Modeling the distribution of ciliate protozoa in the reticulo-rumen using linear programming.

The flow of ciliate protozoa from the reticulo-rumen is significantly less than expected given the total density of rumen protozoa present. To maintain their numbers in the reticulo-rumen, protozoa can be selectively retained through association with feed particles and the rumen wall. Few mathematical models have been designed to model rumen protozoa in both the free-living and attached phases, and the data used in the models were acquired using classical techniques. It has therefore become necessary to provide an updated model that more accurately represents these microorganisms and incorporates the recent literature on distribution, sequestration, and generation times. This paper represents a novel approach to synthesizing experimental data on rumen microorganisms in a quantitative and structured manner. The development of a linear programming model of rumen protozoa in an approximate steady state will be described and applied to data from healthy ruminants consuming commonly fed diets. In the model, protozoa associated with the liquid phase and protozoa attached to particulate matter or sequestered against the rumen wall are distinguished. Growth, passage, death, and transfer of protozoa between both pools are represented. The results from the model application using the contrasting diets of increased forage content versus increased starch content indicate that the majority of rumen protozoa, 63 to 90%, are found in the attached phase, either attached to feed particles or sequestered on the rumen wall. A slightly greater proportion of protozoa are found in the attached phase in animals fed a hay diet compared with a starch diet. This suggests that experimental protocols that only sample protozoa from the rumen fluid could be significantly underestimating the size of the protozoal population of the rumen. Further data are required on the distribution of ciliate protozoa in the rumen of healthy animals to improve model development, but the model described herein does indicate that the attached protozoal population is a significant component of the total rumen protozoal community.

Effects of different protein supplements on omasal nutrient flow and microbial protein synthesis in lactating dairy cows.

Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in 2 replicated 4 x 4 Latin squares to quantify effects of supplementing protein as urea, solvent soybean meal (SSBM), cottonseed meal (CSM), or canola meal (CM) on omasal nutrient flows and microbial protein synthesis. All diets contained (% of dry matter) 21% alfalfa silage and 35% corn silage plus 1) 2% urea plus 41% high-moisture shelled corn (HMSC), 2) 12% SSBM plus 31% HMSC, 3) 14% CSM plus 29% HMSC, or 4) 16% CM plus 27% HMSC. Crude protein was equal across diets, averaging 16.6%. The CSM diet supplied the least rumen-degraded protein and the most rumen-undegraded protein. Microbial nonammonia N flow was similar among the true protein supplements but was 14% lower in cows fed urea. In vivo ruminal passage rate, degradation rate, and estimated escape for the 3 true proteins were, respectively, 0.044/h, 0.105/h, and 29% for SSBM; 0.051/h, 0.050/h, and 51% for CSM; and 0.039/h, 0.081/h, and 34% for CM. This indicated that CSM protein was less degraded because of both a faster passage rate and slower degradation rate. Omasal flow of individual AA, branched-chain AA, essential AA, nonessential AA, and total AA all were lower in cows fed urea compared with one of the true protein supplements. Among the 3 diets supplemented with true protein, omasal flow of Arg was greatest on CSM, and omasal flow of His was greatest on CSM, intermediate on CM, and lowest on SSBM. Lower flows of AA and microbial nonammonia N explained lower yields of milk yield and milk components observed on the urea diet in the companion lactation trial. These results clearly showed that supplementation with true protein was necessary to obtain sufficient microbial protein and rumen-undegraded protein to meet the metabolizable AA requirements of high-producing dairy cows.

Assessment of ruminal bacterial populations and protozoal generation time in cows fed different methionine sources.

Methionine supplemented as 2-hydroxy-4-(methylthio)-butanoic acid (HMB) has been suggested to alter bacterial or protozoal populations in the rumen. Our objective was to determine if source of Met would change microbial populations in the rumen and to compare those results to samples from the omasum. The ruminal and omasal samples were collected from cows fed control (no Met), dl-Met, HMB, or the isopropyl ester of HMB (HMBi; estimated 50% rumen protection) in a replicated 4 x 4 Latin square design. In one square, changes in protozoal populations were determined using microscopic counts and denaturing gradient gel electrophoresis (DGGE), whereas changes in bacterial populations were determined using DGGE and ribosomal intergenic spacer length polymorphism (RIS-LP). Neither the protozoal counts nor the DGGE banding patterns derived from protozoa were different among the dietary treatments or for ruminal vs. omasal samples. As revealed by both DGGE and RIS-LP, bacterial populations clustered by treatments in ruminal and especially in omasal samples. Using cows from both Latin squares, the flow of protozoal cells from the rumen was quantified by multiplying protozoal cell count in omasal fluid by the omasal fluid flow (using CoEDTA as a liquid flow marker) or was estimated by rumen pool size of cells multiplied by either the ruminal dilution rate of CoEDTA (after termination of CoEDTA dosing) or the passage rate of Yb-marked particles. Compared with the omasal fluid flow measurement (16.4 h), protozoal generation time was approximated much more closely using the particulate than the fluid passage rate from the rumen (generation times of 15.7 and 7.5 h, respectively). There seems to be minimal selective retention of protozoal genera in the rumen in dairy cattle fed every 2 h. Data support the validity of the omasal sampling technique under our conditions.

Integration of ruminal metabolism in dairy cattle.

An important objective is to identify nutrients or dietary factors that are most critical for advancing our knowledge of, and improving our ability to predict, milk protein production. The Dairy NRC (2001) model is sensitive to prediction of microbial protein synthesis, which is among the most important component of models integrating requirement and corresponding supply of metabolizable protein or amino acids. There are a variety of important considerations when assessing appropriate use of microbial marker methodology. Statistical formulas and examples are included to document and explain limitations in using a calibration equation from a source publication to predict duodenal flow of purine bases from measured urinary purine derivatives in a future study, and an improved approach was derived. Sources of specific carbohydrate rumen-degraded protein components probably explain microbial interactions and differences among studies. Changes in microbial populations might explain the variation in ruminal outflow of biohydrogenation intermediates that modify milk fat secretion. Finally, microbial protein synthesis can be better integrated with the production of volatile fatty acids, which do not necessarily reflect volatile fatty acid molar proportions in the rumen. The gut and splanchnic tissues metabolize varying amounts of volatile fatty acids, and propionate has important hormonal responses influencing milk protein percentage. Integration of ruminal metabolism with that in the mammary and peripheral tissues can be improved to increase the efficiency of conversion of dietary nutrients into milk components for more efficient milk production with decreased environmental impact.

Omasal ciliated protozoa in cattle, bison, and sheep.

Omasal contents were collected from slaughtered cattle (n = 54), bison (n = 15), and sheep (n = 40) to determine numbers and generic distribution of ciliated protozoa. Total protozoan numbers were significantly lower in omasal contents than in ruminal contents of all three species, but the percent composition of all protozoan genera was similar between omasal and ruminal populations. The highest numbers of omasal protozoa found were 7.61 X 10(5)/g in cattle, 7.01 X 10(5)/g in bison, and 1.29 X 10(6)/g in sheep. Omasal dry matter was significantly higher than ruminal dry matter in all species and ranged up to 51.5% in cattle fed high-concentrate diets. The omasal pH was similar to the ruminal pH in all species. The number of omasal laminae averaged 149, 145, and 74 for cattle, bison, and sheep, respectively. Although protozoan concentrations in omasal contents were approximately 80% lower than those in ruminal contents, the omasum harbored relatively high numbers of ciliated protozoa. The resident omasal protozoa are extremely difficult to remove, particularly in cattle, and apparently are responsible for reinoculating transiently defaunated rumens.

The passage of protozoa from the reticulo-rumen through the omasum of sheep.

1. Protozoa in rumen contents and omasal effluent of growing wethers were counted. The wethers were equipped with rumen and abomasal cannulas, and omasal sleeves attached to the omasal-abomasal orifice. Rumen fluid dilution rates were elevated by continuous infusions of hypertonic mineral solutions (3-4 litres/d) for 24 d. Rumen contents and omasal effluent were sampled between 9 and 21 h during the last 10 d of each experiment. 2. Protozoal concentrations in omasal effluent were only 0.2-0.3 those found in the rumen under normal conditions. The ratio of protozoal concentrations in rumen: those in omasal effluent was for small Diplodinium spp. 4.6 (SD 0.9), for Ophryoscolex spp. 4.3 (SD 1.0), for Dasytricha ruminantium 4.0 (SD 0.5), for Isotricha spp. 3.8 (SD 0.8), for Entodinium spp. 3.6 (SD 0.9) and for Polyplastron multivesiculatum 2.6 (SD 0.5). 3. Elevation of rumen fluid dilution rate by 20 and 55% respectively, increased protozoal concentrations in omasal effluents from 22 to 33% and from 31 to 47% those in rumen contents. The apparent residence times of protozoa in the rumen were decreased 50% by the infusion of a mineral-salt solution. The increase in rumen fluid dilution rate had no significant effect on concentrations of protozoa in the rumen or on the differences of the apparent residence times between different species. The apparent residence time of holotrichs remained the same before and after infusion of the mineral-salt solution. 4. Apparent residence times of individual species of protozoa in the rumen were, under normal feeding conditions, 2.55 d, and were four to six times longer than the mean residence time of CrEDTA in the rumen.

Age group interaction of Haemonchus contortus in premunized lambs.

Lambs premunized with a relatively less pathogenic (RLP) isolate of Haemonchus contortus were challenge exposed each day with 500 3rd-stage larvae (L3) of a normally pathogenic isolate of the same worm, starting on day 9 of the premunition-induced infection. In 6-month-old lambs, there was a fourfold decrease in egg production by the premunizing RLP isolate with challenge exposure compared with egg production in lambs given only the premunizing RLP isolate and not challenge exposed. Premunized lambs were able to carry larger worm burdens with less hemoglobin loss than were nonpremunized challenge-exposed control lambs. Although challenge exposure had affected parasitic egg production by the 9-day-old premunizing RLP worms, the same young infective isolates were able to survive and protect lambs against the additional parasitism.

[Electromyographic analysis of motor perturbations linked with gastrointestinal strongyloidiasis]. / Analyse électromyographique des perturbations motrices liées aux strongyloses gastro-intestinales chez les ovins

The effects of experimental infection of lambs with third stage Trichostrongylus larvae are described. Preceding diarrhea, disturbances in the motility of the reticulum, abomasum and jejunum were observed by electromyography. Disappearance of the migrating myoelectric complexes occurred about 24 h before diarrhea and was accompanied by a decrease in both the frequency of reticular contractions and of contractions propagated through the antro-duodenal junction. The significance of these findings is discussed and compared with natural infestation in the field.