Lactational treatment of bovine mastitis-Development over time and factors influencing cytological cure.

Lactational treatment of bovine mastitis is a major contributor to antibiotic consumption in dairy cattle and is, therefore, important to address in light of the increasing problem of antibiotic resistance. In this large-scale database-based retrospective observational study, we combined electronic health records and routinely measured somatic cell counts from individual cows to create an overview of lactational mastitis treatment in Danish dairy herds from 2010 to 2019. Furthermore, posttreatment somatic cell count was used to approximate treatment success in terms of cytological cure. A generalized logistic regression with mixed effects was performed to combine knowledge on cow-level factors (treatment-, pathogen-, and cow-related) with the new infection risk at the herd level, and to explore the relative effect on cytological cure. The investigation revealed that the total number of lactational treatments appears to have decreased steadily over the study period, whereas treatment duration increased slightly. The proportion of cases treated with penicillin-based protocols and the proportion of milk samples sent for pathogen analysis also decreased. Meanwhile, results from the statistical analysis confirm the importance of cow-related factors, such as parity and lactation stage, for the probability of cytological cure following lactational treatment of mastitis. However, they also disclose that factors that are easier to adjust, such as optimizing treatment duration, including knowledge on causative pathogens and improving the herd-level new infection risk that can be used to positively influence the outcome. Application of this knowledge could potentially assist in promoting a more prudent use of antibiotics for dairy cattle in the future.

Treatment of mild to moderate clinical bovine mastitis caused by gram-positive bacteria: A noninferiority randomized trial of local penicillin treatment alone or combined with systemic treatment.

Bovine mastitis is one of the most important diseases in modern dairy farming, as it leads to reduced welfare and milk production and increased need for antibiotic use. Clinical mastitis in Denmark is most often treated with a combination of local and systemic treatment with penicillin. The objective of this randomized clinical trial was to assess whether worse results could be expected with local intramammary treatment with penicillin compared with a combination of local and systemic treatment with penicillin in terms of the bacteriological cure of mild and moderate clinical mastitis cases caused by gram-positive bacteria. We carried out a noninferiority trial with a noninferiority margin set to a relative reduction in bacteriological cure of 15% between these 2 treatment groups to assess the effect of reducing the total antibiotic use by a factor of 16 for each treated case. Clinical mastitis cases from 12 Danish dairy farms were considered for enrollment. On-farm selection of gram-positive cases was carried out by the farm personnel within the first 24 h after a clinical mastitis case was detected. A single farm used bacterial culture results from the on-farm veterinarian, whereas the other 11 farms were provided with an on-farm test to distinguish gram-positive bacteria from gram-negative or samples without bacterial growth. Cases with suspected gram-positive bacteria were allocated to a treatment group: either local or combination. Bacteriological cure was assessed based on the bacterial species identified in the milk sample from the clinical mastitis case and 2 follow-up samples collected approximately 2 and 3 wk after ended treatment. Identification of bacteria was carried out using MALDI-TOF on bacterial culture growth. Noninferiority was assessed using unadjusted cure rates and adjusted cure rates from a multivariable mixed logistic regression model. Of the 1,972 clinical mastitis cases registered, 345 (18%) met all criteria for inclusion (full data). The data set was further reduced to 265 cases for the multivariable analysis to include only complete registrations. Streptococcus uberis was the most commonly isolated pathogen. Noninferiority was demonstrated for both unadjusted and adjusted cure rates. The unadjusted cure rates were 76.8% and 83.1% for the local and combined treatments, respectively (full data). The pathogen and somatic cell count before the clinical case had an effect on the efficacy of treatment; thus efficient treatment protocols should be herd- and case-specific. The effect of pathogen and somatic cell count on treatment efficacy was similar irrespective of the treatment protocol. We conclude that bacteriological cure of local penicillin treatment for mild and moderate clinical mastitis cases was noninferior to the combination of local and systemic treatment using a 15% noninferiority margin. This suggests that a potential 16-fold reduction in antimicrobial use per mastitis treatment can be achieved with no adverse effect on cure rate.

Invited review: Selective treatment of clinical mastitis in dairy cattle.

Treatment of clinical mastitis (CM) and use of antimicrobials for dry cow therapy are responsible for the majority of animal-defined daily doses of antimicrobial use (AMU) on dairy farms. However, advancements made in the last decade have enabled excluding nonsevere CM cases from antimicrobial treatment that have a high probability of cure without antimicrobials (no bacterial causes or gram-negative, excluding Klebsiella spp.) and cases with a low bacteriological cure rate (chronic cases). These advancements include availability of rapid diagnostic tests and improved udder health management practices, which reduced the incidence and infection pressure of contagious CM pathogens. This review informed an evidence-based protocol for selective CM treatment decisions based on a combination of rapid diagnostic test results, review of somatic cell count and CM records, and elucidated consequences in terms of udder health, AMU, and farm economics. Relatively fast identification of the causative agent is the most important factor in selective CM treatment protocols. Many reported studies did not indicate detrimental udder health consequences (e.g., reduced clinical or bacteriological cures, increased somatic cell count, increased culling rate, or increased recurrence of CM later in lactation) after initiating selective CM treatment protocols using on-farm testing. The magnitude of AMU reduction following a selective CM treatment protocol implementation depended on the causal pathogen distribution and protocol characteristics. Uptake of selective treatment of nonsevere CM cases differs across regions and is dependent on management systems and adoption of udder health programs. No economic losses or animal welfare issues are expected when adopting a selective versus blanket CM treatment protocol. Therefore, selective CM treatment of nonsevere cases can be a practical tool to aid AMU reduction on dairy farms.

Selective treatment of nonsevere clinical mastitis does not adversely affect cure, somatic cell count, milk yield, recurrence, or culling: A systematic review and meta-analysis.

Treatment of clinical mastitis (CM) contributes to antimicrobial use on dairy farms. Selective treatment of CM based on bacterial diagnosis can reduce antimicrobial use, as not all cases of CM will benefit from antimicrobial treatment, e.g., mild and moderate gram-negative infections. However, impacts of selective CM treatment on udder health and culling are not fully understood. A systematic search identified 13 studies that compared selective versus blanket CM treatment protocols. Reported outcomes were synthesized with random-effects models and presented as risk ratios or mean differences. Selective CM treatment protocol was not inferior to blanket CM treatment protocol for the outcome bacteriological cure. Noninferiority margins could not be established for the outcomes clinical cure, new intramammary infection, somatic cell count, milk yield, recurrence, or culling. However, no differences were detected between selective and blanket CM treatment protocols using traditional analyses, apart from a not clinically relevant increase in interval from treatment to clinical cure (0.4 d) in the selective group and higher proportion of clinical cure at 14 d in the selective group. The latter occurred in studies co-administering nonsteroidal anti-inflammatories only in the selective group. Bias could not be ruled out in most studies due to suboptimal randomization, although this would likely only affect subjective outcomes such as clinical cure. Hence, findings were supported by a high or moderate certainty of evidence for all outcome measures except clinical cure. In conclusion, this review supported the assertion that a selective CM treatment protocol can be adopted without adversely influencing bacteriological and clinical cure, somatic cell count, milk yield, and incidence of recurrence or culling.

Heat stress and cow factors affect bacteria shedding pattern from naturally infected mammary gland quarters in dairy cattle.

Mastitis-causing pathogens are shed from infected mammary gland quarters and thus contribute to an increased risk of new intramammary infections. The objective of the current study was to investigate the shedding characteristics of various mastitis-causing pathogens and associated animal-specific (somatic cell score and parity) and environmental (heat stress) factors. In a longitudinal study, infected udder quarters were sampled consecutively on 5 dairy farms in Germany. To capture climatic factors, temperature-humidity index (THI) was calculated. In the laboratory analysis, the pathogens and their counts in the milk samples were determined. A generalized linear mixed model with gamma link was used to evaluate the factors influencing pathogen-shedding characteristics. The variables somatic cell count, pathogen, parity, and THI had significant influence on pathogen shedding. Staphylococci were shed in lower values than streptococci. The pathogen shedding from mammary gland quarters with intramammary infections was higher in the first and second lactation than in higher lactations. Exceeding the THI threshold 60 resulted in higher pathogen counts on the same day. This was only caused by the pathogens yeasts and Streptococcus uberis. Possible mechanisms causing differences in pathogen shedding are changes in the counts due to influenced milk quantities, better growth conditions at higher temperatures, or altered immunological reactions. The mechanisms often remain speculative and require further investigation. The study underlines the contribution of cows with high somatic cell counts regarding the transmission of mastitis pathogens within a herd. Furthermore, it becomes clear that heat stress in Germany influences udder health and that prevention measures are useful.

Comparison of phenotypic and genotypic antimicrobial resistance patterns associated with Staphylococcus aureus mastitis in German and Danish dairy cows.

Staphylococcus aureus is one of the most common pathogens associated with bovine mastitis in Germany and Denmark. Successful therapy is strongly linked to the susceptibility of the pathogen to the administered antimicrobial. An increase in resistant pathogens in human and veterinary medicine has become a concern worldwide and hampers therapy due to reduced susceptibility. In the present study, susceptibility testing was performed for 85 and 93 S. aureus isolates originating from mastitis cases on 12 German and 8 Danish dairy farms, respectively. Phenotypic examination was performed by detection of minimal inhibitory concentration (MIC) values using the broth microdilution method, followed by genotypic investigations of the blaZ and mecA resistance genes via PCR. The tested antimicrobials were the most frequently used ß-lactams in German and Danish dairy farms, including cefquinome, cefoperazone, cephapirin, penicillin, oxacillin, cloxacillin, amoxicillin-clavulanic acid, and cephalexin-kanamycin. Special attention was paid to varying therapy concepts because, in Germany, third- and fourth-generation cephalosporins have been predominantly used in mastitis therapy, whereas in Denmark, restrictive use of penicillin is followed by a general avoidance of cephalosporins. Differences in MIC values were mainly based on determined MIC90 values (MIC at which 90% of isolates are inhibited). In general, Danish S. aureus isolates were inhibited at comparatively lower MIC90 values than S. aureus isolated from German dairy farms for most ß-lactams. No differences were observed regarding cefquinome, because both German and Danish isolates exhibited MIC50 and MIC90 values of 0.5 and 1 µg/mL, respectively. In contrast, the MIC90 for penicillin against German and Danish S. aureus were 0.5 and ≤0.06 µg/mL, respectively. Resistance genes (blaZ, mecA) were only detected in German S. aureus isolates on 3 dairy farms in Germany. A total of 5 isolates tested positive for both blaZ and mecA, whereas 1 isolate carried the blaZ resistance gene only. A direct correlation between frequently used antimicrobials and reduced susceptibility could not be determined based on results of the present study. In addition to further research to determine factors associated with resistance development, we emphasize the urgent need for internationally standardized clinical breakpoints to assess resistance situations more accurately.

Association between teat skin colonization and intramammary infection with Staphylococcus aureus and Streptococcus agalactiae in herds with automatic milking systems.

The objective of this study was to investigate the association between teat skin colonization and intramammary infection (IMI) with Staphylococcus aureus or Streptococcus agalactiae at the quarter level in herds with automatic milking systems. Milk and teat skin samples from 1,142 quarters were collected from 300 cows with somatic cell count >200,000 cells/mL from 8 herds positive for Strep. agalactiae. All milk and teat skin samples were cultured on calf blood agar and selective media. A subset of samples from 287 quarters was further analyzed using a PCR assay (Mastit4 PCR; DNA Diagnostic A/S, Risskov, Denmark). Bacterial culture detected Staph. aureus in 93 (8.1%) of the milk samples and 75 (6.6%) of the teat skin samples. Of these, 15 (1.3%) quarters were positive in both the teat skin and milk samples. Streptococcus agalactiae was cultured in 84 (7.4%) of the milk samples and 4 (0.35%) of the teat skin samples. Of these, 3 (0.26%) quarters were positive in both the teat skin and milk samples. The PCR detected Staph. aureus in 29 (10%) of the milk samples and 45 (16%) of the teat skin samples. Of these, 2 (0.7%) quarters were positive in both the teat skin and milk samples. Streptococcus agalactiae was detected in 40 (14%) of the milk samples and 51 (18%) of the teat skin samples. Of these, 16 (5.6%) quarters were positive in both the teat skin and milk samples. Logistic regression was used to investigate the association between teat skin colonization and IMI at the quarter level. Based on bacterial culture results, teat skin colonization with Staph. aureus resulted in 7.8 (95% confidence interval: 2.9; 20.6) times higher odds of Staph. aureus IMI, whereas herd was observed as a major confounder. However, results from the PCR analyses did not support this association. Streptococcus agalactiae was isolated from the teat skin with both PCR and bacterial culture, but the number of positive teat skin samples detected by culture was too low to proceed with further analysis. Based on the PCR results, Strep. agalactiae on teat skin resulted in 3.8 (1.4; 10.1) times higher odds of Strep. agalactiae IMI. Our results suggest that Staph. aureus and Strep. agalactiae on teat skin may be a risk factor for IMI with the same pathogens. Focus on proper teat skin hygiene is therefore recommended also in AMS.

In vitro ability of mastitis causing pathogens to form biofilms.

This Research Communication describes the study of in vitro biofilm formation of mastitis causing pathogens. Biofilms are communities of bacteria that are attached to a surface and to each other and are embedded in a self-produced matrix of extracellular polymeric substances. Biofilm formation is an important virulence factor that may result in recurrent or persistent udder infections and treatment failure through increased resistance to antibiotics and protection against host defences. In the present study 252 bacterial isolates from milk samples from bovine udder quarters with intramammary infections were examined with Congo Red agar (CRA) method and tube method (TM) for their ability to form biofilms. Both tests revealed a high number of biofilm-positive strains. Literature reports that the cure rates for Staphylococcus aureus infected udders are lower (27%) in comparison to cure rates of Streptococcus uberis (64-81%) or coagulase-negative staphylococci (CNS) mastitis (80-90%). The findings of the present study suggest that biofilm formation is not the main factor for the differences in cure rates of the various bacteria genera, because all tested pathogen groups showed a similarly high proportion of biofilm formation. Further research is needed to detect microbial biofilms on bovine udder epithelia.

Selection of cows for treatment at dry-off on organic dairy farms.

Restrictions regarding the use of antibiotics make selective antibiotic dry cow therapy (DCT) mandatory on organic farms in Germany. This requires methods for identifying cows with an intramammary infection (IMI) at dry-off. The aim of this field study was to create a decision scheme for the use of DCT based on cow level factors associated with IMI at dry-off and the probability of both cure and new infection (NI) during the dry period. Data from 250 cows from five organic farms were collected including somatic cell counts (SCC) from Dairy Herd Improvement (DHI) records, California mastitis test (CMT) results at dry-off, clinical mastitis (CM) history, parity and dry-off treatment. IMI at dry-off were most accurate identified using a geometric mean SCC of 100 000 cells/ml as a threshold at either one or three DHI records prior to dry-off. Using a combination of SCC with either CM history, CMT at dry off or parity slightly increased the sensitivity of detection (SE). The probability of cure of the infection over the dry period increased with use of both antibiotic DCT and application of an internal teat sealant (ITS) and decreased when the dry period was longer than 56 d. The risk of NI decreased with the use of ITS and infections with minor pathogens at dry-off. Compared with the selection performed by the farmers during the study period identification of IMI based on the selection criterion with a defined SCC threshold achieved a higher SE.

New infection rate of bovine mammary glands after application of an internal teat seal at dry-off.

The internal teat sealant OrbeSeal® (Zoetis, Berlin, Germany) is intended to prevent new intramammary infection (IMI) throughout the dry period. The aim of this field study was to determine new infection rates in udder quarters applied exclusively with the sealant at dry-off and untreated ones (control group). For that, the new infection rate of udder quarters treated with the sealant was evaluated in a split-udder design (front right and rear left udder quarters treated, the other ones untreated) in 128 cows from nine dairy farms in North Germany that were healthy in all four udder quarters (i.e. <100 000 cells/ml, bacteriologically negative). After calving, duplicate quarter milk samples were collected twice at DIM (days in milk) 5-12 and 7 d later for culture. The new infection rates for treated and untreated groups were 3·4 and 10·5%, respectively. The results showed that applying a standardised study design with very few confounders under field conditions, using internal teat sealants reduced the new infection rate on quarter level to a third of that of the control group. Thus, internal teat sealants represent a viable option for dry-off treatment of udder-healthy cows.

Efficacy of standard vs. extended intramammary cefquinome treatment of clinical mastitis in cows with persistent high somatic cell counts.

Extended duration of clinical mastitis (CM) treatment has been advocated, although results showing its higher efficacy compared with standard treatment are difficult to compare and seem conflicting. In a non-blinded, positively controlled clinical trial with systematic allocation, the efficacy of a standard, 1·5-d cefquinome treatment (ST), and an extended, 5-d intramammary cefquinome treatment (ET) were evaluated. The latter is frequently performed in cows with persistent high somatic cell count (SCC), expecting a better cure. Therefore, cows with CM immediately preceded by at least two consecutive monthly elevated SCC >200 000 cells/ml, were studied. The primary efficacy criteria were bacteriological cure (BC) and clinical cure (CC), while SCC cure was considered a secondary criterion of cure. Least square means of overall BC were not different after ET (79%, n=206) compared with ST (72%, n=203). ET, as compared with ST, improved BC of CM when caused by streptococci, specifically Streptococcus uberis. At day 1·5, only 13% of quarters showed CC, increasing significantly towards 60% at day 5, and 99% at day 14 and at day 21. No significant difference in CC was present between treatment groups. Overall SCC cure was low (22%) and not significantly different between treatment groups, but significantly higher for cases due to enterobacteriacae compared with staphylococci. In conclusion, ET with cefquinome of CM in cows with a persistent high SCC seems to be only indicated when caused by streptococci, mainly Str. uberis but shows no advantage when no information on bacteriological causes of mastitis is available. In our data, absence of CC directly after ST was not related to eventual BC.

Clinical Presentation, Bacteriologic Findings and Possible Risk Factors for Ischemic Teat Necrosis in Cattle-A Case Series.

Ischemic teat necrosis (ITN) is a growing problem in the dairy industry characterized by teat lesions, necrosis, pruritus and automutilation. Despite the economic and welfare consequences, there is no treatment, and the etiology of the disease remains poorly understood. The aim of this study was to investigate ITN by analyzing its clinical presentation, potential risk factors and microbial involvement. Methods included collection of milk and swab samples from affected cows over a period of one-and-a-half years and completion of questionnaires by veterinarians and farmers. Microbial testing included PCR testing for Treponema spp. and cultural testing by anaerobic and aerobic incubation on blood agar. The results showed a high and significant prevalence of Treponema spp. and Staphylococcus aureus in affected teats compared to non-ITN-affected control teats, indicating their potential role in the development of ITN. Other factors such as edema and milking practices also appear to contribute to the tissue damage. First-lactation and early-lactation heifers are particularly at risk. In conclusion, ITN appears to have a multifactorial etiology with both infectious and non-infectious factors playing a role. Further research is needed to better understand the complex interplay of these factors and to develop effective prevention and management strategies.

Treatment of clinically severe bovine mastitis - a scoping review.

Mastitis is a major health problem for bovines and can be categorized as non-severe or severe, based on clinical symptoms. A severe case of clinical mastitis is usually defined by the cow being affected systemically. It is important to consider how to handle severe cases because these cases can be fatal and cause high production losses. However, there are generally few detailed treatment guidelines. By conducting a scoping review on the topic, we aimed to synthesize the information that is available on treatment and outcomes, as reported from clinical trials and observational studies. This was facilitated by following the PRISMA-guidelines with a stepwise systematic screening of scientific literature on the subject, retrieved via Pubmed and Web of Science, using pre-defined selection criteria. The results yielded a total of 14 reports of treatment and outcomes in cases of naturally occurring severe clinical mastitis. Cross-trial comparison was difficult due to the different exclusion criteria and outcome definitions. Many studies focused on cases caused by gram-negative bacteria treated with intensive antibiotic protocols, often containing antibiotics that are categorized as critical for human health. Few focused on severe cases caused by gram-positive bacteria or on the relative use of non-antibiotic treatment. In general, only a small number of statistically significant differences were found in trials comparing different treatment protocols, with no obvious trends across trials. Our findings emphasize the need for more research into the treatment efficacy of antibiotic and non-antibiotic options for clinically severe mastitis. Furthermore, consideration of how trial conditions relate to the practical circumstances in a field setting could improve the applicability of reported results. This could help to provide practitioners with the information needed to make evidence-based treatment decisions in cases of clinically severe mastitis.

The Influence of Milk Leakage, Udder Pressure and Further Risk Factors on the Development of New Intramammary Infections during the Dry Period of Dairy Cows.

Prevention of new intramammary infection (NIMI) during the dry period (DP) is essential to prevent the development of mastitis in dairy cows. To investigate risk factors for NIMI, 212 cows, comprising a total of 848 udder quarters, were examined in this study. Quarter milk samples were taken on the day of drying off and 7 ± 3 days after calving. Cow- and quarter-level associated risk factors were assessed at the beginning of the DP and after calving. In total, 7.1% of the udder quarters developed an NIMI between the samplings. Non-aureus staphylococci (40.4%) and Gram-negative pathogens (22.8%) were most frequently the cause of NIMI. The observed milk leakage prevalence was 16.7%, with a peak 24 h after drying off. Simultaneously, the udder pressure peaked 24 h after drying off. A significant correlation between milk yield on the day before drying off and milk leakage could be proven. Cows with quarters leaking milk produced an average milk yield of 28.32 kg on the day before drying off. Generalised linear mixed models and odds ratios were calculated to determine the significant risk factors for NIMI during the DP and early lactation. Quarters leaking milk had 3.4 higher odds for NIMI between the samplings compared to quarters without milk leakage. Quarters from cows with dirty udders had 3.1 higher odds of developing an NIMI between the samplings compared to quarters from cows with clean udders. The results of this study demonstrate the importance of dry cow management before drying off and during the critical period of active involution of the udder tissue.

The association between bedding material and the bacterial counts of Staphylococcus aureus, Streptococcus uberis and coliform bacteria on teat skin and in teat canals in lactating dairy cattle.

Several mastitis-causing pathogens are able to colonize the bovine teat canal. The objective of this study was to investigate the association between the treatment of sawdust bedding with a commercial alkaline conditioner and the bacterial counts on teat skin and in the teat canal. The study used a crossover design. Ten lactating Holstein cows that were free of udder infections and mastitis were included in the study. The animals were bedded on either untreated sawdust or sawdust that had been treated with a hydrated lime-based conditioner. Once a day, fresh bedding material was added. After 3 weeks, the bedding material was removed from the cubicles, fresh bedding material was provided, and the cows were rotated between the two bedding material groups. Teat skin and teat canals were sampled using the wet and dry swab technique after weeks 1, 2, 3, 4, 5 and 6. Staphylococcus aureus, Streptococcus uberis, Escherichia coli and other coliform bacteria were detected in the resulting agar plate cultures. The treatment of the bedding material was associated with the teat skin bacterial counts of Str. uberis, Esch. coli and other coliform bacteria. An association was also found between the bedding material and the teat canal bacterial counts of coliform bacteria other than Esch. coli. For Staph. aureus, no associations with the bedding material were found. In general, the addition of a hydrated lime-based conditioner to sawdust reduces the population sizes of environmental pathogens on teat skin and in teat canals.

Management-Associated Risk Factors for Heifer Mastitis before and after Parturition in German Dairy Herds.

Subclinical mastitis in heifers during early lactation affects udder health, future milk production and, therefore, the risk of premature culling. The aim of this cross-sectional study was to identify pre- and post-partum risk factors associated with a high heifer mastitis rate (HMR), and to find out which period (either pre- or post-partum) contains more risk factors and consequently should be the focus of mastitis control in heifers. A total of 77 herds were included in this study and the potential animal- and farm-related risk factors were recorded during a one-time farm visit. The HMR was provided by the dairy herd improvement test (DHI) as the annual average of the past 11 DHIs. For this study, data were analyzed in two models using generalized linear models. Each model examined the association between possible risk factors and HMR, one including only prepartum risk factors and the other one only post-partum risk factors. One identified pre-partum risk factor was the proportion of udder-healthy cows in the herd. Post-partum risk factors were the type of teat cleaning procedure before milking, teat disinfection, treatment of mastitis in heifers, a body condition score (BCS) of >3.0 in fresh heifers, and the combination of a teat cleaning procedure with a teat disinfectant. The results show the importance of the period shortly after calving for udder health in heifers, as four of the five significant risk factors were identified in this period and three of them were related to the milking process. However, further research with a higher number of herds is needed to minimize individual herd effects.

Bacteremia in Severe Mastitis of Dairy Cows.

The aim of this cross-sectional study was to investigate the occurrence of bacteremia in severe mastitis cases of dairy cows. Milk and corresponding blood samples of 77 cases of severe mastitis were bacteriologically examined. All samples (milk and blood) were incubated aerobically and anaerobically to also investigate the role of obligate anaerobic microorganisms in addition to aerobic microorganisms in severe mastitis. Bacteremia occurred if identical bacterial strains were isolated from milk and blood samples of the same case. In addition, pathogen shedding was examined, and the data of animals and weather were collected to determine associated factors for the occurrence of bacteremia in severe mastitis. If Gram-negative bacteria were detected in milk samples, a Limulus test (detection of endotoxins) was also performed for corresponding blood samples without the growth of Gram-negative bacteria. In 74 cases (96.1%), microbial growth was detected in aerobically incubated milk samples. The most-frequently isolated bacteria in milk samples were Escherichia (E.) coli (48.9%), Streptococcus (S.) spp. (18.1%), and Klebsiella (K.) spp. (16%). Obligatory anaerobic microorganisms were not isolated. In 72 cases (93.5%) of the aerobically examined blood samples, microbial growth was detected. The most-frequently isolated pathogens in blood samples were non-aureus Staphylococci (NaS) (40.6%) and Bacillus spp. (12.3%). The Limulus test was positive for 60.5% of cases, which means a detection of endotoxins in most blood samples without the growth of Gram-negative bacteria. Bacteremia was confirmed in 12 cases (15.5%) for K. pneumoniae (5/12), E. coli (4/12), S. dysgalactiae (2/12), and S. uberis (1/12). The mortality rate (deceased or culled) was 66.6% for cases with bacteremia and 34.1% for cases without bacteremia. High pathogen shedding and high humidity were associated with the occurrence of bacteremia in severe mastitis.

Effect of Antibiotic Compared to Non-Antibiotic Dry Cow Treatment on the Bacteriological Cure of Intramammary Infections during the Dry Period-A Retrospective Cross-Sectional Study.

Antimicrobials are widely used to cure intramammary infections (IMI) in dairy cows during the dry period (DP). Nevertheless, the IMI cure is influenced by many factors and not all quarters benefit from antimicrobial dry cow treatment (DCT). To evaluate the true effect of antibiotic DCT compared to self-cure and the role of causative pathogens on the IMI cure, a retrospective cross-sectional study was performed. The analysis included 2987 quarters infected at dry-off (DO). Information on DCT, causative pathogens, somatic cell count, milk yield, amount of lactation, Body Condition Score, and season and year of DO were combined into categorical variables. A generalized linear mixed model with a random cow, farm and year effect and the binary outcome of bacteriological cure of IMI during the DP was conducted. In the final model, a significant effect (p < 0.05) on DP cure was seen for the DO season and the category of causative pathogens (categories being: Staphylococcus aureus, non-aureus staphylococci, streptococci, coliforms, 'other Gram-negative bacteria', 'other Gram positive bacteria', non-bacterial infections and mixed infections), while antibiotic DCT (vs. non-antibiotic DCT) only showed a significant effect in combination with the pathogen categories streptococci and 'other Gram-positive bacteria'.

Severity of Clinical Mastitis and Bacterial Shedding.

The aim of this cross-sectional study was to investigate associated factors of the severity of clinical mastitis (CM). Milk samples of 249 cases of CM were microbiologically examined, of which 27.2% were mild, 38.5% moderate, and 34.3% severe mastitis. The samples were incubated aerobically and anaerobically to investigate the role of aerobic and anaerobic microorganisms. In addition, the pathogen shedding was quantitatively examined, and animal individual data, outside temperature and relative humidity, were collected to determine associated factors for the severity of CM. The pathogen isolated the most was Escherichia coli (35.2%), followed by Streptococcus spp. (16.4%). Non-aureus staphylococci (NaS) (15.4%) and other pathogens (e.g., Staphylococcus aureus, coryneforms) (15.4%) were the pathogens that were isolated the most for mild mastitis. Moderate mastitis was mostly caused by E. coli (38%). E. coli was also the most common pathogen in severe mastitis (50.6%), followed by Streptococcus spp. (16.4%), and Klebsiella spp. (10.3%). Obligate anaerobes (Clostridium spp.) were isolated in one case (0.4%) of moderate mastitis. The mortality rate (deceased or culled due to the mastitis in the following two weeks) was 34.5% for severe mastitis, 21.7% for moderate mastitis, and 4.4% for mild mastitis. The overall mortality rate of CM was 21.1%. The pathogen shedding (back logarithmized) was highest for severe mastitis (55,000 cfu/mL) and E. coli (91,200 cfu/mL). High pathogen shedding, low previous somatic cell count (SCC) before mastitis, high outside temperature, and high humidity were associated with severe courses of mastitis.

Reservoirs of Staphylococcus spp. and Streptococcus spp. Associated with Intramammary Infections of Dairy Cows.

To design cost-effective prevention strategies against mastitis in dairy cow farms, knowledge about infection pathways of causative pathogens is necessary. Therefore, we investigated the reservoirs of bacterial strains causing intramammary infections in one dairy cow herd. Quarter foremilk samples (n = 8056) and milking- and housing-related samples (n = 251; from drinking troughs, bedding material, walking areas, cow brushes, fly traps, milking liners, and milker gloves), were collected and examined using culture-based methods. Species were identified with MALDI-TOF MS, and selected Staphylococcus and Streptococcus spp. typed with randomly amplified polymorphic DNA-PCR. Staphylococci were isolated from all and streptococci from most investigated locations. However, only for Staphylococcus aureus, matching strain types (n = 2) were isolated from milk and milking-related samples (milking liners and milker gloves). Staphylococcus epidermidis and Staphylococcus haemolyticus showed a large genetic diversity without any matches of strain types from milk and other samples. Streptococcus uberis was the only Streptococcus spp. isolated from milk and milking- or housing-related samples. However, no matching strains were found. This study underlines the importance of measures preventing the spread of Staphylococcus aureus between quarters during milking.