Evaluation of a 5'-nuclease (TaqMan) assay for the detection of virulent strains of Yersinia enterocolitica in raw meat and tofu samples

Culture methods for detecting virulent Yersinia enterocolitica require selective enrichment and a series of confirmatory tests that are time-consuming, costly, and laborious. The objective of this study was to evaluate a fluorogenic 5'-nuclease assay for detecting the enterotoxin yst gene of virulent Y. enterocolitica in pure cultures, inoculated ground pork samples, and naturally contaminated food samples. These results were then compared with "gold standard" methods recommended by the U.S. Food and Drug Administration in the Bacteriological Analytical Manual for detecting pathogenic Y. enterocolitica. The 5'-nuclease assay was able to identify the organism in 100% of the repetitions when 10(2) CFU/ml or more organisms were present in pure cultures and 10(3) CFU/g or more organisms were present in ground pork. Similar recovery efficiency on cefsulodin-irgasan-novobiocin (CIN) agar plates was only evident when 10(5) CFU/ml or more organisms were present in pure culture and 10(6) CFU/g or more organisms were present in inoculated ground pork. The 5'-nuclease assay indicated a contamination rate of 35.5% (94/265) in various meats and tofu, whereas the CIN plating method indicated a contamination rate of 28.3% (75/265). This resulted in 100% sensitivity and 64.5% specificity for the 5'-nuclease assay when compared with the standard culture recovery method. Only 75% (60/80) of the Yersinia spp. isolated on CIN was identified as containing a virulence plasmid by autoagglutination and crystal violet binding tests. These results indicate that the true rate of contamination of virulent Y. enterocolitica in pork and other processed meats and foods is being underestimated using current detection methods. This study demonstrates the potential of the 5'-nuclease assay for rapidly and specifically detecting virulent Y. enterocolitica in processed foods with the added advantage of being an automated detection system with high-throughput capability.

Rapid 5' nuclease (TaqMan) assay for detection of virulent strains of Yersinia enterocolitica

We have developed a rapid procedure for the detection of virulent Yersinia enterocolitica in ground pork by combining a previously described PCR with fluorescent dye technologies. The detection method, known as the fluorogenic 5' nuclease assay (TaqMan), produces results by measuring the fluorescence produced during PCR amplification, requiring no post-PCR processing. The specificity of the chromosomal yst gene-based assay was tested with 28 bacterial isolates that included 7 pathogenic and 7 nonpathogenic serotypes of Y. enterocolitica, other species of Yersinia (Y. aldovae, Y. pseudotuberculosis, Y. mollaretti, Y. intermedia, Y. bercovieri, Y. ruckeri, Y. frederiksenii, and Y. kristensenii), and other enteric bacteria (Escherichia, Salmonella, Citrobacter, and Flavobacterium). The assay was 100% specific in identifying the pathogenic strains of Y. enterocolitica. The sensitivity of the assay was found to be >/=10(2) CFU/ml in pure cultures and >/=10(3) CFU/g in spiked ground pork samples. Results of the assay with food enrichments prespiked with Y. enterocolitica serotypes O:3 and O:9 were comparable to standard culture results. Of the 100 field samples (ground pork) tested, 35 were positive for virulent Y. enterocolitica with both 5' nuclease assay and conventional virulence tests. After overnight enrichment the entire assay, including DNA extraction, amplification, and detection, could be completed within 5 h.

Digestibility of prairie hay diets supplemented with different levels of magnesium-mica by beef heifers

Four ruminally fistulated, nonpregnant, nonlactating heifers (515 +/- 7.9 kg) were offered chopped (10-cm screen size) prairie hay for ad libitum consumption with 1.8 kg/d of supplements to provide 0, 45, 113, or 181 g/d of magnesium-mica (MM) in a 4 x 4 Latin square design experiment. Heifers were adapted to diets for 7 d in drylot followed by a 19-d confinement period in individual stalls within a metabolism facility. Total feces and urine were collected for 5 d, daily intake and water consumption were monitored for 16 d, and in situ disappearance of fiber (prairie hay) and CP (soybean meal) were determined during the confinement period. Ruminal samples for fermentation product analyses were collected at feeding and every 2 h thereafter for 12 h on d 18, and rumens were evacuated at 1100 on d 19 to determine rumen fill. Cubic responses (P < .05) to MM level were observed for DM, OM, NDF, and ADF digestion and were characterized by a tendency for improved digestion with 45 g/d compared with the control diet, followed by a suppressive effect on digestion with 113 g/d, then little effect with 181 g/d MM. In situ NDF disappearance at 72 and 96 h tended (P < . 10) to be influenced quadratically by level of MM, but MM level had no apparent effect on ruminal fill and passage rate, ciliated protozoa counts, in situ rate of disappearance of fiber or CP, or nitrogen balance. Therefore, feeding MM at low levels to heifers consuming a prairie hay diet with a 20% CP supplement seemed to be beneficial for feed digestion with no measurable negative impact on intake or ruminal protein or fiber digestion.

Effects of different supplemental sugars and starch fed in combination with degradable intake protein on low-quality forage use by beef steers

Twenty ruminally fistulated steers (Exp. 1, 448 kg and Exp. 2, 450 kg) were used in two consecutive randomized complete block experiments with five treatments in each experiment. The purpose was to evaluate the impact of feeding different supplemental sugars or starch in combination with supplemental degradable intake protein (DIP) on the utilization of low-quality tallgrass-prairie hay. In Exp. 1, steers were given ad libitum access to forage and, except for the negative control (NC), received a limited supply (insufficient to maximize forage use) of supplemental DIP (.031% BW/d, DM basis). In addition to the NC, this experiment included four supplementation treatments in which one of four carbohydrate (CHO) sources (starch, glucose, fructose, or sucrose) was fed at .30% BW of DM/d. In Exp. 2, the treatment structure was identical except that the supplemental DIP level (.122% BW, DM basis) was near the level needed to maximize forage use. Forage OM intake (FOMI) was not affected (P> or =.26) by supplementation in Exp. 1 but was increased (P = .05) in Exp. 2. However, no difference (P> or =.46) in FOMI occurred among CHO sources in either experiment. Total OM and digestible OM intakes were increased (P<.01) by supplementation in both experiments. In Exp. 1, no difference (P>.26) in OM digestion (OMD) occurred among treatments. In Exp. 2, supplementation increased (P<.01) OMD. Additionally, sugars yielded a higher (P = .04) OMD than starch, and the monosaccharides yielded a higher (P = .02) OMD than sucrose. In Exp. 1, NDF digestion (NDFD) was decreased (P = .02) by supplementation, but no differences (P> or =.21) occurred among CHO sources. In Exp. 2, NDFD was increased (P = .03) by supplementation. Additionally, sugars led to higher (P = .05) NDFD than starch, and the monosaccharides led to higher (P = .03) NDFD than sucrose. In both experiments, discernible patterns were observable with regard to the effects of supplementation and type of supplemental CHO on ruminal fermentation characteristics. In conclusion, even though some consistency in fermentation profiles for different carbohydrate sources was evident in both experiments, forage intake and digestion responses were not consistent across experiments. This raises the possibility that carbohydrate source may interact with the amount of supplemental DIP fed and, as such, deserves additional investigation.

Effects of level and source of carbohydrate and level of degradable intake protein on intake and digestion of low-quality tallgrass-prairie hay by beef steers

Ruminally fistulated steers (n = 13; 263 kg) were used in an incomplete Latin square with 13 treatments and four periods to evaluate the effects of level and source of supplemental carbohydrate (CHO) and level of degradable intake protein (DIP) on the utilization of low-quality, tallgrass-prairie hay. Steers were given ad libitum access to forage (5.7% CP, 2.6% DIP, and 74.9% NDF). The supplementation treatments were fashioned as a 2x3x2 factorial arrangement plus a negative control (NC; no supplement). The factors included two DIP levels (.031 and .122% BW) and three CHO sources (starch, glucose, and fiber) fed at two levels (.15 and .30% BW) within each level of DIP supplementation. The effect of supplementation on forage OM intake (FOMI) was dependent (P<.01) on level and source of CHO and level of DIP fed. When DIP was low, forage, total, and digestible OM intakes were generally greater for the starch treatment than for the nonstarch treatments. However, when the DIP level was high, intakes were greater for the nonstarch (i.e., fiber and glucose) treatments. Generally, FOMI decreased (P<.01) when more supplemental CHO was provided. Supplementation typically increased fiber digestion, but the response was dependent (P<.01) on level and source of CHO and level of DIP. Generally, supplements with low levels of CHO improved NDF digestion (NDFD). However, supplements with the high level of CHO decreased NDFD, except for fiber at the high level of DIP. Organic matter digestion was increased by supplementation, but the impact of increasing CHO was dependent (P<.01) on source of CHO and level of DIP. Supplementation treatments had significant impact on ruminal pH, NH3 N, and the total concentration of organic acids as well as their relative proportions. In conclusion, supplemental DIP enhanced the use of low-quality forage; however, the impact of supplemental CHO on low-quality forage use was dependent on source and level of CHO offered, as well as the level of DIP provided.

Effects of tylosin on concentrations of Fusobacterium necrophorum and fermentation products in the rumen of cattle fed a high-concentrate diet

OBJECTIVE

To determine effects of tylosin on ruminal concentrations of Fusobacterium necrophorum and fermentation products in cattle during rapid adaptation to a high-concentrate diet.

ANIMALS

6 steers fitted with ruminal cannulas.

PROCEDURE

Steers were assigned randomly to 2 treatment groups and switched from a 0 to an 85% concentrate diet during a 4-day period. Cattle received this diet, with or without tylosin (90 mg/steer/d), for 4 weeks. Samples of ruminal contents were collected daily beginning 2 days before the treatment protocol and in the first week of concentrate feeding. Four subsequent samples were collected at weekly intervals. Concentration of F. necrophorum in samples was determined, using the most-probable-number technique. Ruminal pH and concentrations of volatile fatty acids (VFA), lactate, and ammonia also were determined. All steers received both treatments separated by 4 weeks (cross-over design), during which time they were fed alfalfa hay only.

RESULTS

In control steers, concentration of F. necrophorum increased in response to the high-concentrate diet. Tylosin-fed steers had lower concentrations of F. necrophorum than control steers at all times during concentrate feeding. However, ruminal pH and concentrations of lactate, VFA, and ammonia did not differ between treatment groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Tylosin caused a significant reduction in ruminal concentrations of F. necrophorum during rapid adaptation to a high-concentrate diet but had no effect on fermentation products. The reduction in ruminal concentration of F. necrophorum helps explain the reduction in prevalence of hepatic abscesses reported in tylosin-fed feedlot cattle.

Effect of virginiamycin on ruminal fermentation in cattle during adaptation to a high concentrate diet and during an induced acidosis

The objective of Exp. 1 was to compare the effects of virginiamycin (VM; 0, 175, or 250 mg x animal(-1) x d(-1)) and monensin/tylosin (MT; 250/ 90 mg x animal(-1) x d(-1)) on ruminal fermentation products and microbial populations in cattle during adaptation to an all-concentrate diet. Four ruminally cannulated, Holstein steers were used in a 4x4 Williams square design with 21-d periods. Steers were stepped up to an all-concentrate diet fed at 2.5% of BW once daily. Ruminal pH, protozoal counts, and NH3-N and VFA concentrations generally were unaffected by VM or MT. Mean counts of Lactobacillus and Streptococcus bovis were lower (P<.05) for VM-treated compared with control or MT-treated steers. Both VM and MT prevented the increase in Fusobacterium necrophorum counts associated with increasing intake of the high-concentrate diet observed in the control. The objective of Exp. 2 was to compare the effects of VM and MT on ruminal pH, L(+) lactate and VFA concentrations, and F. necrophorum numbers during carbohydrate overload. Six ruminally cannulated Holstein steers were assigned randomly to either the control, VM (175 mg/d), or MT (250 + 90 mg/d) treatments. Acidosis was induced with intraruminal administration of a slurry of ground corn and corn starch. The VM and MT premixes were added directly to the slurry before administration. Carbohydrate challenge induced acute ruminal acidosis (pH was 4.36 and L (+) lactate was 19.4 mM) in controls by 36 h. Compared with the controls, steers receiving VM or MT had higher (P<.05) ruminal pH, and the VM group had a lower (P<.05) L (+) lactate concentration. Fusobacterium necrophorum numbers initially increased in VM- and MT-administered steers. In the control steers, F. necrophorum was undetectable by 36 h. Virginiamycin seemed to control the growth of ruminal lactic acid-producing bacteria and, therefore, has the potential to moderate ruminal fermentation in situations that could lead to rapid production of lactic acid.

Bacterial flora of liver abscesses in feedlot cattle fed tylosin or no tylosin

Bacterial flora of liver abscesses from cattle fed tylosin or no tylosin and susceptibilities of the predominant bacterial isolates to tylosin and other antimicrobial compounds were determined. Abscessed livers were collected at slaughter from cattle originating from feedlots that had fed tylosin (n = 36) or no tylosin (n = 41) for at least 2 yr, and segments of livers with one or two intact abscesses were transported to the laboratory. Abscesses were cultured for anaerobic and facultative bacteria. Fusobacterium necrophorum, either as single culture or mixed with other bacteria, was isolated from all abscesses. The incidence of subsp. necrophorum, as part of the mixed infection, was lower (P < .05) in the tylosin group than in the no-tylosin group (33 vs 61%). However, the incidence of Actinomyces pyogenes was higher (P < .01) in the tylosin group than in the no-tylosin group (53 vs 10%). Totals of 119 F. necrophorum and 21 A. pyogenes isolates were used for determinations of susceptibilities to bacitracin, oxytetracycline, chlortetracycline, lasalocid, monensin, tylosin, tilmicosin, and virginiamycin. The minimum inhibitory concentrations (MIC) of antibiotics were determined with a broth microdilution method. The mean MIC of tylosin for F. necrophorum and A. pyogenes were not different between isolates from tylosin and no-tylosin groups. We concluded that continuous feeding of tylosin did not induce resistance in F. necrophorum or A. pyogenes. Also, the higher incidence of mixed infection of F. necrophorum and A. pyogenes in liver abscesses of tylosin-fed cattle suggests a potential synergistic interaction between the two organisms in causing liver abscesses.

Effects of form of the diet on anatomical, microbial, and fermentative development of the rumen of neonatal calves

Eight neonatal, Holstein bull calves were paired by birth date and birth weight and randomly assigned to either a finely ground or unground control diet (chopped hay and rolled grain) to study the effects of the physical form of the diet on anatomical, microbial, and fermentative development of the rumen. The diets varied in particle size but were identical in composition (25% alfalfa hay and 75% grain mix). Calves were fed milk at 8% of birth weight daily until weaning. Feed intake was equalized for each pair of calves. Ruminal fluid samples were collected from ruminal cannulas to determine pH, fermentation products, and buffering capacity and to enumerate bacteria. Calves were slaughtered at 10 wk of age, and weights of the full and empty reticulorumen, abomasum, and omasum were recorded. Ruminal tissue samples were taken to assess papillary development by morphometric measurements. Calves had similar body weights at wk 10. Ruminal pH was affected by age and was lower for calves fed the ground diet. Total anaerobic bacterial counts were not affected by the physical form of the diet; however, calves fed the ground diet had lower numbers of cellulolytic bacteria and higher numbers of amylolytic bacteria than did calves fed the unground diet. Physical form of the diet did not affect the weights of the reticulorumen whether full or empty. However, calves fed the ground diet had heavier omasum weights, both full and empty. Physical form of the diet affected papillary size and shape but did not influence the muscle thickness of rumen. Results indicated that the physical form of the diet had a significant influence on the anatomical and microbial development of the forestomac and, therefore, might influence future performance.

Nutrition and disease

Mortality from digestive diseases in feedlot cattle is second only to that from respiratory diseases. Acidosis and bloat are the major digestive disorders and are likely to continue because of ongoing attempts to improve the efficiency of beef production by feeding more grain and less roughage. Subacute acidosis is probably the most prevalent form of acidosis in feedlots and is difficult to diagnose because of the absence of overt clinical signs. Ruminal changes in subacute acidosis are not as dramatic as those in acute acidosis. Also, the subacute form is not severe enough to induce systemic acidosis. Ruminal acidosis is also a predisposing factor for many other ailments in feedlot cattle such as laminitis, polioencephalomalacia, sudden death syndrome, and liver abscesses. Control of acidosis is achieved largely by sound nutritional management. Antimicrobial compounds (i.e., ionophores and nonionophores), have become management tools to impart stability to ruminal fermentation, modulate feed intake, and control acidosis. Bloat in feedlot cattle can be of free gas or frothy type. Frothy bloat is more common but is rarely the reason for bloat deaths. The economic impact of bloat results mainly from decreased animal performance. The etiology of bloat is complex and is the result of interactions between three major groups of factors: animal, dietary, and microbial. Presently, an effective method to control frothy bloat in feedlot cattle is not available. Ionophore antibiotics, particularly monensin, have been shown to be effective in decreasing the incidence and severity of bloat in cattle.

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.

Biochemical and biological characterizations and ribotyping of Actinomyces pyogenes and Actinomyces pyogenes-like organisms from liver abscesses in cattle

Actinomyces pyogenes is the second most frequently encountered pathogen, next only to Fusobacterium necrophorum, in liver abscesses of feedlot cattle. Ninety-one isolates, presumptively identified as A. pyogenes, isolated from liver abscesses of cattle were studied. Biochemical characteristics determined by the API 20 Strep kit were similar to those reported previously for A. pyogenes isolated from other infections, except that 18% of isolates hydrolyzed esculin. Nine isolates that resembled A. pyogenes in morphology and in certain biochemical characteristics, but fermented mannitol and/or raffinose, were called A. pyogenes-like (APL) organisms. The five antimicrobial agents, bacitracin, chlortetracycline, oxytetracycline, tylosin, and virginiamycin were inhibitory to all strains of A. pyogenes and APLs. Generally, APL organisms had higher mean hemolytic and leukotoxic activities than A. pyogenes. All isolates of A. pyogenes and APLs produced proteases and neuraminidases. Ribotyping with endonucleases, including BstEII, ClaI, EcoRI, EcoRV, HaeIII, MboI, PvuII, SalI, and SmaI alone or in combinations, showed considerable genetic heterogeneity in both A. pyogenes and APLs. No specific ribopattern characteristic of each group was observed with any of the endonuclease used. The origin of A. pyogenes and APLs and the relative importance of APLs in causing liver abscesses in feedlot cattle are not known.

Biochemical and ribotypic comparison of Actinomyces pyogenes and A pyogenes-like organisms from liver abscesses, ruminal wall, and ruminal contents of cattle

OBJECTIVE

To isolate Actinomyces pyogenes and A pyogenes-like (APL) organisms from the ruminal wall and ruminal contents of cattle and compare them with isolates from liver abscesses from the same animals, using ribosomal DNA restriction fragment length polymorphism analysis or ribotyping.

PROCEDURE

Specimens of liver abscesses, ruminal walls, and ruminal contents were collected from 59 cattle at slaughter. All beta-hemolytic, pinpoint colonies that were gram positive, pleomorphic rod-shaped, and catalase negative, and that hydrolyzed casein and gelatin were presumptively identified as A pyogenes and were characterized biochemically, using an identification kit. The isolates that resembled A pyogenes but fermented mannitol or raffinose, or both, were called APL organisms. Isolates from the ruminal wall and ruminal contents were compared with liver abscess isolates from the same animal by use of ribotyping.

RESULTS

Actinomyces pyogenes and APL organisms were isolated more frequently from the ruminal wall than from ruminal contents. Ruminal isolates of A pyogenes and APL had biochemical characteristics similar to those of the isolates from liver abscesses. Among 6 sets of isolates (4 A pyogenes and 2 APL), 2 isolates from liver abscesses had ribopatterns identical to the corresponding ruminal wall isolates. Also, the APL organisms isolated from the ruminal content matched with the corresponding liver abscess isolates for both sets of specimens tested.

CONCLUSIONS

The ruminal wall may be the niche for A pyogenes and APL organisms in the rumen. The genetic similarity, on the basis of ribotyping among isolates from liver abscesses, the ruminal wall, and ruminal contents of the same animal suggests that A pyogenes and APL organisms that cause liver abscesses originate from the rumen.

Antimicrobial susceptibility of Fusobacterium necrophorum isolated from bovine hepatic abscesses

OBJECTIVE

To determine the resistance and susceptibility to antimicrobial compounds of Fusobacterium necrophorum isolates from bovine hepatic abscesses.

PROCEDURE

37 isolates of F necrophorum (21 subsp necrophorum and 16 subsp funduliforme) isolated from bovine hepatic abscesses were obtained from cultures grown and maintained in anaerobic brain heart infusion broth. A broth dilution method was used as an initial screening to determine general susceptibility to 31 antimicrobial compounds. The minimal inhibitory concentrations (MIC) of 19 of the antimicrobial compounds that inhibited growth in the initial test were determined by use of the broth microdilution method.

RESULTS

Fusobacterium necrophorum isolates were generally susceptible to penicillins, tetracyclines (chlortetracycline and oxytetracycline), lincosamides (clindamycin and lincomycin), and macrolides (tylosin and erythromycin), and were resistant to aminoglycosides (kanamycin, neomycin, gentamicin, and streptomycin), ionophores (except narasin), and peptides (avoparcin, polymyxin, and thiopeptin). The 5 antimicrobials (bacitracin, chlortetracycline, oxytetracycline, tylosin, and virginiamycin) that have FDA approval for prevention of liver abscesses in feedlot cattle were inhibitory to F necrophorum. Differences in antimicrobial susceptibility patterns were observed between the 2 subspecies only for clindamycin and lincomycin. The MIC of F necrophorum isolates from antibiotic-fed cattle were similar to those for isolates from nonantibiotic-fed cattle.

CONCLUSIONS

The MIC of FDA-approved antibiotics were not reflective of the efficacy of antibiotics in preventing liver abscesses in feedlot cattle. Also, continuous feeding of tylosin did not appear to select resistant F necrophorum.

Liver abscesses in feedlot cattle: a review

Liver abscesses in slaughtered beef cattle result from aggressive grain-feeding programs. The incidence, averaging from 12 to 32% in most feedlots, is influenced by a number of dietary and management factors. Liver abscesses represent a major economic liability to producers, packers, and ultimately consumers. Besides liver condemnation, economic impacts include reduced feed intake, reduced weight gain, decreased feed efficiency, and decreased carcass yield. Fusobacterium necrophorum, a member of the ruminal anaerobic bacterial flora, is the primary etiologic agent. Actinomyces pyogenes is the second most frequently isolated pathogen. Ruminal lesions resulting from acidosis generally are accepted as the predisposing factors for liver abscesses. F. necrophorum possesses or produces a number of virulence factors that participate in the penetration and colonization of the ruminal epithelium and subsequent entry and establishment of infection in the liver. However, only a few virulence factors have been characterized well. Control of liver abscesses in feedlot cattle generally has depended on the use of antimicrobial compounds. Five antibiotics (i.e., bacitracin methylene disalicylate, chlortetracycline, oxytetracycline, tylosin, and virginiamycin) are approved for prevention of liver abscesses in feedlot cattle. Tylosin is the most effective and the most commonly used feed additive. Tylosin feeding reduces abscess incidence by 40 to 70%. The mode of action of antibiotics in preventing liver abscesses is believed to be via inhibition of ruminal F. necrophorum. Protective immunity against F. necrophorum induced by a variety of antigenic components has ranged from ineffectual to significant protection.

Ruminal microbial and fermentative changes associated with experimentally induced subacute acidosis in steers

We used six ruminally cannulated steers in a two-period crossover design to study ruminal fermentative and microbial changes associated with induced subacute acidosis. Steers were adapted to either an 80% alfalfa hay (hay-adapted)- or corn grain (grain-adapted)-based concentrate diet. After feed was withheld for 24 h, steers were overfed with an all-grain diet at 3.5 x NEm daily for 3 d. Ruminal contents and jugular blood samples were collected before withholding feed and at 0 and 12 h daily for 3 d during the overfeeding period. Ruminal samples were analyzed for pH, lactate, VFA concentrations, and counts of total anaerobic, amylolytic, lactic acid-producing and -fermenting bacteria, and ciliated protozoa. Blood samples were analyzed to assess acid-base status. Ruminal pH declined to a range of 5.5 to 5.0 with increased VFA concentrations, but normal lactate concentrations (<5 mM) were indicative of subacute acidosis. Total viable and amylolytic bacterial counts were higher (P < .05) in grain-adapted than hay-adapted steers. Anaerobic lactobacilli counts increased over time (P < .01) in both groups and were generally higher in grain-adapted than hay-adapted steers. Lactate-utilizing bacteria were initially greater in grain-adapted than hay-adapted steers and increased over time in both groups following grain challenge. Total ciliates were initially higher (P < .05) in grain-adapted than hay-adapted steers and decreased after 48 h in both groups. Blood acid-base changes were minimal. Bacterial changes associated with subacute acidosis resemble those reported during adaptation to grain feeding, and the decline in ciliated protozoa may be the only microbial indicator of a potentially acidotic condition in the rumen.

Ribotyping to compare Fusobacterium necrophorum isolates from bovine liver abscesses, ruminal walls, and ruminal contents

Restriction fragment length polymorphism analysis of rRNA genes was employed to genetically compare Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme isolates from multiple abscesses of the same liver and isolates from liver abscesses, the ruminal wall, and ruminal contents from the same animal. Four livers with multiple abscesses and samples of ruminal contents, ruminal walls, and liver abscesses were collected from 11 cattle at slaughter. F. necrophorum was isolated from all liver abscesses, nine ruminal walls, and six ruminal content samples. Chromosomal DNA of the isolates was extracted and single or double digested with restriction endonucleases (EcoRI, EcoRV, SalI, and HaeIII); then restriction fragments were hybridized with a digoxigenin-labeled cDNA probe transcribed from a mixture of 16S and 23S rRNAs from Escherichia coli. EcoRI alone or in combination with EcoRV yielded the most discriminating ribopatterns for comparison. Within the subspecies multiple isolates from the same liver were indistinguishable based on the ribopattern obtained with EcoRI. The hybridization patterns of liver abscess isolates were concordant with those of the corresponding isolates from ruminal walls in eight of nine sets of samples. None of the six ruminal content isolates matched either the liver abscess isolates or the ruminal wall isolates. The genetic similarity between the isolates from liver abscesses and ruminal walls supports the hypothesis that F. necrophorum isolates of liver abscesses originate from the rumen.

Effect of increasing proportion of supplemental nitrogen from urea on intake and utilization of low-quality, tallgrass-prairie forage by beef steers

Five Angus x Hereford steers with ruminal and duodenal fistulas were used in a 5 x 5 Latin square to determine effects of increasing the proportion of urea in supplemental degradable intake protein (DIP) on intake, fermentation, and digestion. Steers had ad libitum access to low-quality, tallgrass-prairie forage (2.4% CP, 76% NDF). Supplemental DIP (380 g/d) was from sodium caseinate and(or) urea and was balanced with cornstarch to provide a final supplement (approximately 939 g DM/d) that contained 40% CP. The percentages of supplemental DIP from urea were 0, 25, 50, 75, and 100%. Intake of forage OM was not affected (P > or = .30) by urea level. Ruminal and total tract digestibilities of OM and NDF generally responded in a quadratic manner (P < or = .09) to increasing urea, with the lowest values observed at the highest urea level. As a result, digestible OM intake (DOMI) declined (linear, P = .03) with increasing proportions of urea and tended (quadratic, P = .14) to exhibit the largest proportional decline at the highest urea level. The effects of increasing urea on duodenal N flow, microbial efficiency, ruminal contents, and fluid dilution rate were minimal. Ruminal ammonia N and molar percent acetate increased linearly (P < or = .02), whereas most other VFA (except propionate) decreased (P < or = .05) with increasing urea. In conclusion, although forage OM intake was not altered, OM digestion, NDF digestion, and DOMI were lowest when all supplemental DIP was supplied as urea. Changes in fermentation characteristics reflected the change in source of available nitrogen.

Free amino acid supplementation to steers: effects on ruminal fermentation and performance

Three studies were conducted to evaluate amino acid utilization by cattle. In Exp. 1, five steers (580 kg) were fed 86% rolled corn diets with mixtures of amino acids containing up to 6 g/d DL-Met, 24 g/d L-Lys, 6 g/d L-Thr, and 3 g/d L-Trp. Treatments had little effect on ruminal fermentation, diet digestibility, N flow to the duodenum, or microbial efficiency. Ruminal concentrations of Met and Lys increased linearly (P < .05) with amino acid supplementation, whereas Thr responded quadratically, and Trp was not altered. In Exp. 2, four steers (414 kg) were used to measure effects of dietary monensin or laidlomycin propionate in high-grain diets supplemented with amino acids. Ionophores had no significant effect on ruminal fermentation or outflows of amino acids from the rumen. In Exp. 3, 100 steers (287 kg initial BW) were fed diets containing 1% of a nonprotein N source. Treatments were 1) no supplemental N (UREA), 2) UREA plus soybean meal (SBM), 3) UREA plus 2 g/d DL-Met, 8 g/d L-Lys, 2 g/d L-Thr, and 1 g/d L-Trp, or 4) UREA plus 4 g/d DL-Met, 16 g/d L-Lys, 4 g/d L-Thr, and 2 g/d L-Trp. During the growing period (diets based on whole-plant milo silage), gains were higher for SBM-supplemented steers than for UREA steers and intermediate for steers supplemented with amino acids. Few significant differences in performance were observed among treatments during the finishing phase (diets based on dry-rolled corn) or for the entire experiment, but cattle fed SBM or amino acids tended to be fatter and have better marbling scores and quality grades. Amino acids did not greatly alter ruminal fermentation or cattle performance.

Effect of Fusobacterium necrophorum leukotoxoid vaccine on susceptibility to experimentally induced liver abscesses in cattle

The efficacy and the optimum dose of Fusobacterium necrophorum crude leukotoxoid vaccine required to immunize and protect steers against experimentally induced liver abscesses were evaluated. The vaccine consisted of cell-free culture supernatant of a high leukotoxin-producing strain of F. necrophorum, inactivated with formalin and homogenized with an adjuvant. Twenty-five steers were assigned randomly to the following five treatment groups: control; three doses (1.0, 2.0, and 5.0 mL) of the culture supernatant; and 2.25 mL of the concentrated supernatant (equivalent to 5 mL of the original supernatant). Vaccine was injected subcutaneously on d 0 and 21. Blood samples were collected weekly to monitor antileukotoxin antibody titers. Three weeks after the second vaccination (d 42), all steers were injected intraportally with F. necrophorum culture to induce liver abscesses. Three weeks later (d 63), steers were euthanatized and necropsied; livers were examined and protection assessed. Antileukotoxin antibody titers in the control steers generally did not differ from the baseline (wk 0) titers. The titers in the vaccinated groups increased, more so after the second injection, and the increase was generally dose-dependent. Necropsy examination revealed that all steers in the control group had abscesses in the liver. In the vaccinated groups, two of five steers in the 1.0-mL group and one each in the 2.0-, 5.0-, and 2.25-mL (concentrated) groups had liver abscesses. Antileukotoxin antibody titers were higher (P < .05) in steers that did not develop abscesses than in steers that developed abscesses. The difference suggested a protective effect of antileukotoxin antibodies against experimentally induced liver abscesses.

Identification and partial characterization of an Actinomyces pyogenes hemolysin

Twenty-two Actinomyces pyogenes isolates were recovered from hepatic abscesses in cattle and evaluated for hemolysin production. Hemolysin was collected from supernatant of cultures grown in 6% CO2 in brain heart infusion (BHI) broth. The effect of oxidizing and reducing agents, enzymes, temperatures and pH on hemolytic activity were studied using sheep erythrocytes as the target cells. Our study showed that A. pyogenes hemolysin is oxygen stable; sensitive to treatment by protease, trypsin, and amylase; and destroyed by treatment at extreme temperatures (56 and 100 degrees C) and pH (pH 3 and 11). Production of hemolysin was studied in BHI, RPMI-1640, and a defined serum-free A. pyogenes medium under aerobic and anaerobic conditions. Maximum hemolysin was produced in BHI incubated aerobically in 6% CO2 and to a lesser degree anaerobically in RPMI-1640. No hemolysin was produced in the defined A. pyogenes medium. Differential filtration, isoelectric focusing and sodium dodecyl sulfate polyacrylamide gel electrophoresis identified two hemolysin proteins with pI values of 3.40 and 9.45 and estimated molecular masses of 62 and 58 kDa, respectively. Cell-free supernatant samples positive for hemolysin activity also were screened for leukotoxin activity. Significant levels of leukotoxin were detected in all samples screened.

Serum neutralizing antibody response and protection against experimentally induced liver abscesses in steers vaccinated with Fusobacterium necrophorum

OBJECTIVE

To determine the efficacy of leukotoxin-based Fusobacterium necrophorum vaccines and dietary tylosin in providing protection against experimentally induced hepatic abscesses in steers.

DESIGN

30 steers assigned randomly to 6 treatment groups of 5 steers each: 1, phosphate-buffered saline solution (PBSS; control); 2, PBSS control, fed tylosin (100 mg/steer) daily; 3, inactivated whole-cell culture with oil emulsion adjuvant; 4, culture supernatant (crude toxoid) with oil emulsion adjuvant; 5, semipurified leukotoxoid with oil emulsion adjuvant; and 6, semipurified leukotoxoid with saponin adjuvant.

PROCEDURE

Steers were inoculated SC with emulsified antigen or PBSS on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titer. On day 42, all steers were challenge exposed intraportally with F necrophorum culture. Three weeks later (day 63), steers were euthanatized and necropsied to examine liver and assess protection.

RESULTS

Antileukotoxin antibody titers of all vaccinated groups markedly increased from baseline values, and mean titers of vaccinated groups were higher than those of the control and tylosin-treated groups. Steers vaccinated with culture supernatant with oil emulsion adjuvant or semipurified leukotoxoid with saponin adjuvant had the highest mean antibody titers. All 5 steers in the control group developed liver abscesses. Tylosin feeding did not protect steers challenge exposed with F necrophorum intraportally.

CONCLUSIONS

Culture supernatant was more protective than whole-cell culture or semipurified leukotoxin against experimentally induced hepatic abscesses. Partial purification of leukotoxin appeared to reduce its protective immunity.

Ribotyping to differentiate Fusobacterium necrophorum subsp. necrophorum and F. necrophorum subsp. funduliforme isolated from bovine ruminal contents and liver abscesses

Differences in biological activities (hemagglutination, hemolytic, leukotoxic, and virulence) and ribotypes between the two subspecies of Fusobacterium necrophorum of bovine ruminal and liver abscess origins were investigated. Hemagglutination activity was present in all hepatic, but only some ruminal, strains of Fusobacterium necrophorum subsp. necrophorum. Ruminal F. necrophorum subsp. necrophorum had low leukotoxin titers yet was virulent in mice. Fusobacterium necrophorum subsp. funduliforme of hepatic or ruminal origin had no hemagglutination activity, had low hemolytic and leukotoxic activities, and was less virulent to mice. For ribotyping, chromosomal DNAs of 10 F. necrophorum subsp. necrophorum and 11 F. necrophorum subsp. funduliforme isolates were digested with restriction endonucleases (EcoRI, EcoRV, SalI, PstI, and HaeIII) and examined by restriction fragment length polymorphisms after hybridizing with a digoxigenin-labeled cDNA probe transcribed from a mixture of 16 and 23S rRNAs from Escherichia coli. The most discriminating restriction endonuclease enzyme for ribotyping was EcoRI. The presence or absence of two distinct bands of 2.6 and 4.3 kb differentiated the two subspecies. Regardless of the origin, only F. necrophorum subsp. necrophorum, a virulent subspecies, had a ca. 2.6-kb band, whereas F. necrophorum subsp. funduliforme, a less virulent subspecies, had a ca. 4.3-kb band. Ribotyping appears to be a useful technique to genetically differentiate the two subspecies of F. necrophorum.

Fusobacterium necrophorum infections: virulence factors, pathogenic mechanism and control measures

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two types of F. necrophorum, subspecies necrophorum (biotype A) and funduliforme (biotype B), have been recognized, which differ morphologically, biochemically, and biologically. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis) such as bovine hepatic abscesses, ruminant foot abscesses and human oral infections. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins, such as leukotoxin, endotoxin, haemolysin, haemagglutinin and adhesin, have been implicated as virulence factors. Among these, leukotoxin and endotoxin are believed to be more important than other toxins in overcoming the host's defence mechanisms to establish the infection. F. necrophorum is encountered frequently in mixed infections and, therefore, synergisms between F. necrophorum and other pathogens may play an important role in infection. Several investigators have attempted to induce protective immunity against F. necrophorum using bacterins, toxoids, and other cytoplasmic components. Generally, none of the immunogens has afforded satisfactory protection against Fusobacterium infections. Because of the unavailability of suitable immunoprophylaxis, the control of F. necrophorum infection has depended mainly on the use of antimicrobial compounds.

The serum neutralizing antibody response in cattle to Fusobacterium necrophorum leukotoxoid and possible protection against experimentally induced hepatic abscesses

The serum antileukotoxin antibody response and protection against subsequent experimental challenge with Fusobacterium necrophorum were investigated in 30 steers vaccinated with crude F. necrophorum leukotoxoid. Culture supernatant of F. necrophorum, strain 25, containing leukotoxoid was concentrated. The steers were assigned randomly to six groups (n = 5): PBS control with Stimulon adjuvant; vaccinated with concentrated supernatant diluted to provide 2.5, 5.0, 10.0, or 20.0 ml with the water-soluble Stimulon adjuvant; and 5.0 ml with the Ribi oil-emulsion adjuvant. The steers were injected subcutaneously on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titres. On day 42, all the steers were challenged intraportally with F. necrophorum culture. Three weeks later (day 63), the steers were killed and necropsied for examination of their livers and assessment of protection. Steers vaccinated with crude leukotoxoid tended to have higher antileukotoxin titres than the controls, but the difference was not significant. Also, the antibody titre did not appear to be dose-dependent. In the control group, 3 out of 5 steers developed liver abscesses. The incidence of liver abscesses in steers vaccinated with Stimulon adjuvant was not dose related; however, only 8 of the 25 vaccinated steers developed abscesses. None of the steers vaccinated with the 5.0 ml dose with Ribi had any abscesses. Evidence for a relationship between antileukotoxin antibody and protection was shown by the lower titre in those steers that developed abscesses compared to those that did not. It was concluded that antileukotoxin antibody titres probably provided some degree of protection against experimentally induced liver abscesses, but further dose-titration studies using Ribi or possibly another more effective adjuvant will be needed to confirm this.

Responses in ciliated protozoa and rumen fermentation in sheep supplemented with barley plus virginiamycin

An experiment was conducted to determine the changes in the population of ciliate protozoa and the pattern of rumen fermentation in sheep fed a supplement of barley grain on its own or containing virginiamycin. There were three treatment groups with a total of 25 sheep housed in individual pens. All animals were fed chaffed wheaten hay to a maximum of 1.4 kg head-1 day-1. One group received no grain supplement (n = 5), one barley grain (n = 10) and the third barley plus virginiamycin (40 g/t grain; n = 10). The amount of grain was gradually increased over a period of 5 days to a maximum of 700 g of barley or barley plus virginiamycin on day 5. Grain (700 g/head) was then fed twice weekly for a further 18 days. Samples of rumen fluid were taken on days 1, 2, 3, 5*, 6, 9*, 12*, 23* and 24 (* signifies days when 700 g barley was fed). In sheep supplemented with barley the population density of ciliate protozoa was increased (P < 0.01) from day 3 of the 5 day introduction to grain (approximately 170x104 protozoa/mL at day 5), but the increase was not sustained when grain was fed at intervals of 3 or 4 days. In sheep supplemented with barley plus virginiamycin, the population density of ciliate protozoa was increased significantly (P < 0.01) only at days 5 and 6 of the experiment (approximately 100x l04 protozoa/mL at day 5). Sheep supplemented with barley plus virginiamycin at day 5 had a higher concentration of L-lactate (P < 0.05) at 6 and 12 h and propionate (P < 0.05) at 6, 9, 12 and 24 h than sheep supplemented with barley alone. It was concluded that virginiamycin was inhibitory to protozoa during the introduction to grain, and L-lactate accumulation in the rumen of sheep supplemented with barley plus virginiamycin may be a result of altered fermentation associated with reduced numbers of protozoa.

Purification and quantification of Fusobacterium necrophorum leukotoxin by using monoclonal antibodies

Monoclonal antibodies (Mabs) were produced to the leukotoxin of Fusobacterium necrophorum. Two mAbs (F7B10 and E12E9) partially neutralized leukotoxin activity, as determined by a tetrazolium (MTT)-dye reduction assay with bovine polymorphonuclear neutrophils as target cells. Immunoblot analysis showed that both clones reacted with antigens of 110 and 131 kilodaltons. Epitope analysis showed that the two mAbs recognized the same epitope. An affinity column containing immobilized mAb F7B10 was used to purify leukotoxin from crude toxin. Affinity chromatography of 1 ml of culture supernatant resulted in 0.67 microgram or 1350 units of leukotoxin. Leukotoxin was quantitated by a sandwich enzyme-linked immunosorbent assay using mAb F7B10 as the capture antibody and as the biotinylated indicator. The minimal detectable level was approximately 1 ng, corresponding to 2 leukotoxin units in the sample.

Release of free fatty acids from raw or processed soybeans and subsequent effects on fiber digestibilities

Two in vitro experiments were conducted to determine the rates of lipolysis and the extent of biohydrogenation of fat from raw or processed soybeans and to examine the subsequent effects on fiber digestibilities. In Experiment 1, substrates containing soy oil, raw soybeans, extruded soybeans, and soybeans roasted at 132, 146, or 163 degrees C were incubated with ruminal contents for 2, 4, 6, 12, or 24 h; and release of FFA was measured. The FFA released from substrates containing soy oil, extruded soybeans, and raw or roasted soybeans reached maxima at incubations of 4, 6, and 12 h, respectively. As the roasting temperature increased from 132 to 163 degrees C, release of FFA decreased at incubations of 2, 12, and 24 h. Fatty acids in roasted soybeans were subjected to less biohydrogenation than those in raw or extruded soybeans, suggesting that FFA of roasted soybeans are partially protected from ruminal bacteria. In Experiment 2, ground alfalfa hay was added to substrates used previously to determine the effect of release rate of FFA on ADF and NDF digestibilities. At all incubation times, the substrates containing soy oil and extruded soybeans had lower digestibilities, and those containing raw or roasted soybeans had higher digestibilities of NDF and ADF.

Biochemical and biological characterization of ruminal Fusobacterium necrophorum

Biochemical characteristics, biological activities, and antimicrobial susceptibilities of ruminal Fusobacterium necrophorum (eight subsp. necrophorum and eight subsp. funduliforme) and of isolates (three of each subsp.) obtained from bovine hepatic abscesses were determined. F. necrophorum subsp. necrophorum strains had higher phosphatase and DNase activities, produced more leukotoxin, and were more pathogenic to mice than subsp. funduliforme strains. The leukotoxin titer for culture supernatants of ruminal subsp. necrophorum strains was approximately 15 times lower than that of hepatic subsp. necrophorum strains. Hemagglutination activity was present in all hepatic, but only in some ruminal, strains of subsp. necrophorum. The antimicrobial sensitivity profile of the ruminal isolates was similar to that of hepatic isolates.

Biological and biochemical characterization of Fusobacterium necrophorum leukotoxin

Biological and biochemical characteristics of the leukotoxin of Fusobacterium necrophorum were determined. Culture supernatant of F necrophorum was toxic to polymorphonuclear neutrophilic leukocytes from cattle and sheep, but not to those from pigs and rabbits. Culture supernatant and sonicated bacterial cell fractions had low hemolytic activity and did not cause dermonecrosis in a guinea pig. Supernatant-derived leukotoxin was inactivated at 56 C for 5 minutes and became unstable at pH > 7.8 or < 6.6. Chemical treatment with 0.1% sodium dodecyl sulfate, 0.25% sodium deoxycholate, 5.2% sodium sulfide, or 0.25 mM titanium (III) citrate markedly decreased leukotoxicity. Enzymatic treatment with protease, trypsin, and chymotrypsin inactivated the toxin completely, whereas amylase had no effect. Use of protease inhibitors failed to prevent loss of leukotoxin activity. Using membrane partition chromatography and gel filtration, the estimated molecular weight of the toxin was > 300,000. On reduction and denaturation, the toxin dissociated into several components by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Selective enumeration of Fusobacterium necrophorum from the bovine rumen

A culture medium containing lactate as the sole energy source and antibiotics (bacitracin, gentamicin, and streptomycin) was used for selection and enumeration of Fusobacterium necrophorum from bovine ruminal contents. F. necrophorum growth was determined by indole production, and enumeration was performed by the most-probable-number technique. The number of F. necrophorum cells in cattle fed a 100% forage diet was 7 x 10(5)/g of ruminal contents. The number increased (P < 0.05) 10-fold after the diet was changed to 85% corn grain.

Serum neutralizing antibodies against Fusobacterium necrophorum leukotoxin in cattle with experimentally induced or naturally developed hepatic abscesses

The relationship between serum-neutralizing antibody against Fusobacterium necrophorum leukotoxin and hepatic abscesses was investigated in cattle fed diets supplemented with or without tylosin. Sixteen cattle (eight each in tylosin and in control groups) were inoculated intraportally with F. necrophorum. Ultrasonographic scanning showed that all control animals developed hepatic abscesses after inoculation. In the tylosin group, two animals were free of abscess by d 7 and one was free by d 14. Leukotoxin-neutralizing antibody titers were low on d 0, but increased (P < .05) markedly after intraportal inoculation in both groups. In a second study, blood was collected at the time of slaughter from 141 feedlot cattle (36 fed diets with tylosin and 105 fed diets without tylosin), and livers were examined for presence or severity of hepatic abscesses at slaughter. The incidences of hepatic abscesses were 32% in the control group and 6% in the tylosin group. Antibody was detected in all animals; however, antibody titers were greater (P < .05) in cattle with abscessed liver than those without, and greater (P < .01) in the nontylosin than in the tylosin group. Abscess score and antibody titer were correlated (r = .34; P < .0001). We conclude that F. necrophorum leukotoxin is highly antigenic and that anti-leukotoxin antibody titer is related to the severity of hepatic abscesses.

Supplemental fat and ionophores in finishing diets: feedlot performance and ruminal digesta kinetics in steers

One feedlot trial (116 d; 192 steers) with a factorial arrangement of treatments was conducted to determine effects of supplemental fat and ionophores in corn-based finishing diets. Factors were level of fat (0 or 4% tallow) and ionophore type (none [N], lasalocid [L], monensin plus tylosin [MT], or daily rotation of L and MT [LMT]); L, M, and T were fed at 31, 25, and 10 ppm (DM basis), respectively. Fat and ionophore interacted for DMI (P < .10), ADG (P < .01), and gain:feed G/F, P < .05). Compared with 0%-fat diets, 4% fat decreased (P < .005) DMI by steers fed MT by 8.9%. In 0%-fat diets, MT increased (P < .05) ADG and G/F compared with N or L; however, this increase was negated or reversed in 4%-fat diets. Fat and ionophore interacted (P < .16) on dietary NE concentration. In the 0%-tallow diet, MT increased NEm and NE(g) by 5.1 and 7.0%, respectively, but MT had not effect on NE concentration of the 4%-tallow diet. Alternate feeding of L and MT did not increase animal performance above that of separate, continuous feeding. Six ruminally fistulated steers were used in a metabolism study to evaluate potential mechanisms underlying the interactions observed in the feedlot trial. Treatments were the same as the feedlot trial, except that LMT was not included. Ruminal digesta kinetics were not altered (P > .30) by the addition of fat or ionophores to the diet. Fat and ionophore interacted (P < .05) for molar proportions of ruminal acetate and propionate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Aspergillus oryzae fermentation extract (Amaferm) on in vitro fiber degradation

The influence of Aspergillus oryzae fermentation extract (Amaferm) on in vitro fiber degradation was determined by incubating eight ground fibrous feed-stuffs with rumen fluid and buffer inoculum. Amaferm was added at 0, .4, .8, or 1.2 g/L of fermentation mixture. Both NDF and ADF degradabilities were determined after 96 h of incubation. Addition of extract had no effect on NDF or ADF degradability of pure cellulose, low endophyte fescue, wheat straw, corn silage, or prairie hay. Addition of Amaferm at .8 or 1.2 g/L increased NDF and ADF degradations of bromegrass hay and alfalfa hay; its addition at .4 or .8 g/L, but not at 1.2 g/L, increased NDF and ADF degradation of high endophyte fescue hay. In a second set of in vitro fermentations, selective antimicrobials (penicillin, streptomycin, and cycloheximide) were used to assess the influence of Amaferm on various microbial groups. The enhanced fiber degradation by Amaferm was attributed to its stimulation of bacterial activity because its addition to whole rumen fluid without or with cycloheximide increased fiber digestion. In contrast, addition of Amaferm to the whole rumen fluid plus penicillin and streptomycin treatment had no effect on fiber degradation, suggesting that fungal or protozoal activity was not affected by treatment. In conclusion, Amaferm increased fiber digestibility of certain feedstuffs, and the increase was mediated via stimulation of rumen bacterial, but not fungal or protozoal, activities.

Moderation of ruminal fermentation by ciliated protozoa in cattle fed a high-grain diet

The objective of this study was to assess the influence of ciliated protozoa on ruminal fermentation in cattle fed high-grain diets. Six ruminally cannulated steers fed a corn-based grain diet (85% concentrate plus 15% alfalfa hay) at 12-h intervals were assigned randomly to two groups, ciliate free and faunated, in a crossover design. Defaunation was by ruminal emptying, omasal flushing, and treatment with sodium sulfosuccinate. Two to 3 weeks after defaunation, the ruminal contents of all steers were sampled before the morning feeding (0 h) and at 1, 2, 4, 6, 8, and 12 h after feeding to measure pH, analyze fermentation products, and monitor counts of ciliated protozoa and lactic acid-producing and -fermenting bacterial groups. Total numbers of ciliated protozoa in the faunated steers averaged 4.3 x 10(5)/g, and the protozoa consisted of nine genera. Ciliate-free steers had lower (P less than 0.01) ruminal pHs (pH 5.97) than faunated cattle (pH 6.45); however, the treatment-time interaction was not significant. Ruminal lactate and ammonia concentrations were similar in both groups. The total volatile fatty acid concentration was higher (P less than 0.05) in the ciliate-free steers than in the faunated steers and exhibited a treatment-time interaction (P less than 0.05). The acetate-to-propionate ratio was higher (P less than 0.05) in the faunated group than in the ciliate-free group and showed a treatment-time interaction (P less than 0.05). Total anaerobic bacterial counts were about fourfold higher in the ciliate-free group than in the faunated group.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the leukotoxin activity of Fusobacterium necrophorum

The effect of cultural conditions on the production of leukotoxin by biotypes A and B of F. necrophorum was investigated. Biotypes A and B were grown in prereduced, anaerobically sterilized, brain-heart infusion (BHI) broth. The average leukotoxin titer of culture supernatant was 18 times higher from biotype A strains than from biotype B strains. Leukotoxin activity peaked during the late-log and early-stationary phases of growth, then declined precipitously in both biotypes. F. necrophorum biotype A was grown in different media (BHI, liver infusion, and Eugon broths), at various pH (6.6, 7.3, 7.7, and 8.2), incubation temperatures (30, 35, 39, and 43 degrees C), redox potentials (-352 to +375 mV), and iron concentrations (less than 0.2, 4.2, 42.1, and 361.4 microM). Anaerobic BHI broth with pH from 6.6 to 7.7 at 39 degrees C incubation temperature supported maximal F. necrophorum growth and leukotoxin production. The optimum redox potential for F. necrophorum growth was in the range of -230 to -280 mV. However, the presence of titanium III citrate or dithiothreitol (7.78 mM) in the medium decreased (P less than 0.05) the leukotoxicity of F. necrophorum. Low iron concentration (less than 0.2 microM) decreased (P less than 0.05) growth rate but not leukotoxin activity of F. necrophorum, whereas high iron concentration inhibited the leukotoxin activity.

Response of young dairy calves with lasalocid delivery varied in feed sources

Growth, age at weaning, fecal scores, and blood metabolites of young dairy calves were measured to determine the most effective method of lasalocid administration. Forty Holstein bull calves were blocked by date of birth and assigned randomly to one of four treatment groups: no lasalocid; lasalocid in starter; lasalocid in prestarter and starter; or lasalocid in milk, prestarter, and starter for a 12-wk period. Calves were fed milk twice daily until they consumed 227 g/d of prestarter, at which time the p.m. milk feeding was discontinued, and starter was offered for ad libitum intake as a mixture with the 227 g/d of prestarter. When total dry feed consumption reached 1.3% of birth weight, the calf was weaned. When the calf was 5 wk of age, the prestarter was discontinued. Daily gain tended to be greatest during the first 6 wk for the calves receiving lasalocid in milk, prestarter, and starter. These calves also were weaned with less variation in days to weaning. By wk 8 through 12, there were no differences in gain among the treatment groups.

Performance and ruminal function development of young calves fed diets with Aspergillus oryzae fermentation extract

Neonatal Holstein heifer (n = 72) and bull (n = 40) calves were used to study the effects of Aspergillus oryzae fermentation extract (Amaferm) on their performance and on rumen development. The starter diets were formulated to achieve Amaferm consumption of 0, .5, 1, or 3 g per calf daily. Calves were fed milk daily and allowed to consume starter and a mixture of alfalfa and bromegrass hay ad libitum. Weaning was when calves consumed 550 g of starter on 2 consecutive d. Weight gain and feed consumption were recorded weekly. Forty of the heifer calves, 10 from each treatment, were selected randomly to study the effects of Amaferm on ruminal fermentative development. Ruminal fluid samples were collected for pH, ruminal fermentation products, and for bacterial enumerations. Overall, Amaferm-supplemented calves were weaned 1 wk earlier than unsupplemented calves. They had higher total VFA, propionate, and acetate concentrations in the rumen than unsupplemented calves. Total anaerobic, hemicellulolytic, and pectinolytic bacterial counts were higher; cellulolytic bacterial counts tended to be higher for the Amaferm-supplemented calves than for controls. In general, Amaferm-supplemented calves had greater ruminal microbial activity than those not fed Amaferm.

Hepatic ultrasonography and blood changes in cattle with experimentally induced hepatic abscesses

Hepatic abscesses were induced experimentally in 5 steers by inoculating Fusobacterium necrophorum via ultrasonography-guided, percutaneous catheterization of the portal vein. Hepatic ultrasonography was performed to determine the onset and progression of abscessation. Blood samples were collected before and after inoculation for performing leukocyte counts and hepatic function tests. Ultrasonographic evidence of liver abscesses was observed as early as 3 days after inoculation. Abscesses appeared as hyperechoic centers (cellular debris and pus) surrounded by hypoechoic or anechoic areas (fluid). Increases in rectal temperature, leukocyte counts, fibrinogen, globulin, bilirubin, gamma-glutamyltransferase, and sorbitol dehydrogenase concentrations were detected. Hepatic dysfunction was evidenced by decrease in serum albumin concentration and low sulfobromophthalein clearance. The ultrasonographic diagnosis of abscesses correlated well with necropsy findings.

Effects of supplemental tallow on rumen ciliated protozoa in feedlot cattle

Ruminal samples were collected at slaughter from 98 steers consuming a high-grain diet and receiving either no fat, or 2, 4, 6, or 8% supplemental tallow. Tallow supplementation tended (P = 0.11) to increase average ciliated protozoan numbers, however, the occurrence of defaunated animals was higher in the 8% fat treatment than in the control group. Entodinium spp. were the only protozoans that survived in all treatments, and total numbers ranged up to 3.2 x 10(6)/g of ruminal contents. Although increasing tallow supplementation induced a defaunating effect in many animals, the response was unpredictable and protozoa occasionally proliferated irrespective of fat level.

Cantharidin decreases in vitro digestion of alfalfa and smooth bromegrass

Blister beetles (Coleoptera:Meloidae) containing the toxin cantharidin can be incorporated with alfalfa (Medicago sativa L) during forage conservation. Cantharidin inadvertently ingested with animal feed may cause illness or death. Little information is available on the effects of cantharidin on ruminant microbial digestion. The objective of our study was to determine cantharidin effects on digestibility of alfalfa and smooth bromegrass (Bromus inermis Leyss) by measuring in vitro digestible dry matter (IVDDM) and cell wall digestion (CWD). Alfalfa dry matter digestibility, measured after IVDDM at 48 and 96 h fermentation periods, decreased as cantharidin concentration increased. Increasing cantharidin concentration also significantly reduced IVDDM of smooth bromegrass at 24 and 96 h digestion time. The CWD of alfalfa and smooth bromegrass decreased as cantharidin concentration increased. These results indicate that ingestion of cantharidin by ruminants may decrease microbial digestion of fibrous feeds and therefore may decrease the efficiency of feed utilization by ruminants.

Dynamics of ruminal ciliated protozoa in feedlot cattle

Fluctuations in ciliated protozoan concentrations were monitored in 40 individually fed crossbred heifers that were stepped up to an 85% concentrate diet either slowly (12 days) or rapidly (3 days), with or without monensin (30 ppm). Ruminal fluid was withdrawn from all animals by stomach tube at the start of the study, after each group reached full feed, and at 14-day intervals thereafter throughout the finishing period until termination (day 119). Neither monensin nor speed of step-up affected (P greater than 0.10) total protozoan concentrations, ruminal pH, or lactic acid concentrations. Average protozoan concentrations peaked on day 5, progressively declined until day 56, and then increased (P less than 0.05), suggesting an adaptation to ruminal conditions. Concentrations of Isotricha spp. were higher (P less than 0.05) on the final two sampling dates than at any other time. After day 28, Entodinium, Isotricha, and Polyplastron were the only surviving genera. Protozoa were not detected in 11 heifers on day 42 and day 56, but only two animals were defaunated on day 119, indicating either exogenous or endogenous refaunation. Average protozoan concentrations were not different (P greater than 0.25) between ruminal samples collected by stomach tube the day before slaughter (2.8 x 10(5)/g) and digesta samples collected the next day (1.6 x 10(5)/g). In feedlot cattle, defaunation apparently is transitory and individual animals harbor a dynamic protozoan population that fluctuates in response to changing ruminal conditions.

Comparison of soybean meal/sorghum grain, alfalfa hay and dehydrated alfalfa pellets as supplemental protein sources for beef cattle consuming dormant tallgrass-prairie forage

Three experiments were conducted to compare soybean meal/sorghum grain (SBM/SG), alfalfa hay or dehydrated alfalfa pellets (DEHY) as supplemental protein sources for beef cattle grazing dormant range forage. In Exp. 1 (35-d digestion study), 16 ruminally cannulated steers were stratified by weight (average BW 259 kg) and assigned randomly within stratification to: 1) control, no supplement; 2) SBM/SG (25% CP) fed at .48% BW; 3) alfalfa hay (17% CP) fed at .70% BW; or 4) DEHY (17.4% CP) fed at .67% BW. Steers receiving protein supplements displayed at least a twofold increase in forage intake (P less than .10). In addition, steers supplemented with DEHY consumed approximately 15% more forage (P less than .10) than SBM/SG- or alfalfa hay-supplemented steers. Digestible DM intake (kg/d), however, was similar between alfalfa hay- and DEHY-supplemented steers and 20% greater (P less than .10) than for SBM/SG-supplemented steers. In Exp. 2, 82 mature, nonlactating Hereford x Angus cows (average BW 489 kg) were assigned randomly to SBM/SG, alfalfa hay or DEHY supplement treatments, which were replicated in three pastures. Cows supplemented with DEHY gained more weight (P less than .05) during the first 84 d of supplementation and displayed the least amount of weight loss at calving (d 127; P less than .05) and just prior to breeding (P less than .10). In contrast, calving interval (361 d) and pregnancy rate (94%) were unaffected (P greater than .10) by dam's previous supplemental treatment. In Exp. 3, one block (pasture) of cows from Exp. 2 was selected at random and grazing behavior was monitored during week-long periods in January and February. A treatment X time interaction (P less than .05) occurred for total time spent grazing; treatments did not differ in January, but cows supplemented with alfalfa hay spent less time grazing in the February grazing period. In conclusion, DEHY and alfalfa hay appear to be at least as effective as SBM/SG as a supplemental protein source for pregnant grazing cows when supplements are fed on an equal CP and ME basis.

Ruminal ciliated protozoa in cattle fed finishing diets with or without supplemental fat

Ruminal samples were collected at slaughter from 364 unfasted steers fed different finishing diets to obtain information on numbers and species distribution of ciliated protozoa in feedlot cattle. Total numbers of protozoa averaged 1.59 X 10(5)/g of ruminal contents. A total of 47 steers (12.9%) were defaunated, but 4.1% of the steers possessed numbers of protozoa greater than 10(6)/g. Entodinium species did not always dominate the protozoan populations; 41 faunated steers (11.2%) were devoid of entodinia, and 79 additional steers (21.7%) possessed populations dominated (greater than 50%) by other genera. Isotricha was the most commonly occurring genus supplanting Entodinium, but Polyplastron and Epidinium were frequently present in high concentrations. Tallow and soybean soapstock supplementation reduced (P less than .05) numbers of protozoa in steers consuming wheat diets. However, yellow grease supplementation did not affect numbers of protozoa in steers fed either sorghum or corn diets. Average ruminal pH was 6.20 on the wheat diet, 6.05 on the corn diet, and 5.69 and 6.23 for the two sorghum diets, respectively. We found no correlation between ruminal pH and numbers of protozoa on any diet. The presence of relatively high protozoan concentrations and few defaunated animals in feedlot cattle necessitates reevaluation of the role that ciliated protozoa play in ruminal metabolism of animals fed processed, high-concentrate diets.

Steam-rolled wheat diets for finishing cattle: effects of dietary roughage and feed intake on finishing steer performance and ruminal metabolism

Two experiments were conducted to determine the influence of dietary roughage concentration and feed intake on finishing steer performance and ruminal metabolism. In Exp. 1, 126 steers (334 kg) were used in a completely randomized design and fed (120 d) diets of steam-rolled wheat without roughage or containing 5, 10 or 15% roughage (50% alfalfa hay:50% corn silage). Steers fed 5 or 10% roughage gained faster (quadratic, P less than .05) and were more efficient (quadratic, P less than .05) than steers fed 15% or no roughage. In Exp. 2, six ruminally cannulated steers (447 kg) were used in a 6 x 6 latin square design and fed (twice daily) diets of steam-rolled wheat without roughage or containing 5 or 15% alfalfa hay at twice or three times NE required for maintenance. Increasing dietary roughage increased (linear, P less than .01) ruminal liquid passage 38%, indigestible ADF passage 63%, Yb-labeled wheat passage 75% and fiber fill 31%. The rate of in situ starch digestion tended to increase (linear, P = .16), and ruminal VFA concentration was 40 mM higher (P less than .01) at 4 h after feeding with increased roughage. Increased feed intake increased (P less than .05) ruminal starch fill, fiber fill, liquid fill and liquid passage 23%, Yb-labeled wheat passage 50% and Dry-labeled hay passage 20%. It reduced protozoa five- to sixfold (P less than .01) but doubled total bacterial counts (P less than .01). Ruminal NH3N was lower (P less than .01) and total VFA concentration was 50 mM higher (P less than .01) at 4 h after feeding. The acetate:propionate ratio was reduced from 2.3 to 1.3 (P less than .01) with increased intake. Adding roughage to a steam-rolled wheat diet increased passage and tended to increase rate of starch digestion; increased feed intake with its associated effects on ruminal fill and passage dramatically shifted the microbial population and fermentation end products.

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.

Fusobacterium necrophorum and Actinomyces pyogenes associated facial and mandibular abscesses in blue duiker

Anaerobic and aerobic cultures of facial and mandibular abscesses were made from 12 blue duiker (Cephalophus monticola fusicolor) housed at the Deer and Duiker Research Facility of the Pennsylvania State University (USA). Increases in concentrations of total protein and serum globulin occurred in all cases. Actinomyces pyogenes was isolated from nine animals. Fusobacterium necrophorum was present in eight and Bacteroides sp. was found in seven animals; other genera of isolated bacteria included: Streptococcus (from two animals), Lactobacillus (one), Staphylococcus (one) and Actinomyces (two). Eight (67%) of affected animals were less than or equal to 2 yr of age. Facial soft tissues and mandibles were the tissues most often affected. Tissues within the oral cavity were not affected at the time of presentation. A common finding, not reported in other host species with necrobacillosis, was the presence of nondestructive mandibular proliferation.