Use of partial budgeting to determine the economic benefits of antibiotic treatment of chronic subclinical mastitis caused by Streptococcus uberis or Streptococcus dysgalactiae

The economic effect of lactational antibiotic treatment of chronic subclinical intramammary infections due to Streptococcus uberis or Streptococcus dysgalactiae was explored by means of partial budgeting. Effects at cow level and herd level were modelled, including prevention of clinical mastitis episodes and the prevention of transmission of infections. Input variables for our deterministic model were derived from literature or based on 2002/2003 dairy prices and farming conditions in The Netherlands. Sensitivity analysis was used to examine the effect of uncertainty around input variables or changes in price estimates. On farms where pathogen transmission was prevented through proper udder health management, 3-d antibiotic treatment during lactation resulted in an average net profit of euro+11.62 over no treatment while 8-d antibiotic treatment had an average negative net result of euro-21.83. Sensitivity analysis showed that profitability depends on the probability of treatment-induced cure, pathogen transmission rates, culling rate, retention pay-off, and costs of antibiotic treatment. Three-day antibiotic treatment of chronic subclinical streptococcal mastitis is economically profitable over a range of input values for cure probabilities, transmission rates and losses due to culling. In contrast, 8-d lactational treatment is only profitable for very valuable animals, on farms where the risk of pathogen transmission is high and/or when the farmer is likely to cull a high percentage of cows with subclinical mastitis. Because bacterial flora, cow characteristics and management differ widely between farms, the economic outcome of lactational treatment of chronic subclinical streptococcal mastitis may be highly farm-dependent.     

Herd- and cow-level risk factors associated with subclinical mastitis in dairy farms from the High Plains of the northern Antioquia,Colombia

Mastitis is the main disease entity affecting dairy farms in the Colombian High Plains of northern Antioquia, Colombia. However, no previous epidemiologic studies have determined the characteristics that increase the risk of infection in this region, where manual milking is still the prevailing system of milking. A 24-mo longitudinal study was designed to identify the predominant mastitis pathogens and important herd- and cow-level risk factors. Monthly visits were made to 37 commercial dairy farms to collect herd- and cow-level data and milk samples. Herd size varied from 6 to 136 cows (mean 37.0, median 29). Herd-level factors included type of milking system (manual or mechanical) and a range of management practices recommended by the National Mastitis Council (Madison, WI) to prevent mastitis. Individual cow-level risk factors included parity, stage of lactation, breed, udder hygiene, and lameness. A logistic regression analysis was used to investigate associations between herd- and cow-level risk factors with the presence of subclinical mastitis and infection caused by Streptococcus agalactiae at the quarter level. A quarter was considered to have subclinical mastitis if it had a positive California Mastitis Test and was subsequently confirmed to have a somatic cell count of ≥200,000 cells/mL. Any cow with one or more quarters with subclinical mastitis was considered to have subclinical mastitis at the cow level. Using 17,622 cow observations, the mean prevalence of subclinical mastitis at the cow level was 37.2% (95% confidence interval: 31.2, 43.3) for the first month and did not substantially change throughout the study. The predominant microorganisms isolated from quarters meeting the subclinical mastitis definition were contagious pathogens, including Strep. agalactiae (34.4%), Corynebacterium spp. (13.2%), and Staphylococcus aureus (8.0%). Significant variables associated with subclinical mastitis risk at the quarter level included being a purebred Holstein cow, higher parity, and increased months in milk. Variables that were protective for mastitis risk included being a crossbreed cow and adequate premilking udder hygiene. Significant variables associated with Strep. agalactiae infection were higher parity, increased months in milk, and manual milking. Variables that were protective were postmilking teat dipping and adequate cleaning of the udder. The results highlight the importance of hygiene practices in contagious mastitis control in manually milked herds.     

Pathogen-specific production losses in bovine mastitis

Reduction in long-term milk yields represents a notable share of the economic losses caused by bovine mastitis. Efficient, economic, and safe measures to prevent these losses require knowledge of the causal agent of the disease. The aim of this study was to investigate pathogen-specific impacts of mastitis on milk production of dairy cows. The materials consisted of milk and health recording data and microbiological diagnoses of mastitic quarter milk samples of 20,234 Finnish dairy cows during 2010, 2011, and 2012. The 6 most common udder pathogens were included in the study: Staphylococcus aureus, non-aureus staphylococci (NAS), Escherichia coli, Corynebacterium bovis, Streptococcus uberis, and Streptococcus dysgalactiae. We used a 2-level multilevel model to estimate curves for lactations with and without mastitis. The data on lactation periods to be compared were collected from the same cow. To enable comparison among lactations representing diverse parities, the estimated lactation curves were adjusted to describe the cow's third lactation. Mastitis caused by each pathogen resulted in milk production loss. The extent of the reduction depended on the pathogen, the timing of mastitis during lactation, and the type of mastitis (clinical vs. subclinical). The 2 most commonly detected pathogens were NAS and Staph. aureus. Escherichia coli clinical mastitis diagnosed before peak lactation caused the largest loss, 10.6% of the 305-d milk yield (3.5 kg/d). The corresponding loss for Staph. aureus mastitis was 7.1% (2.3 kg/d). In Staph. aureus mastitis diagnosed between 54 and 120 d in milk, the loss was 4.3% (1.4 kg/d). The loss was almost equal in both clinical and subclinical mastitis caused by Staph. aureus. Mastitis caused by Strep. uberis and Strep. dysgalactiae resulted in losses ranging from 3.7% (1.2 kg/d) to 6.6% (2.1 kg/d) depending on type and timing of mastitis. Clinical mastitis caused by the minor pathogens C. bovis and NAS also had a negative effect on milk production: 7.4% (2.4 kg/d) in C. bovis and 5.7% (1.8 kg/d) in NAS when both were diagnosed before peak lactation. In conclusion, minor pathogens should not be underestimated as a cause of milk yield reduction. On single dairy farms, control of E. coli mastitis would bring about a significant increase in milk production. Reducing Staph. aureus mastitis is the greatest challenge for the Finnish dairy sector.     

Bovine subclinical mastitis caused by different types of coagulase-negative staphylococci

Subclinical mastitis caused by intramammary infections (IMI) with coagulase-negative staphylococci (CNS) is common in dairy cows and may cause herd problems. Control of CNS mastitis is complicated by the fact that CNS contain a large number of different species. The aim of the study was to investigate the epidemiology of different CNS species in dairy herds with problems caused by subclinical CNS mastitis. In 11 herds, udder quarter samples were taken twice 1 mo apart, and CNS isolates were identified to the species level by biochemical methods. The ability of different CNS species to induce a persistent infection, and their associations with milk production, cow milk somatic cell count, lactation number, and month of lactation in cows with subclinical mastitis were studied. Persistent IMI were common in quarters infected with Staphylococcus chromogenes, Staphylococcus epidermidis, and Staphylococcus simulans. The results did not indicate differences between these CNS species in their association with daily milk production, cow milk somatic cell count, and month of lactation in cows with subclinical mastitis. In cows with subclinical mastitis, S. epidermidis IMI were mainly found in multiparous cows, whereas S. chromogenes IMI were mainly found in primiparous cows.     

Association between bovine leukemia virus, production, and population age in Michigan dairy herds

The objective of this study was to determine the herd-level effect of bovine leukemia virus (BLV) infection on dairy production, culling, and cow longevity. During routine herd testing, Dairy Herd Improvement Association technicians collected milk samples from about 40 cows from each of 104 randomly selected Michigan dairy herds averaging ≥120 milking cows and 11,686 kg of milk/yr. Milk samples were analyzed for the presence of anti-BLV antibodies by ELISA, and herd- and lactation-specific estimates of BLV prevalence were computed to determine which were the most predictive of herd milk production, culling rate, and cow longevity (proportion of cows in their third or greater lactation). On this basis, the herd BLV index (an unweighted mean BLV prevalence rate for lactation number 1, 2, 3, and ≥4) was selected as the measure of BLV prevalence that was the most highly associated with BLV economic impact. Step-down multivariate analysis was used to determine the extent to which any of 19 herd-level management variables may have confounded the association of BLV index and measures of herd economic impact (milk production and cow longevity). The BLV index was not associated with the 12-mo culling rate, but was negatively associated in the final multivariable model with the proportion of cows that were ≥third lactation, and was negatively associated with herd milk production. In summary, increased prevalence of BLV within Michigan dairy herds was found to be associated with decreased herd milk production and decreased cow longevity. Our results provide evidence that BLV infection is associated with herd-level economic impacts in high-performing dairy herds.     

Costs of mastitis: facts and perception

A model to calculate the economic losses of mastitis on an average Dutch dairy farm was developed and used as base for a tool for farmers and advisors to calculate farm-specific economic losses of mastitis. The economic losses of a clinical case in a default situation were calculated as euro210, varying from euro164 to euro235 depending on the month of lactation. The total economic losses of mastitis (subclinical and clinical) per cow present in a default situation varied between euro65 and euro182/cow per year depending on the bulk tank somatic cell count. The tool was used to measure perception of the total economic losses of mastitis on the farm and the farmers' assessment of the cost factors of mastitis on 78 dairy farms, of which 64 were used for further analyses. Most farmers (72%) expected their economic losses to be lower than those revealed by our calculation made with their farm information. Underestimating the economic losses of mastitis can be regarded as a general problem in the dairy sector. The average economic losses assessed by the farmers were euro78/cow per year, but a large variation was given, euro17-198/cow per year. Although the average assessment of the farmers of the different cost factors is close to the default value, there is much variation. To improve the adoption rate of advice and lower the incidence of mastitis, it is important to show the farmers the economic losses of mastitis on their farm. The tool described in this paper can play a role in that process.     

Factors affecting the lactoferrin concentration in bovine milk

Lactoferrin (LF) concentrations in the milk with different levels of the somatic cell count score were examined using an ELISA to determine whether milk LF concentration is influenced by parity of the cow, stage of lactation, and the somatic cell count. The study animals were 198 Chinese Holstein cows randomly chosen from more than 1,600 cows in 4 dairy farms in the Beijing area. The cows had shown no sign of mastitis for 2 mo. Daily milk production was recorded, and milk samples were taken from individual cow samples. The LF concentration varied between 31.78 and 485.63 μg/mL in milk from normal animals. Lactoferrin was significantly associated with stage of lactation (r = 0.557) and daily milk production (r = −0.472). Nevertheless, there was no significant relationship with parity. Moreover, milk LF concentration tended to be correlated with the somatic cell count score (r = 0.375). This finding suggests that milk LF may be helpful as an indicator for intramammary infection in dairy cows.     

Early detection of subclinical mastitis in lactating dairy cows using cow-level features

Subclinical mastitis in cows affects their health, well-being, longevity, and performance, leading to reduced productivity and profit. Early prediction of subclinical mastitis can enable dairy farmers to perform interventions to mitigate its effect. The present study investigated how well predictive models built using machine learning techniques can detect subclinical mastitis up to 7 d before its occurrence. The data set used consisted of 1,346,207 milk-day (i.e., a day when milk was collected on both morning and evening) records spanning 9 yr from 2,389 cows producing on 7 Irish research farms. Individual cow composite milk yield and maximum milk flow were available twice daily, whereas milk composition (i.e., fat, lactose, protein) and somatic cell count (SCC) were collected once per week. Other features describing parity, calving dates, predicted transmitting ability for SCC, body weight, and history of subclinical mastitis were also available. The results of the study showed that a gradient boosting machine model trained to predict the onset of subclinical mastitis 7 d before a subclinical case occurs achieved a sensitivity and specificity of 69.45 and 95.64%, respectively. Reduced data collection frequency, where milk composition and SCC were recorded only every 15, 30, 45, and 60 d was simulated by masking data, to reflect the frequency of recording of this data on commercial dairy farms in Ireland. The sensitivity and specificity scores reduced as recording frequency reduced with respective scores of 66.93 and 80.43% when milk composition and SCC were recorded just every 60 d. Results demonstrate that models built on data that could be recorded routinely available on commercial dairy farms, can achieve useful predictive ability of subclinical mastitis even with reduced frequency of milk composition and SCC recording.     

Events occurring during the previous lactation,the dry period,and peripartum as risk factors for early lactation mastitis in cows receiving 2 different intramammary dry cow therapies

The objective of this study was to investigate the association between mastitis events occurring during the previous lactation, the dry period, and the peripartum period on the incidence of early lactation mastitis in cows receiving ceftiofur hydrochloride or penicillin dihydrostreptomycin as intramammary dry cow antibiotic therapy. Cows (n = 402) from 2 large dairy farms in Central Florida were enrolled in the study at the time of dry-off processing and were randomly assigned to 1 of 2 dry cow therapies: ceftiofur hydrochloride or penicillin dihydrostreptomycin. Composite milk samples were collected at dry-off and after calving for bacteriological examination and somatic cell count. Peripartal health disorders were monitored during the first 30 d of lactation and included calving difficulty, metritis, ketosis, and left displaced abomasum. Milk production and individual somatic cell scores (SCS) were recorded monthly by the Dairy Herd Improvement Association. The main outcome variables were the risk of clinical mastitis during the first 30 and 60 d of lactation, and the risk of subclinical mastitis at the first 2 monthly Dairy Herd Improvement Association tests after calving (up to 70 d in milk). Additionally, the SCS and the presence of mastitis pathogens in milk at dry-off and at calving were analyzed. Explanatory variables consisted of events occurring during the previous lactation, at dry-off and during the dry period, at calving, and within the first 30 d after calving. Multiple events occurring during the previous lactation had a significant effect on the incidence of mastitis in the subsequent lactation. These events included low milk yield, intermediate lactation length, clinical mastitis, and lactation SCS average. Similarly, intramammary infections with environmental bacteria at dry-off increased the chances of clinical mastitis the first month after calving. Dry-off therapy had a significant effect on mastitis incidence; cows treated with ceftiofur hydrochloride had lower odds of having clinical and subclinical mastitis in the subsequent early lactation compared with cows treated with penicillin dihydrostreptomycin.     

Systematic clinical examinations for identification of latent udder health types in Danish dairy herds

A cross-sectional study was conducted to explore the applicability of systematic clinical examinations of udders as an additional tool for the evaluation of udder health status on dairy farms. During 2000, each of the 16 dairy farms was visited 5 times; 20 cows per farm were chosen at random at each visit for clinical udder examination immediately after milking. The clinical examination included both pathological and morphological variables. One examination per cow was included in the analysis (n = 707 cows). Principal component analysis (PCA) was performed in 3 steps. First, 19 variables characterizing udder and teats were analyzed (PCA 1). Second, the variables parity and stage of lactation were included (PCA 2). Finally, somatic cell count (SCC) and milk yield (PCA 3) were included. The PCA resulted in 4 components that explained 30% of the variation of the data: 1) small udder, 2) distressed udder, 3) mastitis udder, and 4) soiled udder. Variables with high positive correlation to the "small udder" were small udder shape, short teats, and first parity. Impaired teat surface, hard udder texture, and a long udder shape were related to the "distressed udder." The "mastitis udder" was characterized by the clinical variables asymmetry between front quarters, asymmetry between hind quarters, knotty tissue, and acute clinical mastitis. Reduced milk yield and high SCC were related to the "mastitis udder," whereas low SCC was related to the "small udder." The "soiled udder" was related to early lactation. Including this information in the assessment of udder health may be of substantial value for data analysis in farms with suspected under-reporting of clinical mastitis.     

Effect of clinical mastitis on the lactation curve: a mixed model estimation using daily milk weights

The objective of this study was to estimate the milk production losses associated with clinical mastitis using mixed linear models and correlation structures that have not been available previously. Data used included computer-recorded daily milk yields and detailed and accurate recordings of clinical mastitis cases. Two commercial Holstein dairy farms in New York State participated in the study, one with 650 lactating cows and another that began the study with 830 lactating cows and increased to 1120 cows by the end of the study. Cows on both farms were housed in free stall barns and milked 3 times daily in milking parlors. Electrical conductivity was used as a diagnostic aid for clinical mastitis on both farms. Date of clinical onset was recorded for every episode of clinical mastitis as well as for 8 other diseases defined using standardized case definitions (dystocia, milk fever, retained placenta, metritis, ketosis, displaced abomasum, lameness, and cystic ovarian disease) during the study period of October 1, 1999 to July 31, 2001. The mixed linear model for explaining variation in the outcome variable daily milk yield relative to non-mastitic herdmates found the terms for all 9 diseases studied, including clinical mastitis, significant. The model with an autoregressive correlation structure was preferred based on -2 * log likelihood, Akaike's information criterion, and Bayesian information criterion as well as savings in degrees of freedom. Separate analyses were run for first lactation cows and for second-plus lactation cows because their lactation curves were shaped differently. Adjusting for the effects of the other 8 diseases, milk production loss from clinical mastitis during the whole lactation was estimated as approximately 598 kg for second-plus lactation cows. However, cows that contracted mastitis had a daily production advantage of 2.6 kg over their herdmates until they contracted the disease. When compared with this potentially higher milk production, the total loss from clinical mastitis was estimated as 1181 kg.     

Epidemiologic and economic analyses of pregnancy loss attributable to mastitis in primiparous Holstein cows

The main objective of the study reported here was to examine the association between pregnancy loss (PL) and previous exposure to clinical or subclinical mastitis before breeding or during gestation in primiparous Holstein cows. A secondary objective was to estimate the cost of clinical mastitis during gestation, including that of PL attributable to mastitis in study cows. A total of 687 primiparous Holstein cows from 1 dairy farm were included in a matched case-control study. Study cows were declared pregnant via ultrasound on d 33 after timed artificial insemination (TAI). Case cows (n = 78) were those diagnosed as nonpregnant by rectal palpation on d 47 or 75 after TAI. Control cows were those confirmed as pregnant by rectal palpation on d 47 and 75 after TAI. Case cows were matched with eligible controls according to year of calving and calving-to-conception interval ±3 d. Cows were assigned to 1 of 3 groups: (1) cows not affected with clinical or subclinical mastitis; (2) cows affected with subclinical mastitis (Dairy Herd Improvement Association somatic cell score >4.5); and (3) cows affected with clinical mastitis during 2 exposure periods, 1 to 42 d before breeding or during gestation (1 to PL diagnosis day for case cows, and 1 to 75 d for control cows). Conditional logistic regression was used to model the odds of PL as a function of previous exposure to mastitis in study cows. Mastitis before breeding was not associated with PL. The odds of PL were 2.21 times greater in cows affected with clinical mastitis during gestation (95% confidence interval = 1.01, 4.83), compared with cows without mastitis, after controlling for breeding type and lameness. The cost of clinical mastitis during gestation was $149, which includes the cost ($27) of PL attributable to mastitis. In conclusion, this study provides evidence that clinical mastitis during gestation can cause PL in primiparous dairy cows leading to economic losses.     

Genetic and environmental relationships among somatic cell count, bacterial infection, and clinical mastitis.

Incidence of bacterial infection in 9784 lactations of 7763 cows in 31 herds, SCC in 32,448 lactations of 19,764 cows from 54 herds, and incidence of first parity mastitis recorded in the first lactations of 148,143 cows in 828 herds were analyzed. Bacterial infection was analyzed dichotomously by both threshold and linear models. The effects of parity, season, stage of lactation, and parity by stage of lactation interaction on SCC were estimated. Heritability of mean lactation log SCC--corrected for the effects of parity, season, and stage of lactation--varied from .13 to .27 for all parities in different data sets. Heritability of bacterial infection was .04 for the threshold model and .02 for the linear models. Heritability of field-recorded mastitis was .01. The genetic correlation between bacterial infection and SCC was near unity, but the genetic correlation between SCC and mastitis was .3. Selection for lowered SCC should reduce incidence of bacterial infection by 2% per unit of selection intensity.     

Farm business and operator variables associated with bulk tank somatic cell count from dairy herds in the southeastern United States

Mastitis is a worldwide problem in dairy cows and results in reduced milk production, the culling of cows, and other economic losses. Bulk tank somatic cell count (BTSCC) over 200,000 cells/mL often indicates underlying subclinical mastitis in dairy herds. Several preventative measures that can be implemented to help improve the incidence of mastitis exist, but surveys find these practices not fully adopted by producers. The goal of this research was to analyze the farm and operator characteristics associated with BTSCC in dairy herds by analyzing a survey of dairy producers in the southeastern United States. We examined this region because it has experienced a decline in the number of dairy farms, dairy cows, and milk production over the past 2 decades. The southeast region is also associated with higher BTSCC levels than the national average. Dairy farms in Georgia, Mississippi, Kentucky, North Carolina, South Carolina, Tennessee, and Virginia were surveyed. Producers were asked questions about the BTSCC at which they take action to address BTSCC, the information sources they use to learn about and manage BTSCC, farm structure and management characteristics, and attitudinal variables associated with profitability, managerial control, and planning horizon. Least squares regression was used to determine how these factors were associated with BTSCC levels across the 7-state region. Concern over mastitis, financial consequences of mastitis, and increased previous-year BTSCC were associated with higher current BTSCC levels. Obtaining information about mastitis from veterinarians and extension personnel, taking action against mastitis at a BTSCC less than 300,000 cells/mL, and perceived ability to control processes and mastitis incidence were associated with reduced BTSCC. We found average BTSCC was lower in North Carolina and Virginia. These results suggest that proactive producers (i.e., those that perceive they can control BTSCC and seek information from reliable sources), were more likely to report lower BTSCC. As a result, it may be possible to achieve improved milk quality, evident from lowered BTSCC, across the region.     

Stochastic modelling to assess economic effects of treatment of chronic subclinical mastitis caused by Streptococcus uberis

Chronic subclinical mastitis is usually not treated during the lactation. However, some veterinarians regard treatment of some types of subclinical mastitis to be effective. The goal of this research was to develop a stochastic Monte Carlo simulation model to support decisions around treatment of chronic subclinical mastitis caused by Streptococcus uberis. Factors in the model included the probability of cure after treatment, probability of the cow becoming clinically diseased, transmission of infection to other cows, and physiological effects of the infection. Using basic input parameters for Dutch circumstances, the average economic costs per cow of an untreated chronic subclinical mastitis case caused by Str. uberis in a single quarter from day of diagnosis onwards was euro109. With treatment, the average costs were higher (euro120). Thus, for the average cow, treatment was not efficient economically. However, the risk of high costs was much higher when cows with chronic subclinical mastitis were not treated. A sensitivity analysis showed that profitability of treatment of chronic subclinical Str. uberis mastitis depended on farm-specific factors (such as economic value of discarded milk) and cow-specific factors (such as day of diagnosis, duration of infection, amount of transmission to other cows and cure rate). Therefore, herd level protocols are not sufficient and decision support should be cow specific. Given the importance of cow-specific factors, information from the current model could be applied to automatic decision support systems.     

Economic losses from and the national research program on mastitis in the United States.

Scientific papers estimating economic losses from mastitis were reviewed. Reduced milk production from cows with subclinical mastitis was responsible for the largest losses. Losses from mastitis in the United States in 1976 were estimated by usable responses to a survey from 33 states representing 9.5 million cows or 86% of the dairy cow population. Losses of milk yields caused by mastitis were 386 kg/cow per yr and losses of discarded milk 62 kg/cow per yr. Annual losses per cow from mastitis were a) reduced milk production, $81.32; b) discarded milk, $12.88; c) cost of veterinary services, $1.97; d) cost of drugs, !3,86; e) increased labor, $2.28; f) decreased sale value, $5.72; g) increased replacement costs, $9.32; h) total, $117.35. For the 11 million cows in the United States 1976 losses from mastitis were $1.294 billion. Mastitis research was supported publicly at 22 locations under 43 projects. Approximately 24 scientist years were involved and $2.7 million of public funds were expended annually. If economic losses from mastitis were reduced 2% per year for 10 yr by research and expenditures for mastitis research remained the same, the benefit to cost ratio from mastitis research would be approximately 9.6 to 1.     

Estimation of circulating bovine leukemia virus levels using conventional blood cell counts

Bovine leukemia virus (BLV) is widely prevalent in Japanese dairy farms. To control BLV infections in Japan, segregating or managing cows according to their proviral load (PVL) is a rational strategy. This study was conducted to establish a quantitative procedure for estimating blood PVL per microliter using a statistical model to offer a cost-effective alternative to the conventional quantitative real-time PCR method. In total, 250 Holstein cows infected with BLV were identified from 10 commercial dairy farms. Information on age was collected and blood samples were tested for white blood cell and lymphocyte counts and PVL using PCR. Generalized linear models with quasi-Poisson errors were used to estimate PVL by selecting age, logarithm of lymphocyte count, and their interaction term as explanatory variables. To evaluate the model, blood samples of 92 BLV-infected Holstein cows from 2 other commercial dairy farms were tested, and measured PVL values were compared with estimated PVL values by the model. The logPVL per microliter was modeled by positive associations with log lymphocyte count and age and a negative association with the interaction term. In the evaluation, measured PVL values had a strong correlation with estimated PVL values (Spearman's ρ = 0.87). In conclusion, our model provides a cost-effective and more rapid alternative to the conventional method to facilitate test and segregation or management of BLV-suspected cows.     

A stochastic model simulating pathogen-specific mastitis control in a dairy herd

The objective of this study was to develop a model simulating mastitis control in dairy herds and to investigate how sensitive the model is when varying the effect parameters according to the uncertainty. The model simulates 9 pathogen-specific mastitis types, each of which can be subclinical or clinical. The clinical cases can be 1 of 4 severities defined according to the effect of the mastitis case: mild, moderate, severe, and permanent effect. The risk factors include lactation stage, parity, yield level, previous diseases, season, and contagious spread of the infection from herd mates. Occurrence of mastitis is modeled to have direct effects on feed intake, body weight, milk yield, somatic cell count in the milk, subsequent mastitis cases within the cow and in herd mates, voluntary and involuntary culling, mortality, and milk withdrawal. Thirty-five scenarios were simulated to study model behavior and model sensitivity. The consequences per cow/yr of mastitis in the default simulated herd included 0.42 clinical mastitis occurrences, 0.56 subclinical mastitis occurrences, loss of 385-kg milk yield, a 1.3% reduced feed intake, 61-kg milk withdrawal and €146 in reduced economic net return. Based on scenarios demonstrating model behavior and sensitivity analysis, the model appears to produce valid consequences of mastitis control strategies. Representation of the effect of subclinical mastitis and of variation in mastitis severity was concluded in this study to be important when modeling mastitis economics in a dairy herd. The model offers the opportunity to study the long-term herd specific effects of a wide range of control strategies against mastitis.     

Management of Wisconsin dairy herds enrolled in milk quality teams

A study was conducted to characterize Wisconsin dairy herds that enrolled in a team-based milk quality improvement program and to assess association of specific management practices with milking efficiency and milk quality. Management and financial data were obtained from dairy farms (n = 180) that participated in the program. Upon enrollment, herds reported a median bulk milk somatic cell count (SCC) of 333,500 cells/mL, an average of 125 lactating cows, and a mean rolling-herd average of 10,100 kg. Many management practices and bulk milk SCC were strongly associated with herd size and facility type. Managers of herds housed in freestall barns adopted more standardized procedures and recommended management practices compared with managers of herds housed in stall barns. Those managers also reported less bulk milk SCC and greater milk yields, and had a tendency for lower prevalence of subclinical mastitis and reduced estimates of the incidence of clinical mastitis. Managers of freestall herds received more quality premiums for milk shipped, estimated that they had fewer financial losses related to mastitis, and reported more efficient milking performance. A more efficient milking performance did not increase estimates of clinical mastitis or bulk milk SCC. In herds having freestalls, frequent training of employees seemed to be the fundamental factor that increased milking efficiency. Bulk milk SCC was positively associated with standard plate count, estimated rate of clinical mastitis, prevalence of subclinical mastitis, numbers of cows culled for mastitis, and estimated financial losses attributable to mastitis. Herds reporting high bulk milk SCC had an increased prevalence of subclinical mastitis, but incidence did not differ among bulk milk SCC categories. Overall, herds did not discuss milk quality frequently with dairy professionals, and herds having greater bulk milk SCC reported less consultation with their herd veterinarian.     

Genetic diversity and molecular epidemiology of outbreaks of Klebsiella pneumoniae mastitis on two large Chinese dairy farms

Klebsiella pneumoniae is an opportunistic and environmental mastitis-causing pathogen, with potential for contagious transmission. Repetitive element sequence-based PCR was used to determine genetic diversity and explore potential transmission and reservoirs for mastitis caused by K. pneumoniae on 2 large Chinese dairy farms. A total of 1,354 samples was collected from the 2 dairy farms, including milk samples from cows with subclinical and clinical mastitis, bedding, feces, feed, teat skin, and milking liners. Environmental samples were collected from all barns and milking parlors and extramammary samples from randomly selected dairy cows on both farms. In total, 272 and 93 K. pneumoniae isolates were obtained from Farms A and B, respectively (with ~8K and 2K lactating cows, respectively). Isolation rates from clinical mastitis (CM), subclinical mastitis (SCM), and environmental or extramammary samples were 34, 23 and 37%, respectively for Farm A and 42, 3, and 34% for Farm B. The K. pneumoniae isolated from CM milk and extramammary or environmental sources had high genetic diversity (index of diversity >90%) on the 2 farms and from SCM on Farm A. However, on Farm B, 9 SCM isolates were classified as 2 genotypes, resulting in a relatively low index of diversity (Simpson's index of diversity = 0.39; 95% CI = 0.08–0.70). Genotypes of K. pneumoniae causing mastitis were commonly detected in feces, bedding, and milking liners (Farm A), or from teat skin, sawdust bedding, and feed (Farm B). Based on its high level of genetic diversity, we inferred K. pneumoniae was an opportunistic and environmental pathogen causing outbreaks of CM on these 2 large Chinese dairy farms. Nevertheless, that only a few genotypes caused SCM implied some strains had increased udder adaptability and a contagious nature or a common extramammary source. Finally, control of intramammary infections caused by K. pneumoniae on large Chinese dairy farms must consider farm-level predictors, as the 2 outbreaks had distinct potential environmental sources of infection.