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PubMed1996

The effect of amino nitrogen on the energetics of ruminal bacteria and its impact on energy spilling.

The predominant ruminal bacteria that were obtained from a 10(8) dilution of ruminal fluid could be maintained as a mixed population for long periods as long as the bacteria were provided with a complex mixture of carbohydrates. Growth of predominant ruminal bacteria in carbohydrate-limited, ammonia-excess, continuous cultures (0.07/h) had a low requirement for maintenance energy, but the nongrowth energy dissipation of ammonia-limited, carbohydrate-excess, predominant ruminal bacteria was approximately 10-fold higher (0.96 vs. 0.09 mg of hexose equivalent/mg of protein per h, respectively). Mathematical derivations indicated that this additional nongrowth energy dissipation could be accommodated by an energy spilling function that was independent of the growth rate. Peptides and amino acids had little impact on the yield of carbohydrate-limited, ammonia-excess, continuous cultures (0.07/ h), but amino N greatly increased the growth rate and yield of excess-energy batch cultures. The change in growth rate and yield that was dependent on amino N indicated that the energy-excess batch cultures had the same capacity to spill energy as did the ammonia-limited, carbohydrate-excess, predominant ruminal bacteria (0.80 vs. 0.86 mg of hexose equivalent/mg of protein per h, respectively). When the energy-excess batch cultures were provided with amino N, the growth rate increased, the difference in anabolic and catabolic rates was smaller, and less energy was spilled.

Amino Acids↗
PubMed1996

Do ruminal bacteria exchange genetic material?

This paper discusses the reasons and current evidence for gene transfer between ruminal bacteria and other bacteria in the environment, possible routes for genetic exchange, and candidate genes. Gene transfer between ruminal bacteria has been demonstrated in vitro; however, success has been only minimal in obtaining plasmids and other self-transmissible genetic material from ruminal bacteria. The application of molecular biology techniques with ruminal microorganisms should permit the opportunity for an in vivo assessment of gene transfer. Studies that could provide pertinent information for ruminal microbiologists and dairy nutritionists are outlined.

Animals↗
PubMed1996

Why don't ruminal bacteria digest cellulose faster?

The bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus generally are regarded as the predominant cellulolytic microbes in the rumen. Comparison of available data from the literature reveals that these bacteria are the most actively cellulolytic of all mesophilic organisms described to date from any habitat. In light of numerous proposals to improve microbial cellulose digestion in ruminants, it is instructive to examine the characteristics of these species that contribute to their superior cellulolytic capabilities and to identify the factors that prevent them from digesting cellulose even more rapidly. As a group, these species have extreme nutritional specialization. They are able to utilize cellulose (or in some cases xylan) and its hydrolytic products as their nearly sole energy sources for growth. Moreover, each species apparently has evolved to similar maximum rates of cellulose digestion (first-order rate constants of 0.05 to 0.08 h-1). Active cellulose digestion involves adherence of cells to the fibers via a glycoprotein glycocalyx, which protects cells from protozoal grazing and cellulolytic enzymes from degradation by ruminal proteases while it retains-at least temporarily-the cellodextrin products for use by the cellulolytic bacteria. These properties result in different ecological roles for the adherent and nonadherent populations of each species, but overall provide an enormous selective advantage to these cellulolytic bacteria in the ruminal environment. However, major constraints to cellulose digestion are caused by cell-wall structure of the plant (matrix interactions among wall biopolymers and low substrate surface area) and by limited penetration of the nonmotile cellulolytic microbes into the cell lumen. Because of these constraints and the highly adapted nature of cellulose digestion by the predominant cellulolytic bacteria in the rumen, transfer of cellulolytic capabilities to noncellulolytic ruminal bacteria (e.g., by genetic engineering) that display other desirable properties offers limited opportunities to improve ruminal digestion of cellulose.

Animals↗
PubMed1996

Why are ruminal cellulolytic bacteria unable to digest cellulose at low pH?

Ruminant animals depend on cellulolytic ruminal bacteria to digest cellulose, but these bacteria cannot resist the low ruminal pH that modern feeding practices can create. Because the cellulolytic bacteria cannot grow on cellobiose at low pH, pH sensitivity is a general aspect of growth and not just a limitation of the cellulases per se. Acid-resistant ruminal bacteria have evolved the capacity to let their intracellular pH decrease, maintain a small pH gradient across the cell membrane, and prevent an intracellular accumulation of VFA anions. Cellulolytic bacteria cannot grow with a low intracellular pH, and an increase in pH gradient leads to anion toxicity. Prevotella ruminicola cannot digest native cellulose, but it grows at low pH and degrades the cellulose derivative, carboxymethylcellulose. The Prevotella ruminicola carboxymethylcellulase cannot bind to cellulose, but a recombinant enzyme having the Prevotella ruminicola catalytic domain and a binding domain from Thermomonspora fusca was able to bind and had cellulase activity that was at least 10-fold higher. Based on these results, gene reconstruction offers a means of converting Prevotella ruminicola into a ruminal bacterium that can digest cellulose at low pH.

Animals↗
PubMed1996

Response of cows fed a low crude protein diet to ruminally protected methionine and lysine.

Ten cows (mean = 128 DIM) were utilized in a replicated 5 x 5 Latin square design and fed diets formulated to supply adequate (18% CP) or inadequate (14% CP) Met and Lys. A prototype supplement of ruminally protected Met and Lys was added to the 14% CP diet to provide 0, 50, 100, and 150% of the predicted deficiency of Met and Lys. The DMI; yields of milk, 3.5% FCM, total N, protein N, and whey N; plasma concentrations of Arg, Cit, His, Ile, Leu, Orn, Phe, Pro, Tyr, Val, and urea N were greater for cows fed the 18% CP diet. Supplementing ruminally protected Met and Lys to the 14% CP diet did not affect DMI or yields of milk, 3.5% FCM, milk CP, and milk SNF. Milk fat yield was affected quadratically because it was greater when 0 or 150% of the deficiency of Met and Lys was supplied. Percentages of CP and casein N in milk increased linearly as cows were fed increasing amounts of ruminally protected Met and Lys. Plasma concentrations of urea N, Met, and Lys increased when ruminally protected Met and Lys were fed; however, other nutrients probably were limiting for synthesis of milk and milk protein when cows were fed a 14% CP diet because yields of each were not increased by ruminally protected Met and Lys.

Amino Acids↗
PubMed1997

Influence of time of feeding a protein meal on ruminal fermentation and forestomach digestion in dairy cows.

Four ruminally and duodenally cannulated dairy cows in midlactation were fed twice daily a mixed diet of alfalfa silage and whole-crop oat silage and a concentrate consisting of primarily barley grain. A high protein supplement was fed at approximately 15% of the estimated dry matter intake of the mixed diet once daily at 0830 h, 0.5 h after the morning meal (day), or at 0030 h, 7.5 h after the evening meal (night). Cows fed the protein supplement during the night had higher apparent forestomach digestion of organic matter and crude protein. Ruminal concentrations of all volatile fatty acids, except isobutyrate, were higher for cows fed the protein supplement during the night. Although ruminal pH and concentrations of ammonia N did not differ between treatments, time by treatment interactions indicated that the feeding times of the protein supplement influenced diurnal patterns of ruminal fermentation. The flow of nonbacterial nonammonia N at the duodenum, as a proportion of N intake, was lower for cows fed the protein supplement during the night, but production of milk fat was higher. Results were consistent with a mechanism whereby protein fed during the night stimulated ruminal fermentation, particularly during the night, resulting in greater forestomach digestion of organic matter and less escape of dietary protein from the forestomach. Clearly, the different feeding times of this protein supplement changed the nutritional value of the overall diet.

Ammonia↗
PubMed1997

Effect of processing high moisture ear corn on ruminal fermentation and milk yield.

Thirty-six multiparous dairy cows (8 fitted with ruminal cannulas) and 16 primiparous dairy cows were blocked by days in milk and parity and assigned to one of four diets containing 53% alfalfa silage [dry matter (DM) basis] plus 1) high moisture ear corn, 2) high moisture ear corn plus expeller soybean meal, 3) ground high moisture ear corn, or 4) ground high moisture ear corn plus expeller soybean meal. The high moisture ear corn was rolled before ensiling at 68% DM. Ground high moisture ear corn was prepared by further grinding through a 9.5-mm screen; grinding reduced the geometric mean particle size from 4.33 to 1.66 mm. Diets contained 1.69 Mcal of net energy for lactation/kg of DM. Relative to cows fed diet 1, milk yield was 4 kg/d greater for cows fed diet 2; numerically, milk yield was about 2 kg/d greater for cows fed diets 3 and 4 than for cows fed diet 1. Yield of milk components also was greater for cows fed diets 2 and 3 but not for cows fed diet 4. Intake of DM and yield of 4% FCM were greatest for cows fed diet 3 and lowest for cows fed diet 1. Digestibilities of DM, organic matter, starch, neutral detergent fiber, and acid detergent fiber were increased, and ruminal NH3 concentration was depressed, by the grinding of high moisture corn; expeller soybean meal increased ruminal NH3. Total volatile fatty acid concentration was not different among in vivo treatments, but the molar proportion of acetate decreased, and propionate increased, for cows fed diet 3. The grinding of high moisture corn significantly decreased pH, increased total volatile fatty acid concentration, and increased the rate of decline of NH3 concentration in ruminal in vitro incubations. Grinding improved the utilization of high moisture corn by lactating cows by stimulating ruminal fermentation.

Ammonia↗
PubMed1997

Varying degradation rates of total nonstructural carbohydrates: effects on ruminal fermentation, blood metabolites, and milk production and composition in high producing Holstein cows.

Twelve multiparous Holstein cows (6 ruminally cannulated and 6 intact) at 56 to 77 d of lactation were used in an experiment with a 3 x 6 Latin square design. Cows were fed three total mixed rations that varied in degradation rates of total nonstructural carbohydrates (6.04, 6.98, and 7.94%/h). No interactions between treatment and square were detected. Higher ruminal degradation rates of dietary total nonstructural carbohydrates increased the nonammonia N (NAN) pool of the liquid fraction but did not alter the dry matter or volume of fractional pools, microbial NAN pools, or microbial composition. Treatment did not affect dry matter intake, total concentrations of volatile fatty acids, or fiber digestibility. As ruminal degradation rates of total nonstructural carbohydrates increased, the following effects were observed: 1) the turnover rates of solids increased linearly; 2) ruminal NH3 N concentrations and degradabilities of organic matter and N decreased, but propionate concentrations, bacterial efficiency, and total NAN flows tended to increase; 3) blood glucose and insulin concentrations were not affected, but blood urea N and nonesterified fatty acids were decreased; 4) intestinal and total tract digestibilities of organic matter and total nonstructural carbohydrates increased; and 5) milk production and milk true protein content and yield increased, but energetic efficiency of milk production did not change. The highest dietary ruminal degradation rate of total nonstructural carbohydrates increased the amount of nutrients digested in the intestine and increased milk production.

Animals↗
PubMed1998

Effect of Aspergillus oryzae extract alone or in combination with antimicrobial compounds on ruminal bacteria.

The effect of an Aspergillus oryzae fermentation extract on the growth rates of pure cultures of ruminal bacteria was determined. Bacteria were grown in an anaerobic ruminal fluid and carbohydrate medium. A sterile filtrate made with 10% A. oryzae was added to the medium at 2 or 5% (vol/vol) to provide a final A. oryzae concentration of 2 or 5 mg/ml, respectively. The filtrate had no effect on the growth rates of 10 of the 19 ruminal bacteria tested; however, the filtrate increased the growth rates of the bacteria that digest fiber, Ruminococcus albus and Fibrobacter succinogenes, and the bacteria that utilize lactate, Megasphaera elsdenii, Selenomonas lactilytica, and Selenomonas ruminantium. No differences in growth rate were detected between the two concentrations of A. oryzae filtrate. We also investigated the interactions between A. oryzae and antimicrobial compounds on the growth rates of six species of ruminal bacteria that had shown positive responses or no response to the filtrate. The addition of A. oryzae filtrate to medium containing chlortetracycline or neomycin tended to diminish the negative effects of those compounds on the growth rates of some ruminal bacteria, although the bacteria had no positive growth response to the filtrate alone. In contrast, the combination of A. oryzae filtrate and tylosin decreased the growth rate of Sel. ruminantium D. These results indicated that A. oryzae stimulates growth of some bacteria that digest fiber and ferment lactate in the rumen and interacts positively or negatively with certain antimicrobial feed additives.

Animal Feed↗
PubMed1998

Effect of wheat straw treated with alkali on ruminal function and lactational performance of dairy cows.

Two experiments were conducted to evaluate the effects of wheat straw treated with alkali on ruminal function and lactational performance of dairy cows. In Experiment 1, four ruminally fistulated Holsteins cows (X = 57 d of lactation) were fed four diets that contained 0, 20, 30, or 40% (dry basis) wheat straw treated with 3% NaOH plus 3% Ca(OH)2 in a 4 x 4 Latin square. The diets contained 60, 40, 30, and 20% (dry basis) prebloom alfalfa haylage to result in a 60: 40 ratio of forage to concentrate. In Experiment 2, 12 (X = 149 d of lactation) midlactation Holstein cows were fed diets containing 0 or 20% treated wheat straw to measure lactational performance during a 12-wk period. In Experiment 1, no effect of diet was observed on ruminal pH, osmolality, digestion of neutral detergent fiber of straw, or 4% fat-corrected milk. However, the dry matter intake of cows fed diets containing the two highest concentrations of treated straw was depressed and was associated with a significant body weight loss. The ruminal rate of passage of treated straw was not affected by diet; however, rate of passage of alfalfa haylage decreased when straw was included in the diet. In Experiment 2, no effect on cow performance was observed when straw treated with alkali was included at 20% of the diet. Inclusion of up to 20% wheat straw treated with 3% NaOH plus 3% Ca(OH)2 in diets of lactating cows resulted in ruminal function and performance that were similar to those of cows fed diets that contained alfalfa haylage only.

Animal Nutritional Physiological Phenomena↗
PubMed1998

Glucose metabolism and milk yield of cows infused abomasally or ruminally with starch.

The effect of ruminal or abomasal starch infusion on milk yield and glucose metabolism of early lactation cows was measured. Four cows were continuously infused in the rumen or abomasum with partially hydrolyzed starch (1500 g/d) or were not infused (control) for three 14-d periods during wk 4 to 12 postpartum. Milk yield averaged over 40 kg/d throughout the experiment. Milk and milk lactose yields tended to increase when starch was infused and DMI was decreased, regardless of the site of infusion. Starch infusion increased mean insulin concentration and tended to decrease the concentration of serum nonesterified fatty acids. Ruminal starch infusion did not affect glucose irreversible loss rate but tended to increase glucagon concentration and decrease glucose oxidation. The increased milk yield that occurred when starch was infused ruminally relative to the milk yield of control cows could be a result of increased microbial protein supply or increased energy availability. Compared with ruminal starch infusion, abomasal starch infusion tended to increase the irreversible loss rate of glucose and to increase glucose oxidation. Abomasal infusion tended to increase plasma insulin concentration and to decrease the nonesterified fatty acid concentration relative to ruminal infusion. Infusion of starch abomasally resulted in increases of most uses of glucose, including milk lactose production, glucose oxidation, and the possible storage of glucose as body fat, which indicates that the early lactation dairy cow has a greater capacity for glucose metabolism than is provided by voluntary feed intake of average diets, but that not all available glucose is partitioned to the mammary gland. These data should be useful in testing current concepts and equations in nutritional and metabolic models of dairy cattle.

Abomasum↗
PubMed1999

Estimation of the digestible energy of ruminant feedstuffs by the combined bag technique.

The combined bag technique was used to estimate digestible energy of ruminant feedstuffs. Samples of corn, barley, and sorghum grains; soybean and sunflower meals; corn and wheat silages; and vetch and wheat hays were incubated in dacron bags in the rumens of dairy cattle for 3 to 72 h. Bags containing residues after 12 h of ruminal incubation were introduced into the duodenum and recovered from feces. Feeds and ruminal and intestinal residues were analyzed for dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber, and nonstructural carbohydrates. The effective ruminal degradability of OM was higher in grains (639 g/kg of DM) and in protein supplements (609 g/kg of DM) than in forages (373 g/kg of DM). For grains and forages, carbohydrates contributed most of the degradable OM in the rumen, but, in protein supplements, about 50% of the ruminally degradable OM originated from carbohydrate. For protein supplements, 54% of the OM that disappeared postruminally was CP, but, in the grains and forage ingredients, CP contributed less than 20% of the postruminal OM that disappeared. In grains and forages, 83% of total tract disappearance of OM was from carbohydrates. For protein supplements, CP contributed 50% to overall OM disappearance. The calculated energy equivalent of digested matter averaged among feeds was 4.71 kcal/g. A high correlation was found between digestible energy estimated by the combined bag technique and the respective National Research Council values. The combined bag technique is a useful tool for the estimation of digestible energy in feedstuffs.

Animal Feed↗
PubMed1999

The relaxant effects of parathyroid hormone(1-34) and parathyroid hormone-related protein(1-34) on ovine reticulo-ruminal smooth muscle in vivo.

The motility of the reticulo-rumen has been measured in trained, conscious sheep using inflated balloons temporarily introduced to selected regions of that forestomach. The frequency and amplitude of the contractions of the reticulum and both the A and B waves of contraction of the rumen were measured under the same conditions before, during and after the administration of an i.v. bolus of either parathyroid hormone (PTH(1-34)) or PTH-related protein (PTHrP(1-34)) followed by its i.v. infusion. These two peptides are known to share a common receptor in other organs, e.g. the kidney. In this study they both showed an inhibitory effect on reticulo-ruminal motility. The effect of PTHrP(1-34) on the rate of ruminal blood flow was also examined and a significant reduction observed, after a transient increase. The secretion of endogenous PTH(1-34) was stimulated by a 32% reduction in the plasma calcium ion concentration induced by an i.v. infusion of sodium citrate. Associated with this were significant reductions in reticulo-ruminal motility, e.g. the reduction in the mean amplitude of the reticular contractions reflected the reduction in plasma calcium ion concentration. When the PTH(1-34)/PTHrP(1-34) receptor was blocked with [Asn10,Leu11,D-Trp12]PTHrP(7-34) before and during the induction of hypocalcaemia, all but one of the parameters of reticulo-ruminal motility were normalized. Indeed, by the day following the administration of this blocking agent, all these parameters had returned to their normal range. It is concluded that stimulation of the PTH(1-34)/PTHrP(1-34) receptor in reticulo-ruminal smooth muscle reduces the motility of this tissue and may play a role in the depression of motility of the digestive tract which is characteristic of clinical milk fever in the dairy cow.

Animals↗
PubMed1999

Nested reverse transcriptase-polymerase chain reaction (RT-PCR) for typing ruminant pestiviruses: bovine viral diarrhea viruses and border disease virus.

A nested reverse transcription (RT) polymerase chain reaction (PCR) assay was evaluated for differentiating reference bovine viral diarrhea virus (BVDV) strains, BVDV from diagnostic accessions, modified-live virus (MLV) BVDV strains in bovine viral vaccines, and a reference border disease virus (BDV). The detection level of this assay was compared to viral infection in cell culture. The PCR assay was used to distinguish 3 ruminant pestiviruses, types 1 and 2 BVDV, and type 3 BDV. The consensus (first) PCR assay detected all 3 ruminant pestiviruses, a result of the shared sequence homology. The consensus PCR product was subjected to a second (nested) PCR which used type-specific primers. The nested PCR was able to differentiate the 3 ruminant pestiviruses. Viral stocks of BVDV were diluted 10-fold and processed for the 2-step PCR assay. The sensitivity of this 2-step PCR assay was compared to viral infectivity in cell culture based on identical volumes of the system tested (cell culture assay and processing for RNA). The RT-PCR type-specific assay differentiated BVDV laboratory reference strains (12), diagnostic laboratory isolates (15), 2 MLV BVDV vaccine strains, and a BDV strain. The 30 ruminant pestiviruses typed included: (1) 27 reference strains and diagnostic laboratory isolates; 18 cytopathic (CP) type 1 strains, 3 CP type 2 strains, 3 noncytopathic (NCP) type 1 strains, and 3 NCP type 2 strains; (2) 2 MLV strains, type 1; and (3) 1 CP BDV type 3. The PCR assay had a detection limit of 10 TCID50/0.025 mL of virus when 3 separate BVDV were tested. This 2 step RT-PCR assay would be useful for the typing of ruminant pestiviruses, particularly BVDV isolates from the diagnostic laboratory.

Animals↗
PubMed1999

Formaldehyde treatment suppresses ruminal degradation of phytate in soyabean meal and rapeseed meal.

Most of the P in oilseed meal is in the form of phytate P, and phytate forms complexes with protein. Phytate P has been considered to be absorbed easily in ruminants because of phytate degradation in the rumen. Treatment of oilseed meals with formaldehyde improves the nutritional value of protein through suppressing its ruminal degradation. The present experiment was conducted to study the effects of formaldehyde treatment on phytate degradation in the rumen. The ruminal degradation of phytate in formaldehyde-treated soyabean meal or rapeseed meal was determined by a nylon-bag technique in sheep. Soyabean meal and rapeseed meal were treated with formaldehyde at levels of 3, 5 or 10 g/kg. Treatment with formaldehyde suppressed phytate and protein degradation in both the oilseed meals. Compared with the regular soyabean meal, the regular rapeseed meal showed lower degradability of phytate in the rumen. These results suggest that treatment with formaldehyde suppresses ruminal degradation of phytate in oilseed meal. Thus, the absorption of P from oilseed meal is probably decreased by this treatment in ruminants.

Analysis of Variance↗
PubMed1975

Oil coating of dietary protein for the ruminant.

Diets containing expeller-extracted linseed meal treated with corn oil, lard or coconut oil were fed to lambs to determine the effectiveness of coating the protein in reducing its ruminal degradation. Three common indicators of nitrogen metabolism in the ruminant were used in evaluation: ruminal ammonia, blood plasma ammonia and plasma urea. Eight crossbred lambs, averaging 27 kg in weight, were allotted to the four diets which were fed at a rate of 350 g at 12-hour intervals. Ruminal ammonia, plasma ammonia and plasma urea were monitored at 0, 2, 4, 6 and 8 hr after feeding. Lambs consuming coconut oil-treated linseed meal produced less rumen ammonia (average of .5 mg/100 ml across all collection times) than those fed normal linseed meal (10.3 mg/100 ml). Lambs fed corn oil-treated and lard-treated linseed meal had ruminal ammonia levels intermediate to those fed normal and coconut oil-treated linseed meal. Levels of plasma ammonia and plasma urea nitrogen of normal linseed meal were significantly higher than the same measures with the oil-treated linseed meals. Differences in plasma ammonia and urea nitrogen were not significant among the three oil-treated diets.

Ammonia↗
PubMed1989

The interaction of ruminant IgG with receptor type II for IgG on human phagocytes.

The interaction of ruminant IgG with human phagocytes was assessed using Fc receptor (FcR)-mediated ingestion and the triggering of a respiratory burst as effector functions indicative of receptor-specific interaction. In monomeric form, ruminant IgG was three to five orders of magnitude less potent than homologous IgG in inhibiting FcR-specific phagocytosis by monocytes. However, when attached to tanned sheep erythrocytes (Es-T), ruminant IgG was opsonic, as it promoted enhanced phagocytosis of Es-T, comparable to ingestion of rabbit IgG-coated Es. This phagocytosis was inhibitable by high concentrations of human IgG in the fluid phase. Moreover, Es-T precoated with ferritin could be opsonized to a similar degree by anti-ferritin IgG from rabbit and cow. However, only bovine IgG1, but not IgG2, was opsonic. Bovine and goat IgG of some, but not other, suppliers were inactive. Similar results were obtained by measuring the respiratory burst triggered by heat-aggregated IgG, using a luminol-enhanced chemiluminescence assay. Thus, human IgG and ruminant IgG stimulated monocytes and, to a lesser extent, polymorphonuclear leucocytes (PMN), to generate CL. Depending on the manufacturer, some preparations of bovine and goat IgG were inactive, and bovine IgG2 failed to induce CL. These findings prove that certain ruminant IgG preparations, including bovine IgG1 interacting weakly with homologous PMN and monocytes, do interact with human PMN, monocytes and macrophages in a FcR-specific manner when offered in complexed form. Inhibition studies suggest that bovine IgG1 interacts mainly with human FcR type II. In contrast, bovine IgG2, regarded as cytophilic for homologous PMN, fails to interact with human PMN, monocytes and macrophages.

Animals↗
PubMedDate not supplied

TSE eradication in small ruminants--quo vadis?

The term of 'TSE infections in small ruminants' summarises BSE as well as classical and the recently discovered atypical scrapie infections in sheep and goats. There are fundamental differences between the TSE infections in small and large ruminants. Other than in bovines the TSE pathogenesis in small ruminants implies that various peripheral tissues become infectious long before the onset of clinical symptoms. At least in sheep, classical scrapie is efficiently transmitted horizontally within affected flocks. On the other hand, BSE poses a distinctly higher zoonotic risk than scrapie. Therefore, regulatory measures for the protection of animals and humans from a BSE infection must be substantially different for large and small ruminants. While culling of the birth and feeding cohort of a BSE affected cattle is considered to be effective to prevent any further BSE cases in the affected herd, an effective BSE and classical scrapie eradication programme in small ruminants requires a much more stringent eradication strategy and the rendering of all susceptible animals. The situation became even more complicated when atypical scrapie cases with divergent transmission and pathogenesis characteristics and with a novel biochemical phenotype of the infectious agent came into play. The discovery of these atypical scrapie cases has initiated a discussion about the suitability of the current TSE eradication measures in sheep (which are selective breeding and genotype based culling), in particular when such cases were also found in sheep carrying the believed scrapie resistant genotypes.

Animals↗