The Persistent Isolation of Salmonella typhimurium from the Mammary Gland of a Dairy Cow

The contamination of cheese by Salmonella typhimurium serotype 10 resulted in the bacteriological examination of raw milk from 327 farms on Prince Edward Island. A milk sample from a bulk tank from one farm was positive for this pathogen. The possible source was linked to the isolation of the strain from the milk from one quarter of one cow. Although the cow was asymptomatic for any clinical illness other than a chronic staphylococcal mastitis in two quarters, the animal continued to shed Salmonella in the milk during a 36 day period. Necropsy failed to reveal a source of the infection.     

A case of bovine raw milk contamination with Listeria monocytogenes

ABSTRACT: During routine sampling of bulk raw milk on a dairy farm, the pathogenic bacteria Listeria monocytogenes was found to be a contaminant, at numbers < 100 cfu/ml. A strain with an indistinguishable pulsed-field gel electrophoresis pattern was isolated from the bulk milk two months later. Environmental swabs taken at the dairy environment were negative for the presence of L. monocytogenes, indicating a possible case of excretion of the L. monocytogenes directly into the milk. Milk samples were collected from the individual cows and analysed, resulting in the identification of L. monocytogenes excretion (at 280 cfu/ml) from one of the 4 mammary quarters of one dairy cow out of 180. When the infected cow was isolated from the herd, no L. monocytogenes was detected from the remaining herd. The pulsed-field gel electrophoresis pattern of the strain from the individual cow was indistinguishable from that originally isolated from the bulk milk. The infected cow did not show any clinical signs of disease, nor did the appearance of the milk have any physical abnormalities. Antibiotic treatment of the infected mammary quarter was found to be ineffective. This study shows that there can be risks associated with direct contamination of raw milk with L. monocytogenes.     

Mycoplasmal mastitis in a dairy herd

In October 1985, mycoplasmas were isolated from bulk tank milk samples in a large Florida dairy (greater than 1,400 lactating cows). At that time, measures to isolate and control the spread of infection were instituted. In an initial screening test, Mycoplasma bovis was isolated from 21 of 153 milking string samples (milk from all quarters of 10 cows/string). Composite quarter milk samples from all quarters of every individual lactating cow in the herd were obtained for culture in November 1985 and December 1985. In October, 88 of 1,535 (5.7%) cows were identified as Mycoplasma-positive. An additional 31 Mycoplasma-infected cows were identified in December. The dairy elected to maintain the infected cows in a separate Mycoplasma-positive subherd, which would be milked at the end of each milking session. Seven additional Mycoplasma-positive cows were identified at initiation of lactation. All newly identified infected cows were transferred to the Mycoplasma-positive subherd. After segregation of Mycoplasma-positive cows, bulk tank milk samples obtained routinely from the main herd remained culture negative throughout the study. From February 1986 to October 1986, quarter milk samples were obtained monthly from cows in the Mycoplasma-positive subherd. Any cow that developed clinical mastitis or substantial decrease in milk production was, at the discretion of the herdsman, culled. Of the 126 cows in the subherd, 22 (17.5%) were culled for mastitis, 35 (27.8%) were culled for low production, and 9 (7.1%) were culled for other reasons. Of the remaining 60 cows, 16 (12.7% of the 126 cows) were Mycoplasma-positive on the basis of results from one or more samples obtained after February 1986.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

<Emphasis Type="Italic">Staphylococcus aureus</Emphasis> intramammary infection affects milk yield and SCC of dairy cows

Staphylococcus aureus (S. aureus) is the most prevalent infectious microorganism affecting dairy cattle worldwide, and its pathogenic characteristics facilitate its spread in dairy herds. S. aureus intramammary infections (IMI) are mainly subclinical, and associated losses can exceed average herd losses where the pathogen is not isolated. However, the extent it affects milk composition at udder and quarter levels is still unknown, and cow composite milk losses may be underestimated due to the dilution effect. The aim of this study was to investigate the effects of S. aureus subclinical mastitis on mammary quarter milk yield and composition. In order to determine the effects of the pathogen on milk yield and composition at quarter level, a pairwise comparison of infected and non-infected mammary quarters (n?=?28) from two dairy herds was carried out. Quarters were individually milked, and milk production and composition were assessed. S. aureus has increased somatic cell counts at quarter level; however, no effect of S. aureus IMI on milk lactose, fat, and protein contents was observed. Fat yield from infected quarters decreased, but losses due to the infection caused by S. aureus were not associated with quarter positioning in cows.     

Use of partial budgeting to determine the economic outcome of Staphylococcus aureus intramammary infection reduction strategies in three Ohio dairy herds

Efforts to reduce the prevalence of Staphylococcus aureus intramammary infection were monitored in 3 Ohio dairy herds. Bacteriologic culturing of milk from all lactating cows in each herd was completed multiple times to identify infected cows and monitor reduction. Partial budgeting techniques were used to determine the economic outcome of the reduction program. Of particular emphasis was the economic impact of culling to maintain or achieve milk quality premium payments on the basis of bulk tank somatic cell counts. The prevalence of S aureusinfected cows was reduced in each herd. Culturing of milk from all lactating cows appeared to be an effective method to identify infected cows. Although numbers were limited, it also appeared that culturing of composite quarter samples was effective as a herd screening test to identify S aureus-infected cows. Bacteriologic culturing had a negative financial impact in all 3 herds. Using partial budgeting to assess the economic impact of the programs, it was determined that 2 herds experienced negative financial impacts as a result of an excess culling rate when compared with a 12-month baseline period prior to the initiation of the project. All herds had increased milk production per cow during the study as measured by the mature-equivalent method. However, when actual production was considered, increased milk production in each herd was not as great as that of other Ohio herds enrolled on Dairy Herd Improvement Association testing programs.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

A case-control study of Nocardia mastitis in Ontario dairy herds

A case-control study was conducted to identify milking hygiene and udder therapy factors associated with a diagnosis of Nocardia mastitis in dairy herds from which milk samples are submitted to the Ontario Ministry of Agriculture and Food, Veterinary Laboratory Services, Guelph laboratory. The data were collected by telephone interview from 31 case and 31 control herds.

After analytical control for confounders, blanket dry cow therapy and a dry cow antibiotic product were associated with a diagnosis of Nocardia mastitis in a herd, whereas another dry cow antibiotic product had a sparing effect.

In comparison to mastitis pathogens susceptible to dry cow antibiotic therapy, Nocardia species were isolated infrequently from milk specimens submitted to the Guelph mastitis laboratory.

     

The contribution of mammary infections by coagulase-negative staphylococci to the herd bulk milk somatic cell count

Quarter foremilk samples were taken at 2–3 weekly intervals for several years in a experimental herd comprising about 45 cows. The samples were submitted to bacteriological analysis and somatic cell counting. The most prevalent quarter infections from 1982 to 1988 were by coagulase-negative staphylococci (15–20% of all the quarters sampled). Most of these (75.6%) persisted until drying-off Dry cow therapy eliminated 86.5% of these infections. Comparison of udder quarters within cows, involving 775 samples from pairs of non-infected quarters and quarters infected by coagulase-negative staphylococci, yielded geometric means of somatic cell counts of 210 000 and 420 000 cells/ml, respectively. The correlation (r=0.87) between the herd bulk milk somatic cell count (SCC) and its estimation from the quarter milk somatic cell count performed on the same day allowed us to evaluate the contribution of the different categories of quarters, according to their infection status, to the herd bulk milk SCC. Quarters infected by a major pathogen (8.5% of samples) gave rise to 46.6% of the total number of cells, while quarters infected by coagulase-negative staphylococci (17.8% of samples) gave rise to 18.1%. Although coagulase-negative staphylococci represented only a secondary source of somatic cells as compared to major pathogens, they were not a negligible source considering the threshold of 300 000 somatic cells advocated for herd milk of good quality.     

Bovine mycoplasma mastitis from intramammary inoculation of small numbers of Mycoplasma bovis. I. Microbiology and pathology

Intrammary inoculation of 70 colony forming units (cfu) of Mycoplasma bovis into one quarter of four previously non-infected cows resulted in severe mastitis in inoculated and uninoculated quarters. Hematogenous spread of the infection was most likely, as mycoplasma was isolated from the peripheral blood of three of four cows and the milking machine was designed to prevent quarter to quarter communication of milk and air. The presence of large numbers of mycoplasma exceeding 10⁶ cfu/ml of milk preceded the onset of overt sero-purulent mastitis by 1–3 days. In general, the severity, duration of the infection and within cow spread of mastitis to adjacent quarters after the inoculation of 70 cfu was indistinguishable from naturally occurring mycoplasma mastitis.The pathology of the chronically infected quarters consisted of alveolar involution and moderate to severe mononuclear infiltration and an increase in interalveolar and loose connective tissue. The quarters of one cow resolving the infections at the time of slaughter were not as severely affected and contained numerous milk-producing alveoli and many alveoli with hyperplasia of the alveolar cells.     

Some observations on canine toxoplasmosis

An inhibitor typing scheme, based on the production of and sensitivity to bacteriocin-like inhibitor substances was used to identify strains of Streptococcus uberis obtained from skin swabs and milk samples of dairy cows. Thirty-nine isolates from one herd were compared, with one isolate examined per site for any sampling day. Eighteen different inhibitor profiles were observed from these isolates. When several isolates were obtained from various skin sites on a cow on the same day, the inhibitor profiles were all different. In three cases, Str. uberis was simultaneously isolated from milk sample and teat surface of the same quarter, but similar inhibitor profiles were only observed for one pair of isolates. Furthermore, when several isolates were obtained by repeated swabbing of a single skin site on a cow on the same day, differences in the inhibitor profiles were again seen. It is likely that numerous strains of Str. uberis are capable of producing clinical mastitis since a comparison of ten isolates obtained from cases of clinical mastitis revealed eight different inhibitor profiles.

Monthly sampling (April–November) of eleven cows revealed that Str. uberis could be isolated from the skin of the abdominal wall, medial thigh, udder and teats, but was not isolated from the rectum of any of the cows. Str. uberis was more frequently isolated from the skin and milk samples during the winter when the cows had been dried off, than during the spring and autumn.     

Distribution of Serotypes of Group-B Streptococci in Herds and Cows Within an Area of Denmark

During a 3-year period strains of Group-B streptococci from 1227 (94.6 %) of a total of 1297 cases of bovine mastitis were serologically typed. Twenty-seven different antigenic combinations were found. Ab. 70 % of the strains carried polysaccharide antigens among which Type III was predominant (57 %). The protein antigen X was widespread (62 %), and 5 % of the strains were non-type able.Type Ic predominated among “false positive” bulk milk isolates (52.2 %, 12/23), but was rarely isolated from quarter milk samples (3%).Variation in the antigenic structure of infecting strains occurred to some extent and involved at least 10.8 % (132/1227) and probably 25.2 % (132/523) of the strains. Within a herd the antigenic variation was limited, however. Hence a definition of a herd type was possible. During the period of investigation infections caused by Herd Type III decreased numerically while the number of herds infected by other types remained almost stable.     

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.     

Occurrence of Prototheca zopfii, a mastitis pathogen, in milk

Prototheca zopfii was isolated from cow-composite milk and bulk tank milk by a new selective Prototheca enrichment method. Repeated testing of cow-composite milk from individual cows resulted in P. zopfii isolation data indicating a strong statistical correlation of P. zopfii with specific cows. Prototheca sp. were isolated from the milk of 31 of 79 cows in a single herd, and contamination was discounted as the source. Prototheca sp. were also recovered from 28 of 787 bulk tank milk samples from the Eastern U.S.A., and 22 of 69 temperature control milk samples from pooled dairy farm milk from delivery trucks.     

The use of the log-linear model to evaluate the effects of three herd factors on Streptococcus agalactiae mastitis occurrence in California, 1977

Epidemiologic relationships among Streptococcus agalactiae infected dairy herds and herd size, location and California Dairy Herd Improvement Association (CDHIA) participation were examined using log-linear methodology. Dairies located in five out of the six California Bureau of Animal Health veterinary districts were studied. Data sources included the Dairy Cattle Data Base, which uniquely identifies each of the 2875 dairies in California, the 1977 statewide CDHIA year-end summary report and microbiological results from a 1977 statewide survey of bulk tank milk samples. These data were merged, fitted and the best model selected using likelihood-ratio statistics. The model included all four “main effects”, the six possible “1st-order effetss” and the “2nd-order effect” due to the interaction of herd size, location and CDHIA participation. Subsequently, a logit model was used to estimate the effect of the independent herd factor variables (size, location and CDHIA participation) on the log odds of the dependent S. agalactiae variable. This model required conditioning on the three-way relationship among the independent variables.medium-sized, non-CDHIA herds in district 2 (northcentral California) showed the highest expected odds (3.37) for S. agalactiae in bulk tank milk, while small, CDHIA herds in district 3 (northcentral coastal California) produced the lowest odds (0.39).     

Vaccination using phase I vaccine is effective to control Coxiella burnetii shedding in infected dairy cattle herds

The effectiveness of the vaccination of dairy cows combined or not with antibiotics (i.e. oxytetracycline) to control Coxiella burnetii (Cb) shedding at herd level was investigated in 77 Q fever clinically affected herds. In addition to nulliparous heifers’ vaccination, one out of the four following medical strategies was randomly assigned to dairy cows in each herd: vaccination (using a phase I vaccine) alone, vaccination combined with oxytetracycline, oxytetracycline alone or nothing. Their effectiveness to reduce Cb load in quarterly samples of bulk tank milk (BTM) and of pooled milk of primiparous (MP) was assessed through logistic hierarchical models. A significant reduction in Cb load was observed in herds where the vaccination of ≥80% of dairy cows was implemented; whereas the use of antibiotics was uneffective. Our findings support the interest of a whole vaccination strategy and provide evidence for decreasing the use of antibiotics in dairy cattle herds.     

Quarter,cow, and farm risk factors for intramammary infections with major pathogens relative to minor pathogens in Thai dairy cows

A cross-sectional study was carried out from May to September 2011 on 35 smallholder dairy farms in Chiang Mai, Thailand, to identify the quarter, cow, and farm factors that relate to intramammary infections (IMI) from major specified pathogens, compared to infections from minor pathogens. Data on general farm management, milking management, and dry cow management were recorded for each herd. Quarter milk samples were collected from either clinical or subclinical mastitis quarters. Dependent variables were binary data defining the specified major pathogens, including Streptococcus agalactiae (7.1 %), Streptococcus uberis (9.4 %), Streptococcus dysgalactiae (4.0 %), and other streptococci (16.7 %), as a case, and all minor pathogens as a control, in each dependent variable. The occurrence of S. agalactiae IMI was lower in first-parity cows and cows with short milking time. Cows with body condition score (BCS) <2.5 had higher occurrence of S. agalactiae IMI. The occurrence of S. uberis IMI was higher in quarters with California mastitis test (CMT) score 2, score 3, and having clinical mastitis and in farms with increasing age of vacuum system. Quarters with CMT score 3, having clinical mastitis, cow with manual milking after detaching milking cluster, and farms with high bulk milk somatic cell counts (BMSCC >500,000 cells/ml) had higher occurrence of S. dysgalactiae IMI. For other streptococci, quarters having clinical mastitis, BCS <2.5, and pulling down of milking cluster while milking increased occurrence of other streptococci IMI relative to minor pathogen IMI. These results highlight the importance of individual cow factors, milking characteristics, and BMSCC in determining the risk of IMI from major pathogens.     

Increasing prevalence of Coxiella burnetii seropositive Danish dairy cattle herds

A study based on bulk tank milk samples from 120 randomly selected dairy cattle herds was conducted to estimate the prevalence of Coxiella burnetii seropositive dairy herds, to describe the geographical distribution, and to identify risk factors. Using the CHEKIT Q-fever Antibody ELISA Test Kit (IDEXX), the study revealed a prevalence of 79.2% seropositive herds, 18.3% seronegative herds, and 2.5% serointermediate herds based on the instructions provided by the manufacturer. Multifactorial logistic regression showed statistically significant associations (P < 0.01) between C. burnetii seropositivity and increasing herd size (OR = 1.02 per cow increment) and increasing regional average number of cattle per dairy herd (OR = 1.02 per animal increment). Herds >150 cows had 17.9 times higher odds of testing positive compared to herds <80 cows. The regional average number of cattle herds per square kilometer was borderline significantly related to the occurrence of seropositive dairy herds (P = 0.06). The results indicate an increased prevalence of seropositive dairy herds since the previous survey in 2008 and an adverse impact of increasing herd size and cattle density on the risk of seropositivity.     

Bulk tank milk analysis: factors associated with appearance of Mycoplasma sp. in milk

Factors associated with the presence of Mycoplasma sp. in bulk tank milk samples were evaluated from 664 herds during 2.25 years. Milk quality components were not strongly related to the presence of Mycoplasma sp. in bulk tank milk. The presence of other contagious mastitis pathogens, Staphylococcus aureus and Streptococcus agalactiae, was also not related to the presence of mycoplasma, suggesting that the aetiology and transmission of mycoplasma mastitis were different from transmission of other contagious mastitis pathogens. The occurrence of the first isolation of mycoplasma from a bulk tank was not correlated to season of the year. Mycoplasma in bulk tank milk samples were more likely to be found in herds shipping more milk, an indirect measure of herd size. This suggests that larger herds are more likely to have mycoplasma mastitis. However, the first appearance of mycoplasma mastitis in a bulk tank sample was followed by a sample without this pathogen in more than 60% of herds. Mycoplasma sp. was not detected in any herd a year after first isolation. These findings suggest that this pathogen could be controlled and eliminated from herds.