Nonsevere Clinical Mastitis Research Articles

Financial implications of treating nonsevere Gram-negative clinical mastitis in three California dairies

On 3 large California dairies, 415 lactating cows with nonsevere clinical mastitis (CM) and infected with Gram-negative (GN) bacteria were randomly assigned to one of 3 treatment groups: nontreated control (CON - 135 cases), 2d ceftiofur HCl (SP2 - 133 cases), or 5d ceftiofur HCl (SP5 - 147 cases). Bacteriological cure (BC), clinical cure (CC), mastitis recurrence (MR), culling/death, and overall treatment success differed among treatment groups. Although duration of milk withheld due to mastitis therapy was higher for SP5 (9.4 d), there was no difference between CON (6.9 d) and SP2 (7.1 d). Culling and death rates due to GN CM were the main effects that impacted partial cost calculations. Of study cows culled across the 3 herds, a higher proportion of CON cows (25%) were culled compared with SP2 (11%) or SP5 (18%). Mastitis-related expenses were higher ($550) for CON than SP2 ($343) or SP5 ($423). Results of this partial budget evaluation for the 3 California dairies indicated economic justification for treating cases of nonsevere GN CM with ceftiofur HCl for 2 d.

Evaluation of point-of-care tests for identification of pathogens to inform clinical mastitis treatment decisions in pasture- and confinement-managed dairy cows in Australia

To support antimicrobial stewardship in livestock production, there is a growing array of point of care diagnostics to guide antimicrobial treatment. The primary objective of this observational study was to evaluate the diagnostic performance of 5 point of care tests currently available in Australia for guiding lactational treatment of non-severe clinical mastitis. A secondary objective was to describe the pathogen profiles of mastitis-causing organisms in cows managed in barns ("intensive") and on pasture ("non-intensive"). Foremilk samples (n = 641) were collected by farm staff in dairy herds in Australia (n = 30) and tested at a university laboratory using a reference test and 5 index tests. The reference test was aerobic culture on Trypticase Soy Agar with 5% sheep blood followed by MALDI-TOF for identification of isolates. The following point of care tests were evaluated as index tests: Accumast®, biplate, Check-Up, Mastatest®, and 3M Petrifilm. We found that 23% of samples were contaminated, with the median herd contamination prevalence being 22%. After excluding contaminated samples, the most common diagnoses (according to the reference test) in intensive herds were no growth (31.7%), Klebsiella spp. (28.1%), E. coli (15.0%), and Strep. uberis (8.4%). The most common diagnoses in non-contaminated samples from cows in non-intensive herds were Strep. uberis (35.0%), no growth (26.9%), and E. coli (13.3%). After 24 h of incubation, all index tests demonstrated limited diagnostic sensitivity for identification of pathogens of interest (range: 0.06 to 0.63). Diagnostic performance was better at the group-level, with sensitivity and specificity for identification of non-contaminated gram-positive growths (i.e., cases that are widely considered to be candidates for antimicrobial treatment) being 0.84 and 0.75 (biplate), 0.76 and 0.90 (Accumast), 0.89 and 0.79 (Check-Up), 0.67 and 0.83 (Petrifilm), and 0.55 and 0.81 (Mastatest). In intensive herds, 22.7 to 40% of cases were classified as antimicrobial treatment candidates by index tests, which was less than for cows in non-intensive herds (41.3 to 61.0%). Despite limited diagnostic reliability at genus and species level, and the need to ensure samples are collected aseptically, our findings indicate that implementation of selective treatment protocols using the tests evaluated in this study would likely reduce antimicrobial usage in Australian herds.

Confirmed bacteriological diagnosis and cure of non-severe Gram-positive clinical mastitis cases enrolled in a randomized clinical trial based on results of on-farm culture

Our objectives were to describe the confirmed bacteriological diagnosis of mastitis pathogens cultured from cases of non-severe clinical mastitis (CM) identified as Gram-positive (GP) using on-farm culture and to compare differences in bacteriological cure (BC) based on antimicrobial (AM) therapy. Cows that developed non-severe CM in a single quarter were enrolled in a randomized clinical trial based on microbial growth on GP selective agars. Cows were randomly assigned to receive a once-daily intramammary treatment: 3d hetacillin (n = 69), 3d ceftiofur (n = 69), 8d ceftiofur (n = 70) or to a non-treated group (n = 32). Etiologies were confirmed with MALDI-TOF using frozen duplicate milk samples. The crude proportion of BC was determined using milk samples collected at 14, 21 and 28 d after enrollment for cases caused by Streptococci, non-aureus staphylococci (NAS), Strep-like organisms (consisting of Enterococcus and Lactococcus.; SLO) and Staph. aureus. Multivariable models were used to determine the effect of AM treatment on BC cure at d 21 for a subset of cases that had complete data for all covariates (n = 88). Growth on GP agar resulted in enrollment of 240 cases with confirmed etiologies distributed as Strep. spp (21.7%; n = 52), Lact. spp (19.2%; n = 46), NAS (16.3%; n = 39), Staph aureus (6.3%; n = 16), Entero spp (5.0%; n = 12) and others (10%; n = 24). Thirty-five (14.5%) duplicate milk samples collected from enrolled cows had no significant growth in the lab while 16 (6.7%) were contaminated. Among sampling dates, combined crude BC for cases caused by target pathogens ranged from 68 to 71%. Crude BC ranged from 58 to 73% for the small group of non-treated cases (n = 12) and 69–71% for the combined group of cases that received IMM AM (n = 113). Among all groups and all follow-up dates, crude BC was least for cases caused by Staph. aureus (ranging from 33 to 43%), followed by cases caused by SLO (58–67%), NAS (79–80%) and Strep. spp. (81–91%). The proportion of BC at 21d (LSM ± SE) did not vary between all cases that received AM (0.77 ± 0.06) and cases in the non-treated group (0.73 ± 0.16). The odds of BC at 21d was about 5x greater for cases that occurred in primiparous as compared with multiparous cows and decreased 1.3-fold for each 1 log unit increase in SCC before the case. While this study does not have sufficient power to detect small differences in BC among pathogen groups or treatments, our results demonstrate that CM is caused by a wide diversity of GP bacteria with varying ranges of BC. These results provide justification for inclusion of negative control groups in future studies and confirm that important characteristics such as parity and history of subclinical mastitis influence the probability of BC.

Comparison of Minimum Inhibitory Concentrations of Selected Antimicrobials for Non-Aureus Staphylococci, Enterococci, Lactococci, and Streptococci Isolated from Milk Samples of Cows with Clinical Mastitis.

The objective of this study was to compare the minimum inhibitory concentrations of antimicrobials included in a commercial broth microdilution panel among Gram-positive pathogens that caused non-severe clinical mastitis on three Michigan dairy farms. Duplicate quarter milk samples were collected from eligible quarters of cows enrolled in a randomized clinical trial, cultured in a university laboratory, and identified using MALDI-TOF. Etiologies were grouped by genus as Enterococcus species (n = 11), Lactococcus species (n = 44), non-aureus Staphylococcus species (n = 39), or Streptococcus species (n = 25). Minimum inhibitory concentrations (MICs) were determined using the mastitis panel of a commercially available broth microdilution test. In vitro susceptibility was determined using approved guidelines and included breakpoints for mastitis pathogens, or when not available, breakpoints from other species. Most isolates were inhibited at or below breakpoints that demonstrated in vitro susceptibility. The proportions of susceptible isolates varied among pathogens for pirlimycin, penicillin, and tetracycline. The greatest proportion of resistance was observed for pirlimycin, tetracycline, and sulfadimethoxine. Survival analysis was performed to evaluate differences in MICs among pathogen groups. MIC values varied among pathogens for ceftiofur, cephalothin, erythromycin, penicillin, pirlimycin, and tetracycline. However, nearly all isolates were susceptible to ceftiofur and cephalothin, indicating that pathogen differences in MIC are not likely clinically relevant, as these are the two most commonly administered mastitis treatments in the United States. While differences in vitro susceptibility were observed for some antimicrobials, susceptibility was high to cephalosporin-based IMM treatments that are most commonly used and did not vary among pathogens.

Efficacy of targeted therapy of environmental mastitis using on-farm culturing in small dairy herds

The aim of the study was to evaluate treatment protocols for improvement of clinical and bacteriological cure rate of non-severe clinical mastitis (CM) and selective dry cow therapy (SDCT). Mastitis management based on on-farm commercial culture system MicroMastTM and data analysis were implemented into two dairy herds. Quarters with evidence of Gram-positive agents were treated using benzyl penicillin or amoxicillin and/or by amoxicillin with clavulanic acid. In herd A, 31 quarters of non-severe CM were recorded. Of them, Streptococcus uberis was isolated in 16 (51.6%), non-aureus staphylococci (NAS) in 8 (25.8%), E. coli in 5 (16.1%) and no growth in 2 (6.5%) cases. Bacteriological cure was observed in 24/29 (82.8%) quarters. Antimicrobial consumption was reduced from 3.56 to 2.33 doses per case. Under the SDCT protocol, 28 quarters (13.2%) of 53 cows dried-off were included, achieving a reduction by 86.8% on the quarter level. In herd B, 23 quarters of non-severe CM were recorded. Of them, S. uberis and Escherichia coli were identified equally in 8 (34.8%) samples and NAS in 2 (8.7%) samples and with no growth in 5 (21.7%) cases. Bacteriological cure was achieved in 17/18 quarters (94.4%). Antimicrobial consumption was reduced from 4.45 to 1.83 doses per case. Only 5 (1.7%) quarters of 72 cows were included for SDCT with reduction in consumption of antimicrobials by 98.3% on the quarter level. In summary, innovated treatment protocols based on results of on-farm culture enabled a significant reduction of antimicrobial consumption and improvement of bacteriological cure rate in conditions of practise.

Metritis and clinical mastitis events in lactating dairy cows were associated with altered patterns of rumination, physical activity, and lying behavior monitored by an ear-attached sensor

Understanding changes in parameters recorded by automated health monitoring systems based on ear-attached sensors on the days immediately before and after diagnosis of metritis and clinical mastitis can help develop dairy cow health monitoring strategies. The objective of this observational cohort study was to characterize rumination time, physical activity, and lying time monitored by an ear-attached sensor before, during, and after clinical diagnosis (CD) of metritis and clinical mastitis. Lactating Holsteins monitored daily for 21 d in milk for detection of health disorders were retrospectively included in the no clinical health disorder group (NCHD; n = 616) if no disorders were diagnosed. Cows were included in the metritis (MET; n = 69) or clinical mastitis (MAST; n = 36) group if diagnosed only with nonsevere metritis (watery, reddish, and fetid uterine discharge with or without pyrexia) or nonsevere clinical mastitis (visibly abnormal milk secretion with or without signs of udder inflammation, with no pyrexia and no systemic signs of disease), respectively. Cows diagnosed with severe metritis (signs of metritis plus systemic signs of disease) or severe clinical mastitis (signs of mastitis plus pyrexia and systemic signs of disease), and cows diagnosed with nonsevere metritis or clinical mastitis plus another disorder within -7 to +7 d of CD of metritis or clinical mastitis diagnosis, were included in the metritis plus (MET+; n = 25) or the clinical mastitis plus (MAST+; n = 15) group, respectively. Cows were fitted with an ear-attached accelerometer to measure rumination time, physical activity, and lying time. Mean daily values, mean value absolute change, and relative change for the mean daily value from 3 or 5 d before CD to the nadir for cows with metritis and clinical mastitis, respectively, were analyzed with linear mixed models with or without repeated measures. Rumination time and physical activity were lesser, and lying time was greater for the MET and MET+ groups than for the NCHD group for most days from -4 to +7 d of CD of metritis. Generally, daily rumination time, physical activity, and lying time differences were greater and more prolonged between the MET+ and NCHD than between the MET and NCHD groups. Similarly, cows in the MAST and MAST+ groups had lesser rumination time and physical activity than cows in the NCHD group for several days before diagnosis. Lying time was greater for the MAST+ than the NCHD group on d -1 and 0 relative to CD. Absolute values and relative changes from 3 d before CD to the day of the nadir for rumination time and physical activity, or peak for lying time, were different for cows in the MET and MET+ groups than for the NCHD group. Similar results were observed for the MAST and MAST+ groups compared with the NCHD group. For cows with metritis, either an increase in rumination time and physical activity or a decrease in lying time was observed from the day of CD to resolution of clinical signs, but no changes were observed for the NCHD. Cows with clinical mastitis and the NCHD group had different rumination times, physical activity, and lying times on the day of CD and resolution of clinical signs, but cows with clinical mastitis had no significant changes from the day of CD to resolution of clinical signs. We conclude that cows affected by metritis and clinical mastitis presented substantial alterations of the patterns of rumination time, physical activity, and lying time captured by an ear-attached sensor. Thus, automated health monitoring systems based on ear-attached sensors might be used as an aid for identifying cows with metritis and clinical mastitis. Moreover, behavioral parameter changes after CD might be good indicators of resolution of clinical signs of metritis but not mastitis.

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.

Non-inferiority Trial Investigating the Efficacy of Non-steroidal Anti-inflammatory Drugs and Antimicrobial Treatment of Mild to Moderate Clinical Mastitis in Dairy Cows With Long-lasting Udder Diseases.

To reduce ineffective antimicrobial usage in the treatment of non-severe clinical mastitis (CM) in cows with long-lasting udder diseases, non-antibiotic therapy with a non-steroidal anti-inflammatory drug (NSAID) was conducted and evaluated in a non-blinded, positively controlled, non-inferiority trial. Therefore, three-time systemic ketoprofen treatment at intervals of 24 h was evaluated in comparison with the reference treatment of solely antibiotic therapy in a field study on nine free-stall dairy farms located in Northern Germany. Cows with previous CM cases in current lactation and/or with long-lasting high somatic cell counts in preceding dairy herd improvement test days were randomly allocated to one of the two treatment groups in cases of mild to moderate CM. Quarter foremilk samples of the affected quarters were taken for cyto-bacteriological investigation before treatment as well as ~14 and 21 d after termination of therapy. Both treatment groups were compared regarding the bacteriological cure (BC) as the primary outcome. Clinical cure (CC) and no CM relapse within 60 d after the end of treatment (no R60) were chosen as secondary outcomes. The study resulted in the following outcomes: Streptococcus uberis was most frequently identified in microbiological culture from pre-treatment samples, followed by Staphylococcus aureus and Escherichia coli and other coliforms. No significant differences between the NSAID treatment and the reference treatment were detected regarding CC and CM recurrence (no R60). Although the sole ketoprofen therapy resulted in a numerically lower likelihood of BC, there were no significant differences to the reference treatment. Considering the selection criteria in this study, the results indicate that in mild to moderate CM cases exclusive treatment with ketoprofen may constitute an alternative to antimicrobial intramammary therapy, providing an opportunity for reduction of antibiotic usage. However, non-inferiority evaluations were inconclusive. Further investigations with a larger sample size are required to confirm the results and to make a distinct statement on non-inferiority.

Laboratory-based evaluation of a simplified point-of-care test intended to support treatment decisions in non-severe bovine clinical mastitis

To limit the use of antimicrobials in dairy cattle, farmers are increasingly encouraged to adopt targeted treatment decisions based on knowledge of the pathogens causing clinical mastitis (CM), whereby treatment of non-severe CM is generally recommended for gram-positive mastitis but not for gram-negative or culture-negative mastitis. The objectives of this study were to conduct a laboratory-based evaluation of the performance of a simplified slide test as a tool to differentiate gram-positive CM from other cases of CM, and to compare its performance against a commercially available on-farm test that is commonly used in our area (VétoRapid). Test outcomes after 24-48 h incubation were compared to results from bacteriological culture and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS). Milk samples (n = 156) were obtained from cases of severe and non-severe CM on seven farms and collected by farm personnel. After removal of small numbers of contaminated samples and organisms with unknown species identity, the simplified slide test showed high sensitivity and accuracy (>80%), similar to the comparator test. For most outcomes of interest (culture positive, Escherichia coli, or gram-positive growth), the specificity of the slide test was higher than the specificity of the comparator test. When considering non-severe cases of CM only, and interpreting detection of gram-positive organisms as indicative of the need for antimicrobial treatment, the simplified test had higher specificity (77.4% v. 60.4%) and higher positive predictive value (79.7% v. 70.0%) than the comparator test and similar sensitivity (83.9% v. 87.5%). The proportion of sampled CM cases, contaminated samples and gram-positive mastitis cases - which affects the positive and negative predictive value, the economic value of diagnostic testing and its potential to reduce antimicrobial use - differed between farms. The simplicity and accuracy of the slide test could make it an attractive tool for farmers to target antimicrobial treatment of non-severe clinical mastitis.

Critically important antimicrobials are generally not needed to treat nonsevere clinical mastitis in lactating dairy cows: Results from a network meta-analysis

There is ongoing debate regarding whether critically important antimicrobials (CIA) should be used to treat infections in food-producing animals. In this systematic review, we determined whether CIA and non-CIA have comparable efficacy to treat nonsevere bovine clinical mastitis caused by the most commonly reported bacteria that cause mastitis worldwide. We screened CAB Abstracts, Web of Science, MEDLINE, Scopus, and PubMed for original epidemiological studies that assessed pathogen-specific bacteriological cure rates of antimicrobials used to treat nonsevere clinical mastitis in lactating dairy cows. Network models were fit using risk ratios of bacteriological cure as outcome. A total of 30 studies met inclusion criteria. Comparisons of cure rates demonstrated that CIA and non-CIA had comparable efficacy for treatment of nonsevere clinical mastitis in dairy cattle. Additionally, for cows with nonsevere clinical mastitis caused by Escherichia coli and Klebsiella spp., bacteriological cure rates were comparable for treated versus untreated cows; therefore, there was no evidence to justify treatment of these cases with CIA. Our findings supported that CIA in general are not necessary for treating nonsevere clinical mastitis in dairy cattle, the disease that accounts for the majority of antimicrobial usage in dairy herds worldwide. Furthermore, our findings support initiatives to reduce or eliminate use of CIA in dairy herds.

Knowledge, attitude and practices of Swiss dairy farmers towards intramammary antimicrobial use and antimicrobial resistance: A latent class analysis

Understanding farmers’ mindsets is important to improve antimicrobial stewardship in the dairy industry. This cross-sectional study aimed to determine farmers’ knowledge, attitude, and practices with respect to lactational intramammary antimicrobial use (AMU) and antimicrobial resistance (AMR) in Swiss dairy herds. Based on their approach towards subclinical mastitis (SCM) and non-severe cases of clinical mastitis (CM), subgroups of farmers were identified and compared regarding their knowledge, attitude and practices towards AMU and AMR. After conducting qualitative interviews to develop a questionnaire, an online survey was sent to 1296 randomly selected Swiss dairy farmers. Information was gathered on demographic data and farmers’ knowledge, attitude, and practices towards AMU and AMR. A latent class analysis was performed to identify subgroups of farmers based on management of SCM and non-severe CM cases. Based on the results of 542 completed questionnaires, poor knowledge with respect to AMU and AMR was identified, as well as discrepancies between farmers’ perceptions and their actual practices. Farmers approached cows with SCM and non-severe CM similarly, indicating they perceived both mastitis states as the same disease. Intramammary antimicrobial products containing cefquinome, which is a highest priority critically important antimicrobial, were among the 3 most commonly applied intramammary antimicrobials. Five latent classes of farmers were identified based on their management towards SCM and non-severe CM. One group of farmers (18.5% of respondents) indicated that they did not treat those mastitis cases, one group only treated SCM cases (13.8% of respondents), one group only treated non-severe CM cases (28.6% of respondents) and the largest group treated both mastitis states (39.1% of respondents). The latter group was subdivided into a latent class of farmers following guidelines for AMU/AMR (25.5% of respondents) and a group of farmers that were not strictly following these guidelines (13.7% of respondents). Regional differences between farmers, according to altitude and language region, explained some of the variation in latent class membership. Latent class membership was associated with farmers’ attitude to use antimicrobials as little as possible and with using antimicrobials only after performing bacteriological and susceptibility testing. This study gave detailed insight into Swiss farmers’ knowledge, attitude, and practices regarding AMU and AMR and provides opportunities to improve antimicrobial stewardship in Swiss dairy herds. The identified groups of farmers, based on their management practices regarding SCM and non-severe CM, may help to design tailored intervention strategies for improving prudent AMU in the heterogeneous population of dairy farmers in Switzerland.

Molecular epidemiology of nonsevere clinical mastitis caused by Klebsiella pneumoniae occurring in cows on 2 Wisconsin dairy farms

The objective of this study was to describe diversity of Klebsiella pneumoniae isolated from milk collected at detection of nonsevere (abnormal milk or abnormal udder) clinical mastitis (CM) and during a follow-up period. Cases were detected in cows enrolled in a randomized clinical trial (n = 168) conducted using 2 related Wisconsin dairy farms. Cases were randomly assigned to receive 2 d (n = 18) or 8 d (n = 18) of intramammary infusions with an approved product containing ceftiofur hydrochloride or assigned to a negative control group (n = 17). Milk samples were collected from affected quarters at detection and during a 28-d follow-up period. Sufficient DNA was recovered from 53 of 54 Kleb. pneumoniae cultured from quarter milk samples collected at detection of the incident case. Additional Kleb. pneumoniae were recovered from milk samples collected from the same quarters at 14, 21, and 28 d after case detection (n = 35), at detection of recurrent cases in the same quarter (n = 14), and from new cases of CM (n = 3) occurring in enrolled quarters. All Kleb. pneumoniae were used for molecular typing by pulsed-field gel electrophoresis and 90% similarity was used to define homology. Of Kleb. pneumoniae recovered from incident cases, unique strains (n = 41) were identified in milk samples collected from cows on farm A (n = 19) and farm B (n = 22), whereas 12 clonal strains were identified with 8 found only in milk collected from farm A and 4 found in milk samples collected from cows on both farms. Heterogeneous strains of Kleb. pneumoniae genotypes were isolated from incident cases of CM. However, when intramammary infection persisted or when recurrence of CM occurred, clonal strains were isolated at 14, 21, or 28 d. Similar strains of Kleb. pneumoniae genotypes caused persistent CM. In conclusion, initial cases of CM were caused by a wide genetic diversity of Kleb. pneumoniae, but when IMI persisted, the same strain often persisted within the mammary gland up to 28 d.

Understanding the economic impact of mastitis therapy

Mastitis occurs on all dairy farms, and veterinarians can help producers reduce losses and promote more judicious antimicrobial usage. In the US, 7 intramammary (IMM) antibiotics are approved for treatment of mastitis, but no antibiotics are approved for systemic treatment of mastitis. Most cases of clinical mastitis present with mild or moderate clinical signs and there is no evidence that use of systemic antimicrobials is of benefit. Farmers typically underestimate costs associated with treatment of clinical mastitis, and about 75% of costs are associated with milk discard. Selection of drugs and duration of treatment are both areas that can have significant impact on economic losses associated with mastitis therapy. The distribution of etiologies is associated with the value of antimicrobial therapy, and use of intramammary antibiotics should be determined based on knowledge of etiology. Clinical outcomes of most mastitis cases that are culture-negative or caused by E. coli are not improved by use of antimicrobials, and considerable losses can be incurred when longer-duration therapy is used as the standard protocol. When etiology of non-severe clinical mastitis is unknown, use of narrow-spectrum IMM antimicrobials for short duration results in optimal economic outcomes.

Short communication: Longitudinal study of quarter-level somatic cell responses after naturally occurring, nonsevere clinical mastitis diagnosed as culture negative, or caused by Escherichia coli or Klebsiella pneumoniae, and randomly assigned to a no-treatment group or to receive intramammary ceftiofur

The objective of this study was to describe weekly quarter-level somatic cell count (QSCC) after occurrence of nonsevere clinical mastitis (CM) that was diagnosed as culture negative, or caused by Escherichia coli or Klebsiella pneumoniae. All cases occurred in cows enrolled in negatively, controlled randomized clinical trials. We hypothesized that after occurrence of CM, QSCC patterns would vary among etiologies and this effect would not be mitigated by treatment using intramammary (IMM) ceftiofur. Data from two previously published randomized clinical trials performed on 3 Wisconsin dairy farms were used. Only cases confirmed as culture negative (NG) or E. coli or Kleb. pneumoniae (GRAMNEG) were used for analysis. In NG, cows were assigned to no antimicrobial treatment (negative control, n = 44) or 5 d of once daily IMM (n = 41) infusions with an approved product containing ceftiofur hydrochloride. In GRAMNEG, cows were assigned to IMM treatment with the same ceftiofur product for 2 different durations (2 d, n = 36; or 8 d, n = 38) or no antimicrobial treatment (negative control, n = 36). For quarters enrolled in NG, no significant differences were identified for weekly QSCC between quarters in the treated or negative control groups (5.4 log10SCC for both groups). For quarters enrolled in GRAMNEG, no significant differences were identified for QSCC between quarters that received the 2-d (6.2 log10SCC) or 8-d (6.3 log10SCC) IMM treatment or were in the negative control group (6.0 log10SCC). At the pathogen level, regardless of treatment, QSCC varied among pathogens and log10SCC were 5.4 (culture negative), 5.8 (E. coli), and 6.2 (Kleb. pneumoniae). Patterns of QSCC of CM diagnosed as culture negative and E. coli were similar in magnitude and time to resolution of the inflammatory response. In conclusion, as compared to CM diagnosed as culture negative or caused by E. coli, CM caused by Kleb. pneumoniae was associated with poorer outcomes. Regardless of IMM ceftiofur treatment, the immune response of the cow resulted in rapid reduction of SCC of quarters diagnosed as culture negative and quarters with CM caused by E. coli. In contrast, the SCC remained elevated for quarters with CM caused by Kleb. pneumoniae and a greater proportion of those cases remained chronically infected.

The microbiome of Escherichia coli and culture-negative nonsevere clinical mastitis: Characterization and associations with linear score and milk production

Culture-negative and Escherichia coli cases are uncommonly treated in pathogen-based protocols for nonsevere mastitis. High-throughput 16S rRNA sequencing might reveal the presence of other pathogens and can provide information on microbial diversity. The objective was to explore the milk microbiome at the time of the mastitis event (enrollment) and its association with survival in the herd, milk production, and postevent linear score (LS) for cows with clinical mastitis characterized as negative or E. coli by culture. Fifty E. coli-positive and 35 culture-negative samples from cases were enrolled. No cases were treated with antimicrobials. All E. coli-positive quarters were characterized as transient; microbiological culture of samples taken 15 d postmastitis were negative for this organism. However, a difference in α-diversity (Shannon index) was present between enrollment and follow-up samples (3.8 vs. 5.1). When α-diversity was explored for enrollment E. coli samples, no relationship was observed between the Shannon indices of these samples and postmastitis LS. Alpha-diversity of the enrollment samples was lower for E. coli-positive cows that subsequently had greater losses in milk production. This difference was explained by a greater relative abundance of the family Enterobacteriaceae (67.8 vs. 38.4%) for cows that dropped in production. Analysis of composition of the microbiome identified one phylum, Proteobacteria, that differed between E. coli-positive cows that dropped in production and those that did not. Evaluation of β -diversity found no statistical relationship between postmastitis LS and the microbiome. When evaluating α- and β-diversities and composition of the microbiomes for culture-negative quarters, no associations were found for milk production changes and postmastitis LS. Three cows did not remain in the herd, limiting the ability to analyze survival. The findings suggest that a contributing factor to negative outcomes in E. coli-positive cows is relative abundance of this pathogen, and that no single or collective group of bacterial families is associated with milk production changes or postmastitis LS in culture-negative quarters. Although additional studies should be performed, the absence of associations between outcomes explored and microbial profiles in this study suggests that we are not missing opportunities by not treating nonsevere E. coli or culture-negative mastitis cases.

The microbiome of Escherichia coli and culture-negative nonsevere clinical mastitis

Culture-negative and Escherichia coli cases are uncommonly treated in pathogen-based protocols for nonsevere clinical mastitis (CM). High-throughput sequencing might reveal missed treatment opportunities in regards to the presence of other pathogens and can provide information on microbial diversity. We wished to explore the milk microbiome and its association with milk production and postevent linear score (LS) for cows with CM characterized as negative or E. coli by culture. Our first objective was to explore the microbiome of cows with E.coli CM to determine if microbial profiles differ between cows that had positive (no drop in milk production or a next-test LS of <4.0) or negative (a drop in milk production or a next test LS of ~4.0) outcomes when not treated. Our second objective was to explore the microbiome of cows with culture-negative CM to determine if microbial profiles differ between cows that had positive or negative outcomes. Characterizing these associations will improve our understanding of CM, allowing for more effective treatment strategies.

Promoting prudent use of antimicrobials on moderate-sized dairies

Selective treatment strategies for clinical mastitis (CM) promote targeted treatment of cases that will benefit from antibiotics, such as quarters infected with gram-positive organisms. A published trial by our group evaluated outcomes for the use of 24 h turnaround of culture results 7 d/wk to guide treatment decisions. In that study, cultures were performed at a certified diagnostic laboratory allowing for accuracy ofresults and confirmation of contagious and more obscure organisms. However, many dairies may not have access to a reference laboratory with a 24 h turnaround. The purpose was to determine if a selective treatment protocol for non-severe CM could be effectively implemented on the moderate-sized dairies of NY (500 to 1000 cows) that might not have daily access to a professional diagnostic laboratory.

Randomized noninferiority field trial evaluating cephapirin sodium for treatment of nonsevere clinical mastitis

The general objective of this study was to evaluate whether cephapirin sodium is noninferior compared with a positive control broad-spectrum product formulated with a combination of antimicrobials for intramammary treatment of nonsevere clinical mastitis. In addition, we compared the efficacy of treatments on the cure risks of pathogen groups (gram-positive, gram-negative, and cultures with no growth) based on culture results. A total of 346 cows distributed in 31 commercial dairy herds were selected to participate in the study, although only 236 met the criteria for evaluation of microbiological cure. Coagulase-negative staphylococci were the most isolated gram-positive pathogens in pretreatment milk samples, whereas the most common gram-negative bacterium was Escherichia coli. Cows attending the postadmission criteria were treated with 4 intramammary infusions (12 h apart) of one of the following antimicrobials: 300 mg of cephapirin sodium + 20 mg of prednisolone (CS), or the positive control treatment formulated with a combination of antimicrobials (200 mg of tetracycline + 250 mg of neomycin + 28 mg of bacitracin + 10 mg of prednisolone; TNB). Noninferiority analysis and mixed regression models (overall and considering the pathogen groups) were performed for the following outcomes: bacteriological cure (absence of the causative pathogens in cultures performed in milk samples collected at 14 and 21 ± 3 d after enrollment), pathogen cure (absence of any pathogen on both follow-up samples), clinical cure (absence of clinical sign in the milk and mammary gland at 48 h after the last antimicrobial infusion), extended clinical cure (normal milk and normal gland on the second posttreatment sample collection (d 21), and linear score of somatic cell count cure [linear score of somatic cell count recovery (≤4.0) on d 21 ± 3 after enrollment]. No significant differences were observed between treatments regarding any of the evaluated outcomes in both regression models (overall and considering the pathogen groups). Noninferiority of CS relative to TNB was inconclusive for bacteriological cure (CS = 0.68; TNB = 0.73) and clinical cure (CS = 0.88; TNB = 0.94), as the confidence intervals crossed the pre-stated margin of noninferiority (Δ = -0.15). Cephapirin sodium was noninferior compared with TNB for pathogen cure (CS = 0.36; TNB = 0.35), extended clinical cure (CS = 0.93; TNB = 0.92), and linear score of somatic cell count cure (CS = 0.29; TNB = 0.28). In conclusion, the use of intramammary CS for treatment of nonsevere clinical mastitis has similar efficacy as a treatment regimen with a combination of antimicrobial agents (tetracycline + neomycin + bacitracin), although noninferiority analysis showed inconclusive results for bacteriological and clinical cures.

Randomized non-inferiority trial comparing two commercial intramammary antibiotics for the treatment of non-severe clinical mastitis in dairy cows

No new antimicrobials have been approved for the treatment of mastitis since 2006; it would be beneficial to perform controlled field trials comparing 2 existing treatments. Non-inferiority trials are valuable in this regard, as they do not require a negative control as in a randomized, controlled FDA drug trial. If a therapy with similar efficacy is available, decision making criteria can include convenience, lower costs, less side effects, improved delivery systems, and better integration into current protocols. The purpose was to perform a non-inferiority comparison of 2 intramammary treatments for clinical mastitis (CM). We intended to show that hetacillin had comparable efficacy to the reference treatment, ceftiofur when considering cure and survival indices.

Randomized noninferiority trial comparing 2 commercial intramammary antibiotics for the treatment of nonsevere clinical mastitis in dairy cows.

The purpose was to evaluate 2 intramammary treatments for mild-to-moderate cases of clinical mastitis in a noninferiority comparison. Noninferiority trials are intended to show whether a given treatment, hetacillin potassium, has at least comparable efficacy as the reference treatment, ceftiofur hydrochloride. Treatments can be deemed inferior to the reference treatment by an amount less than the margin of noninferiority, or inconclusive if the confidence interval crosses the margin of noninferiority. Cows with clinical mastitis from 6 farms were considered for enrollment. Using a randomized design, cows with mild or moderate mastitis in 1 quarter were assigned to on-label treatment with either ceftiofur or hetacillin. A total of 596 cows met the criteria needed for continued enrollment. Treatment distribution resulted in 309 cows in the ceftiofur group and 287 cows in the hetacillin group. Mixed regression analysis was performed for the following outcomes: bacteriological cure, pathogen cure, clinical cure, postevent milk production and linear score, and survival to d 30 and 60. Cox proportional hazards analysis was used to describe treatment effect on survival and mastitis risks. Bacteriological cure, defined as absence of causative organism in samples retrieved at d 14 and 21 postmastitis, was similar between groups. No significant statistical differences were found in cure risk, and noninferiority of hetacillin relative to ceftiofur for bacteriological cure was conclusive (hetacillin=67%, ceftiofur=72%). Absence of a pathogen on both follow-up samples designated a cow as a pathogen cure. Pathogen cure was similar between treatment groups and noninferiority of hetacillin relative to ceftiofur was shown (hetacillin=35%, ceftiofur=32%). Clinical cure (hetacillin=68%, ceftiofur=64%), postevent milk production (hetacillin=37.0kg, ceftiofur=38.2kg), and linear scores (hetacillin=3.4, ceftiofur=3.1) were also not statistically different between treatment groups. Noninferiority of hetacillin relative to ceftiofur was shown for survival to d 30 and survival to d 60, whereas hetacillin was more likely to have a clinical cure than ceftiofur by d 4. No differences were seen between groups when Cox proportional hazards were performed, neither for exit from the herd in the 60 d following the event nor in the risk for a subsequent mastitis event. These findings can be used to develop farm-specific protocols for clinical mastitis treatment.