Effects of reduced intramammary antimicrobial use during the dry period on udder health in Dutch dairy herds.

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.

Short communication: prevalence, risk factors, and a field scoring system for udder cleft dermatitis in Dutch dairy herds.

Udder cleft dermatitis (UCD) is a well-known disorder in dairy cows. Veterinary literature about this subject, however, is scarce. The objectives of this study were to define a clinical scoring system for UCD, estimate the within-herd prevalence of UCD, and identify potential risk factors of UCD at cow and herd level. On 20 randomly selected dairy farms in the Netherlands, each lactating cow was photographed from a ventral, lateral, and caudal position. A scoring system with 6 categories of severity of UCD was proposed based on the ventral photographs. Cow measures such as udder width and depth, and front quarter attachment were determined from the lateral and caudal photographs. A questionnaire was conducted on each farm during farm visits. Udder cleft dermatitis, defined as a score 3 or higher, was detected in 5.2% of the 948 cows involved in this study. Within-herd prevalences of UCD ranged between 0 and 15% and UCD was found in 16 (80%) of the participating farms. Cows with a deep udder (relative to the hock), large front quarters, and a small angle between udder and abdominal wall were more likely to develop UCD. Production level and use of a footbath were identified as being positively associated with herd-level UCD prevalence. Herd size and average bulk milk somatic cell count did not seem to be associated with UCD prevalence. Because of the small herd sample size, no firm conclusions were drawn on herd-level risk factors. However, results from this study can be used in designing a future longitudinal UCD study. The prevalences of UCD found in the present study illustrate the current UCD situation in the Netherlands. Our results demonstrate that multiple potential risk factors of UCD could be identified at both the cow and herd level.

Incidence of subclinical mastitis in Dutch dairy heifers in the first 100 days in lactation and associated risk factors.

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.

On-farm udder health monitoring.

In this article an on-farm monitoring approach on udder health is presented. Monitoring of udder health consists of regular collection and analysis of data and of the regular evaluation of management practices. The ultimate goal is to manage critical control points in udder health management, such as hygiene, body condition, teat ends and treatments, in such a way that results (udder health parameters) are always optimal. Mastitis, however, is a multifactorial disease, and in real life it is not possible to fully prevent all mastitis problems. Therefore udder health data are also monitored with the goal to pick up deviations before they lead to (clinical) problems. By quantifying udder health data and management, a farm is approached as a business, with much attention for efficiency, thought over processes, clear agreements and goals, and including evaluation of processes and results. The whole approach starts with setting SMART (Specific, Measurable, Acceptable, Realistic, Time-bound) goals, followed by an action plan to realize these goals.

The effect of bluetongue virus serotype 8 on milk production and somatic cell count in Dutch dairy cows in 2008.

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.

Antimicrobial susceptibility of coagulase-negative staphylococci isolated from bovine milk samples.

The aim of this study was to examine whether antimicrobial resistance profiles of coagulase-negative Staphylococcus (CNS) species isolated from milk of dairy cows differed between bacterial species, and to compare results obtained by phenotypic and genotypic profiling of resistance to penicillin, oxacillin and macrolide-lincosamide (ML) antibiotics. Of 170 CNS isolates, 83 (48.8%) were phenotypically susceptible to all antimicrobial agents tested in minimum inhibitory concentration (MIC) assays, 40.6% expressed resistance to a single compound or a single class of compounds, and 10.6% to multiple drug classes. Nine percent, 68%, 19%, 4% and 1% of isolates were negative for all resistance genes tested by PCR or positive for one, two, three or four resistance genes, respectively. Phenotypic resistance and detection of resistance genes other than blaZ were relatively rare in Staphylococcus chromogenes, which was the most common CNS species (36% of 170 genotypically identified isolates). In Staphylococcus epidermidis, which was the second most common CNS species (14% of isolates), phenotypic penicillin resistance was significantly more common than in other CNS species. Almost half of the S. epidermidis isolates carried multiple resistance genes and 30% carried the methicillin resistance gene mecA. Survival analysis using MIC values showed significant associations between phenotypic and genotypic resistance profiles. We conclude that CNS species from bovine milk differ significantly in phenotypic and genotypic antimicrobial resistance profiles, which has implications for treatment and management decisions.

Field comparison of real-time polymerase chain reaction and bacterial culture for identification of bovine mastitis bacteria.

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.

Effect of prepartum dry cow antibiotic treatment in dairy heifers on udder health and milk production.

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.

Technical note: use of transfer RNA-intergenic spacer PCR combined with capillary electrophoresis to identify coagulase-negative Staphylococcus species originating from bovine milk and teat apices.

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.

Prevalence and herd-level risk factors for intramammary infection with coagulase-negative staphylococci in Dutch dairy herds.

In this study, the prevalence of intramammary infection (IMI) with coagulase-negative staphylococci (CNS) in The Netherlands was estimated on 49 randomly selected herds with at least 40 lactating cows. In total, 4220 quarter milk samples were collected. The prevalence of CNS IMI in The Netherlands was estimated at 10.8% at quarter level and 34.4% at cow level, making it the most frequently isolated group of pathogens. Fourteen species of CNS were identified; the most frequently isolated species was Staphylococcus chromogenes (30.3%) followed by Staphylococcus epidermidis (12.9%) and Staphylococcus capitis (11.0%). Prevalence of CNS IMI was higher in heifers compared to older cows. Geometric mean quarter SCC of CNS-positive quarters was 109,000 cells/ml, which was approximately twice as high as culture-negative quarters. Quarters infected with S. chromogenes, S. capitis and Staphylococcus xylosus had a higher SCC (P<0.05) than culture-negative quarters, while quarters that were culture-positive for S. epidermidis and Staphylococcus hyicus tended to have a higher SCC than culture-negative quarters. An increased prevalence of CNS IMI was associated with the herd-level variables source of drinking water not being tap water, housing of dry cows in one group instead of multiple groups, measurement of cow SCC every month, udder health monitoring by the veterinarian, pasturing during outdoor season, percentage of stalls contaminated with milk, and BMSCC>250,000 cells/ml. Although a causal relation between these factors and prevalence of CNS is not proven and for some factors not even likely, knowledge of the associations found may be helpful when approaching CNS problems on dairy farms.

Performance of API Staph ID 32 and Staph-Zym for identification of coagulase-negative staphylococci isolated from bovine milk samples.

In this study, the accuracy of two phenotypic tests, API Staph ID 32 and Staph-Zym, was determined for identification of coagulase-negative staphylococci (CNS) from bovine milk samples in comparison with identification based on DNA-sequencing. A total of 172 CNS isolated from bovine milk were classified into 17 species. The most frequently isolated species based on rpoB sequencing were Staphylococcus chromogenes and Staphylococcus epidermidis, followed by Staphylococcus xylosus, Staphylococcus warneri and Staphylococcus equorum (37, 13, 9, 8 and 6% of isolates, respectively). The API Staph ID 32 correctly identified 41% of the CNS isolates. Best agreement with rpoB sequence based species identification was found for S. epidermidis, Staphylococcus hyicus and S. xylosus (100, 89 and 87%, respectively). The positive predictive value was 89, 100 and 52%, respectively. Poor sensitivity was observed for 3 of the 5 most frequently found species, S. chromogenes (37%), Staphylococcus warneri (15%) and S. equorum (0%) albeit with specificity of 100%. The Staph-Zym needed additional tests for 66% of the isolates and identified 31% of the CNS isolates correctly. Good sensitivity was found for S. epidermidis, S. simulans and S. xyloxus (100, 78 and 73%, respectively). The positive predictive value was 89, 78 and 98%, respectively. Poor sensitivity was observed for S. chromogenes, S. warneri and S. equorum (0, 54 and 0%, respectively) but with a specificity of 100, 99 and 100%, respectively. Both phenotypic tests misidentified a large proportion of CNS isolates and were thus unsuitable for identification of CNS species from bovine milk samples.

Screening of bovine coagulase-negative staphylococci from milk for superantigen-encoding genes.

A collection of 102 coagulase-negative staphylococci (CNS), isolated from cases of subclinical and clinical bovine mastitis and belonging to 10 different species, were screened by PCR for the presence of genes encoding enterotoxins and enterotoxin-like toxins (sea, seb, sec, sed, see, seg, seh, sei, sej, selk, sell, selm, seln, selo, selp, selq and selu), toxic shock syndrome toxin-1 (tst), and exfoliative toxins A and B (eta and etb). No toxin gene sequences were amplified from any of the isolates, indicating that superantigens encoded by genes detectable by the PCR tests used were not involved in the development of subclinical and clinical mastitis in cattle infected with the CNS isolates tested.

[Mycoplasma mastitis in dairy cattle]. / Mycoplasma mastitis bij het rund.

The most important characteristics of Mycoplasma mastitis on dairy farms are described, based on two case studies. Clinical symptoms, diagnostics, epidemiology, and a plan of action are presented. In the herds investigated, Mycoplasma mastitis was characterized by multiple affected quarters unresponsive to treatment with antibiotic and/or anti-inflammatory agents. Most striking were a sandy sediment, brown colouring, and rice-like structure of the milk of affected animals. Clinical symptoms differed in the two affected herds. Diagnosis was based on bacteriological investigation of samples of milk and synovial fluid taken from infected cows. Affected animals were culled immediately, and the herds were monitored by repeated testing of bulk milk samples. It was concluded that a consequence of the increasing size of cattle herds in the Netherlands is that subclinical/clinical Mycoplasma mastitis may be diagnosed more frequently than in the past. In the case of Mycoplasma mastitis, farmers and veterinary practitioners are advised to draw up a plan of action together, incorporating aspects such as diagnostics at cow level, direct culling of affected animals, hygiene during milking, including post-milking teat disinfection, and routine monitoring of bulk milk. Unpasteurized milk should not be given to calves.

[Sensitivity to various antibiotics of coagulase-negative staphylococci isolated from samples of milk from Dutch dairy cattle]. / Gevoeligheid voor diverse antibiotica van coagulase negatieve staphylococcen, geïsoleerd uit melkmonsters van Nederlands rundvee.

During recent years the prevalence of coagulase-negative staphylococci in milk samples from Dutch dairy cows has increased. In 1999 16.2% of the bacteria isolated from milk collected from cows with subclinical mastitis were coagulase-negative staphylococci. In 2004 this proportion was 42.2%. The proportion of coagulase-negative staphylococci of the bacteria isolated from milk samples from cows with clinical mastitis was 7.3% in 1999 and 14.1% in 2004. In this study, the susceptibility of 108 coagulase-negative staphylococci to oxacillin, cefquinome, streptomycin, neomycin, penicillin, and the combination of nafcillin, penicillin, and streptomycin was tested. The isolates were cultured from milk collected from cows with mastitis and typed using the Api-Staph system. Eight species were identified. Staphylococcus chromogenes was the predominant species (41.7%), followed by Staphylococcus xylosus (15.7%) and Staphylococcus simulans (10.2%). With the agar dilution method all strains proved to be sensitive to cefquinome and 90% to oxacillin. Three isolates (2.8%) were mecA-positive. Despite the agar dilution results, these three isolates should be considered resistant to all beta-lactam antibiotics (penicillins, penicillins combined with a beta-lactamase inhibitor and all generations of cephalosporins). In the agar diffusion test, all isolates proved to be sensitive to the combination of nafcillin-penicillin-streptomycin, 99% were sensitive to neomycin and 1% intermediate sensitive, and 95% were sensitive to streptomycin, 4% resistant, and 1% intermediate sensitive. The coagulase-negative staphylococci were highly resistant to penicillin (37.4%), although the level of resistance varied between species, from 0% for Staphylococcus simulans to 100% for Staphylococcus saprophyticus. Because coagulase-negative staphylococci are resistant to several antibiotics, sensitivity testing is important for targeted treatment of mastitis.

[An outbreak of Klebsiella pneumoniae mastitis]. / Een uitbraak van Klebsiella pneumoniae mastitis.

A serious outbreak of mastitis caused by Klebsiella pneumoniae is described. Shortly after drying off, three cows died of mastitis caused by Klebsiella pneumoniae and five other cows became seriously ill but survived. Sawdust contiminated with Klebsiella pneumoniae was identified as the most likely source of these infections. In addition to detection of possible sources of infection, another important aspect of eradication is the detection of quarters infected with Klebsiella pneumoniae. Rigorous application of these measures led to resolution of the outbreak within a few months.

[Mastitis caused by Yersinia pseudotuberculosis in a cow]. / Mastitis bij het rund door Yersinia pseudotuberculosis.

Subclinical mastitis with a raised somatic cell count was diagnosed in a cow in her fifth lactation. It was caused by Yersinia pseudotuberculosis, which can also infect humans. This is the first time that Yersinia pseudotuberculosis has been isolated from a mastitis sample in The Netherlands. Despite treatment with antibiotics in the dry period, Yersinia pseudotuberculosis was still present in the same quarter in the subsequent lactation. The somatic cell count was still high and milk production was much lower than in previous lactation. The pathogen did not spread to other quarters of the same cow or to herd mates on the farm over a 1-year period.

In vitro growth inhibition of major mastitis pathogens by Staphylococcus chromogenes originating from teat apices of dairy heifers.

Earlier field observations suggest that teat apex colonization by Staphylococcus chromogenes pre-partum in dairy heifers protects udder quarters against elevated somatic cell counts early post-partum. To explain these findings, the in vitro inhibitory capability of S. chromogenes from teat apices of heifers towards some major mastitis pathogens was tested using a modified cross-streaking method. Two out of 10 S. chromogenes isolates, both originating from two different teats from the same heifer, consistently inhibited growth of all Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus uberis strains, but none of the Escherichia coli strains. The present study, therefore, supports the protective effect of teat apex colonization by S. chromogenes by in vitro production of inhibitory substances.