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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 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.

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.

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)

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.

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.

Seventeen ponies were infected with Salmonella typhimurium and then 15 were variously stressed by transportation and/or surgery and 9 were given oxytetracycline. Indications of Salmonella reactivation occurred in all the stressed ponies. Diarrhea due to a reactivation of the Salmonella infection did not develop until greater than 3 days after stress, although maximal shedding of organisms occurred within 24 hours. A neutropenia generally occurred within 24 hours after stress and lasted about 5 days. A rectal temperature greater than 39 C usually did not occur. An increase in serologic titer was noticed in about half of the ponies. Transportation had a major role in reactivating the Salmonella infection, and 1 pony died of peracute colitis. The use of oxytetracycline prolonged the excretion of Salmonella; therefore, this drug should not be used after stress, particularly transportation, in ponies that have diarrhea or are known to be Salmonella carriers.