B.H.P. van den Borne

What veterinarians need to know about communication to optimise their role as advisors on udder health in dairy herds

Abstract The veterinary practitioner is one of the most important advisors for farmers in the field of udder health. He or she has the tools to improve udder health if farmers are motivated to do so. Many farmers think that udder health is important, but this does not always mean that management of mastitis is up to standard. Many veterinarians are of the opinion that they are unable to convince their clients of the possible profits to be gained from investing in management of mastitis. Something is required to bridge this gap. This article, based on data and experiences from The Netherlands, describes the communication issues that can be considered in order to improve the role of the veterinarian as advisor, to achieve better udder health. The outcome is beneficial for both farmers and veterinarians, the former for reasons of economics, welfare and ease of work; the latter because it creates extra, challenging work. It is concluded that the veterinary practitioner is in an ideal situation to advise and motivate farmers to improve udder health but, to do this, the means of communication need to take account of the different learning styles of farmers. The most important aspects of such communication are found to be a pro-active approach, personalisation of messages, providing a realistic frame of reference for the farmer, and use of the farmers social environment. Importantly, all persons and organisations in a farmers social environment should articulate the same message.

Host adaptation of bovine Staphylococcus aureus seems associated with bacteriological cure after lactational antimicrobial treatment

Staphylococcus aureus causes a wide range of diseases in multiple species. Some sequence types (ST) are observed in a variety of hosts, whereas other strains are mainly associated with bovine mastitis, suggesting host adaptation. We propose that host adaptation of Staph. aureus may influence bacteriological cure of bovine subclinical mastitis after antimicrobial treatment. To test this hypothesis, multilocus sequence typing was performed on Staph. aureus isolates from 60 treated and 79 untreated control quarters that were obtained from well-defined cohorts of dairy cows from a recently conducted randomized field trial on early treatment of subclinical mastitis. Bovine-associated ST were distinguished from non-bovine-associated ST based on the literature and public databases. The association between host adaptation and bacteriological cure was investigated using population-averaged logistic regression models. Thirteen ST were identified, with approximately 80% of isolates belonging to bovine-associated ST. The odds for cure were around 2.5 times as high for non-bovine-associated ST as for bovine ST in treated quarters, whereas no difference in spontaneous cure was observed in untreated control quarters. In addition, host adaptation was related to known predictors of cure, such as penicillin susceptibility and somatic cell count. All isolates belonging to non-bovine-associated ST were resistant to penicillin, whereas the majority of isolates belonging to bovine-associated ST were penicillin susceptible. Penicillin-resistant bovine-associated strains were associated with high somatic cell counts compared with other strains. The correlation between penicillin resistance, cell counts, and host adaptation may affect the association between host adaptation and cure. For diagnostic purposes, a simple and fast alternative to multilocus sequence typing of Staph. aureus to determine host adaptation may be valuable.

Bioeconomic modeling of lactational antimicrobial treatment of new bovine subclinical intramammary infections caused by contagious pathogens

This study determined the direct and indirect epidemiologic and economic effects of lactational treatment of new bovine subclinical intramammary infections (IMI) caused by contagious pathogens using an existing bioeconomic model. The dynamic and stochastic model simulated the dynamics of Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli during lactation and the dry period in a 100-cow dairy herd during 1 quota year. Input parameters on cure were obtained from recent Dutch field data. The costs of clinical IMI, subclinical IMI, and intervention were calculated into the combined total annual net costs of IMI per herd. The cost effectiveness of 4 scenarios with lactational intervention was determined; scenarios included no intervention, treatment after 1 mo of infection, treatment after 2 mo of infection, and treatment after 1 mo of infection and culling of uncured cows after 2 mo of infection. Model behavior was observed for variation in parameter input values. Compared with no lactational intervention, lactational intervention of new subclinical IMI resulted in fewer clinical flare ups, less transmission within the herd, and much lower combined total annual net costs of IMI in dairy herds. Antimicrobial treatment of IMI after 1 mo of infection and culling of uncured cows after 2 mo of infection resulted in the lowest costs, whereas treatment after 2 mo of infection was associated with the highest costs between the scenarios with intervention. Changing the probability of cure resulted in a nonlinear change in the cumulative incidence of IMI cases and associated costs. Lactational treatment was able to prevent IMI epidemics in dairy herds at high transmission rates of Strep. uberis, Strep. dysgalactiae, and E. coli. Lactational treatment did not limit the spread of Staph. aureus at high transmission rates, although the associated costs were lower compared with no intervention. To improve udder health in a dairy herd, lactational treatment of contagious subclinical IMI must therefore be preceded by management measures that lower the transmission rate. Lactational treatment of environmental subclinical IMI seemed less cost effective. Detection of subclinical IMI needs improvement to be able to most effectively treat subclinical IMI caused by contagious pathogens during lactation.

Therapeutic effects of antimicrobial treatment during lactation of recently acquired bovine subclinical mastitis: two linked randomized field trials.

Two linked randomized field trials were performed on 39 herds in the Netherlands to 1) determine therapeutic effects of antimicrobial treatment of recently acquired subclinical mastitis (RASCM) during lactation, 2) evaluate the effect of duration of subclinical mastitis on therapeutic outcome, and 3) identify factors related to the therapeutic success of RASCM. Cows with a first elevated composite somatic cell count (CSCC) after 2 consecutive low CSCC measurements were eligible for enrollment in trial 1 (treatment at the first elevated CSCC). Quarter milk samples were collected to determine bacteriological status for major pathogens and coagulase-negative staphylococci. Cows with one or more culture-positive quarters with a quarter somatic cell count (QSCC) >or=100,000 cells/mL were defined to have RASCM and were randomly assigned treatment or control (no treatment). Untreated cows from trial 1 that had a second elevated CSCC at the next milk recording were eligible for enrollment in trial 2 (treatment at the second elevated CSCC). In trial 2, staphylococci-positive cows (Staphylococcus aureus and coagulase-negative staphylococci) were randomly assigned to treatment or control. Farmers used their own treatment protocols to treat quarters in both trials. Bacteriological cure was defined as absence of the pathogen identified pre-intervention in 2 samples post-intervention; QSCC, CSCC, and milk yield were also analyzed. Hierarchical logistic and linear models were used to determine therapeutic effects and to identify factors related to therapy outcome. Treated quarters had a higher bacteriological cure rate than control quarters for all pathogens in both trials. Treatment resulted in lower QSCC and CSCC, whereas milk yield was not affected by treatment. Bacteriological cure of RASCM was better in quarters with a low QSCC pre-intervention and in coagulase-negative staphylococci-positive quarters. Control quarters with a single culture-positive sample pre-intervention also had a higher bacteriological cure than control quarters with >or=2 culture-positive samples. Time of antimicrobial treatment affected bacteriological cure for penicillin-sensitive Staph. aureus. Bacteriological cure tended to be higher for Staph. aureus after treatment at the first elevated CSCC compared with treatment at the second elevated CSCC. Thus, early treatment of Staph. aureus might be more effective than later treatment.

Variation in herd level mastitis indicators between primi- and multiparae in Dutch dairy herds

Composite somatic cell count data from the national test day recording and reported cases of farmer diagnosed clinical mastitis were used to estimate the occurrence of mastitis from July 2004 to June 2005 in primi- and multiparae in the Netherlands. Herds had to participate in the test day recording and had to have at least 50 cows. A random selection of 396 of these dairy herds provided composite somatic cell count data, while 205 dairy herds additionally reported on clinical mastitis cases. Prevalence of subclinical mastitis was calculated per herd as the proportion of cows with somatic cell count>200,000cells/ml. The incidence rate to clinical mastitis was calculated as the number of clinical mastitis cases divided by the number of cow days at risk per herd. Negative binomial models were used to correct for overdispersion. Mean herd level subclinical mastitis prevalence was 12.8% (95% CI: 12.2-13.5%) in primi- and 27.1% (95% CI: 26.2-28.1%) in multiparae. Mean herd level clinical mastitis cases were observed 20.2 (95% CI: 18.3-22.4) and 39.6 (95% CI: 37.1-42.3) times per 100 cow-years at risk, respectively. Some herds had a high mastitis occurrence in one parity group, while it was low in the other. Parity-specific monitoring is needed to identify such herds.

Relationship between somatic cell count status and subsequent clinical mastitis in Dutch dairy cows

High composite somatic cell counts (CSCC) in dairy cows may develop into clinical mastitis (CM), suggesting that prevention or intervention of high CSCC may prevent CM later in lactation. The objective of this study was to quantify the relationship between high CSCC in dairy cows and the first subsequent case of CM in the same lactation. Farmer-diagnosed cases of CM and test day CSCC measurements during 1 year of 13,917 cows in 196 randomly selected Dutch dairy herds were available for analysis. Cows were followed in 1 lactation from the first test day postpartum until CM, drying off, culling or end of study. Cox proportional hazards models with time-varying CSCC levels were used to estimate the effect of high CSCC (≥200,000cells/ml) on the time until the first case of CM. A shared frailty effect was included to adjust for clustering of cows within herds. The proportion of cows developing CM after a CSCC measurement was 11%. Primiparae with a high CSCC had a 4-fold higher hazard for subsequent CM than primiparae with a low CSCC; multiparae with a high CSCC had a 2-fold higher hazard than multiparae with a low CSCC. Additionally, multiparae with a low CSCC had a 2-fold higher hazard for CM occurrence than primiparae with a low CSCC. Increasing the threshold for high CSCC showed that the risk for CM increased. If the last CSCC before CM was low, CSCC information of 2 preceding test days was more predictive than CSCC information from only the last test day. When the last CSCC was high, CSCC information of 2 preceding test days did not have added predictive value. This study identified that approximately 25% of first subsequent CM cases after a CSCC measurement can potentially be prevented when cows are prevented to get high CSCC or when high CSCC cows are removed from the population. This corresponded with a decrease in the proportion of lactating cows with CM after a CSCC measurement from 11% to 7%.

A longitudinal study investigating the prevalence of Staphylococcus aureus genotype B in seasonally communal dairy herds

Staphylococcus aureus is a major mastitis-causing pathogen. Various genotypes have been recently identified in Switzerland but Staph. aureus genotype B (GTB) was the only genotype associated with high within-herd prevalence. The risk of introducing this Staph. aureus genotype into a herd may be increased by frequent animal movements. This may also be the case when cows from different herds of origin are commingled and share their milking equipment for a limited period of time. The aim of the present study was to determine the prevalence of Staph. aureus GTB in seasonally communal dairy herds before and after a summer period when dairy farming is characterized by mixing cows from different herds of origin in 1 communal operation. In addition, the environment was investigated to identify potential Staph. aureus GTB reservoirs relevant for transmission of the disease. A total of 829 cows from 110 herds of origin in 9 communal operations were included in the study. Composite milk samples were collected from all cows during the first or second milking after arrival at the communal operation and again shortly before the end of the season. Swab samples from the environment, involved personnel, and herding dogs present were collected before the cows arrived. At the end of the season, sampling of personnel was repeated. All samples were analyzed for the presence of Staph. aureus GTB using an established quantitative PCR. At the beginning of the season, Staph. aureus GTB-positive cows were identified in 7 out of 9 communal operations and the within-communal operation prevalence ranged from 2.2 to 38.9%. At the second sampling, all communal operations were Staph. aureus GTB positive, showing within-communal operation prevalence from 1 to 72.1%. The between-herd of origin prevalence increased from 27.3 to 56.6% and the cow-level prevalence increased from 11.2% at the beginning of the season to 29.6% at the end of the season. On 3 different communal operations, Staph. aureus GTB-positive swabs from seasonally employed personnel were identified at the end of the season. The results indicate that Staph. aureus GTB can easily spread in communal operations when cows from different herds of origin are mixed during the summer season. Effective management measures need to be designed to prevent the spread of Staph. aureus GTB in seasonally communal herds.

Genotype-specific risk factors for Staphylococcus aureus in Swiss dairy herds with an elevated yield-corrected herd somatic cell count

Bovine mastitis is a frequent problem in Swiss dairy herds. One of the main pathogens causing significant economic loss is Staphylococcus aureus. Various Staph. aureus genotypes with different biological properties have been described. Genotype B (GTB) of Staph. aureus was identified as the most contagious and one of the most prevalent strains in Switzerland. The aim of this study was to identify risk factors associated with the herd-level presence of Staph. aureus GTB and Staph. aureus non-GTB in Swiss dairy herds with an elevated yield-corrected herd somatic cell count (YCHSCC). One hundred dairy herds with a mean YCHSCC between 200,000 and 300,000cells/mL in 2010 were recruited and each farm was visited once during milking. A standardized protocol investigating demography, mastitis management, cow husbandry, milking system, and milking routine was completed during the visit. A bulk tank milk (BTM) sample was analyzed by real-time PCR for the presence of Staph. aureus GTB to classify the herds into 2 groups: Staph. aureus GTB-positive and Staph. aureus GTB-negative. Moreover, quarter milk samples were aseptically collected for bacteriological culture from cows with a somatic cell count ≥150,000cells/mL on the last test-day before the visit. The culture results allowed us to allocate the Staph. aureus GTB-negative farms to Staph. aureus non-GTB and Staph. aureus-free groups. Multivariable multinomial logistic regression models were built to identify risk factors associated with the herd-level presence of Staph. aureus GTB and Staph. aureus non-GTB. The prevalence of Staph. aureus GTB herds was 16% (n=16), whereas that of Staph. aureus non-GTB herds was 38% (n=38). Herds that sent lactating cows to seasonal communal pastures had significantly higher odds of being infected with Staph. aureus GTB (odds ratio: 10.2, 95% CI: 1.9-56.6), compared with herds without communal pasturing. Herds that purchased heifers had significantly higher odds of being infected with Staph. aureus GTB (rather than Staph. aureus non-GTB) compared with herds without purchase of heifers. Furthermore, herds that did not use udder ointment as supportive therapy for acute mastitis had significantly higher odds of being infected with Staph. aureus GTB (odds ratio: 8.5, 95% CI: 1.6-58.4) or Staph. aureus non-GTB (odds ratio: 6.1, 95% CI: 1.3-27.8) than herds that used udder ointment occasionally or regularly. Herds in which the milker performed unrelated activities during milking had significantly higher odds of being infected with Staph. aureus GTB (rather than Staph. aureus non-GTB) compared with herds in which the milker did not perform unrelated activities at milking. Awareness of 4 potential risk factors identified in this study guides implementation of intervention strategies to improve udder health in both Staph. aureus GTB and Staph. aureus non-GTB herds.

A multiarm randomized field trial evaluating strategies for udder health improvement in Swiss dairy herds.

The aims of this study were to quantify the effectiveness of specialist advice about udder health in Swiss dairy herds and to compare 3 different udder health improvement strategies against a negative control group. In 2010, 100 Swiss dairy herds with a high (between 200,000 and 300,000 cells/mL) yield-corrected bulk milk somatic cell count (YCBMSCC) were recruited for a 1-yr multiarm randomized field trial. The herds were visited between September and December 2011 to evaluate udder health-management practices and then randomly allocated into 1 of 4 study arms containing 25 herds each. The negative control study arm received neither recommendations for improving udder health nor any active support. The remaining 75 farmers received a herd-specific report with recommendations to improve udder health management. The positive control study arm received no further active support during 2012. The veterinarian study arm received additional support in the form of monthly visits by their herd veterinarian. Finally, the study group study arm received support in the form of bimonthly study group meetings where different topics concerning udder health were discussed. One year later, implementation of recommendations and changes in udder health were assessed. Of the recommendations given, 44.3% were completely implemented, 23.1% partially, and 32.6% were not implemented. No differences in implementation of recommendations were noted between the 3 study arms. At study enrollment, farmers were asked for the study arm of their preference but were subsequently randomly assigned to 1 of the 4 study arms. Farmers that were assigned to the study arm of their preference implemented more recommendations than farmers assigned to a study arm not of their preference. No decrease in the within-herd prevalence of cows that had a high (≥200,000 cells/mL) composite somatic cell count was observed in herds that had a YCBMSCC ≥200,000 cells/mL at the start of intervention. However, the 3 study arms with intervention (positive control, the veterinarian, and the study groups) prevented an increase in the within-herd prevalence of cows that had a high somatic cell count in herds with a low YCBMSCC at the start of the intervention compared with the negative control study arm. In the year after sending the report, herds assigned to the study group study arm had a reduced incidence rate of treated mastitis cases in comparison with the year before sending the report.

The effect of a national control program on mastitis occurrence in the Netherlands

A 5-year national mastitis control program was initiated in the Netherlands in 2005. Knowledge transfer and improvements of dairy farmers’ motivation towards udder health were used as means to decrease mastitis occurrence in Dutch dairy herds. The aim of this study was to determine the effect of the control program on (sub)clinical mastitis occurrence and on farmers’ mindset and behaviour in relation to clinical mastitis. Two identical surveys were conducted in the same herds at the beginning and end of the control program to quantify the change in mastitis occurrence and farmers’ mindset and behaviour. Prevalence of high composite somatic cell count (CSCC) and incidence rate of farmer-diagnosed clinical mastitis (IRCM) were compared between both surveys. The change in farmers’ mindset and behaviour towards udder health was associated with the change in IRCM in 104 dairy herds using factor analyses and linear regression models. There was no significant decrease in high CSCC prevalence between both surveys. However, IRCM decreased from 33.5 in 2004/2005 to 28.1 quarter cases per 100 cow-years at risk in 2009. The variation in the change in IRCM was mainly explained by the 2004/2005 IRCM (29%) and factors describing the change in farmers’ mindset (20%). These factors described a change in the perceived lack of control, a change in the perceived lack of influence on sources of mastitis, and a change in the worries about mastitis. This study indicated that udder health was improved in the Netherlands over the course of a mastitis control program. Changing dairy farmers’ mindset seemed effective in decreasing clinical mastitis occurrence in dairy herds.