Mycoplasma mastitis: a review of transmission and control

The Mycoplasma sp. that cause mastitis are simple, cell wall-less, bacteria that can colonize and cause diseases in other extramammary sites in the bovine. Prevalence of mycoplasma mastitis appears to be increasing in many locations throughout the world. The best method to identify this group of pathogens is through direct culture on mycoplasma agar media. However, limitations with this culture procedure are the duration of culture, 10 days, special conditions required and thus added expense, and the lack of primary specificity to distinguish between true pathogens and commensal organisms. Thus culture of bulk tank milk samples has been advocated as a primary screening method to determine the mycoplasma status of a herd. This monitoring system is reasonably successful but the sensitivity of detection of Mycoplasma sp. in bulk tank milk is affected by a significant minority of cows that might shed the organism at levels below the threshold of detection. Contagious mastitis control procedures have been effective in controlling outbreaks of mycoplasma mastitis. Yet new methods of control might be warranted, methods that may prevent the outbreak. Current data suggests that a significant number of new outbreaks may occur via internal or animal-to-animal transmission of mycoplasma mastitis pathogens from asymptomatic carriers.     

Prevalence of contagious mastitis pathogens in bulk tank milk in Prince Edward Island

The purpose of this study was to 1) estimate the herd prevalence of contagious mastitis pathogens in bulk milk from Prince Edward Island (PEI) dairy farms, 2) determine the association between bulk milk culture results and mean bulk milk somatic cell count (BMSCC), and 3) investigate the agreement of repeated bulk milk cultures. Three consecutive bulk milk samples were obtained at weekly intervals from all 258 PEI dairy herds and were cultured using routine laboratory methods. Cumulative prevalence of Staphylococcus aureus, Streptococcus agalactiae, and Mycoplasma spp. (M. bovis and M. alkalescens) was 74%, 1.6%, and 1.9%, respectively. Bulk milk somatic cell count of Staph. aureus-positive herds was higher than that of negative herds. Agreement for Staph. aureus isolation between 3 consecutive tests was moderate (kappa = 0.46). Mycoplasma bovis and M. alkalescens in bulk milk are being reported for the 1st time in PEI ever and in Canada since 1972.     

Between-herd prevalence of Mycoplasma bovis in bulk milk in Flanders, Belgium

Mycoplasma bovis (M. bovis) is a highly infectious pathogen of cattle causing pneumonia, polyarthritis, otitis, and less frequently, subcutaneous abscesses, abortions and meningitis. Ineffective drugs treatments, culling of infected cows and loss of milk production can lead to significant economic loss on dairy farms. The early detection of cows excreting M. bovis bacteria to prevent mastitis outbreaks is warranted. Reports suggest that the risk of M. bovis mastitis is higher in larger dairy herds. The objective of this study is to estimate the herd-level prevalence of M. bovis in Flanders, Belgium by culturing bulk tank milk samples taken from dairy farms. Three bulk tank milk samples per dairy herd were taken over four weeks, with collection intervals of two weeks. Culturing was done after pre-incubation using modified Hayflicks media to increase the chances of recovery of bacteria. For the identification of M. bovis, tDNA intergenic spacer PCR was used. In three herds (1.5%) of the 200 herds sampled, M. bovis was isolated from one of the three consecutive bulk tank milk samples. We conclude that in Flanders in 2009 at least 1.5% of the dairy herds had one or more cows excreting M. bovis in the milk. The frequent monitoring of bulk tank milk to detect the presence of M. bovis, especially in expanding herds on farms that often purchase replacement animals, should be encouraged in order to detect the presence of M. bovis and to monitor the success of control procedures following an outbreak of mycoplasmal mastitis in the herd.     

Relationship between mastitis pathogen numbers in bulk tank milk and bovine udder infections in California dairy herds

Samples of bulk tank milk and cow-composite milk from 23,138 dairy cows from 50 California dairies were examined by use of microbiologic procedures. The number of colonies of mastitis pathogens isolated per milliliter of bulk tank milk (used as a predictor of the percentage of infected cows in the herd) was evaluated, using simple regression analysis and Spearman's rank correlation. Correlations between the pathogens and the percentage of cows in each herd shedding the pathogens were found for Streptococcus agalactiae (r = 0.71) and mycoplasma (r = 0.59), but were considerably lower for other pathogens. When greater than or equal to 4,000 colonies of Streptococcus agalactiae were found per milliliter of bulk tank milk, at least 7% of the cows in the herd was shedding this organism. However, a pattern was not found between the number of mycoplasma colonies per milliliter of bulk tank milk and the percentage of infected cows in the herd.     

Incidence and transmission of Mycoplasma bovis mastitis in Holstein dairy cows in a hospital pen: A case study

The objective was to determine the incidence and transmission of mycoplasma mastitis in the hospital pen in a dairy herd of 650 lactating cows after a hospital pen was established following an outbreak of this disease. Mycoplasma mastitis status was monitored for 3 months through repeated collection of milk samples from cows with clinical mastitis (CM) and from bulk tank milk. During the outbreak 13 cows were diagnosed with Mycoplasma bovis CM, 1 cow with Mycoplasma sp. mastitis and 8 cows showed signs of arthritis, 3 of which were confirmed as having M. bovis arthritis. M. bovis isolates from cows with CM, arthritis and bulk tank milk had indistinguishable chromosomal digest pattern fingerprints. Incidence rates of M. bovis CM cases in the milking and hospital pens were 0.01 and 1.7 cases per 100 cow-days at risk. Approximately 70% of cows with M. bovis CM became infected within 12 days of entering the hospital pen. Transmission of M. bovis in the hospital pen occurred as 3 episodes. Each episode corresponded to the introduction of a cow with M. bovis CM from a milking pen. Evidence indicates that cows with M. bovis CM from milking pens were the source of transmission of the disease in the hospital pen and thus their presence in the hospital pen appeared to be a risk factor for transmission of M. bovis mastitis in this single case study herd.     

Culture of bulk tank milk as a mastitis screening test: A brief review

The culture of a sample of bulk tank milk may be a useful technique by which to screen herds for major mastitis pathogens. Staphylococcus aureus and Streptococcus agalactiae, if identified on a culture of a sample of bulk milk, reliably indicate infection of the udder. Environmental bacteria, such as the other streptococci and coliforms, are unlikely to be indicative of the proportion of cows infected with these organisms.Samples of bulk milk are readily obtainable and can be rapidly and inexpensively cultured to screen large numbers of herds for mastitis-causing bacteria, yet the performance of the test has only recently been formally assessed for its ability to correctly classify herds according to infection status.A single culture of bulk tank milk has been found to be a test with low sensitivity and high specificity for determining the presence of S. agalactiae or S. aureus in the herd. This means that many infected herds will be called negative, but few uninfected herds will be classified as positive.The literature assessing the performance of bulk tank milk culture in comparison with other mastitis screening tests, the use of bulk milk culture for prevalence surveys, and factors affecting these results is discussed.     

Coagulase-positive staphylococcal mastitis in a herd with low somatic cell counts

An increase in clinical mastitis infections was observed in a high-producing 77-cow Holstein herd. Low bulk tank somatic cell counts and individual cow Dairy Herd Improvement Association somatic cell counts observed before, during, and after the epizootic were suggestive of herd environmental mastitis. However, bacteriologic culture survey of the total herd indicated that, in addition to infections possibly attributable to environmental pathogens, 22% (17/77) of the cows were infected with coagulase-positive Staphylococcus spp. Conceivably, investigative efforts and management changes, without bacteriologic culturing, might have resulted in reduction of the clinical infection rate in this herd. However, the continued high prevalence of a contagious pathogen with potential future implications would have gone unnoticed. Somatic cell count in milk from individual cows generally is a useful tool for monitoring the probability of intramammary infection, but must be complemented with bacteriologic culture of milk to determine whether contagious or environmental pathogens are responsible.     

Aetiology of clinical mastitis in six Somerset dairy herds.

Clinical mastitis was monitored in six Somerset dairy herds for one year. The herds all had three-month geometric mean bulk milk somatic cell counts of less than 250,000 cells/ml. Escherichia coli was the predominant pathogen isolated on all the farms and in all months of the year. Environmental pathogens accounted for 61.4 per cent of all cases of clinical mastitis and for 79.3 per cent of the mastitis cases in which an aetiological agent was identified. The mean annual incidence was 41.6 cases per 100 cows (range 14 to 75). Affected cows suffered a mean of 1.5 cases and 16.4 per cent of quarters suffered at least one repeat case. Mastitis due to E. coli was more severe than mastitis due to other causes and it tended to be more severe in early lactation and during the housing period. Mastitis was significantly more severe (grades 2 and 3) in the herd with the lowest bulk milk somatic cell count and in the herd which was kept indoors throughout the year than in the other four herds. Mastitis was fatal in 2.2 per cent of cases and resulted in the death of 0.6 per cent of the lactating cows.     

The use of high somatic cell count prevalence in epidemiologic investigations of mastitis control practices

A series of least-squares analytical models were developed in a cross-sectional epidemiologic study of the observed variability in within-herd high somatic cell count (SCC) prevalence, a measure of mastitis prevalence in dairy herds. The dependent variable, high SCC prevalence, was calculated as the 12-month rolling herd average percentage of lactating cows with milk SCC in excess of 283 000 cells ml⁻¹.

The first analysis involved the results of a bacteriologic survey of bulk-tank milk samples for the presence of Streptococcus agalactiae and coagulase-positive staphylococci, the two most common contagious intramammary pathogens. The presence of either pathogen in bulk-tank samples was associated with significantly higher high SCC prevalence.

The second analysis involved responses to a questionnaire concerning management and mastitis control practices. Both the practices of post-milking teat dopping and dry-cow antibiotic therapy were associated with significantly lower high SCC prevalence.

The third analysis combined the data collected for the first two analyses so that the independent variables included both bulk-tank bacteriologic results and management and mastitis control practices. This model was able to explain a greater proportion of the variability in high SCC prevalence than either of the other two models. There were three variables associated with significant decreases in high SCC prevalence namely the absence of Streptococcus agalactiae in the bulk tank milk, the adoption of post-milking teat dipping and the practice of dry-cow antibiotic therapy of all cows.

Milk somatic cell counting is now widely accepted and practiced in many countries, and individual-cow SCC data are available from large numbers of herds at a minimal expense. By corroborating the role of post-milking teat dipping and dry-cow antibiotic therapy in mastitis control programs, this study establishes the usefulness of high SCC prevalence data for epidemiologic studies of mastitis control practices.     

Clinical Bovine Mycoplasmal Mastitis: An Epidemiologic Study of Factors Associated with Problem Herds

The California Dairy Herd Improvement Association records of 29 California dairies which experienced clinical mycoplasmal mastitis between January 1975 and December 1977 were examined and compared to the records of selected control herds. A 15-fold greater risk of clinical mycoplasmal mastitis was found among large herds as compared to small herds. On average, herds with clinical mycoplasmal mastitis culled 5 % more cows than did control herds (33 % vs 28 %). No difference was found in average milk production. These findings compare closely with the findings of a previous report where infected herds were identified by the presence of pathogenic mycoplasma in bulk tank milk. The similarity of results support the use of frequent bacteriologic culture of bulk tank milk as a routine surveillance strategy for mycoplasmal mastitis in endemic areas. The similarity of results also supports the use of routine clinical diagnostic data in the study of the epidemiology of diseases of veterinary importance.     

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.     

Prevalence of mycoplasmal bovine mastitis in California

Seven species of mycoplasma plus one or more unknown species were found to cause bovine mastitis in California. Both the frequency of cases and number of species of mycoplasma in samples received at the laboratory have increased from 1976 to 1978. By survey, nearly 4% of samples of bulk tank milk from dairy farms were found to contain mycoplasma of potential pathogenic significance. Acholeplasma laidlawii was frequently isolated from samples both from cows and from farm bulk tanks during wet, rainy weather in the spring of 1978, apparently as contaminants only. The prevalence of positive bulk tank milk samples in an area appeared to parallel the prevalence of clinical mycoplasmal mastitis problem herds.     

An investigation of risk factors for nocardial mastitis in central Alberta dairy herds

A case-control study was undertaken during the summer of 1989 in central Alberta dairy herds to identify independent predictors of nocardial mastitis. Thirty-seven herds with nocardial mastitis were matched with control herds based on herd size, milk production, and enrolment in Alberta Dairy Herd Improvement Services. Control herds were considered free of nocardial mastitis based on negative cultures of four weekly bulk tank milk samples and one composite milk sample collected during the same period from each lactating cow in the herd. A detailed questionnaire on herd management was completed during farm visits. The use of blanket dry cow therapy was not found to be a risk factor for nocardial mastitis. Dry cow therapy with intramammary products containing neomycin and the use of multidose vials of dry cow medications were the only predisposing factors identified as being significantly associated with nocardial mastitis in central Alberta dairy herds. Use of neomycin as a dry cow therapy increased the odds of nocardial mastitis occurring in these dairy herds by 169 times.     

Isolation of Mycoplasma bovis from bulk milk

The prevalence of mycoplasma in Vermont dairy farms was determined by two surveys conducted in March 1983 and January 1984. Bulk tank milk samples representing 74% and 62% of the herds respectively were cultured. Mycoplasma bovis was detected in 3 of the 2,346 bulk samples collected in the initial survey. The infection rate was 1.3 herds per thousand (95% confidence interval: 0.6-2.0 herds per thousand). No positive cultures were obtained in the second survey.     

An investigation of bulk tank milk selenium levels in the San Joaquin Valley of California

We evaluated selenium determination of bulk milk tank samples as an alternative to testing blood selenium for evaluating herd selenium status in DHIA dairy herds in the San Joaquin Valley of California. A method of determining milk selenium levels using inductively coupled plasma spectrometry is described. Mean bulk tank milk selenium levels were 0.0224 mg/L (Range 0.0126-0.0418 mg/L). No statistically significant relationships were found between bulk tank milk selenium levels of a herd and calving interval, days open or log somatic cell counts. Mean herd blood and milk levels were directly proportional to bulk tank milk selenium levels. Within a herd milk selenium levels of a cow were directly proportional to the cow's blood selenium level. Herd selenium levels were not significantly related to soil selenium levels. Determination of bulk tank milk selenium levels has the potential to be a low cost, non-invasive means of evaluating herd selenium levels in order to determine selenium deficiency. Further studies with this technique in areas which are deficient in selenium may provide estimates of the sensitivity, specificity and predictive value of bulk milk tank selenium for determining selenium deficiency in dairy herds.     

Bulk milk urea concentrations and their relationship with cow fertility in grazing dairy herds in southern Chile

Milk urea determination is being used as a broad indicator of protein/energy imbalance in dairy herds. The main purpose of this study was to compare blood and bulk milk urea values in grazing herds, to evaluate their seasonal variation under South Chilean conditions, and to examine their potential relationships with herd fertility. The association between herd blood urea concentration (mean of seven lactating cows) and bulk milk urea concentration (tank containing milk from the previous 24 h) was determined in 21 diary herds. Reference values, seasonal and herd variance, and the frequency of herds with values outside a range of 2.5 to 7.3 mmol/l were determined in bulk milk samples obtained monthly for a period of one year from 82 suppliers at two creameries located in southern Chile. Finally, bulk milk urea was measured every two weeks in samples from 24 herds, and the first service conception rate (FSCR) from 2153 dairy cows was determined. Mean bulk urea concentration was highly correlated with mean herd blood urea concentration (r = 0.95; p < 0.01). Mean urea concentration in the bulk milk samples obtained during one year from 82 herds was 4.9 +/- 1.2 mmol/l, with a range of 1.5 to 11.6 mmol/l. The highest values were found during spring and the lowest values during the summer. There was a high seasonal variation (CV = 13-47%) and between-herd variation (CV = 20-31%). Out of a total of 984 samples, 5.4% had urea values > 7.3 mmol/l and 3.8% had values < 2.5 mmol/l. Of the 82 herds, 27% had values outside the reference interval (2.5-7.3 mmol/l) on two or more occasions. FSCR was lower in herds when the bulk milk urea was > 7.3 mmol/l (50.7%) than in cows, where the urea concentration was < 5.0 mmol/l (73.8%) at the time of insemination. The study concluded that bulk milk urea concentrations provided information similar to herd blood urea concentrations in local grazing dairy herds. There was a high frequency of herds with abnormal values, with large variations between herds and between seasons. Increased milk urea concentrations during spring were associated with lower conception rates.     

Mastitis, polyarthritis and abortion caused by Mycoplasma species bovine group 7 in dairy cattle

OBJECTIVE: To report an outbreak of mastitis, polyarthritis and abortion caused by Mycoplasma sp bovine group 7 in three large, centrally-managed dairies and to review the relevant literature. DESIGN: Epidemiological, clinical and laboratory data were analysed, collated and reported. Multidisciplinary procedures were employed. These included clinical assessment and comprehensive laboratory investigations of affected calves, aborted foetuses and milk samples. Mycoplasma cultures and genetic analyses of isolates were undertaken to identify the aetiological agent. RESULTS: About 30% of 240 calves usually kept in a calf rearing facility developed severe polyarthritis as a result of Mycoplasma sp bovine group 7 infection between 2 and 3 weeks of age. Multiple abortions occurred on these farms. Mycoplasma sp bovine group 7 was recovered from the fibrinopurulent synovial exudates of four 14-day-old calves, from the stomach contents and lungs of two aborted foetuses, from 14 of 21 bulk milk and four of 10 mastitic quarters. Three bulk colostrum samples cultured during the outbreak were negative for mycoplasma. CONCLUSION: Mycoplasma sp bovine group 7 caused significant economic losses as a result of polyarthritis, abortion and mastitis. The disease probably originated from udder infections with spread being facilitated by the decreased use of tetracycline in the treatment of mastitis. Neonatal calves were most likely infected by the consumption of milk contaminated with the organism. Abortions presumably resulted from mycoplasmaemia. This appears to be the first report in Australia of bovine abortion resulting from Mycoplasma sp infection.     

Epidemiological Study of Non‐contagious Intramammary Infections in Nine Commercial Dairy Herds following a Staphylococcus aureus Control Programme

Changes in prevalence in intramammary infection, by pathogen type, in herds applying a stringent contagious mastitis control programme was studied. Enrollment of 1651 lactating cows and collection of milk samples was made in this ancillary study to a cohort study of the dynamics of mastitis prevalence after adoption of a strict contagious mastitis control programme that targeted the elimination of mastitis caused by Staphylococcus aureus. Nine commercial dairies in Italy were used. Aseptic collection of milk samples from all lactating cows was performed at the time of enrollment, from all cows within 7–14 days of entering the lactating herd after the date of enrollment, and from all lactating cows at 2, 4, 7, 10 and 14 months after the date of enrollment. Prevalence of intramammary infection by pathogen type was determined from culture of milk samples. Application of the strict contagious mastitis programme did not lead to an increased risk of non‐contagious mastitis. The risk of coliform, environmental streptococcal and coagulase‐negative staphylococcal intramammary infections decreased after adoption of the programme. The data reported herein indicate that the overall risk for any intramammary infections decreases with adoption of a strict contagious mastitis programme, and that such a programme therefore does not necessarily lead to an increase in environmental mastitis.     

Bulk tank milk urea nitrogen: Seasonal patterns and relationship to individual cow milk urea nitrogen values

The objectives of this study were: 1) to determine if bulk tank milk urea nitrogen (BTMUN) and whole herd weighted average of the individual cow MUN levels (WHMUN) were equivalent measurements of herd MUN status; and 2) to determine the seasonal variation in BTMUN concentrations in Prince Edward Island (PEI) dairy herds. For BTMUN-WHMUN correlation testing, bulk tank milk samples from 176 herds were tested for MUN once every 1 to 2 wk between September 1999 and August 2002, as part of routine BTM testing for milk components. During this 3-year period, all herds had all milking cows tested for MUN once a month at the same lab. The WHMUN levels (weighted for milk production) were calculated for each month, and were compared to BTMUN levels using a concordance correlation coefficient (CCC) and a graphic procedure. Tests were only compared if they occurred on the same date, producing a final dataset of 669 comparisons. The BTMUN had good (but not perfect) correlation with WHMUN (CCC = 0.91). This high reliability extended to both the pasture and non-pasture seasons, various milk sampling protocols, and all herd sizes seen in PEI. For evaluating the seasonal variation of BTMUN, the 3 y worth of data (24 803 observations) were divided into 15 seasonal categories, 5 seasons per year (early, mid, and late pasture, and early and late stable). Using linear mixed modelling, significantly (P < 0.05) higher BTMUN values were found during the mid and late pasture seasons of 2000, likely because the precipitation was unusually high during this period, enhancing pasture growth.     

Bovine mastitis in Ontario due to Mycoplasma agalactiae subsp. bovis.

Bovine mastitis caused by Mycoplasma agalactiae subsp. bovis was first diagnosed in 16 of 55 cows in an Ontario herd in Feburary 1972. A total of 182 of 598 (30.4%) cows from 33 of 64 (51.5%) farms in widely separated areas of the province were culturally positive. Herd incidence varied from 15 to 40% with one closed herd having an incidence of 61%. Four herds were investigated culturally and serologically by the growth inhibition test for 15 months. In the acute phase the organism was present in the milk in extremely high numbers and could still be isolated from a few cows after eight to 12 months. The sera from 89.5% of the animals with clinical mycoplasma mastitis produced a zone of surface "film" and/or colony inhibition and some cows remained positive for six to 12 months. The disease was experimentally reproduced with a pure culture of the organism isolated from the milk of a cow from one of the herds.