of DM), or RNA:N, RNA:organic matter, N:organic matter, and diaminopimelic acid:organic matter ratios. However, there were differences between fresh and frozen samples for all measurements except diaminopimelic acid concentration, and the diaminopimelic acid:organic matter ratio, suggesting that freezing ruminal fluid is not appropriate for obtaining truly representative bacterial samples.

Factors affecting the rate of breakdown of bacterial protein in rumen fluid

1. The cellular proteins of Butyrivibrio fibrisolvens, Lactobacillus casei, Megasphaera elsdenii, Selenomonas ruminantium and Streptococcus bovis were labelled by growth in the presence of L-[14C]leucine, and the breakdown of labelled protein was measured in incubations of these bacteria with rumen fluid to which unlabelled 5 mM-L-leucine was added. The rate of protein breakdown was estimated from the rate of release of radioactivity into acid-soluble material. 2. Protein breakdown occurred at different rates in different species. The mean rates for B. fibrisolvens, L. casei, M. elsdenii, Sel. ruminantium and Str. bovis were 28.6, 18.1, 17.7, 10.5 and 5.3%/h respectively in samples of strained rumen fluid (SRF) with different protozoal populations. Rates of 3%/h or less were found in SRF from ciliate-free sheep or in faunated SRF from which protozoa had been removed by centrifugation. Further removal of mixed rumen bacteria had little effect. Suspensions of washed protozoa degraded bacterial protein at rates which were of the same order as those found in SRF. 3. The rate of breakdown of bacterial protein in different samples of SRF tended to increase as the numbers of small entodiniomorphid protozoa increased. The numbers of larger entodiniomorphs and holotrichs had no obvious influence on this rate. 4. Autoclaved and u.v.-treated bacteria were generally no different from live bacteria in their susceptibility to breakdown in SRF from faunated sheep, indicating that endogenous protein turnover was not a significant cause of bacterial protein catabolism. 5. The rate of bacterial protein breakdown was unrelated to the proteolytic activity of SRF. 6. It was concluded that predation by small protozoa is by far the most important cause of bacterial protein turnover in the rumen, with autolysis, other lytic factors and endogenous proteolysis being of minor importance.

Microbial protein and peptide metabolism in rumen fluid from faunated and ciliate-free sheep

1. Protease and deaminase activities and the metabolism of peptides were measured in rumen fluid from ciliate-free sheep and from sheep with a limited population of small entodinia. The same measurements were repeated following inoculation of the latter group with a more typical mixed ciliate population. 2. Protease and dialanine uptake activities of mixed rumen micro-organisms were not significantly influenced by protozoa. Trialanine uptake, leucine aminopeptidase (EC 3.4.11.1), deaminase and trypsin-like protease activities were 70, 107, 73 and 91% higher with the limited population, and 72, 58, 64 and 55% higher when mixed protozoa were present, indicating a major role for the protozoa in these activities.

Effect of defaunation and refaunation of the rumen on rumen fermentation and N-flow in the duodenum of sheep

In order to confirm earlier fragmentary results, the effect of defaunation and refaunation of the rumen on the fermentation pattern and flow of N-components in the proximal duodenum of two sheep was investigated. Defaunation had no effect on acetic acid as a proportion of the total volatile fatty acids in the rumen, while the proportions of propionic acid increased with a concomitant decrease in butyrate. Refaunation resulted in lower acetic acid and higher butyric acid proportions. The concentration of ammonia N in the rumen was clearly decreased after defaunation, already indicating an effect of the elimination of protozoa on nitrogen metabolism in the rumen. Defaunation also increased significantly the flow of total N, non ammonia N and individual and total amino acids in the proximal duodenum. Defaunation resulted in higher bacterial growth efficiency, significantly in one sheep, but the decrease after refaunation was statistically significant for both sheep. Determination of rumen digestibility of organic matter and acid detergent fibre (ADF) revealed lower values in the absence of the protozoa, while total digestibility was only influenced to a much lower extent. This indicated a shift of digestion from rumen to the lower digestive tract. Finally, earlier work is discussed in the light of the present findings.

Contribution of protozoa to lysine synthesis in the in vitro rumen microbial ecosystem

Isotopic tracer experiments were conducted in vitro to determine contribution of protozoa toward the biosynthesis of lysine in the rumen microbial ecosystem. The presence of protozoa in a rumen microbial suspension always increased lysine synthesis from aspartate. Rumen contents from a faunated goat produced a higher amount of lysine than did those from a defaunated one.