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The objective of this study was to ascertain the value of variables measured on bulk tank and composite milk samples as predictors, respectively, of the level of mastitis in herds and individual cows. The standard of comparison was the results obtained by bacteriological examination of the secretion from individual mammary quarters. It was found, whether sampling at the herd or cow level, that of the three variables measured on each sample, namely somatic cell count, percentage of cell volume in channel 8 (includes cells with individual volumes from 89.2 to 178.3 μm3) and presence or absence of Streptococcus agalactiae , that the ability of the first two variables to discriminate (predict) was not significantly improved by the inclusion of the latter variable. Using values for the former two variables as measured on bulk tank milk and collected at the time of quarter sampling, it was possible to correctly classify 45.5% of the study herds into one of the three quarter infection rate categories considered, namely, 25%. The percentage of herds correctly classified was increased to over 80% by inclusion of five monthly counts recorded previous to the time of quarter sampling. Using the same two variables but measured on composite milk samples, 79.4% of cows were correctly classified as being either positive or negative when a positive cow was defined as one having at least one positive quarter. The overall percentage of cows correctly classified decreased from 79.4 to 77.9% when an attempt was made to distinguish between negative cows and cows with one positive quarter. However, this overall percentage progressively increased to 92.7% as the definition of a positive cow was changed from one having one positive quarter to one having two, three or four positive quarters. The procedure shows promise for monitoring the level of mastitis infection in either dairy herds or cows but requires further refinement before consideration could be given to its implementation.

The efficacy of bacitracin methylene disalicylate (BMD) in the management of necrotic enteritis (NE) when fed in combination with narasin was investigated in a floor-pen study of 2,000 broiler chickens using a Clostridium perfringens inoculum challenge model. Treatments consisted of 1) nonchallenged-nonmedicated; 2) challenged-nonmedicated; 3) challenged-narasin (70 ppm); 4) challenged-BMD (55 ppm); 5) challenged-narasin (70 ppm) + BMD (55 ppm). Medication was provided in the feed from Day 0 to trial termination on Day 41. C. perfringens challenge occurred from Day 14 to 16. BMD and narasin, fed alone and in combination, reduced (P < 0.05) mortality due to NE when compared to challenged-nonmedicated birds. NE lesion scores (Days 0 through 41) were lower among birds fed BMD and narasin, alone and in combination, compared to challenged-nonmedicated birds. Improvements in NE mortality and NE lesion scores were greatest for the BMD + narasin-medicated birds, followed by the BMD-alone, and then narasin-alone treated birds. BMD and narasin, alone and in combination, provided improvements (P < 0.05) in average daily gains over the entire study (Days 0 to 41). The results of this study demonstrate the effectiveness of BMD and narasin in the management of NE in broiler chickens.

The efficacy of tylosin phosphate for the treatment of necrotic enteritis (NE) was investigated in a floor pen study of 2,000 broiler chickens. A model in which Clostridium perfringens was administered in the feed on Days 14 to 16 was used to initiate an outbreak of NE. Treatments, allocated at the pen level in a randomized complete block design, consisted of five levels of tylosin phosphate (0, 50, 100, 200, or 300 ppm) administered in the feed on Days 15 to 22, following the identification of an outbreak of NE on Day 15. Mortality due to NE was significantly reduced (P < 0.05) for medicated birds at all dose levels of tylosin phosphate compared to unmedicated birds. Mean NE lesion scores on Day 17 were significantly reduced (P < 0.05) by all levels of tylosin treatment compared to those of unmedicated birds, decreasing linearly from 2.66 at 0 ppm to 0.38 at 100 ppm and 0 at higher doses. Tylosin at all levels provided improvement in Day 29 body weight, average daily gain, feed to gain ratio, and average daily feed intake compared to unmedicated birds. The results of this study provide evidence that tylosin phosphate, when administered in feed, is effective in the treatment of clinical outbreaks of NE in broiler chickens and suggest that the optimal dose for this purpose is 100 ppm.

An overview is presented of some members of the HAP group important in animal disease. An attempt has been made to highlight the economic importance of these diseases and to alert us to the importance of research that will lead to their prevention and control.

SUMMARY. The efficacy of narasin in the control of necrotic enteritis (NE) was investigated in a floor pen study of 2000 broiler chickens using a Clostridium perfringens feed inoculum challenge model. Treatments were 1) nonmedicated, nonchallenged; 2) nonmedicated, challenged; 3) narasin, nonchallenged; 4) narasin, challenged. Narasin was administered at 70 ppm in the feed from day 0 to trial termination on day 41. Challenge inoculum contained approximately 1 X 108 colony-forming units CP/ml and was administered from day 14 to day 16. In the unmedicated groups, challenged birds had significantly (P 0.05) and significantly (P < 0.05) lower huddling scores on days 16 and 17 than unmedicated. Coccidiosis lesion scores were zero for birds euthanatized from all treatment groups on day 17, suggesting that the beneficial effects of narasin were not due to prevention of coccidiosis. This study thus provides evidence that narasin is effective in the prevention of necrotic enteritis in broiler chickens.

Special standards for Somatic Cell Counting (SCC) were developed at the Central Milk Testing Laboratory in Guelph for Ontario laboratories performing the tests. One laboratory used a Coulter milk counter for composite herd samples, two laboratories used five Fossomatic counters for cow samples, while the fourth used a Coulter counter for research purposes. Standards were prepared at low, medium and high count levels from fresh herd milks containing somatic cells near levels of 100,000, 500,000 and 1,000,000/ml. As the lifespan of the suspensions of somatic cells was three months, they were prepared in sufficient quantities to test daily for 3 months, and to be used throughout the day for calibration maintenance. The actual counts in the standards were established by direct microscopic somatic cell count (DMSCC) performed in two laboratories simultaneously with exchange of slides. Counts were re-confirmed every week by the same DMSCC procedures. The standards are suitable for initial calibration, daily calibration maintenance, daily instrument performance appraisal and trouble-shooting. In daily use each laboratory tests each standard five times each morning on each instrument. The same vials are used throughout the day, every 0.5 h for appraisal of continuous calibration and instrument function. The mean and standard deviations of standards are determined and compiled for each day.

Morphology, biochemical reactions, pigmentation, antigens, and cell envelope proteins were examined in 12 strains of Haemophilus somnus, Haemophilus agni, Histophilus ovis, and Actinobacillus seminis. All of the strains except A. seminis are related and are considered as a single Haemophilus-Histophilus (HH) group. In immunodiffusion tests, HH group bacteria had at least two antigens common to all members of the group, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that they have similar cell envelope protein profiles. A quantitatively variable yellow pigment with absorption maxima of 430 to 435 nm was present in strains of H. somnus and H. agni. The HH group did not produce catalase and grew only in air containing 10% CO2. Of 10 HH group bacteria, 9 required thiamine monophosphate for growth. A. seminis was distinguished from the HH group by its lack of yellow pigment, production of catalase, growth in air, lack of a thiamine monophosphate requirement, and different cell envelope protein profile. In gel immunodiffusion tests, A. seminis antigens produced two lines of partial identity with the HH group when antiserum against H. somnus was used. Reference strains of Haemophilus influenzae, Actinobacillus lignieresii, and Haemophilus haemoglobinophilus were compared with the test strains. In immunodiffusion tests, a single antigen was found to be common to H. haemoglobinophilus, A. seminis, and the HH group. No similarities between any of the test strains and H. influenzae or A. lignieresii were noted. The close relationship of H. somnus, H. agni, and Histophilus ovis suggests that these unofficially named bacteria may belong to a single taxon.

Synopsis A study has been made of the intestinal flora of chickens aged between 2 and 6½ weeks. No major differences were found when rations containing 9 or 25% fish meal were compared or when two different sources of fish meal were used. Throughout the period investigated, it was confirmed that the lactobacilli are the only group of organisms generally present in the small intestine in numbers exceeding 104/g. Clostridia were regularly found at 102 to 104/g, but Clostridium welchii was isolated from only occasional samples. In the caeca, the total number of bacteria present at 2, 3, 4 and 6½ weeks was about 1011/g. Of these it was generally possible to isolate more than 20% using an anaerobic roll‐tube technique and oxygen‐free CO2. Many different types of anaerobes were isolated including strictly anaerobic budding bacteria which had not previously been studied. During the growth of the bird the flora changed. Anaerobic streptococci (peptostreptococci) predominated at 2 weeks but gradually decreased so ...

Teats were dipped immediately after milking in (a) an iodophor diluted to contain 1.0 per cent available iodine; (b) P.V.P.—Hibitane, containing 1.6 per cent Hibitane (Chlorhexidine); and (c) P.V.P.—Hibitane containing 0.5 per cent Hibitane. After each cow was milked the teat cups were rinsed briefly and “pasteurized” at 165–170°F for 15 seconds. Teat-dipping alone reduced dramatically the number of micrococci on the inflations but was only partially effective in reducing the percentage of inflations carrying haemolytic staphylococci, except when the 1.6 per cent P.V.P.—Hibitane was used. This material was, however, somewhat irritating to the teats. Teat cup pasteurizing alone partially reduced the percentage of teat cups carrying haemolytic staphylococci, but had little effect on the number of micrococci initially present on the inflations. It appears that the combination of these simple practices will go far towards eliminating the teat-skin and milking machine inflations as reservoirs of haemolytic staphylococci.

A survey to assess the knowledge and perception regarding mastitis of 1200 randomly selected Ontario dairy producers was conducted using a mailed questionnaire. Other data were provided by the Ontario Milk Marketing Board and the Dairy Herd Improvement Association. In general, producers were less aware of subclinical than clinical mastitis and did not appreciate the losses in production associated with it. Approximately 40% of producers were not familiar with mastitis in its subclinical form.Many producers have not adopted practices that have been advocated for the integrated control of mastitis. For example, 35.5% of producers surveyed used single service paper towels and 38% regularly used teat dips and dry cow antibiotic therapy.

Nineteen antisera produced in pigs against 14 enteropathogenic and five nonenterotoxigenic porcine strains of Escherichia coli were tested for their ability to inhibit gut loop fluid accumulation induced by homologous and heterologous organisms. In addition, four antisera produced in pigs by an intensive series of intravenous inoculations and three by a less intensive series of intramuscular injections of a polyvalent E. coli vaccine were evaluated. Antisera were also produced in rabbits against eight strains of porcine enteropathogens and tested in pig gut loops. Fluid inhibiting activity was detected in prevaccinal sera of pigs but not of rabbits. This activity was significantly increased following immunization. When single strains of E. coli were used for immunization the activity of the antisera against heterologous organisms varied considerably from one test strain to another and was usually much less than that against the homologous organism. The activity against heterologous organisms could not be associated with relatedness of the O, K and H antigens of the vaccine and the test strains. Antisera produced against a vaccine made by combining three strains were shown to exert inhibitory effects on heterologous organisms similar to those against homologous organisms. Considerably less activity against homologous and heterologous organisms was present in antisera produced by the series of intramuscular compared with the series of intravenous injections.

The type of drinker used for poults influenced the level of free available chlorine (FAC) in chlorinated water as well as the total plate count, fecal coliform count, and number of salmonellae in chlorinated and non-chlorinated drinking water. Nipple drinkers maintained higher levels of FAC in drinking water than Swish-cups, Swish-cups maintained higher levels than MarkIII, and MarkIII maintained higher levels than trough drinkers. The level of FAC retained in the water in trough drinkers was insufficient to exert a bactericidal effect against coliforms and salmonellae. Chlorination of drinking water and the resulting diminished number or absence of salmonellae in the drinking water did not lower the number of salmonellae per gram of cecal contents in challenged or unchallenged but exposed poults. The number of salmonellae per gram of cecal contents decreased significantly (P less than 0.01) in poults between 14 and 21 days of age, irrespective of whether or not the poults drank chlorinated water.

The necropsy records of dairy cows with mastitis were reviewed from the provincial veterinary laboratory in Guelph (44 cases of mastitis in nine years) and from the Ontario Veterinary College (168 cases in 14 years). Mastitis was considered to be the primary cause of death in 167 of 212 cows (79%). Of these 167 cases of mastitis, Escherichia coli was involved in 107 (64%), Klebsiella sp. in 12 (7%) and Staphylococcus aureus in 11 (7%). Bacteriology was not reported in 22 cases. Coliform mastitis, the most commonly identified type of fatal mastitis, was characterized histologically by the presence of infarcted areas in affected glands and by the lack of demonstrable bacteria, and was thus easily identified from fatal mastitis caused by S. aureus.

The capability of a commercial Haemophilus somnus bacterin to protect cattle against experimentally induced thromboembolic meningoencephalitis was examined. Eighteen cattle were vaccinated twice, 8 were vaccinated once, and 14 were nonvaccinated controls. Serum antibody responses to vaccination were measured by gel immunodiffusion, bacterial agglutination test, and complement-fixation test. Deaths occurred in 8 of the 14 controls, 3 of the cattle vaccinated once, and 3 of the cattle vaccinated twice. Two vaccinations were found to give significant protection against challenge exposure (P less than 0.05). There were no cattle which gave positive reactions in the gel immunodiffusion test, and significant changes in bacterial agglutination test titers were not seen in the cattle after vaccination. There was a significant (P less than 0.01) increase in the complement-fixation test titers of cattle vaccinated twice. Serum antibody titers were unrelated to the outcome of challenge infection, regardless of vaccination status, in any of the serotests.

Of 23 cattle inoculated IV with Haemophilus somnus, 16 (70%) died of thromboembolic meningoencephalitis. The inoculum was prepared from a minimally subcultured isolate of H somnus that was passaged through a calf by intracisternal inoculation immediately before use. Serum antibody titers, as measured by 7 serologic tests, were not correlated with the animal's susceptibility to infection. All cattle that died had a mean 4-fold increase in agglutination titer during the acute phase of the disease, 2 to 4 days after inoculation. Similarly, high acute-phase titers were demonstrated in 15 cattle with naturally occurring disease. Haemophilus somnus was isolated more frequently and in greater numbers from the CNS and urinary tract than from other organs of cattle that died.

Haemophilus somnus was isolated from 40 of 79 unprocessed bovine semen samples, 14 of 23 preputial washings of bulls and three of eight preputial washings of steers. The results indicate nonvenereal colonization of the male urogenital tract. It is suggested that dissemination of H. somnus from the urogenital tract may be of significance in the epizootiology of H. somnus associated diseases.

Yersinia enterocolitica (Ye) 0:9 is an organism of great significance in veterinary medicine largely as a result of its cross-reaction with Brucella abortus (Ba). Boty Ye 0:9 and Ba possess somatic antigens in common; as a result of which animals exposed to Ye 0:9 have an immune response which is distinguishable only with difficulty from that induced by Ba. Cattle were exposed to Ye 0:9 by the oral or intramammary routes. Oral exposure failed to generate significant serologic response. In contrast, intramammary inoculation produced a marked response. Serum antibodies provoked in this manner reacted strongly with Ba. The anti-Brucella response provoked by inoculation of Yersinia was sufficient to render milk and serum Brucella-seropositive as measured by the standard milk ring and serum agglutination tests. While both Ba and Ye 0:9 have 9 antigens in common, they differ significantly with respect to motility. Thus Ba is always non motile while Ye is motile when grown at room temperature. The presence of Yersinia H agglutinins in serum were shown to be evidence of previous exposure to Ye. The H agglutinins were not generated by Brucella infection. A rapid H agglutination test was shown to provide this differentiation without interference from cross-reacting O antigens. Results of Ba O and Ye O and OH antigens used in the agglutination test were found useful to differentiate antibodies against Ba from those induced by Ye 0:9 in cattle sera. The existence of enterobacterial common antigen (ECA) in Ye and its absence in Ba were utilized in an attempt to provide a method to distinguish Brucella infections from those with cross-reacting Yersinia.(ABSTRACT TRUNCATED AT 250 WORDS)

"Haemophilus somnus' was isolated from 77% of 31 reproductive tracts of bulls from an Ontario slaughterhouse. Identification of H somnus was based on morphologic and cultural characteristics and on fluorescent antibody and immunodiffusion tests, using antisera prepared against a known pathogenic encephalitic isolate of H somnus. The infection rate and distribution of H somnus within the tract were as follows: preputial orifice--71% preputial cavity--71%; urinary bladder--26%; accessory sex glands--19% and ampulla of ductus deferens--10%. Isolates were not obtained from the testes or epididymides. On 2 occasions, H somnus was isolated in pure culture from the preputial cavity. A higher prevalence of infection was found in young bulls. There were no differences found in infection rates between breeds. Differences in hemolytic activity and minor antigenic variation between isolates indicated that a series of biotypes within the species H somnus may exist. The study indicates that organisms presently identified as H somnus may normally form part of the flora of the bovine prepuce and that dissemination from the male bovine reproductive tract is one possible means of infection in H somnus-associated diseases. The pathogenic significance of genital isolates of H somnus awaits further study.

Three strains of Hemophilus somnus were infused into the posterior cervix of six pregnant cows. The organism persisted in the cervicovaginal region for eight to 87 days, and at parturition H. somnus was isolated from chorioallantois in four of six cows; placentitis developed, and fetal membranes were retained. All calves were born alive and no H. somnus was recovered from them. One cow died 14 days after parturition. The death was attributed to severe necrotizing metritis; H. somnus was not isolated from the uterus at death, but was isolated from the placenta at parturition and cervicovaginal mucus two days later.

The oral administration of a 1:20 (wt/vol) dilution of adult turkey cecal contents to poults on the day of hatching protected more than 80% of the poults against challenge at 24 hr of age with approximately 10(3) colony-forming units (CFU) of a nalidixic-acid-resistant strain of Salmonella typhimurium. All untreated poults similarly challenged were colonized. Protection was lost when the challenge dose was 10(6) or greater. When the microflora treatment followed salmonella challenge by 6 hours or more, protection was reduced. If poults were colonized by S. typhimurium, the organisms were found always in the ceca and infrequently in other parts of the intestinal tract. When poults shedding salmonella were mixed with treated poults, more than 70% of the latter remained free of the organism.

A mild form of strangles caused by an atypical Streptococcus equi was recognized on a large horse breeding farm. The organism differed from most S equi isolates by disappearance of the mucoid capsule by 24 hours of culture, leaving a matt-type colony. Typically, the clinical signs were a transient (24-48 hour) fever, profuse nasal discharge, and anorexia. In about half the affected animals, there was moderate mandibular lymph node enlargement, and these glands usually ruptured or were drained. The use of a passive hemagglutination antibody test showed that subclinical infection was widespread in horses on the farm.

Mammary glands of 6 lactating Holstein cows were inoculated with Haemophilus somnus strain 43826. Three cows developed chronic mastitis and shed bacteria for up to 1 year. Three cows developed acute gangrenous mastitis, with evidence of bacteremia and endotoxemia. Cows with gangrenous mastitis had lower somatic cell counts early after inoculation in affected quarter secretions compared with those in cows that developed chronic mastitis. Cows with gangrenous mastitis developed hypocalcemia, hypoalbuminemia, azotemia, hyperbilirubinemia, mildly increased serum aspartate aminotransferase and creatine kinase activity, and a marked neutropenia with a degenerative left shift. Histopathologic examination of gangrenous quarters revealed edema, necrosis, and vascular thrombosis with few inflammatory cells. A limited survey failed to recover H somnus from dairy cows with clinical mastitis or from mammary secretions from 41 beef cattle at an abattoir.

An observational study of Corynebacterium bovis was conducted in 74 Ontario dairy herds. The levels of infection with C. bovis were 19.9, 36.2 and 85.6% at the quarter, cow and herd level, respectively. Teat disinfection was found to be the variable best able to distinguish between herds with a high or low C. bovis quarter infection rate. Mean total milk somatic cell counts for 1103 quarters and 107 cows infected with only C. bovis ranged between 150,000 and 200,000/mL and were significantly higher than for uninfected quarters or cows. The rate of infection with mastitis pathogens was not significantly different in quarters previously colonized with only C. bovis compared to previously uninfected quarters.

Somatic cell counts were performed monthly on bulk tank milk samples for all producers in the Ontario counties of Hastings, Lennox/Addington and Prince Edward throughout 1978 and 1979. Other data were obtained via a structured questionnaire and from the records of the Ontario Milk Marketing Board. Many producers have not adopted practices that have been advocated for the integrated control of mastitis. For example, 43.3% of producers surveyed used single service paper towels, 63.3% regularly used teat dip and 56.5% dry cow therapy. The mean of the average monthly somatic cell count for all producers for 1978 was 621.1 x 10(3) cells/mL. This latter value was used to divide the producers into case (higher than average) and control (lower than average) groups. Control herds averaged 95.9 liters more shipped milk per cow per month than case herds. Milk from control herds averaged 0.22 percentage points higher than case herds for each of average fat and lactose, and 0.16 percentage points higher for protein. The linear regression of monthly shipped milk on the respective monthly bulk tank somatic cell count indicated a loss of 13.26 L/cow/month for each 100,000 increase in somatic cell count.

A commercial latex agglutination test for the detection of Group B streptococcal antigens was used to detect infection due to Streptococcus agalactiae in whey of bovine milk samples. Fifteen out of 17 known infections were detected, but it was necessary to incubate the wheys at 37 degrees C for 18 hours in nine of the samples. It was found that the latex agglutination test could detect Group streptococcal carbohydrate antigens in whey samples from artificially infected quarters from one to four days after failure to detect the organism on culture or after antibiotic therapy of the affected quarter.

In laboratory trials, a fourth-passage culture of adult chicken cecal contents was protective against challenge with Salmonella typhimurium in turkey poults raised on wood-shavings poultry litter. The culture was not protective against pre-treatment exposure to hatchery-introduced S. bredeney and was inhibited in poults that had received an antibiotic injection at the hatchery. The inhibitory effect of the hatchery antibiotic could be avoided if the cecal-culture treatment was delayed by 3 to 4 days after antibiotic injection. Under field conditions, there was a significant reduction in the salmonella contamination of turkeys and their environment when cecal culture was given to poults raised on wood-shavings litter sprayed with a quaternary ammonium compound. When used alone, both the cecal culture and the litter disinfectant were ineffective in preventing the establishment of S. heidelberg infection. Further studies are required to confirm the possibility of a synergistic effect between the two treatments. For the control of salmonella in turkeys, use of cecal cultures may be limited by the interference of antibiotics and by their failure to protect against pretreatment exposure to salmonella.

The biochemical and morphological characteristics of 104 strains of Corynebacterium bovis isolated from bovine milk samples and the C. bovis reference strain were found to be uniform. Valuable criteria for identification were presence of catalase and oxidase, production of acid from glucose and fructose and a requirement for enriched basal media. Six strains of human and three strains of bovine origin were found to be inconsistent with the reference strain.

Antigens extracted from Haemophilus somnus were examined for their suitability as vaccines for prevention of thromboembolic meningoencephalitis and as antigens in immunologic tests for detection of susceptible cattle. Saline extraction of whole H somnus cells produced an outer membrane complex (OMC) that contained 2 major antigens when tested against antiserum to intact cells by immunoelectrophoresis. Anion exchange chromatography was used to separate an anionic antigen (AA) from the more cationic antigen (CA). According to chemical analysis and polyacrylamide gel electrophoresis, both AA and CA were complex mixtures--probably, outer membrane fragments. Enzyme-linked immunosorbent assays were used to measure serum levels of immunoglobulin (Ig) G and IgM against AA and CA in cattle vaccinated with whole cells, OMC, CA, or AA. Protection of vaccinated cattle was assessed after IV challenge exposure to H somnus. Moderate IgG and IgM responses occurred when cattle were given 2 vaccinal doses of 0.1 mg or 1.0 mg of whole cells, OMC, or AA. Two of 10 cattle given 2 vaccinal doses (1.0 mg) of OMC died after IV challenge exposure, whereas 8 of the 10 controls died, indicating significant protection (P less than 0.05). All of the 10 cattle given 2 vaccinal doses (1.0 mg) of AA were protected from IV challenge exposure, whereas 5 controls died (P less than 0.05). Two vaccinal doses of either 0.1 mg or 1.0 mg of CA produced high IgG and IgM responses. However, 3 of 10 cattle given 2 vaccinal doses (1.0 mg) of CA died after IV challenge exposure, as did 3 of the 10 controls, indicating that CA was not protective.(ABSTRACT TRUNCATED AT 250 WORDS)

Colonization with Corynebacterium bovis was established in 59 of 64 (92%), 58 of 59 (98%) and 19 of 34 (56%) of uninfected bovine mammary quarters following inoculation of 83.3 X 10(4) colony-forming units (CFU) of the organism into the teat cistern, 4.7 X 10(3) CFU 5 mm into the teat duct or by exposure of the teat orifice to a milk culture containing 1.6 X 10(7) CFU/mL respectively. Mean somatic cell counts for foremilk samples from 122 quarters were significantly higher after colonization with C. bovis (145,900/mL) compared to before exposure (130,900/mL).

Upper respiratory disease has been a serious problem in Standardbred horses on racetracks in Ontario, with outbreaks occurring once or twice annually in late winter and early spring seasons. To determine the causes of these epidemics, a 3-year investigation was carried out in which nasal swabs and serum samples were obtained at intervals from apparently healthy horses and from horses suffering from upper respiratory disease. The nasal swabs were used to isolate bacteria and viruses. The serum samples were examined for the presence and level of antibodies to equine influenza viruses and equine herpesvirus 1. None of the bacteria isolated were associated with the outbreaks of disease. Equine herpesvirus 2 was isolated 72 times from both diseased and apparently healthy horses. Equine herpesvirus 1 was isolated 10 times from horses with respiratory disease, both during and between epidemics. Influenza equine/1 virus was isolated seven times and influenza equine/2 was isolated once during severe outbreaks of upper respiratory disease. Serological evidence confirmed that influenza viruses were the causes of the major epidemics, with the equine/1 strain being involved most often.

The production of M-protein antigen of Streptococcus equi was studied during in vitro growth in equine blood and in various media. Of 11 S equi strains studied, seven which had initially possessed 0.04 mg or less M-protein per 10 mg of streptococcal cell extract showed an increase in M-protein content after successive culture in heparinised horse blood. Maximum proliferation occurred in Todd-Hewitt (TH) medium with added 0.2 per cent w/v glucose when compared with TH medium alone or TH medium with 2 per cent w/v sucrose, starch, neopeptone or normal horse serum. The M-protein of these strains did not change after the addition of either neopeptone or normal horse serum to TH medium but declined with the addition of sugars. In experiments involving phagocytosis of S equi by equine polymorphs, the percentage of polymorphs which engulfed cocci was higher with a capsule-deficient strain (69.0 +/- 11.6 per cent) than with five typical encapsulated strains (21.1 +/- 7.0 per cent to 30.9 +/- 13.3 per cent). Phagocytosis of five typical strains was greater after growth in a trypsin-containing medium than in medium devoid of trypsin. Trypsin-grown cells took longer to kill mice than did normal cells. It was concluded that M-protein was one of the factors involved in the virulence of S equi.

The API 20E System and the Encise Enterotube were evaluated for the identification of the Enterobacteriaceae isolated from clinical specimens of animal origin at a veterinary diagnostic laboratory. Compared to conventional tubed media, the API 20E System identified 235 of 240 isolates (97.9%) correctly. The Encise Enterotube correctly identified 229 of the 240 isolates (95.4%). Thus, both these identification systems could be used to replace conventional methods for identifying members of this family isolated from animal origin.

The effectiveness of a teat dip with dodecyl benzene sulfonic acid (1.94%) for the prevention of intramammary infections was determined in cows experimentally challenged with Streptococcus agalactiae and Staphylococcus aureus. The infection rates with Streptococcus agalactiae and Staphylococcus aureus were 62.5% and 75% in undipped quarters, 12.5% and 21.5% in dipped quarters with a reduction rate of 80% and 71% respectively. The significance of some findings in relation to mastitis control are discussed.

Three clinically normal cows were inoculated with viable Yersinia enterocolitica O9 by the intramammary route. This provoked an increase in the somatic cell count in milk from the inoculated quarter, but no obvious clinical response. Yersinia enterocolitica was isolated only sporadically from these cattle after inoculation. All cows showed a marked serologic response to Y enterocolitica and Brucella abortus. The anti-Brucella response provoked by inoculation of Yersinia was sufficient to render milk and serum Brucella-seropositive, as measured by the standard milk ring test, the quantitative milk ring test, and the serum agglutination test.

Infection of the mammary gland (mastitis) was produced by infusing ten quarters 2/cow x 5 cows) with Staphylococcus aureus strain 305. Mastitic and normal quarters were then infused with a preparation containing two levels of penicillin G (100,000 and 200,000 IU) in 10 mL of 3% aluminum monostearate and peanut oil. Milk penicillin levels were determined prior to treatment and twice daily for eight milkings after treatment. Normal and mastitic quarters infused with 200,000 IU had higher peak levels than those infused with 100,000 IU. Milk penicillin levels were similar in mastitic and normal quarters for the first three milkings after treatment. However, residues persisted for a longer time in milk from mastitic quarters. Penicillin was not detected in milk from the untreated control quarters nor in serum samples assayed during the experiment. The in vitro penicillin G sensitivity of the udder pathogen (MIC=0.039 and MBC=0.078 IU) was well below the milk penicillin levels for the first five milkings in all cases. However, infection recurred in two of the ten quarters (one receiving 100,000 IU and one receiving 200,000 IU).

The effect of manipulating adult turkey cecal contents was assessed. Treatment of day-old poults with cecal contents diluted up to 1/3000 protected 90% of the birds against subsequent challenge with 10(3) colony-forming units of Salmonella typhimurium. The addition of penicillin G and streptomycin to adult cecal contents reduced their protective effects by 20% and 50%, respectively. When cecal contents were heat-treated at 65 C for 15 minutes or filter-sterilized, the protective properties were lost. Anaerobic cultures of cecal contents in reinforced clostridial medium afforded protection against challenge, but protection was lost on subsequent subcultures. Thioglycollate broth culture of cecal contents did not protect.

An experimental and statistical model was developed to study the effect of antibiotics in feed on the fecal shedding of Salmonella. the model design consisted of 3 groups of 4 to 10 experimentally infected ducks each; group 1 was given no medication, group 2 was given a small dose of antibiotic, and group 3 was given a large dose of antibiotic as feed supplement for growth promotion. The test for the null hypothesis and Fisher's exact test were used for evaluating the significance of the results on each sampling day and for the experimental totals. Experimental results of the model showed that, whereas oxytetracycline (OTC) significantly (P less than 0.05) decreased the duration of shedding of OTC-sensitive Salmonella, it significantly increased the duration of shedding of OTC-resistant Salmonella. Evaluation of zinc bacitracin by this model indicated that zinc bacitracin either produced a moderate increase in the duration of fecal shedding or failed to alter the duration of fecal shedding of Salmonella. Seemingly, it is necessary to select a sensitive and a resistant Salmonella strain to evaluate the effects of antibiotics in feed.

Minimal inhibitory concentration (M.I.C.) values as determined by an agar-plate-dilution method for 60 bacterial isolates, consisting of Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus of animal origin against 20 antimicrobial drugs are presented. Of all the drugs, gentamicin had the best in vitro antibacterial activity in terms of M.I.C. when considering all the species of organisms together, while spectinomycin had the least activity.An inoculum replicator was a convenient tool in carrying out the agar-plate-dilution method.A comparison of the M.I.C. values of 42 isolates of S. typhimurium with the results obtained by low level method and the Bauer-Kir-by method showed that with few exceptions, there is a general agreement.