Predicting sensitivity of repeated environmental sampling for Mycobacterium avium subsp. paratuberculosis in dairy herds using a Bayesian latent class model.

Between-herd transmission of Mycobacterium avium subsp. paratuberculosis (MAP) by subclinically infected cattle is an important risk which can hamper effective control of paratuberculosis. Knowledge of herd status would substantially reduce this risk; MAP positive farms can be detected with environmental sampling. The objective of this study was to compare cumulative sensitivities of annual environmental sampling with two or four samples per sampling event without knowledge of true herd status and to calculate the number of sampling events to achieve a cumulative sensitivity of at least 0.9. Data from three repeated sampling events in two study populations, one with 55 herds (two samples/event) and another with 30 herds (four samples/event) including test results, herd and sample characteristics and prior prevalence estimates, were derived from the Alberta Johne's Disease Initiative (Alberta, Canada). A recursive Bayesian latent class model was used to predict the cumulative sensitivity of repeated environmental sampling events. A sampling scheme with four samples per sampling event had a higher cumulative sensitivity than an alternative scheme with two samples. To achieve a cumulative sensitivity of at least 0.9 with 95% probability, eight sampling events with two environmental samples per set, or four sampling events with four samples per set were required. Further model assessment demonstrated that these results can only be generalized to cattle populations with a similar within-herd prevalence to those studied here (approximately 0.08). Nonetheless, these results could help predict herd-level prevalence in cattle populations after environmental testing and provide information regarding the uncertainty behind status estimates for herds repeatedly tested using environmental samples.

Associations between Streptococcus uberis strains from the animal environment and clinical bovine mastitis cases.

Bovine clinical mastitis quarter foremilk samples were collected from 15 German dairy farms for the isolation of Streptococcus uberis strains. Samples were also collected from the 8 spots where Streptococcus uberis was most expected in the dairy environment to investigate the transmission behavior of Streptococcus uberis within the farm. The selected environmental spots for sampling were the inner surface of the milking liner, drinking troughs (on pasture and in the barn), exit area of milking parlor, bedding material from the lying area in the barn, passageway to pasture, lying area of soil or vegetation on pasture, and the barn area in front of the milking parlor. We performed pulsed-field gel electrophoresis on 237 Streptococcus uberis isolates to identify environmental strains that matched those from mastitis milk. The same strains were detected on the passageway to the pasture, milking parlor waiting area, in one of the liners, and a drinking trough. Streptococcus uberis strains showed high variability within farms and because identical strains (in mastitis milk and environment) were found in different environmental localizations, its transmission appears to be farm specific. Thus, to establish a farm-specific mastitis control strategy, the main environmental sources of Streptococcus uberis must be analyzed for matching strains. A molecular method such as pulsed-field gel electrophoresis is an important tool that can be used to obtain the necessary information.

Reduction of viable Mycobacterium avium ssp. paratuberculosis in slurry subjected to anaerobic digestion in biogas plants.

Cattle infected with Mycobacterium avium ssp. paratuberculosis (MAP) shed the bacterium in their feces. This may lead to considerable concentrations of MAP in slurry, which has been postulated to contribute to MAP transmission when this slurry is used as fertilizer. For other bacterial species, anaerobic digestion has been shown to reduce bacterial load and to increase the safety of organic waste. Therefore, the objective of this study was to investigate the effects of anaerobic digestion in biogas plants on MAP survival in slurry from 16 dairy farms with a history of MAP infection. Presence of MAP was determined using MAP culture and a commercial MAP IS900 quantitative PCR (qPCR) applied on untreated slurry samples, slurry samples after primary fermentation, and digestate. Unfermented slurry samples from most enrolled farms tested positive for MAP, via both culture and qPCR. After the fermentation process, MAP could no longer be cultured in most samples, with the exception of 2 samples from farms where high numbers of MAP-shedding cows were kept at the time of sampling. A Bayesian binomial model predicted a probability of 93% for a MAP-negative culture result after fermentation. In most samples, MAP DNA was still detectable when using the IS900 qPCR. The probability of a negative result in qPCR was estimated to be 27%. Results of this study indicate that subjecting MAP-positive slurry to anaerobic digestion in biogas plants leads to a reduction of viable MAP below the detection limit; however, MAP DNA remained detectable. It remains undetermined whether MAP DNA detected in fermentation products is a residue of MAP degradation or belongs to viable MAP below the detection limit or in a dormant state. In conclusion, subjecting MAP-positive slurry to anaerobic mesophilic digestion reduces viable MAP concentration below the detection limit. The use of digestion products as fertilizer on pasture and agricultural soils instead of untreated slurry may therefore reduce the risk of MAP transmission.

Decline of antibody response in indirect ELISA tests during the periparturient period caused diagnostic gaps in Coxiella burnetii and BVDV serology in pluriparous cows within a Holstein dairy herd.

In cattle, indirect enzyme-linked immunosorbent assay (ELISA) tests are commonly used in serological routine diagnostics. In a longitudinal study design, changes in relative optical density (OD) from drying-off until week 11 after calving were analyzed in blood and milk samples from pluriparous dairy cows (n=21) using a commercial indirect anti-C. burnetii ELISA test. In a second part of this study, changes over time were evaluated in blood and milk samples of 11 of these cows in an indirect ELISA detecting anti-Bovine viral diarrhea virus (BVDV) antibodies. Regarding the cows which were still in the herd at the time of calving, blood serological qualitative changes from positive to negative or indeterminate were demonstrated in 7/20 cows (35%) for the anti-C. burnetii indirect ELISA and in 2/10 cows (20%) for the anti-BVDV indirect ELISA, respectively, during the period from 14days ante partum to calving. Relative OD in the anti-C. burnetii and the anti-BVDV indirect ELISA tests followed basically similar courses over time. In blood serum, relative OD initially increased after drying-off, before a drop around calving was observed. After the colostrum period, relative OD in blood serum showed an increase until week 11 of lactation. In colostrum samples, relative OD levels were higher than in milk samples obtained one day before drying-off. After parturition, relative OD in milk decreased until week 6 of lactation in the anti-C. burnetii indirect ELISA and until week 11 in the anti-BVDV indirect ELISA, respectively. In conclusion, blood serological investigations in periparturient dairy cows using indirect ELISA kits should be avoided.

Susceptibility to cephalosporins of bacteria causing intramammary infections in dairy cows with a high somatic cell count in Germany.

The objective of this cross-sectional study was to determine the minimal inhibitory concentrations of cephalosporins of the first (cefalonium and cefapirin) and fourth generation (cefquinome) against bacteria isolated from intramammary infections in dairy cows with elevated somatic cell counts in Germany. Additionally, possible regional differences of the minimal inhibitory concentrations within Germany should be evaluated. In total, 6936 quarter milk samples from cows with a somatic cell count >200,000cells/ml were taken in 43 herds. The concentrations of the first generation cephalosporins inhibiting at least 90% of the isolates of a pathogen (MIC90) were ≥64µg/ml against Gram-negative bacteria and enterococci whereas the respective MIC90 against the other Gram-positive bacteria were ≤4µg/ml. The MIC90 of cefquinome were ≥16µg/ml against Gram-negative bacteria, bacilli and enterococci, and ≤2µg/ml against the other Gram-positive bacteria. Only the minimal inhibitory concentrations against coagulase-negative staphylococci differed significantly between regions in parametric survival models with shared frailties for the herds. However, the minimal inhibitory concentrations of cefquinome against staphylococci were higher than the minimal inhibitory concentrations of the tested cephalosporins of the first generation. Therefore, cefquinome should not be the first choice to treat staphylococcal mastitis in dairy cows.

Investigation of the association between the test day milk fat-protein ratio and clinical mastitis using a Poisson regression approach for analysis of time-to-event data.

The objective of the present study was to investigate the association between the milk fat-protein ratio and the incidence rate of clinical mastitis including repeated cases of clinical mastitis to determine the usefulness of this association to monitor metabolic disorders as risk factors for udder health. Herd records from 10 dairy herds of Holstein cows in Saxony, Germany, from September 2005-2011 (36,827 lactations of 17,657 cows) were used for statistical analysis. A mixed Poisson regression model with the weekly incidence rate of clinical mastitis as outcome variable was fitted. The model included repeated events of the outcome, time-varying covariates and multilevel clustering. Because the recording of clinical mastitis might have been imperfect, a probabilistic bias analysis was conducted to assess the impact of the misclassification of clinical mastitis on the conventional results. The lactational incidence of clinical mastitis was 38.2%. In 36.2% and 34.9% of the lactations, there was at least one dairy herd test day with a fat-protein ratio of <1.0 or >1.5, respectively. Misclassification of clinical mastitis was assumed to have resulted in bias towards the null. A clinical mastitis case increased the incidence rate of following cases of the same cow. Fat-protein ratios of <1.0 and >1.5 were associated with higher incidence rates of clinical mastitis depending on week in milk. The effect of a fat-protein ratio >1.5 on the incidence rate of clinical mastitis increased considerably over the course of lactation, whereas the effect of a fat-protein ratio <1.0 decreased. Fat-protein ratios <1.0 or >1.5 on the precedent test days of all cows irrespective of their time in milk seemed to be better predictors for clinical mastitis than the first test day results per lactation.

Social influences on the duration of antibiotic treatment of clinical mastitis in dairy cows.

Clinical mastitis of dairy cows is a visible inflammation of the udder, which is usually caused by bacteria and treated with antibiotics. Although pressure is increasing to reduce antibiotic usage in livestock in the European Union, feedback from the field suggests that clinical mastitis treatment is frequently repeated after the initial per-label treatment, thereby extending treatment duration. The aim of this study was to explore the social factors influencing farmers' decision-making on the duration of antibiotic treatment of clinical mastitis. In total, 38 dairy farmers in the Netherlands (n=17) and Germany (n=21) were interviewed in a qualitative semi-structured way. Extended treatment was defined as any treatment longer than that given in label directions. Of the 38 farmers, 30 reported routine and 7 occasional extended antibiotic treatment. The interviewed farmers were sensitive toward social norms of other farmers and recognition for good stockmanship. Extended treatment is perceived as part of the social norm of "being a good farmer." The participants' perception was that mastitis is not treated "thoroughly" if clinical symptoms were still visible at the time of cessation of treatment, because it may persist or recur. As a result, treatment was frequently extended by repeating the initial label treatment. Farmers, specifically the more "cow-oriented" farmers, expressed insecurity on how to treat mastitis effectively. This insecurity made them more sensitive to comply with other farmers' injunctive ("what ought to be") and descriptive ("what is done") norms and the perceived veterinarians' informational norm that extended treatment is better, resulting in an approved social norm. Social approval reduces the insecurity of being perceived as a poor farmer; thus, extended treatment is emotionally rewarded. This social reward apparently outweighs the higher costs of more waste milk and more antibiotic usage. Perceived positive reference groups with whom the farmer identifies and regularly communicates face to face, such as other farmers, the herd veterinarian, and other farm advisors, confirm the farmer's judgment on extending treatment and influences him or her toward socially accepted behavior. Society was the most negative reference group, barely influencing farmers' decision-making on treatment. The emotional gap between farmers and society is large and probably difficult to overcome. Legislation may reduce antibiotic usage, if doable and controllable. Evidence-based information on treatment efficacy or practical on-farm decision support indicating when to end treatment may be able to change social norms of "thorough" treatment, especially when communicated by a positive reference group such as veterinarians. Because prudent antibiotic use is hindered by perceived subjective norms on optimal duration of antibiotic treatment, more research is needed, particularly on the optimal duration of antibiotic treatment of specific pathogens as related to cure and recurrence of clinical mastitis.

Longitudinal study of the effects of teat condition on the risk of new intramammary infections in dairy cows.

Machine milking-induced alterations of teat tissue may impair local defense mechanisms and increase the risk of new intramammary infections. The objective of the current study was to assess the influence of short-term and long-term alterations of teat tissue and infectious status of the udder quarter on the risk of naturally occurring new intramammary infections, inflammatory responses, and mastitis. Short-term and long-term changes in teat condition of right udder quarters of 135 cows of a commercial dairy farm in Saxony-Anhalt, Germany, were recorded monthly for 10 mo using simple classification schemes. Quarter milk samples were collected from all examined quarters at each farm visit. Bacteriological culture results and somatic cell counts of quarter milk samples were used to determine new inflammatory responses (increase from ≤100,000 cells/mL to >100,000 cells/mL between 2 samples), new infections (detection of a pathogen from a quarter that was free of the same pathogen at the preceding sampling), and new mastitis (combination of new inflammatory response and new infection). Separate Poisson mixed models for new inflammatory responses, new infections, and new mastitis caused by specific pathogens or groups of pathogens (contagious, environmental, major, minor, or any) were used to estimate risk ratios and 95% confidence intervals. Data preparation and parameter estimation were performed using the open source statistical analysis software R. We observed no effect of any variable describing teat condition on the risk of new intramammary infections, inflammatory responses, or mastitis. Intramammary infections of the same udder quarter in the preceding month did not affect risk either.

[Recurrent clinical mastitis in dairy cattle - importance and causes]. / Rezidivierende klinische Mastitiden bei Milchkühen - Bedeutung und Ursachen.

Clinical mastitis as a frequently recurrent event can cause substantive economic loss on dairy farms. The reason for recurrent mastitis can be either a persistent infection of the bovine mammary gland by a mastitis pathogen or a reinfection of a quarter or udder after bacteriological cure. The virulence properties of a mastitis pathogen and the cure odds of an individual cow determine the development of persistent infections. Clinical episodes may alternate with periods without symptoms in the course of persistent infections. Strategies to reduce cases of recurrent mastitis have to include improved treatment concepts and measures to decrease new infection rates. The present literature review summarises the knowledge of definitions, frequencies, causes and effects of recurrent mastitis.