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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.

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 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.

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.

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.

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.

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 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.

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).

Lymphocyte stimulation was observed in whole equine blood in the presence of phytohaemagglutinin and M protein extracted from a typical strain of Streptococcus equi. Blood samples were collected from several healthy horses and horse and pony foals and cultured in vitro with varying concentrations of phytohaemagglutinin and M protein for several days. Phytohaemagglutinin was found to induce lymphocyte stimulation in these animals. Highest mean stimulation indices in horse foals (49.3 +/- 24.4) and pony foals (54.7 +/- 32.0) were observed with 0.625 and 1.25 micrograms/mL phytohaemagglutinin, respectively, at either 72 or 96 hours of incubation. Significantly higher radioactive counts per minute in horse and pony foals were recorded in blood cultures incubated with 0.625 and 1.25 micrograms/mL phytohaemagglutinin. M protein induced a dose related stimulation response in adult horses. Maximum stimulation indices were observed against 125 micrograms/mL M protein at 96 hours. These stimulation indices were higher in adult horses (40.0 +/- 2.2) than observed in pony foals (14.4 +/- 15.7). Higher stimulation levels in adult horses indicated either nonspecific stimulation against M protein or previous exposure of these animals to S. equi.

Mycoplasma organisms were readily recognized in samples of milk or udder secretions from cows with clinical Mycoplasma bovis mastitis when these samples were stained with 0.01% acridine orange at pH 3.0. Samples could be stored at -4 degrees C for several days or subjected to repeated freezing and thawing without loss of staining or fluorescence properties. Use of this procedure in diagnostic laboratories on suspect samples from cows with clinical mastitis could hasten inauguration of control measures against this highly contagious disease by several days; however, definitive diagnosis still requires standard culture methods.