Negatively controlled trial investigating the effects of dry cow therapy on clinical mastitis and culling in multiparous cows.

Blanket dry cow therapy (DCT) is a major contributor to overall antibiotic usage on dairy farms in the United States. With low prevalence of intramammary infections at dry-off in US herds today, alternative DCT approaches have been the focus of much research. We hypothesized that complete cessation of DCT [i.e., use of internal teat sealants (ITS) only at dry-off] could be a practical alternative to blanket DCT in well-managed herds. The objective of this negatively controlled clinical trial was to determine the effects of DCT on clinical mastitis (CM) and removal from the herd during the dry period and the first 200 d of the subsequent lactation in multiparous dairy cows treated with only ITS at dry-off. As a secondary objective, we conducted exploratory analysis to identify subpopulations in the herd (based on parity, previous CM history, and dry-period length) where DCT would not affect postcalving udder health, to generate hypotheses about potential alternative selective DCT programs. The study was conducted in a commercial dairy herd in South Dakota from June 2020 to January 2021. Dry-off sessions (n = 43) were scheduled such that all cows at a given session were dried off using ITS alone (ITS only, n = 20 sessions, n = 1,108 cows) or an intramammary DCT product containing 500 mg of cloxacillin (Dry-Clox, Boehringer Ingelheim) followed by ITS (ITS+ABX, n = 23 sessions, n = 1,331 cows). Culling and CM events were recorded by farm workers who were blinded to the treatment status of cows. Hazard ratios (HR) for the effects of the treatment group on CM and removal from the herd were estimated using multivariable Cox proportional hazards, adjusting for the clustered treatment allocation strategy. Risk of removal from the herd during the dry period was lower in ITS+ABX than ITS-only cows (1.1 vs. 2.7%; HR = 0.45; 95% CI: 0.25 to 0.81). Risk of removal from the herd during the first 200 d of lactation was similar in ITS+ABX and ITS-only cows (17.3 vs. 18.0%; HR = 0.98; 95% CI: 0.82 to 1.18). Risk of CM during the first 200 d of lactation was lower in ITS+ABX cows (6.9%; HR = 0.56; 95% CI: 0.41 to 0.76) compared with ITS-only cows (13.4%). The beneficial effects of DCT on CM and removal from the herd were consistently observed across strata of parity, previous CM history, and dry-period length, indicating that no subpopulations could be identified to withhold DCT. The findings from this study indicate that the omission of DCT from the dry-off procedure, when udder health is not taken into consideration, in multiparous cows can have a negative effect on cow health and welfare. Findings from previous research suggest that culture- or algorithm-guided selective dry cow therapy are likely to be safer approaches to improving antibiotic stewardship.

Prevalence, antibiotic resistance, virulence and genetic diversity of Staphylococcus aureus isolated from bulk tank milk samples of U.S. dairy herds.

BACKGROUND: Colonization of dairy cows by Staphylococcus aureus (S. aureus), especially those which are multi-drug resistant and toxin producing, is a concern for animal health and well-being as well as public health. The objective of this study was to investigate the prevalence, antibiotic resistance, gene content and virulence determinants of S. aureus in bulk tank milk samples (BTM) from U.S. dairy herds. RESULTS: BTM samples were collected, once in winter and once in summer, from 189 U.S. dairy herds. Of 365 BTM samples cultured, the sample and herd prevalence of S. aureus in BTM was 46.6% (170 of 365 samples) and 62.4% (118 of 189 herds), respectively. Among a subset of 138 S. aureus isolates that were stored for further analysis, 124 were genome sequenced after being confirmed as S. aureus using phenotypic tests. The most commonly identified antimicrobial resistance-associated gene was norA (99.2%) and mecA gene responsible for methicillin resistance (MRSA) was identified in one isolate (0.8%). The most frequently detected putative virulence genes were aur (100%), hlgB (100%), hlgA, hlgC, hlb (99.2%), lukE (95.9%) and lukD (94.3%). In the 53 staphylococcal enterotoxin positive isolates, sen (37.9%), sem (35.5%), sei (35.5%) and seg (33.1%) were the most frequently detected enterotoxin genes. Among the 14 sequence types (ST) and 18 spa types identified, the most common was ST2187 (20.9%) and t529 (28.2%), respectively. The most predominant clone was CC97 (47.6%) followed by CC unknown (36.3%). The single MRSA isolate belonged to ST72-CC8, spa type t126 and was negative for the tst gene but harbored all the other virulence genes investigated. CONCLUSION: Our findings indicated a high prevalence of S. aureus in BTM of U.S. dairy herds, with isolates showing little evidence of resistance to antibiotics commonly used to treat mastitis. However, isolates often carried genes for the various enterotoxins. This study identified predominant genetic clones. Despite lower prevalence, the presence of MRSA and multi-drug resistant strains in BTM poses a significant risk to animal and public health if their number were to increase in dairy environment. Therefore, it is necessary to continuously monitor the use of antibiotics in dairy cows.

Evaluation of the matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) system in the detection of mastitis pathogens from bovine milk samples.

MALDI-TOF is a chemistry analytical tool that has recently been deployed in the identification of microorganisms isolated from nosocomial environments. Its use in diagnostics has been extremely advantageous in terms of cost effectiveness, sample preparation easiness, turn-around time and result analysis accessibility. In the dairy industry, where mastitis causes great financial losses, a rapid diagnostic method such as MALDI-TOF could assist in the control and prevention program of mastitis, in addition to the sanitation and safety level of the dairy farms and processing facility. However, the diagnostic strengths and limitations of this test method require further understanding. In the present study, we prospectively compared MALDI-TOF MS to conventional 16S rDNA sequencing method for the identification of pathogens recovered from milk associated with clinical and subclinical bovine mastitis cases. Initially, 810 bacterial isolates were collected from raw milk samples over a period of three months. However, only the isolates (481) having both 16S rDNA sequencing and MALDI-TOF identification were included in the final phase of the study. Among the 481 milk isolates, a total of 26 genera (12 g-postive and 14 g-negative), including 71 different species, were taxonomically charecterized by 16S rDNA at the species level. Comparatively, MALDI-TOF identified 17 genera (9 g-positive and 8 g-negative) and 33 differernt species. Overall, 445 (93%) were putatively identified to the genus level by MALDI-TOF MS and 355 (74%) were identified to the species level, but no reliable identification was obtained for 16 (3.3%), and 20 (4.2%) discordant results were identified. Future studies may help to overcome the limitations of the MALDI database and additional sample preparation steps might help to reduce the number of discordances in identification. In conclusion, our results show that MALDI-TOF MS is a fast and reliable technique which has the potential to replace conventional identification methods for common mastitis pathogens, routinely isolated from raw milk. Thus it's adoption will strengthen the capacity, quality, and possibly the scope of diagnostic services to support the dairy industry.

Effects of an 8-Week Dairy Production Medicine Course on Veterinary Student Self-Confidence and Perceptions of Knowledge and Skills Used by Dairy Veterinarians.

The 8-week dairy production medicine course at the National Center of Excellence in Dairy Production Medicine Education for Veterinarians is designed to equip senior veterinary students with the knowledge and skills needed to serve the dairy industry. Course developers identified 59 topics of importance for dairy production medicine veterinarians. Students (N = 50) were surveyed before and after the course to determine their perceptions of (a) the importance of the 59 topics for their intended positions and (b) their knowledge and skill in those areas. We expected the course to affirm or strengthen perceptions of importance and increase confidence. Students rated 57 of the topics as moderately or very important before the course. Ratings were unchanged (56 topics) or increased (3 topics) after the course. Before the course, students believed they had a lot of knowledge and skill in just one area: animal behavior and handling. At the end of the course, students believed they had a lot of knowledge and skill in 21 areas; confidence ratings were higher for 47 of the 59 topics. Alumni were surveyed 1-2 years after graduation to determine the importance of the 59 topics to their positions, their impressions about how well the course prepared them in those areas, and whether they referred back to course materials. Feedback was used to adjust the course. The topics alumni rated as most important were similar to those students predicted would be most important. Seventy-five percent of alumni used the course website as a resource in practice.

Methods Used to Assess Student Performance and Course Outcomes at the National Center of Excellence in Dairy Production Medicine Education for Veterinarians.

Between 2012 and 2014, three cohorts of senior veterinary students participated in an 8-week dairy production medicine course created by the National Center of Excellence in Dairy Production Medicine Education for Veterinarians. One goal of this course is to better prepare veterinary students to serve the increasingly complex needs of the dairy industry. In this article, we describe the assessment methods and student performance outcomes of those first three cohorts. A combination of assessment methods was used, including pre- and post-testing; instructor observations and scores on individual and group projects, including a final integrative project; and peer evaluation. Student feedback, collected via anonymous survey, provided insight into students' perceptions about the course and their learning. Performance and feedback suggest that the course was successful in preparing students for careers using skills in dairy production medicine. Pre- and post-testing was conducted for most topic modules in the course. The mean (median) pre- and post-test scores were 47% (50% ) and 83% (88%), respectively. The mean improvement in score was significant (p < .002) for all modules and cohorts. Students indicated a moderate or high degree of confidence in performing dairy production medicine skills after each module. Of students in cohorts 1, 2, and 3, respectively, 55%, 75%, and 82% felt they could provide dairy production medicine services (e.g., records analysis, problem investigation, protocol and standard operating procedure design) either alone or with some mentoring, immediately after graduation. In addition, assessment results and student feedback enabled timely course modifications during these first three cohorts.

Development and Implementation of a National Center of Excellence in Dairy Production Medicine Education for Veterinary Students: Description of the Effort and Lessons Learned.

The need for consortial programs to provide advanced education in food animal veterinary production medicine has been recognized and lauded for nearly three decades. This article describes one effort to create a dairy production medicine curriculum funded by a United States Department of Agriculture (USDA) Higher Education Challenge Grant. This National Center of Excellence in Dairy Production Medicine Education for Veterinarians is housed at the Dairy Education Center of the University of Minnesota and the project was a collaboration of the University of Minnesota, the University of Illinois, the University of Georgia, and Kansas State University. The article reviews the need for innovative ways to educate students who will optimally serve the dairy industry, provides a broad overview of the process of developing and delivering the eight-week dairy production medicine curriculum, and describes the challenges faced and lessons learned as a result of offering such a program.

Evaluation of rapid culture, a predictive algorithm, esterase somatic cell count and lactate dehydrogenase to detect intramammary infection in quarters of dairy cows at dry-off.

Our objective was to compare four tests to standard milk culture followed by MALDI-ToF in quarters of cows at dry-off. Cows (n = 432) were randomly selected from seven U.S. dairy herds already participating in a multi-site clinical trial in summer 2018. Aseptic foremilk samples were collected from quarters (n = 1728) two days prior to dry-off, and subjected to index and reference tests. The four index tests included rapid culture, a predictive algorithm, an esterase strip test measuring somatic cell count (SCC) and a cow-side lactate dehydrogenase (LDH) test. Rapid culture was performed by inoculating quarter milk samples onto a commercial rapid culture plate. Plates were evaluated by technicians after 30-40 h of incubation at 37 ± 2 °C. Quarters were classified as infected if any bacterial growth was observed. For the algorithm test method, all quarters were classified as infected if the cow met any of the following criteria: 1) any Dairy Herd Improvement Association (DHIA) test with a SCC > 200,000 cells / ml during the current lactation or 2) two or more clinical mastitis cases during the current lactation. Esterase-SCC and cow-side LDH tests involved adding milk to the test strip and reading for color changes. For esterase-SCC and cow-side LDH tests, low (≥250 cells / ml and ≥100 U / L) and high (≥500 cells / ml and ≥200 U / L) thresholds were used to classify quarters as infected or not. Composite samples (4 × 2 mL quarter-milk samples commingled) were also tested for rapid culture, esterase-SCC and cow-side LDH tests, such that if a composite sample was positive, then all quarters contributing to that sample were classified as infected. The reference test was traditional aerobic culture conducted in an accredited laboratory using MALDI-ToF for identification of isolates. Traditional culture was only conducted on quarter-milk samples, and consequently, IMI was always considered at the quarter-level. Unconditional logistic regression was used to estimate sensitivity (SE), specificity (SP), apparent prevalence, positive predictive values (PPV) and negative predictive values (NPV) for each index test. Cohen's Kappa (κ) was used to measure agreement between tests. Algorithm, esterase-SCC and cow-side LDH tests had poor agreement with the reference test (κ ranging from 0.01 to 0.12), while rapid culture had fair agreement (κ = 0.28). No test had concurrently high SE and SP. Negative predictive values were moderate to high for all tests.

Prior Experience, Career Intentions, and Post-Graduate Positions of Veterinary Students Who Participated in an 8-week Dairy Production Medicine Course.

Three cohorts of senior veterinary students (n = 50) from seven United States (US) colleges of veterinary medicine took an 8-week dairy production medicine course at the Dairy Center of Excellence in Production Medicine Education for Veterinarians (DCE) between 2012 and 2014. Participants completed a questionnaire before and after the course and 1 to 2 years after graduation. Objectives were to determine the prior academic training and livestock experience of course participants, to compare students' career aspirations before and after taking the course, and to identify factors associated with post-graduate position. Response rates were 58%-96%. Most students had taken undergraduate animal science courses (83%), worked (76%) and/or lived (52%) on a livestock operation, participated in youth livestock activities (63%), worked at a mixed practice (71%), taken production medicine-related elective courses (65%), taken other food animal rotations (91%), and/or done dairy externships (65%) before taking the DCE course. Students who were very likely to pursue a dairy-focused position before taking the course (36%) remained committed after the course, whereas students who were not likely initially (39%) were not further motivated by the course. Students who had worked with a dairy veterinarian were more likely to pursue a dairy-focused position than those who had not. Most course alumni accepted positions in mixed practice, with a ≥ 50% (54%) or < 50% (23%) dairy component, and post-graduate positions were consistent with students' predictions. Students who held an undergraduate degree or had worked for a dairy veterinarian were more likely to accept a dairy-focused practice position than those who did not.

Treatment of mastitis in cattle.

The understanding of mastitis, its cause, and the rationale for treatment or nontreatment of mastitis under various circumstances continues to evolve. This article presents research-based evidence about the use or nonuse of drugs to treat mastitis. Nondrug factors involved in decision making about mastitis, including cow characteristics and the epidemiology of mastitis, are also briefly discussed. This article provides information that helps in the making of knowledgeable, evidence-based decisions about therapy for mastitis. Focus is primarily on the use of antimicrobial drugs.