Risk factors for bovine mastitis in the Central Province of Sri Lanka

A study of the risk factors associated with mastitis in Sri Lankan dairy cattle was conducted to inform risk reduction activities to improve the quality and quantity of milk production and dairy farmer income. A cross-sectional survey of randomly selected dairy farms was undertaken to investigate 12 cow and 39 herd level and management risk factors in the Central Province. The farm level prevalence of mastitis (clinical and subclinical) was 48 %, similar to what has been found elsewhere in South and Southeast Asia. Five cow level variables, three herd level variables, and eight management variables remained significant (p?相似文献   

National intervention study of mastitis control in dairy herds in England and Wales

An intervention study was carried out on 52 dairy farms in England and Wales to determine whether the implementation of a well-specified mastitis control plan in herds with an incidence of clinical mastitis of more than 35 cases per 100 cows per year would reduce the incidence of clinical mastitis, and also reduce the incidence of increases in the somatic cell counts of individual cows. A clearly defined plan for the diagnosis and control of mastitis was developed by two veterinary specialists from the research literature. The herds were randomly allocated to receive the plan either at the start of the study (intervention herds) or after one year (control herds). Data on mastitis management and the farm environment were collected during farm visits. After one year there was a significant 22 per cent reduction in the proportion of cows affected with clinical mastitis on the intervention farms compared with the control farms. There were also significant reductions of approximately 20 per cent in the incidence of clinical mastitis and in the occurrence of increases in the somatic cell counts of individual cows from below, to above 200,000 cells/ml.     

An investigation of risk factors for nocardial mastitis in central Alberta dairy herds

A case-control study was undertaken during the summer of 1989 in central Alberta dairy herds to identify independent predictors of nocardial mastitis. Thirty-seven herds with nocardial mastitis were matched with control herds based on herd size, milk production, and enrolment in Alberta Dairy Herd Improvement Services. Control herds were considered free of nocardial mastitis based on negative cultures of four weekly bulk tank milk samples and one composite milk sample collected during the same period from each lactating cow in the herd. A detailed questionnaire on herd management was completed during farm visits. The use of blanket dry cow therapy was not found to be a risk factor for nocardial mastitis. Dry cow therapy with intramammary products containing neomycin and the use of multidose vials of dry cow medications were the only predisposing factors identified as being significantly associated with nocardial mastitis in central Alberta dairy herds. Use of neomycin as a dry cow therapy increased the odds of nocardial mastitis occurring in these dairy herds by 169 times.     

Bayesian evaluation of budgets for endemic disease control: An example using management changes to reduce milk somatic cell count early in the first lactation of Irish dairy cows

The aim of this research was to determine budgets for specific management interventions to control heifer mastitis in Irish dairy herds as an example of evidence synthesis and 1-step Bayesian micro-simulation in a veterinary context. Budgets were determined for different decision makers based on their willingness to pay. Reducing the prevalence of heifers with a high milk somatic cell count (SCC) early in the first lactation could be achieved through herd level management interventions for pre- and peri-partum heifers, however the cost effectiveness of these interventions is unknown. A synthesis of multiple sources of evidence, accounting for variability and uncertainty in the available data is invaluable to inform decision makers around likely economic outcomes of investing in disease control measures. One analytical approach to this is Bayesian micro-simulation, where the trajectory of different individuals undergoing specific interventions is simulated. The classic micro-simulation framework was extended to encompass synthesis of evidence from 2 separate statistical models and previous research, with the outcome for an individual cow or herd assessed in terms of changes in lifetime milk yield, disposal risk, and likely financial returns conditional on the interventions being simultaneously applied. The 3 interventions tested were storage of bedding inside, decreasing transition yard stocking density, and spreading of bedding evenly in the calving area. Budgets for the interventions were determined based on the minimum expected return on investment, and the probability of the desired outcome. Budgets for interventions to control heifer mastitis were highly dependent on the decision maker's willingness to pay, and hence minimum expected return on investment. Understanding the requirements of decision makers and their rational spending limits would be useful for the development of specific interventions for particular farms to control heifer mastitis, and other endemic diseases.     

Quarter,cow, and farm risk factors for intramammary infections with major pathogens relative to minor pathogens in Thai dairy cows

A cross-sectional study was carried out from May to September 2011 on 35 smallholder dairy farms in Chiang Mai, Thailand, to identify the quarter, cow, and farm factors that relate to intramammary infections (IMI) from major specified pathogens, compared to infections from minor pathogens. Data on general farm management, milking management, and dry cow management were recorded for each herd. Quarter milk samples were collected from either clinical or subclinical mastitis quarters. Dependent variables were binary data defining the specified major pathogens, including Streptococcus agalactiae (7.1 %), Streptococcus uberis (9.4 %), Streptococcus dysgalactiae (4.0 %), and other streptococci (16.7 %), as a case, and all minor pathogens as a control, in each dependent variable. The occurrence of S. agalactiae IMI was lower in first-parity cows and cows with short milking time. Cows with body condition score (BCS) <2.5 had higher occurrence of S. agalactiae IMI. The occurrence of S. uberis IMI was higher in quarters with California mastitis test (CMT) score 2, score 3, and having clinical mastitis and in farms with increasing age of vacuum system. Quarters with CMT score 3, having clinical mastitis, cow with manual milking after detaching milking cluster, and farms with high bulk milk somatic cell counts (BMSCC >500,000 cells/ml) had higher occurrence of S. dysgalactiae IMI. For other streptococci, quarters having clinical mastitis, BCS <2.5, and pulling down of milking cluster while milking increased occurrence of other streptococci IMI relative to minor pathogen IMI. These results highlight the importance of individual cow factors, milking characteristics, and BMSCC in determining the risk of IMI from major pathogens.     

奶牛乳房炎的研究进展及防控措施

奶牛乳房炎发病率高且危害大,在奶牛养殖中属于常见疾病。该病主要是由于病原微生物入侵奶牛乳腺组织而引发的局部炎症,其不仅会造成奶牛产奶量降低,而且还会影响牛奶的品质。由于治疗过程中的兽药残留和由某些病原微生物感染引起的奶牛乳房炎治愈率低等问题,奶牛乳房炎的防治显得极为重要。从病原菌的种类、致病机理以及诊断方法和防控措施等方面介绍了奶牛乳房炎的研究进展,以期为奶牛乳房炎的科学防治提供参考。     

Effect of dry period length on the effect of an intramammary teat sealant on the risk of mastitis in cattle treated with antibiotics at drying off

AIM: The aim of this study was to evaluate, under farm conditions, the use of a teat sealant in addition to whole herd dry cow antibiotic therapy on the risk of clinical mastitis in dairy cattle at pasture, and to evaluate the impact of dry period length on that risk and the impact of the teat sealant on that risk.

METHODS: Dairy cows in three herds which used routine whole herd antibiotic therapy were randomly assigned to receive either treatment with an internal teat sealant (n=322) or no additional treatment (n=313) at drying-off between March and May 2010. All clinical mastitis cases during the dry period and to the end of the subsequent lactation were recorded by farm staff; factors affecting risk of clinical mastitis were then analysed using a Cox proportional hazards model.

RESULTS: Median duration of the dry period was 112 days with >25% of cows having a dry period >130 days. The incidence risk of mastitis during lactation for cows treated with teat sealant was 9.9 (95% CI=6.9–13.7) cases per 100 cows compared with 17.9 (95% CI=13.8–22.6) cases per 100 cows for cows treated with antibiotic alone. The addition of a teat sealant to dry cow antibiotic therapy decreased the risk of clinical mastitis only in the first 33 days after calving (Hazard risk 0.24 (95% CI=0.12–0.48)). Length of dry period did not significantly affect the risk of clinical mastitis, or the effect of adding teat sealant to dry cow antibiotic therapy on the risk of clinical mastitis.

CONCLUSIONS: In these herds where, based on the mastitis history, whole herd antibiotic therapy had been recommended, the use of a teat sealant significantly reduced the risk of clinical mastitis. This effect was limited to the first 33 days after calving; subsequently there was no significant effect of treatment. There was no effect of dry period length on risk of clinical mastitis, nor any significant interaction with treatment.

CLINICAL RELEVANCE: Combination therapy with teat sealant and antibiotic was effective under New Zealand conditions in herds using whole herd antibiotic treatment at drying off. Teat sealant reduced risk of clinical mastitis in cattle with dry periods substantially longer than 100 days, and there was no evidence that this effect changed as dry period length increased.     

Bayesian analysis of a mastitis control plan to investigate the influence of veterinary prior beliefs on clinical interpretation

The fundamental objective for health research is to determine whether changes should be made to clinical decisions. Decisions made by veterinary surgeons in the light of new research evidence are known to be influenced by their prior beliefs, especially their initial opinions about the plausibility of possible results. In this paper, clinical trial results for a bovine mastitis control plan were evaluated within a Bayesian context, to incorporate a community of prior distributions that represented a spectrum of clinical prior beliefs. The aim was to quantify the effect of veterinary surgeons’ initial viewpoints on the interpretation of the trial results.A Bayesian analysis was conducted using Markov chain Monte Carlo procedures. Stochastic models included a financial cost attributed to a change in clinical mastitis following implementation of the control plan. Prior distributions were incorporated that covered a realistic range of possible clinical viewpoints, including scepticism, enthusiasm and uncertainty. Posterior distributions revealed important differences in the financial gain that clinicians with different starting viewpoints would anticipate from the mastitis control plan, given the actual research results. For example, a severe sceptic would ascribe a probability of 0.50 for a return of <£5 per cow in an average herd that implemented the plan, whereas an enthusiast would ascribe this probability for a return of >£20 per cow. Simulations using increased trial sizes indicated that if the original study was four times as large, an initial sceptic would be more convinced about the efficacy of the control plan but would still anticipate less financial return than an initial enthusiast would anticipate after the original study. In conclusion, it is possible to estimate how clinicians’ prior beliefs influence their interpretation of research evidence. Further research on the extent to which different interpretations of evidence result in changes to clinical practice would be worthwhile.     

Economic aspects of reproductive failure in dairy cattle. I. Financial loss at farm level

Some years ago, systematic research was initiated to improve quantitative insight into the economic impact of diseases and disease control in livestock. This paper deals with the financial loss at farm level caused by reproductive failure in dairy cattle. Economic calculations concerning the calving interval of cows which differ in age, relative production level and persistence of milk production during lactation were made. On average, an optimal interval of 1 year or less was established, while the loss per day lengthening of the interval (norm-loss) amounted to 1–2 Dutch guilders (Dfl.). Also, 676 norm-losses due to forced replacement because of reproductive failure were determined, dependent on age and relative production level of the culled cow and average herd life of the farm. On average, this norm-loss was determined to be almost Dfl. 500 per culled cow. Based on 71 farms in an investigation in the province of Overijssel, total loss per farm was determined, using the calving interval data, forced replacement data and norm-loss rate described above. On average, the calculated loss amounted to Dfl. 63 per cow per year, of which Dfl. 35.50 resulted from sub-optimal calving interval and Dfl. 27.50 from forced replacement due to reproductive failure. Costs for veterinary treatment and drugs were not included in these elements. Total loss due to reproductive failure was estimated to average about Dfl. 80 per cow per year, which equals about 2% of the gross production value or 10% of an average farmer's income.Finally, considerable differences in loss between farms have been determined. The difference between the 20% of farms with the highest and the 20% of farms with the lowest calculated loss is even more than the average loss. Thus improvment may be achieved on many farms, e.g., with the help of a herd health programme.     

Effects of a two-year dairy herd health management programme on udder health, use of antibiotics and longevity

Since 2003, the Research Institute of Organic Agriculture (FiBL) is realizing a herd health management programme ("pro-Q" project) focussing on udder health. The objectives of the project are: (1) to reduce antibiotic mastitis treatments, (2) to optimise udder health and (3) to improve longevity, measured as averaged number of herd lactations. The farms get expert advice in prevention and treatment on herd- and animal-level. After 2 years, treatment recordings of the 65 investigated farms showed that antibiotic mastitis therapies were reduced from 38 to 26 treatments per 100 cows and year (equals a reduction of 32%). Lactation numbers of the herds increased significantly by 0.2 lactations from 3.3 to 3.5 lactations per cow. Udder health remained constant over all farms during 2 years: theoretical bulk milk cell counts averaged constantly at around 180000 cells/ml. Improvement of udder health on farm level was significantly influenced by higher somatic cell count when the project started and enhanced by farmer's motivation and farm-veterinarians' commitment to the project.     

Investigation of mastitis problems on farms.

The production of high-quality milk is a high-priority issue for dairy farmers and milk processors. The investigation of mastitis problems on dairy farms is an area of increasing demand and is an ideal way for veterinary practitioners to increase involvement in production medicine programs. Goals for the amount of clinical and subclinical mastitis should be predefined on dairy farms, and a herd investigation initiated when needed. The use of a structured approach to mastitis problems can identify risk factors for infection, result in rapid resolution of mastitis problems, and hasten the application of appropriate preventive practices.     

Economic aspects of mastitis: new developments

Good udder health is not only important for the dairy farmer but, because of increasing interest of consumers in the way dairy products are produced, also for the dairy production chain as a whole. An important role of veterinarians is in advising on production diseases such as mastitis. A large part of this advice is given around the planning of management to maintain or improve the udder health status of a farm. Mastitis is a costly disease, due to losses (a reduction of output due to mastitis) and expenditure (additional inputs to reduce the level of mastitis). Worldwide, published estimates of the economic losses of clinical mastitis range from ?1 to ?7 per cow on a farm, with large differences between farms, e.g. in The Netherlands, losses due to clinical and subclinical mastitis varied between ?7 and ?98 per cow per year. Moreover, farmers tended to underestimate these costs. This indicates that for a large proportion of farms there are many avoidable losses. In order to provide good support to farmers' decision-making, it is important to describe the mastitis setting not only in terms of disease, e.g. incidence of clinical mastitis, but also in monetary terms; and to make good decisions, it is necessary to provide the dairy farmer with information on the additional expenditure and reduced losses associated with alternative decisions. Six out of 18 preventive measures were shown to have a positive nett benefit, viz blanket use of dry-cow therapy, keeping cows standing after milking, back-flushing of the milk cluster after milking a cow with clinical mastitis, application of a treatment protocol, washing dirty udders, and the use of milkers' gloves. For those measures that included a large amount of routine labour or investment, the reduced losses did not outweigh the additional expenditure. The advisor cannot expect that measures that are cost-effective are always implemented. Reasons for this are the objectives of the dairy farmer can be other than maximisation of profit, resources to improve the mastitis situation compete with other fields of management, risk involved with the decision, economic behaviour of the dairy farmer, and valuation of the cost factors by the dairy farmer. For all decision-makers this means that, although financial incentives do have an effect on the management of mastitis, it is not always sufficient to show the economic benefits of improved management to induce an improvement of management of mastitis.     

Costs associated with selected preventive practices and with episodes of clinical mastitis in nine herds with low somatic cell counts

Nine dairy herds (mean size, 149 cows) with bulk-tank milk somatic cell counts of less than 300,000 cells/ml and greater than 80% of cows with Dairy Herd Improvement Association linear somatic cell counts less than or equal to 4 were selected for study. Each herd was monitored for 12 consecutive months. Duplicate quarter-milk specimens were collected from each cow for bacteriologic culturing at beginning of lactation, cessation of lactation, and at the time of each clinical episode of mastitis. Streptococcus agalactiae was never isolated and Staphylococcus aureus was isolated from less than 1% of all quarters. There were 554 episodes of clinical mastitis. During the year of study, the incidence rate of clinical mastitis varied from 15.6 to 63.7% of cows among the 9 herds. Mean costs per cow per year in herd for mastitis prevention were: $10 for paper towels, $3 for nonlactating cow treatment, and $10 for teat disinfectants. Mean cost associated with clinical mastitis was $107/episode. Approximately 84% ($90) of the costs attributed to a clinical episode were associated with decreased milk production and nonsalable milk. Costs of medication and professional veterinary fees per clinical episode varied significantly among the 9 herds. Three of the herds did not have a veterinarian treat a clinical episode of mastitis during the year of study even though 2 of these herds had the first and third highest incidence rates of clinical mastitis. When calculated on a per cow in herd basis, mean costs of $40/cow/year were attributed to clinical mastitis.(ABSTRACT TRUNCATED AT 250 WORDS)     

A case-control study of Nocardia mastitis in Nova Scotia dairy herds

A case-control study was conducted to identify herd production, housing, and hygienic and therapeutic factors associated with a diagnosis of Nocardia mastitis in dairy herds in Nova Scotia. The data were collected by on-farm interviews with owners of 54 case and 54 control herds.

Logistic regression was used to study risk factors. The use of dry cow products containing neomycin, including two specific dry cow products, was strongly associated with a diagnosis of Nocardia mastitis in a herd. Other factors which increased the risk of Nocardia mastitis were higher levels of production, larger herd size, and a large percentage of cows treated with dry cow products. These results are compared to results from a similar study carried out in Ontario.

     

奶牛临床型乳房炎大肠杆菌的分离与鉴定

奶牛乳房炎是奶牛养殖业常见的一种临床疾病,该病是由大肠杆菌、链球菌、葡萄球菌等病原微生物引起的奶牛乳房发炎。该病的发生常常给奶牛养殖业带来极大的损失。本试验采集南京某奶牛场临床型乳房炎患牛的乳汁,并分离到3株细菌,经过对这3株细菌进行分离培养、形态染色、生化试验、药敏试验、致病性试验和血清型鉴定,结果表明这3株细菌均为O2血清型大肠杆菌,为临床预防和治疗提供了依据。     

Coagulase-positive staphylococcal mastitis in a herd with low somatic cell counts

An increase in clinical mastitis infections was observed in a high-producing 77-cow Holstein herd. Low bulk tank somatic cell counts and individual cow Dairy Herd Improvement Association somatic cell counts observed before, during, and after the epizootic were suggestive of herd environmental mastitis. However, bacteriologic culture survey of the total herd indicated that, in addition to infections possibly attributable to environmental pathogens, 22% (17/77) of the cows were infected with coagulase-positive Staphylococcus spp. Conceivably, investigative efforts and management changes, without bacteriologic culturing, might have resulted in reduction of the clinical infection rate in this herd. However, the continued high prevalence of a contagious pathogen with potential future implications would have gone unnoticed. Somatic cell count in milk from individual cows generally is a useful tool for monitoring the probability of intramammary infection, but must be complemented with bacteriologic culture of milk to determine whether contagious or environmental pathogens are responsible.     

Study on risk factors and their association with subclinical mastitis in lactating dairy cows in Trinidad

A cross-sectional study was conducted on dairy farms in eight milking centres in Trinidad to determine the prevalence of risk factors for mastitis and to assess their relationship to occurrence of subclinical mastitis. The California mastitis test (CMT) was used to determine the prevalence of subclinical mastitis by estimating the somatic cell counts in bulk and composite milk. Of a total of 177 dairy farms studied, 121 (68.4%), 39 (22.0%) and 17 (9.6%) practised semi-intensive, extensive and intensive management systems, respectively. A total of 129 (72.9%), 37 (20.9%) and 11 (6.2%) farms milked cows in parlours, stanchions and pasture/out-on-field, respectively. Based on sanitary practices, 40 (22.6%), 123 (69.5%), and 14 (7.9%) farms were classified as good, fair, and poor, respectively, while 76 (42.9%) and 60 (33.9%) farms reported to rarely experience and frequently experience water shortages, respectively. Amongst the 177 farms, only seven (4.0%) used machine-milking primarily, 152 (85.9%) screened for mastitis as a routine, 18 (10.2%) teat dipped, and 49 (27.7%) practised dry cow therapy. To detect mastitis, of 152 farms involved, 20 (13.2%) used the strip cup while only two (1.3%) employed the CMT. Pipe-borne water delivered directly from the hose was the only source of water to 91 (51.4%) farms while seven (4.0%) and eight (4.5%) farms used only well and surface water (ponds and rivers), respectively. Based on bulk milk samples, the farm prevalence of subclinical mastitis was 60.5% (107 of 177) with a range from 33.3% (centre 5H) to 100.0% (centre 2B). The difference was statistically significant (P < 0.01; chi 2). However, using composite milk, the farm prevalence of subclinical mastitis was 52.5% (93 of 177) with a range from 21.2% (centre 5H) to 92.9% (centre 2B) and again, the difference in prevalence was statistically significant (P < 0.001; chi 2). Subclinical mastitis was detected in 150 (45.0%) of 333 lactating cows screened and the range of prevalence was from 17.9% (centre 5H) to 56.3% (centre 1C). The difference was statistically significant (P < 0.001; chi 2). Of a total of 14 risk factors for mastitis studied which were related to animal husbandry, personnel, mastitis control and water, only two, the herd size and practice of dry cow therapy were significantly (P < 0.05; chi 2) associated with subclinical mastitis. It was concluded that the high prevalence of subclinical mastitis in Trinidad dairy herds could significantly reduce milk production with associated economic loss. Although a majority of the risk factors studied were not found to be significantly associated with the occurrence of subclinical mastitis possibly due to confounding factors, the need to eliminate or reduce these risk factors cannot be over-emphasized.     

Serratia-mastitis in cows as a herd problem

Clinical mastitis with infection of Serratia marcescens occurred in a tied-up dairy herd in Sweden on a scale widely exceeding what has hitherto been reported in veterinary literature. The herd contained 37 milking cows before the disease period but only 14 at slaughter 21 months later in spite of some recruitment. A very large number of mastitis cases, usually rather mild and of short duration, had then occurred--during one single month not less than 47 cases. Hardly any cow escaped the disease. Instead, the single cows fell ill at short intervals with mastitis in the same quarter as previously or in another quarter. Antibiotic therapy in clinical cases, dry cow therapy and teat dipping had no obvious effect. Serratia marcescens was isolated in all 14 slaughtered cows in one or more quarters. The morphological changes were remarkably mild. Isolated Serratia strains revealed no distinctive marks compared with ordinary saprophytic strains in laboratory tests. Serratia-contaminated sawdust used as litter was possibly the source of infection and the milking machine possibly the tool for the transmission of bacteria to the udder, in the latter case by the aspiration of contaminated sawdust when the claw was attached or detached, or it fell off during milking. The pathogenicity of the bacteria and the susceptibility of the cows to udder infection may have been increased.     

Prevalence of clinical mastitis in 38 Waikato dairy herds in early lactation

AIM: To determine the prevalence of clinical mastitis in spring-calving dairy herds in the Waikato Region of New Zealand and to identify factors associated with variation in the prevalence of clinical mastitis between herds. METHOD: A total of 799 quarters from 595 dairy cows from 38 dairy herds were diagnosed by herd owners as having clinical mastitis between 8 July and 21 August 1997. Quarters diagnosed with clinical mastitis were sampled for bacterial culture and somatic cell count, and the presence of clots in the milk and the presence of udder oedema were assessed by a technician or veterinarian. RESULTS: Clinical mastitis was diagnosed in an average (+/-s.e.m.) of 9.9% (+/-0.8%, range 0.9-21.4%) of calved cows within the herds. Bacteria were not cultured from an average of 12.4 % (+/- 2.0%, range 0.0-45.5%) of cows and 22.3% (+/- 2.4%, range 0.0-54.0%) of quarters diagnosed as having clinical mastitis. There were significant differences between herds in the proportion of cows diagnosed with mastitis and in the proportion of clinical mastitis cases from which bacteria were not cultured. A decreased prevalence of clinical mastitis (p<0.001) was associated with an increased percentage of the herd treated with dry cow antibiotics. An increased prevalence of clinical mastitis (p<0.0001) was associated with both an increased percentage of cows treated in the previous season with lactating cow antibiotics and an increased percentage of heifers in the herd. Herds that were fed supplements before or during lactation had a higher prevalence of clinical mastitis than herds that were not fed supplements (p<0.001). An increased proportion of quarters diagnosed with clinical mastitis that did not culture bacteria was associated with an increased prevalence of clinical mastitis (p<0.001). The proportion of quarters that the technician or veterinarian found with evidence of clinical mastitis (i.e. a somatic cell count >500,000 cells/ml and the presence of either clots or udder oedema) within a herd was inversely related to the proportion of quarters within a herd from which no bacteria were isolated. CONCLUSION: There was a large variation in the prevalence of clinical mastitis and in the proportion of clinical quarters from which no bacteria were grown between herds. Management factors such as the use of dry cow therapy, feeding regimes and heifer replacement rates all affected the prevalence of clinical mastitis. Herd owners appear to differ in the sensitivity and specificity of their diagnosis of clinical mastitis, with bacteria not isolated from up to 50% of quarters diagnosed with clinical mastitis in some herds. Improvements in the specificity of herd owner diagnosis of clinical mastitis may reduce the use of antibiotics for mastitis during lactation and hence may reduce the risk of antibiotic contamination of milk supplied for human consumption.     

Within herd comparison of teat dipping and dry cow therapy with only selective dry cow therapy in six herds

A within herd comparison of teat dipping and dry cow therapy (full treatment) with only selective dry cow therapy (partial treatment) was carried out in six commercial dairy herds for a two year period. In four herds, the incidence of clinical mastitis was 2 to 12 per cent higher in the partial treatment group. In another herd, in which the pattern of clinical mastitis isolates was unusual in that minor pathogens were isolated from 30 per cent of mastitis cases, the incidence was 43 per cent higher in the partial treatment group. In the remaining herd the incidence was 10 percent higher in the full treatment group. Streptococcus uberis mastitis was more common in the partial treatment groups of five herds; coliform mastitis was more common in the full treatment groups of two herds and similar in both groups in the other herds. High rates of coliform mastitis were associated with poor herd environmental conditions but this was not true for Strep uberis mastitis. Rates of staphylococcus aureus and Strep dysgalactiae mastitis were low in all herds. The level of major pathogen infection in cows completing the trial in all herds increased in the partial treatment group from 5 per cent of quarters at the start to 12 per cent at the finish of the trial. In the full treatment group, however, there was only a small increase in this level. In contrast, levels of Corynebacterium bovis infection increased by 17 per cent in both treatment groups. Continued use of teat dipping and dry cow therapy was associated with a higher rate of coliform mastitis in two of the three herds where there were poor standards of hygiene and husbandry.