Performance studies of an enzyme-linked immunosorbent assay for detecting Staphylococcus aureus antibody in bovine milk.

An enzyme-linked immunosorbent assay (ELISA) for detecting Staphylococcus aureus antibody in bovine milk samples was examined for repeatability. A set of 51 bovine milk samples from 4 universities with confirmed culture results was assembled, and a panel of 30 milk samples was randomly selected. When the selected panel was tested at the collection laboratory, there was 97% agreement between the ELISA and the culture test. The panel was tested with the ELISA by the 4 university laboratories. Results were scored by both visual and optical density reader methods. When compared to reference ELISA results, the university laboratory ELISA results showed an agreement of 99.8% for negative samples, 98% for positive samples, and 99% for all samples. Additional studies on 19 milk samples that cultured positive for bacteria other than S. aureus showed 100% specificity. Overall comparison of ELISA and culture results showed high agreement between the 2 techniques. Disagreement appeared to result from explainable differences in antibody and bacterial levels and not from errors in either of the 2 techniques.

Association of Mycobacterium paratuberculosis infection with reduced mastitis, but with decreased milk production and increased cull rate in clinically normal dairy cows.

Approximately 45 Holstein cows that were Mycobacterium paratuberculosis-positive on the basis of fecal culture results were maintained at any one time in a 210-cow dairy herd. Farm management participated in the New York State Paratuberculosis Eradication Program. Paratuberculosis-positive cows were grouped separately from paratuberculosis-negative cows, but they were otherwise managed identically. During a 1-year study, 180 paratuberculosis-negative cows and 113 clinically normal paratuberculosis-positive cows were identified. Quarter milk samples (n = 6,100) were aseptically collected for microbiologic culture of mastitis pathogens from paratuberculosis-negative cows, and 3,129 quarter samples were obtained from paratuberculosis-positive cows. Dairy Herd Improvement Association (DHIA) records were used to monitor milk somatic cell count linear scores, mature equivalent milk production, new mastitis infections, and chronic mastitis infections. For second-lactation cows greater than 100 days in milk production, and increasing with age beyond that point, paratuberculosis-positive cows had lower mature equivalent milk production than did negative herdmates. Rates of new and chronic mastitis infections, as measured by DHIA linear scores were significantly (P < 0.05, P = 0.05, respectively) lower in cows with nonclinical paratuberculosis. Infected cows were culled from the herd at a faster rate than were paratuberculosis-negative herdmates. Therefore, paratuberculosis was associated with financial loss attributable to reduced milk production and increased culling of infected cows.

Ecologic study of the risk factors for environmental mastitis in cows.

An index was developed to measure the proportion of intramammary infections caused by environmental microorganisms on dairy farms. This environmental index can be interpreted as the probability that an intramammary infection was caused by an environmental pathogen, rather than by a contagious pathogen. Using the environmental index as the outcome variable, risk factors for environmental mastitis were studied on 10 dairy farms in New York. Turning the cows outside was associated with lower environmental index, and having cows drink from a stream increased the environmental index. Selective (rather than uniform) nonlactating cow intramammary treatment was related to a lower environmental index (apparently because the farms practicing selective nonlactating cow treatment suffered from epizootics of contagious mastitis).

Efficacy of florfenicol for treatment of clinical and subclinical bovine mastitis.

OBJECTIVE: To evaluate efficacy of florfenicol treatment for bovine mastitis caused by Streptococcus agalactiae, Staphylococcus aureus nonagalactiae streptococci, coagulase-negative staphylococci, Escherichia coli, Klebsiella sp, and others. DESIGN: Double blind study with cases randomly assigned to 1 of 2 treatment groups. SAMPLE POPULATION: 861 cows/10 commercial dairy farms. PROCEDURE: Experimental (750 mg of florfenicol) or control (200 mg of cloxacillin) treatment was administered by intramammary infusion every 12 hours for 3 treatment to all cases. Treatments were randomly assigned identified only by numerical labels. To retain blinding, the longer withdrawal time was adhered to for all cases. Cases remained in the study only if there was no other treatment. Quarter samples were recultured 14, 21, and 28 days later. If all samples after day 1 were culture negative, the case was defined as cured. If only 1 of the follow-up results was positive, the case was considered cured if the day-28 somatic cell count was < 300,000/ ml. Failure of treatment was defined as 2 or more culture positive follow-up samples. RESULTS: Florfenicol and cloxacillin did not differ significantly in efficacy versus clinical (n = 85) or subclinical (n = 71) bovine mastitis, or for any etiologic agent (X2). Overall cure rates for mastitis were: Str agalactiae, 5 of 8 (63%); Sta aureus, 5 of 54 (9%); Streptococcus sp, 16 of 35 (46%); Staphylococcus sp, 7 of 33 (21%); E coli, 5 of 11 (46%); Klebsiella sp, 3 of 6 (50%); others, 1 of 9 (11%); and all cases, 42 of 156 (27%). CONCLUSIONS: Florfenicol did not offer any advantage over cloxacillin in efficacy against bovine mastitis. Overall cure rates were low. As with most mastitis treatment regimens poor efficacy may be partly attributable to the short duration of treatment.

Isolation of L-form variants after antibiotic treatment in Staphylococcus aureus bovine mastitis.

An unstable L-form of Staphylococcus aureus was identified in milk samples from 3 quarters of 2 cows after treatment with cloxacillin. Milk samples incubated on standard 5% blood agar plates were culture-negative for 7 to 30 days after treatment, but S aureus was reisolated in 80% of 66 samples by additional culturing on enriched L-form media when incubated in 10% CO2 at 37 C. The organism was identified at various phases of reversion of L-form agar and was confirmed on transfer to blood agar plates.

Milk production, water consumption, and somatic cell count responses of cows subject to one to two volts of alternating current.

A dairy farm located in central New York was visited because of complaints of electrical shock in the farmhouse shower and the milk house sink. As much as 2 volts AC of potential difference was measured between the waterline and the cow platform (cow-contact voltage). Voltage was coming from the primary neutral wire. The farm's electrical service was modified so that the farmstead could be connected or disconnected from the primary neutral wire at 2-week intervals for 12 weeks. When connected to the primary neutral wire, voltage between waterline and floor ranged between 0 and 1.8 volts, producing estimated current flow through cows of 3.6 to 4.9 mA; when disconnected from primary neutral wire, voltage between waterline and floor was less than 0.1 volt. There was no difference in mean milk production, bulk tank milk somatic cell count, or water consumption among periods when cows were exposed or unexposed to voltage. Despite statistical nonsignificance, the values for somatic cell count were lower and water consumption was higher when cows were exposed to voltage than when they were not.

Association between management practices, dairy herd characteristics, and somatic cell count of bulk tank milk.

OBJECTIVE: To determine whether particular dairy management practices and herd characteristics were associated with somatic cell count (SCC) of bulk tank milk. DESIGN: Analysis of records. SAMPLE POPULATION: Milk samples collected from 59,435 cows housed in 843 dairy herds between March 1992 and June 1994. PROCEDURE: Results of bacterial culture of milk samples and data on farm housing, sanitation, milking system, and management were collected. Multiple regression analysis was used to determine sources of variation in bulk tank milk SCC among herds. RESULTS: Prevalence of Streptococcus agalactiae and Staphylococcus aureus mastitis was associated with bulk tank milk SCC. In herds free of S agalactiae mastitis, prevalence of S aureus and Corynebacterium bovis mastitis were important. For herds without S agalactiae mastitis, use of sawdust bedding was associated with a decrease in SCC and a dirty loose housing area was associated with an increase. Increased milk production, repeated mastitis control visits, and use of particular predip compounds were significantly associated with reduced SCC in all herds, regardless of whether any cows in the herd had S agalactiae mastitis. In herds with S agalactiae mastitis, use of iodine (certain concentrations), chlorhexidine, peroxide, or sodium chlorite-lactic acid as a predip was associated with a decrease in SCC. Only use of sodium chlorite-lactic acid predip was significantly associated with a decrease in SCC in herds without S agalactiae mastitis. CLINICAL IMPLICATIONS: Important factors associated with bulk tank milk SCC were prevalence of S agalactiae and S aureus mastitis, careful application of particular predip compounds, avoiding a dirty loose housing area, and use of a service to regularly monitor prevalence of mastitis in the herd.

Procedures for mastitis diagnosis and control.

Procedures for mastitis diagnosis and control include culturing individual cow and bulk tank milk samples, antibiotic susceptibility testing, and evaluation of somatic cell count reports and clinical mastitis treatment records. Integrated use of such procedures is necessary for effective mastitis diagnosis and control.

Immunization and immunity.

The defense mechanism of the mammary gland is a complex system in which each component's function is not independent of the other. The various components of nonspecific resistance, antibody production and cell-mediated immune response can act to the benefit or detriment of the host. Our ability to predict and control each of these responses is limited. Zealous efforts to enhance one area irrespective of the others may not work to the benefit of the animal. High antibody levels have not always provided protection against mastitis, whereas cell-mediated responses may produce either a beneficial or harmful hypersensitivity response. Until antigenic effects are better understood and product safety is assured, vaccination against mastitis will be limited in its beneficial value. The use of biologic products may eventually become a practical approach in controlling mastitis by maintaining herd resistance; however, these products are no substitute for a good mastitis control program of teat dipping, dry-cow therapy, milking-equipment maintenance, proper milking sanitation, and good milking practices. Mastitis control cannot be purchased in a bottle.

N-acetyl-beta-D-glucosaminidase, etiologic agent, and duration of clinical signs for sequential episodes of chronic clinical mastitis in dairy cows.

This study examined effects of repeated episodes of clinical mastitis in chronically infected quarters on milk N-acetyl-beta-D-glucosaminidase activity and duration of clinical signs. Milk samples were collected at each clinical onset from 49 chronic mastitis cases on a 1700-cow Michigan dairy farm. There were 49 first episodes of clinical mastitis, 49 second episodes, and 13 episodes of third or more. Agents isolated were Staphylococcus aureus (18.4%), Staphylococcus (7.3%), no growth (20.2%), environmental pathogens (streptococci other than agalactiae, Escherichia coli, Klebsiella spp., Enterobacter spp., and Citrobacter spp.) (22.0%), other pathogens (Serratia spp., Bacillus spp., diphtheroids [Corynebacterium spp. and Actinomyces pyogenes], Pseudomonas spp., and Nocardia spp.) (11.9%), mixed pathogens (two agents isolated) (12.8%), and contaminated samples (7.3%). Etiologic agents, duration of clinical signs, and NAGase did not differ by episode number. The correlation between log of NAGase and log of time until clinical recovery was .34. The relationship between NAGase and duration of clinical signs was strongest for second episodes, and weakest for third and greater episodes of chronic mastitis.

Association between neutral-to-earth and cow contact voltage on New York dairy farms.

Cow contact (or "stray") voltage has been associated with various health and management problems in dairy cows. Neutral-to-earth voltage (voltage between the service entrance neutral bus and a reference ground rod) has been equated with cow contact voltage in previous research. To investigate the association between these two voltages, single ("instantaneous") and continuous voltmeter measurements were made at 97 farms in New York. A small positive correlation was found between all single neutral-to-earth and cow contact measurements. Eleven farms with continuous neutral-to-earth readings of .5 V or greater were resurveyed. Eight of the resurveyed farms showed a small or nonexistent correlation between the two voltages. Neutral-to-earth voltage is not recommended as an indicator to predict the presence or magnitude of cow contact voltage.

Segregation or use of separate milking units for cows infected with Staphylococcus aureus: effects on prevalence of infection and bulk tank somatic cell count.

Dairy herds (n = 76) with an initial prevalence of Staphylococcus aureus IMI > or = 10% were included in this study. Criteria were that herds did not change teat dipping or dry cow treatment practices, did not segregate cows that were positive for S. aureus at the initial visit, and did not cull > 50% of cows found to be positive on the initial visit. During a follow-up period (6 to 24 mo), segregation or separate milking of cows that were positive for S. aureus reduced prevalence from 29.5 to 16.3% and bulk tank SCC from 600,000 to 345,000/ml. Prevalence of S. aureus mastitis was unchanged for herds that did not segregate cows with S. aureus, 22.5 to 20.2%, and the reduction in SCC from 698,000 to 484,000 for nonsegregated herds was also smaller. Segregation of cows that were known to be positive for S. aureus is an effective mastitis control practice.

Use of augmented cultural techniques in the diagnosis of the bacterial cause of clinical bovine mastitis.

Preculture incubation, preculture freezing, and increased plate inoculation volumes were tested in an attempt to increase the recovery rate of pathogens in milk from cases of clinical bovine mastitis. Culture of milk from 291 cases of clinical bovine mastitis was performed using standard milk culture techniques (.01 ml of fresh milk streaked on trypticase soy agar plates with 5% sheep blood and .1% esculin). The sensitivity of this method was compared with that of cultures performed using augmented techniques: 4 and 18 h of preculture incubation; preculture freezing of samples overnight at -20 degrees C; and increasing the plate inoculation volume to .05 and .1 ml for fresh, incubated, and frozen samples. Preculture incubation and larger plate inoculation volumes significantly increased the recovery rate of bacterial pathogens over the standard culture method. The greatest improvement in sensitivity without a concomitant increase in contamination was achieved when samples were incubated for 4 h and plates were inoculated with .1 ml of the sample. Recovery was enhanced significantly by this method for several organisms, including environmental streptococci and coliform bacteria. Freezing milk before culture yielded a significantly higher positive culture rate overall, but freezing did not affect the positive culture rate of any individual bacterial species.

Effect of milk sample delivery methods and arrival conditions on bacterial contamination rates.

A cross sectional study was performed of factors believed to contribute to the contamination of bovine milk sample cultures submitted to the Ithaca Regional Laboratory of the Quality Milk Promotion Services/New York State Mastitis Control. Of 871 samples entered in the study, 137 (15.7%) were contaminated. There were interactions between the sample source (veterinarian vs dairyman), delivery method, and time between sample collection and arrival at the laboratory. If only those samples collected and hand delivered by the dairyman within 1 day of collection were compared to a like subset of samples collected and hand delivered by veterinarians, no statistically significant differences in milk sample contamination rate (MSCR) were found. Samples were delivered to the laboratory by hand, US Postal Service, United Parcel Service, via the New York State College of Veterinary Medicine Diagnostic Laboratory, or Northeast Dairy Herd Improvement Association Courier. The MSCR was only 7.6% for hand delivered samples, while 26% of Postal Service samples were contaminated. These rates differed significantly from other delivery methods (P less than 0.0001). The USPS samples arrived a longer time after sampling than did samples sent by other routes, and time had a significant effect on MSCR (0 to 1 day, 8.9%; greater than 1 day, 25.9%; P less than 0.01). Samples packaged with ice packs sent by routes other than the Postal Service had a lower MSCR than those not packaged with ice packs, but ice packs did not reduce the MSCR for samples sent by the Postal Service.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison between tail vein and jugular vein cannulation in cattle.

Blood samples obtained simultaneously from the jugular and tail (coccygeal) veins during induction of bovine mastitis infection and after administration of 250 IU of adrenocorticotropin did not differ in percentage of hematocrit, concentration of total corticosteroid in plasma, or concentrations of total circulating erythrocytes and leukocytes. Patency of the tail vein cannula was maintained for 1 mo. Tail vein cannulation is a practical alternative to jugular cannulation in cattle.

Microbiological results from milk samples obtained premilking and postmilking for the diagnosis of bovine intramammary infections.

Bacteriological culture results were compared between 336 pairs of quarter milk samples collected premilking and postmilking. Using a positive result on either premilking or postmilking samples as the definitive diagnosis, premilking sampling sensitivity was 91% for Staphylococcus aureus, 91% for coagulase-negative staphylococci, and 97% for Streptococcus other than agalactiae. Postmilking sampling sensitivities were 81, 45, and 58%, respectively, for the same pathogens. Requiring both premilking and postmilking samples for the definitive diagnosis, specificities were 92, 86, and 95% for premilking sampling alone and 96, 98, and 99% for postmilking sampling alone. Such differences in specificity would result in major differences in predictive value of a positive culture for herds with a low prevalence. Multiple isolates were significantly more common from premilking samples.

Mastitis due to Mycoplasma in the state of New York during the period 1972-1990.

Between January 1972 and December 1990, bulk-tank (n = 721) and cow (n = 9,163) milk samples from dairy herds in New York State were examined by bacteriologic procedures for Mycoplasma. The organism was found in 165 herds in 42 counties, and in 2.3 and 11.7% of the tank and cow samples, respectively. Mycoplasma bovis was isolated in 164 herds, M. californicum was isolated in 1. Highest incidence of mycoplasmal clinical mastitis occurred during the winter. The disease resulted in culling of 30-70% of the cows in several herds. Eighty-six of the positive herds were located in the western part of the state. This area had more large herds (greater than 200 cows) compared to the rest of the state; however, herd size was not a risk factor. Purchased animals added to herds without quarantine, poor hygiene during mastitis treatment, and personnel in contact with mastitic cows or infected milk were involved in outbreaks and disease transmission.

Efficacy of postmilking disinfection with benzyl alcohol versus lodophor in the prevention of new intramammary infections in lactating cows.

Five Michigan dairy herds participated in a split-herd study to compare the efficacy of two postmilking teat dips in the prevention of new intramammary infections (IMI) in lactating cows. Three hundred seventy cows were assigned to 4% benzyl alcohol, and 387 cows were assigned to 1% iodophor germicidal teat dip. The teat dips were applied by directly immersing the teats immediately after milking. Once a group was assigned to a teat dip, cows in that group maintained on that same teat dip throughout the trial. Total new IMI numbered 254 and 201 for cows treated with benzyl alcohol and iodophor germicidal teat dip, respectively. Staphylococcus spp. (52.0%), Staphylococcus aureus (20.1%), and Corynebacterium bovis (12.2%) were the predominant pathogens that caused new IMI in cows treated with benzyl alcohol. Staphylococcus spp., Staph. aureus, and C. bovis, respectively, were the pathogens responsible for 69.7, 12.4, and 4.5% of the new IMI in cows treated with iodophor. The incidences of new IMI caused by Staph. aureus (0.66 new IMI/100 milking quarters per mo), C. bovis (0.38 new IMI/100 milking quarters per mo), and all pathogens (3.15 new IMI/100 milking quarters per mo) were higher in cows treated with benzyl alcohol than in cows treated with iodophor (0.29, 0.11, and 2.35 new IMI/100 milking quarters per mo, respectively). Incidence of new IMI did not differ between groups for other pathogens. One percent iodophor prevented new IMI caused by contagious pathogens more effectively than did benzyl alcohol.

Evaluation of methods for the diagnosis of Streptococcus agalactiae intramammary infections in dairy cattle.

The sensitivity, specificity, and positive and negative predictive values were compared for six methods of collecting or culturing milk samples for the diagnosis of chronic Streptococcus agalactiae intramammary infection. Cows in four dairy herds were cultured three times in 2 wk to determine infection status. At the second sample period, individual quarter and composite milk samples were taken before and immediately after milking, and two volumes of milk from the composite samples were streaked on culture plates. The sensitivity, specificity, and predictive values for these cultures ranged between 95 and 100% for all diagnostic methods, and no significant differences were found between methods. The results indicate that when either quarter or composite samples are collected before or immediately after milking, 95 to 100% of S. agalactiae culture-positive cows will be infected with S. agalactiae in herds with a prevalence of S. agalactiae between 35 and 55%. A similar proportion of culture-negative cows will be uninfected.

Effectiveness of educational efforts in implementing mastitis control procedures in commercial dairy herds.

One hundred-fifty diarymen in north-eastern Ohio, whose herds had a history of persistently high Wisconsin Mastitis Test scores, were invited to participate in this project, with 43 agreeing to do so. These dairymen were divided into two experimental groups and one control group to determine the effectiveness of two intensities of educational effort on adoption of mastitis control procedures and to demonstrate the effectiveness of mastitis control recommendations. A teat dipping and dry cow therapy program was adopted by more herds in the group with intense educational effort than in the intermediate or control group. Percents of herds in each group utilizing this program in 1977 (start of project), 1978, and 1979 were 8, 75, and 92 for the intense group; 30, 50, and 50 for the intermediate group; and 10, 27, and 27 for the control group. Prevalence of infection declined more rapidly in the intense group with 42, 28, and 24% of cows infected; 39, 25, and 30% in the intermedia, and 56, 35, and 42% in the control group in 1977, 1978, and 1979. Those herds adopting a teat dipping and dry cow therapy program had infection prevalence of 41, 25, and 20% of cows; bulk tank Wisconsin Mastitis Test scores of 15.5, 14.7, and 11.4; and milk production per cow per day of 18.4, 18.4, and 17.5 kg in 1977, 1978, and 1979.