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A high percentage of heifers calve with intramammary infections. One of the measures available to control intramammary infections is treatment with antibiotics before calving. In this study, the effects of prepartum treatment of nonlactating heifers with a 600-mg cloxacillin dry cow treatment on the prevalence of culture-positive milk samples at calving and 10 to 14 d in milk (DIM), the incidence of clinical mastitis, somatic cell count (SCC), and milk production during first lactation were quantified. A total of 184 heifers on 13 dairy farms were treated with antibiotics 8 to 10 wk before the expected calving date. Another 185 heifers served as untreated controls. Coagulase-negative staphylococci were the most frequently isolated group of bacteria in the treatment and control groups at calving (32 and 42%), and at 10 to 14 DIM (15 and 19%), respectively. The prevalence of minor pathogens at calving was lower in the treatment group compared with the control group (34 and 43%, respectively). Staphylococcus aureus was the most frequently isolated major pathogen in the treated and control heifers at calving (4 and 5%) and at 10 to 14 DIM (2 and 3%), respectively. The prevalence of major pathogens was lower in the treated heifers at 10 to 14 DIM compared with the control group (4 and 6%, respectively). Cumulative incidence risk of clinical mastitis during the lactation was 9 and 18% in the treatment and control groups, respectively. Treatment with cloxacillin 8 to 10 wk before calving resulted in a lower prevalence of culture-positive milk samples at calving and lower quarter milk SCC in early lactation [30,000 ± 4,600 (standard deviation) cells/mL in treated heifers versus 40,000 ± 4,600 cells/mL in control heifers], and was associated with lower average test-day SCC (55,000 ± 1,400 cells/mL in treated heifers versus 71,000 ± 1,500 cells/mL in control heifers) and lower incidence of clinical mastitis throughout lactation. The improved udder health resulted in a higher average test-day milk production in the first lactation (24.5 ± 3.2 kg in treated heifers versus 23.6 ± 3.1 kg in control heifers). Dairy farms with heifer mastitis problems need to analyze their mastitis management. Prepartum treatment of heifers with dry cow antibiotics may be helpful by decreasing the prevalence of mastitis-causing pathogens at calving and at 10 to 14 DIM. [ABSTRACT FROM AUTHOR]

Abstract In this paper a review is given of frequently used mastitis diagnostic methods in modern dairy practice. Methods used at the quarter, cow, herd and regional or national level are discussed, including their usability for performance monitoring in udder health. Future developments, such as systems in which milk-derived parameters are combined with modern analytical techniques, are discussed. It is concluded that, although much knowledge is available and science is still developing and much knowledge is available, it is not always fully exploited in practice.

Abstract During routinely screening (50.000 milk samples on an annual basis) 14 MRSA ST398 strains were identified in the period of January 2008 to September 2008 in 14 different dairy herds located in the provinces Overijssel and Gelderland, The Netherlands. Molecular analysis was performed by Cfr9I PFGE, ST398-specific diagnostic PCR, spa typing, SCCmec typing and Panton-Valentine Leukocidin (PVL) gene PCR. The molecular analyses of 14 MRSA (one MRSA strain per herd) strains revealed that all strains belong to ST398 with 3 closely related spa types (t011, t108 and t889, all commonly found in pigs) and carry 2 different SCCmec types, IVa and V. All MRSA strains were resistant to two or more classes of antibiotics and also PVL negative. The majority of farms (n = 9, 64%) harboured combined livestock with both cows and pigs present. Our study contributes to the growing evidence that MRSA ST398 is transmitted among various animal species and can be considered as an etiological agent of mastitis in dairy cows.

Heifer mastitis is a problem and risk factors may differ between heifers and older cows. The aim of this study was to estimate the heifer subclinical mastitis (HSCLM) incidence based on elevated somatic cell count (SCC) in the first 100 d in lactation and the associated risk factors in Dutch dairy herds. In 2008, 173 farmers filled in a questionnaire regarding housing and herd management factors potentially related to udder health. In addition, monthly milk production and SCC data from all cattle were provided by the Dutch Royal Cattle Syndicate (CRV, Arnhem, the Netherlands). Heifer subclinical mastitis incidence was calculated at the herd level as the number of heifer cases divided by the number of heifers at risk in the first 100 d in milk. Linear regression models were used for the analyses. On average, 25.5% [95% confidence interval (CI): 23.9 to 27.0%] of the heifers had subclinical mastitis. Heifers with a high SCC (>150,000 cells/mL) on the first test day after calving that returned to SCC levels below the cut-off continued to have a higher SCC throughout the study period compared with heifers with a low SCC (=150,000 cells/mL) at the first test day after calving. Housing heifers together with lactating cows close to calving was protective from HSCLM incidence compared with separate housing (-4.5%; 95% CI: -8.7 to -0.2%). In addition, herds in which the farmer removed supernumerary teats of calves had a 7.0% (95% CI: 2.8 to 11.3%) lower HSCLM incidence and day and night grazing was also protective (-5.9%; 95% CI: -10.6 to -1.3%). Herds that were milked with an automatic milking system had, on average, a 6.9% (95% CI: 2.2 to 11.5%) higher HSCLM incidence and submitting milk samples for bacteriological culturing in the previous year was also associated with a higher HSCLM incidence (4.1%; 95% CI: 1.1 to 7.1%). Heifer subclinical mastitis is prevalent in all dairy herds, with a large variation in incidence. A high SCC in heifers at the first test day after calving appears to indicate a prolonged effect on udder health. Several management factors were found to be associated with HSCLM incidence that may help in reducing HSCLM. [ABSTRACT FROM AUTHOR]

Coagulase-negative staphylococci (CNS) are the most frequently isolated bacteria in milk samples from cows with and without mastitis. Elucidating their relevance in bovine udder health is hampered because identification at the species level, if done at all, used to be performed based on phenotypic features. To provide a rapid, cheap, and easy-to-use genotypic technique that can be used to identify CNS species from milk and teat apices from cows, the performance of transfer RNA-intergenic spacer PCR (tDNA-PCR) in combination with capillary electrophoresis was evaluated. After updating the tDNA library with CNS reference strains, 288 field isolates were identified with tDNA-PCR and gene sequencing, and the latter was used as the reference method. The field isolates were divided in 2 groups of 144. Isolates of the first group were identified with tDNA-PCR with a typeability of 81.9% and an accuracy of 94.1%. Peak patterns of these isolates were then added to the tDNA library with species identity as determined by DNA sequencing. The second group was identified with the updated tDNA library, resulting in 91.0% typeability and 99.2% accuracy. This study showed that the updated tDNA-PCR in combination with capillary electrophoresis was almost as accurate as gene sequencing but faster and cheaper (only $3 per isolate), and is a useful tool in observational studies concerning the epidemiology of bovine CNS species. [ABSTRACT FROM AUTHOR]

Dry cow therapy (DCT) in the Netherlands changed from mainly blanket to selective antimicrobial DCT. This transition was supported by a national guideline, with the individual somatic cell count (SCC) at the last milk recording before dry-off as the main selection criterion for antimicrobial DCT. The aim of this retrospective observational study is to evaluate the SCC dynamics during the dry period at the herd and individual dry period level following the national transition from mainly blanket to selective antimicrobial DCT. At the herd level, we used 2 data sets to evaluate the SCC dynamics during the dry period: (1) a national data set containing 3,493 herds with data available from 2011 through 2015 and (2) a veterinary practice data set containing 280 herds with data available from 2013 through 2015. The herd level analysis was carried out using key performance indicators provided via milk recording (CRV, Arnhem, the Netherlands): the percentage of cows that developed a new intramammary infection (IMI) during the dry period and the percentage of cows cured of an IMI during the dry period. The effect of DCT at individual dry period level was analyzed with a mixed-effects logistic regression model based on 4,404 dry periods from 2,638 cows in 20 herds within the veterinary practice data set. For these 20 herds, individual SCC data from milk recordings and individual cow DCT were available from 2013 through 2015. No significant changes were observed to the SCC dynamics during the dry period at the herd level. The percentage of cows that developed a new IMI during the dry period ranged between 16 and 18%, and the percentage of cows cured from an IMI during the dry period ranged between 74 and 76%. At the individual dry period level, a low SCC at the first milk recording following a dry period was associated with the use of intramammary antimicrobial DCT with or without the concurrent use of an intramammary teat sealer [odds ratio (OR) = 2.16 and OR = 2.07, respectively], the use of DCT with an intramammary teat sealer only (OR = 1.35), and a low SCC at the last milk recording before dry-off (OR = 1.78). This study demonstrates that the selection of cows for DCT without antimicrobials based on SCC thresholds at the last milk recording is possible without significant changes to udder health and reduced the use of antimicrobials., (The Authors. Published by FASS Inc. and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).)

The effect of bluetongue virus serotype 8 (BTV-8) infections was quantified on milk production and udder health. From July 2008 to December 2008, 1,074 seronegative cows in 15 herds that were not vaccinated against BTV-8 were tested every 3 wk for BTV-8 antibodies. Sampling stopped when cows seroconverted. Test-day records were provided and 3 traits were defined to evaluate the effect of BTV-8 on milk production and udder health: 1) the difference between observed and predicted fat- and protein-corrected milk production; 2) the natural logarithm of the somatic cell count (lnSCC); and 3) the occurrence of a new high SCC. In the default model, the variables were assumed influenced by BTV-8 when the test-day record of the seroconverted cow was taken within 30 d before seroconversion, thus, in the period in which the cow was infected. In sensitivity analyses, the time intervals were varied in which BTV-8 was assumed to affect milk production and udder health. During the study, 185 cows (17%) had a subclinical infection and seroconverted and 77 had a test-day result within 30 d before seroconversion. In this period, in cows that seroconverted, the fat- and protein-corrected milk production was 52 (95% confidence interval: 26 to 77) kg less than in the period before and after seroconversion and was 51 (95% CI: 26 to 76) kg less than in cows that remained seronegative. When the time interval was increased to within 42 d before seroconversion, the milk production in BTV-8-seroconverted cows decreased by 61 (95% CI: 28 to 94) kg compared with the period before and after seroconversion and decreased by 59 (95% CI: 27 to 92) kg compared with cows that remained BTV-8 seronegative. No significant effect of BTV-8 was found on SCC and odds for a high SCC. Subclinical BTV-8 infection in dairy cattle results in a decreased milk production., (Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Fast and reliable identification of the microorganisms causing mastitis is important for management of the disease and for targeting antimicrobial treatment. Methods based on PCR are being used increasingly in mastitis diagnostics. Comprehensive field comparisons of PCR and traditional milk bacteriology have not been available. The results of a PCR kit capable of detecting 11 important etiological agents of mastitis directly from milk in 4h were compared with those of conventional bacterial culture (48h). In total, 1,000 quarter milk samples were taken from cows with clinical or subclinical mastitis, or from clinically healthy quarters with low somatic cell count (SCC). Bacterial culture identified udder pathogens in 600/780 (77%) of the clinical samples, whereas PCR identified bacteria in 691/780 (89%) of the clinical samples. The PCR analysis detected major pathogens in a large number of clinical samples that were negative for the species in culture. These included 53 samples positive for Staphylococcus aureus by PCR, but negative by culture. A total of 137 samples from clinical mastitis, 5 samples from subclinical mastitis, and 1 sample from a healthy quarter were positive for 3 or more bacterial species in PCR, whereas culture identified 3 or more species in 60 samples from clinical mastitis. Culture identified a species not targeted by the PCR test in 44 samples from clinical mastitis and in 9 samples from subclinical mastitis. Low SCC samples provided a small number of positive results both in culture (4/93; 4.3%) and by PCR (7/93; 7.5%). In conclusion, the PCR kit provided several benefits over conventional culture, including speed, automated interpretation of results, and increased sensitivity. This kit holds much promise as a tool to complement traditional methods in identification of pathogens. In conventional mastitis bacteriology, a sample with 3 or more species is considered contaminated, and resampling of the cow is recommended. Further study is required to investigate how high sensitivity of PCR and its quantitative features can be applied to improve separation of relevant udder pathogens from likely contaminants in samples where multiple species are detected. Furthermore, increasing the number of species targeted by the PCR test would be advantageous., (Copyright © 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

This study was designed to identify risk factors for intramammary infections with Streptococcus uberis and Staphylococcus aureus under field conditions. An 18-mo survey with sampling of all quarters of all lactating cows at 3-wk intervals was carried out in three Dutch dairy herds with medium bulk milk somatic cell count (200,000 to 300,000 cells/ml). Quarter milk samples were used for bacteriology and somatic cell counting. Data on parity, lactation stage, and bovine herpesvirus 4-serology were recorded for each animal. During the last year of the study, body condition score, and teat-end callosity scores were recorded at 3-wk intervals. A total of 93 new infections with Strep. uberis were detected in 22,665 observations on quarters at risk for Strep. uberis infection, and 100 new infections with Staph. aureus were detected in 22,593 observations on quarters at risk for Staph. aureus infection. Multivariable Poisson regression analysis with clustering at herd and cow level was used to identify risk factors for infection. Rate of infection with Strep. uberis was lower in first- and second-parity cows than in older cows, and depended on stage of lactation in one herd. Quarters that were infected with Arcanobacterium pyogenes or enterococci, quarters that had recovered from Strep. uberis- or Staph. aureus-infection in the past, and quarters that were exposed to another Strep. uberis infected quarter in the same cow had a higher rate of Strep. uberis infection. Teat-end callosity and infection with coagulase-negative staphylococci or corynebacteria were not significant as risk factors. Rate of Staph. aureus infection was higher in bovine herpesvirus 4-seropositive cows, in right quarters, in quarters that had recovered from Staph. aureus or Strep. uberis infection, in quarters exposed to other Staph. aureus infected quarters in the same cow, and in quarters with extremely callused teat ends. Infection with coagulase-negative staphylococci was not significant as a risk factor. The effect of infection with corynebacteria on rate of infection with Staph. aureus depended on herd, stage of lactation, and teat-end roughness. Herd level prevalence of Strep. uberis or Staph. aureus, and low quarter milk somatic cell count were not associated with an increased rate of infection for Strep. uberis or Staph. aureus.

An outbreak of Streptococcus uberis mastitis was described to gain insight into the dynamics of Strep. uberis infections at a herd level. Data were obtained from a longitudinal observational study on a commercial Dutch dairy farm with good udder health management. Quarter milk samples for bacteriological culture were routinely collected at 3-wk intervals from all lactating animals (n = 95 +/- 5). Additional samples were collected at calving, clinical mastitis, dry-off, and culling. During the 78-wk observation period, 54 Strep. uberis infections were observed. The majority of infections occurred during a 21-wk period that constituted the disease outbreak. The incidence rate was higher in quarters that had recovered from prior Strep. uberis infection than in quarters that had not experienced Strep. uberis infection before. The incidence rate of Strep. uberis infection did not differ between quarters that were infected with other pathogens compared with quarters that were not infected with other pathogens. The expected number of new Strep. uberis infections per 3-wk interval was described by means of a Poisson logistic regression model. Significant predictor variables in the model were the number of existing Strep. uberis infections in the preceding time interval (shedders), phase of the study (early phase vs. postoutbreak phase), and prior infection status of quarters with respect to Strep. uberis, but not infection status with respect to other pathogens. Results suggest that contagious transmission may have played a role in this outbreak of Strep. uberis mastitis.

Thirty-eight bovine mammary Staphylococcus aureus isolates from diverse clinical, temporal, and geographical origins were genotyped by pulsed-field gel electrophoresis (PFGE) after SmaI digestion of prokaryotic DNA and by means of binary typing using 15 strain-specific DNA probes. Seven pulsed-field types and four subtypes were identified, as were 16 binary types. Concordant delineation of genetic relatedness was documented by both techniques, yet based on practical and epidemiological considerations, binary typing was the preferable method. Genotypes of bovine isolates were compared to 55 previously characterized human S. aureus isolates through cluster analysis of binary types. Genetic clusters containing strains of both human and bovine origin were found, but bacterial genotypes were predominantly associated with a single host species. Binary typing proved an excellent tool for comparison of S. aureus strains, including methicillin-resistant S. aureus, derived from different host species and from different databases. For 28 bovine S. aureus isolates, detailed clinical observations in vivo were compared to strain typing results in vitro. Associations were found between distinct genotypes and severity of disease, suggesting strain-specific bacterial virulence. Circumstantial evidence furthermore supports strain-specific routes of bacterial dissemination. We conclude that PFGE and binary typing can be successfully applied for genetic analysis of S. aureus isolates from bovine mammary secretions. Binary typing in particular is a robust and simple method and promises to become a powerful tool for strain characterization, for resolution of clonal relationships of bacteria within and between host species, and for identification of sources and transmission routes of bovine S. aureus.

One hundred and fifty-nine cases of clinical Staphylococcus aureus mastitis were analyzed to detect factors associated with bacteriological cure after therapy. On 100 Dutch dairy farms, data were collected from four clinical trials with five intramammary treatment regimes designed to treat beta-lactamase-positive pathogens. Infected quarters were treated three times, with a 12-h interval between treatments. Treatment was extended for 2 d if results of the trial treatment were, according to the owner, not satisfactory. The overall bacteriological cure rate was 52%. The bacteriological cure rate of clinical beta-lactamase-negative S. aureus mastitis was significantly higher than that of clinical beta-lactamase-positive S. aureus mastitis. Bacteriological cure was also significantly higher if somatic cell count of the cow was low at the milk recording prior to the onset of the clinical mastitis. The bacteriological cure rate of clinical beta-lactamase-negative S. aureus mastitis was also significantly higher after an extended treatment compared with no extended treatment. The seriousness of the various clinical symptoms and the bacteriological cure rate of clinical S. aureus mastitis were not associated.

The objective of this study was to determine the factors that were associated with the cure of subclinical mastitis caused by Staphylococcus aureus treated during lactation. One hundred forty-three quarters that were infected with S. aureus were available from a number of treatment trials. Analysis of these data showed that the most important factors associated with cure were age of the cow, somatic cell count at the time of treatment, presence of the infection in the front quarters, and stage of lactation. Other factors, such as number of infected quarters per cow and sensitivity or resistance of the strain to penicillin, were not significant. Because of the relatively low probability of cure, it is important to know risk factors for cure and, hence, to choose cows for treatment with great care. Using these data, a prediction equation was developed to determine the cure rate of subclinical mastitis caused by S. aureus when treated during lactation.

Data from five dry cow antibiotic therapy trials were analyzed. Records were only included for cows with > or = 1 culture-positive quarters that were subclinically infected with Staphylococcus aureus. Data for 406 quarters affected with S. aureus from 283 cows on 73 farms were analyzed for quarters, cows, and herds. The probability of cure of an infected quarter decreased when SCC increased, when another quarter was infected in the same cow, when the infection was in a hind quarter, and when the percentage of samples that were positive for S. aureus was higher before drying off. Variables predicting complete bacteriological cure of a cow were log SCC, age of the cow, and the number of infected quarters. The probability of a cure decreased as SCC increased. The probability of cure decreased as age increased, and cows with more than one quarter infected were .57 times less likely to be cured than cows with 1 infected quarter.