Post-milking teat dip use in dairy herds with high or low somatic cell counts.

Milk samples for bacteriologic culture were submitted from 71 dairy herds, 24 with low somatic cell count (SCC) and 47 with high SCC and high prevalence of subclinical mastitis. At the time of sample submission to the Mastitis Diagnostic Laboratory of Pennsylvania State University, information regarding the herd mastitis control practices was collected. A combined program of post-milking teat dipping (PMTD) and antibiotic treatment of all cows at the start of the nonlactating period was practiced more frequently for herds with low SCC, (P less than 0.001) than for herds with high SCC. Among all herds for which PMTD was practiced, a higher proportion (P less than 0.001) of those for which chlorhexidine-based products were used had low SCC than high SCC. Conversely, a higher proportion of herds for which a dip with an acrylic latex barrier was used had high SCC rather than low SCC (P = 0.002). For herds with high prevalence of subclinical mastitis, and despite a program of PMTD and treatment of all cows at the start of the nonlactating period, a change to a different germicidal teat dip product may be indicated to help reduce prevalence of infection.     

Udder health and risk factors for subclinical mastitis in organic dairy farms in Switzerland

A study was performed in 1997 to estimate the prevalence and to investigate the etiology of subclinical mastitis in Swiss dairy herds managed under guidelines of controlled organic farming. It was planned as a longitudinal study over a period of 1 year and included a stratified random sample of 152 certified organic farms and 1907 cows. Two farm visits (the first from June to October when cows were on pasture, the second from January to March when cows were confined to barns) were performed on each farm. At each visit, farm management and individual-cow data (with emphasis on milking procedures and udder sanitation) were recorded. California mastitis tests (CMTs) were performed on each udder quarter of all cows in lactation. Milk samples with CMT >1+ were submitted for somatic cell counting (SCC), bacteriological examination and to test for antibiotic susceptibility. The SCC and germ-cell counts of monthly bulk-tank milk samples were available through Dairy Inspection and Advisory Services and milk production data of 567 herd-book cows were available from breeding associations. Possible individual and environmental predictors of subclinical mastitis were identified using logistic models adjusted for clustering of the data at herd and cow levels. Data were analyzed separately for cows from 7 to 100 and from 101 to 305 days post partum. Prevalences of subclinical mastitis at the quarter level were 21.2% for lactation period 7–100 days and 34.5% for 101–305 days post partum. The geometric mean SCC in bulk-tank milk samples was 85.6×10³ cells/ml. Samples at 7–100 and 101–305 days post partum were positive for Staphylococcus aureus in 16.0 and 7.4%, for coagulase-negative Staphylococci in 51.5 and 50.6%, for Streptococcus agalactiae in 0.0 and 0.8%, for other Streptococci in 19.4 and 15.6%, for E. coli in 1.0 and 0.4%, and for Corynebacterium bovis in 25.7 and 45.1%, respectively. Risks of subclinical mastitis increased significantly with increasing days post partum and advancing age of cow. Cows that were sampled when staying in alpine dairies had considerably higher risks of subclinical mastitis than cows staying in home barns. Significantly lower risks of subclinical mastitis were observed in farms where CMT was performed regularly as a control measure. Bacteria in milk from cows with mastitis exhibited antibiotic resistance at a comparable frequency as found previously in conventional farms.     

Prevalence of staphylococcal species in four dairy herds

The prevalence of staphylococcal species isolated from bovine mammary glands was determined in four dairy herds. Staphylococcus aureus and S hyicus were the predominant organisms isolated from cows in a herd with a bulk milk somatic cell count (SCC) greater than 900 X 10(3). One herd with a bulk milk SCC of 565 X 10(3) had a high incidence of S aureus while the predominant coagulase-negative species were S epidermidis and S hyicus. S hyicus predominated in two herds with bulk milk SCC less than 200 X 10(3); prevalence of S aureus was low. The impact of herd management practices such as post-milking teat antisepsis on distribution of staphylococcal species is discussed.     

The economic impact of mastitis-control procedures used in Scottish dairy herds with high bulk-tank somatic-cell counts.

We used multiple-regression analysis of field data to quantify the marginal impacts of various mastitis-control procedures on bulk-tank somatic-cell count (BTSCC). Estimates of milk-yield depression and the probability of herds paying a BTSCC penalty due to the presence of subclinical mastitis were made. An assessment of the economic efficiency of mastitis control by high BTSCC producers was also made using a loss-expenditure frontier. Significant interactions were detected between premilking udder-preparation methods (UP) and post-milking teat disinfection (PMTD), and also between the milking system of the herds and both the use of dry-cow therapy (DCT) and a regular milking-machine test (MMT). Udder preparation involving washing was associated with a higher SCC and had a detrimental effect on the efficacy of PMTD. Amongst herds facing a high-BTSCC problem (BTSCC >400,000 cells/ml), herds using PMTD without UP (regardless of the type of milking system), those using DCT (in parlour systems), and those with a parlour system having their milking machines tested obtained returns of Pound Sterling 1.4, Pound Sterling 3.9 and Pound Sterling 1.1, respectively, per Pound Sterling 1 investment in each of these procedures as a result of reductions in milk-yield losses and BTSCC penalties. The minimum total cost of disease within these herds was Pound Sterling 65.50/cow/year (due to Pound Sterling 41.40 revenue losses plus Pound Sterling 24.10 mastitis-control expenditure) attained by herds which had a parlour system and used DCT, MMT and PMTD (without UP). However, the average cost of subclinical mastitis for all high-BTSCC farms was Pound Sterling 100/cow/yr; hence, the difference (pound Sterling 34.50) could be saved by the more-efficient application of mastitis-control procedures.     

Application of the California mastitis test in intramammary Streptococcus agalactiae and Staphylococcus aureus infections of camels (Camelus dromedarius) in Kenya

A study was conducted on 207 lactating camels in six herds in Kenya to evaluate the California mastitis test (CMT) for the detection of intramammary infections (IMIs) caused by Streptococcus agalactiae and Staphylococcus aureus and to investigate the prevalence of both the pathogens in the camel udder. IMI with S. agalactiae was found in 12% of all camels sampled. IMI with S. aureus was present in 11% of all camels sampled. The herd-level prevalence of IMI varied between 0 and 50% for S. agalactiae and between 0 and 13% for S. aureus. Longitudinal observations over 10–12 months confirmed persistent infections for both pathogens. Observations in one herd suggested that camel pox was a contributing factor in spreading and exacerbating S. agalactiae udder infections.

The CMT had quarter-level sensitivities of 77 and 68% for S. agalactiae and S. aureus in camels, respectively. The CMT specificities were 91% for both the pathogens.     

Herd management and prevalence of mastitis in dairy herds with high and low somatic cell counts

Thirty-two dairy herds, 16 with low somatic cell counts (LSCC; Dairy Herd Improvement Association 12-month mean herd SCC less than or equal to 150,000 cells/ml) and 16 with high somatic cell counts (HSCC; Dairy Herd Improvement Association 12-month mean herd SCC greater than or equal to 700,000 cells/ml) were evaluated to determine the relationship between the prevalence of mastitis in each herd and each herd's mastitis control and management practices. Once for each herd, duplicate quarter milk samples were collected from the lactating cows, a survey of herd mastitis control, milking hygiene, and management practices of each herd was performed, and milking-machine function was evaluated. Of the 16 herds with LSCC, 2 (12.5%) had Streptococcus agalactiae isolated and 7 (44%) had Staphylococcus aureus isolated. Both organisms were found in all of the herds with HSCC. In herds with LSCC, the mean percentage of quarters infected with Str agalactiae was 0.1%, the mean percentage infected with streptococci other than Str agalactiae was 1.9%, and the mean infected with S aureus was 0.7%. In herds with HSCC, 25.7% of the quarters were infected with Str agalactiae, 3.7% were infected with streptococci other than Str agalactiae, and 7.6% were infected with S aureus. A program of postmilking teat dipping and treatment of all cows at the beginning of the nonlactating period was practiced more frequently in the herds with LSCC (81.3%) than in the herds with HSCC (37.5%). Major differences were not found between the 2 groups of herds in the use of the more common milking hygiene techniques or in the maintenance and functional characteristics of the milking equipment.     

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)     

Mycoplasma mastitis in dairy cattle

The most important characteristics of Mycoplasma mastitis on dairy farms are described, based on two case studies. Clinical symptoms, diagnostics, epidemiology, and a plan of action are presented. In the herds investigated, Mycoplasma mastitis was characterized by multiple affected quarters unresponsive to treatment with antibiotic and/or anti-inflammatory agents. Most striking were a sandy sediment, brown colouring, and rice-like structure of the milk of affected animals. Clinical symptoms differed in the two affected herds. Diagnosis was based on bacteriological investigation of samples of milk and synovial fluid taken from infected cows. Affected animals were culled immediately, and the herds were monitored by repeated testing of bulk milk samples. It was concluded that a consequence of the increasing size of cattle herds in the Netherlands is that subclinical/clinical Mycoplasma mastitis may be diagnosed more frequently than in the past. In the case of Mycoplasma mastitis, farmers and veterinary practitioners are advised to draw up a plan of action together, incorporating aspects such as diagnostics at cow level, direct culling of affected animals, hygiene during milking, including post-milking teat disinfection, and routine monitoring of bulk milk. Unpasteurized milk should not be given to calves.     

Factors Associated with Mastitis in Ontario Dairy Herds: A Case Control Study

Data from Ontario dairy cattle herds which had had a high average milk gel index for 1978 (cases) and from other herds which had had a low average during the same period (controls) were collected and analyzed using case control techniques. The purpose of the study was to contrast factors of husbandry and management between the two groups and to determine the relative contribution of each of these factors on mastitis (as determined indirectly by the milk gel index) at the herd level.

Control herds had higher average production levels than did case herds, shipping 1807 litres more milk per cow per year. Milk from control herds averaged 0.06 percentage points higher in butterfat, 0.19 percentage points higher in lactose and 0.05 percentage points lower in total protein. However, many factors can influence production, therefore these latter differences, in both shipped milk and composition, can not be attributed solely to differences in the prevalence of mastitis between the two groups.

Control herds were more likely to use teat dip, receive regular veterinary service, use dry cow antibiotic preparations and have knowledge concerning subclinical mastitis than were case herds. Control herds also tended to raise more of their own replacements, have a higher culling rate for reasons of low production and have a more modernized dairy operation. Case herds, on the other hand, were more likely to scrutinize foremilk, use more milking units per operator and wait longer between the start of stimulation and attachment of the milking unit.

The study confirms, under natural field conditions, the importance of integrated mastitis control practices and also reaffirms the relative importance of practices such as the use of teat dips and dry cow antibiotic preparations.

     

Comparative efficacy of three dry-cow antibiotic formulations in spring-calving New Zealand dairy cows

AIM: To evaluate the efficacy of a dry-cow antibiotic preparation containing cloxacillin plus ampicillin in a formulation that gives a 10-week duration of action, in comparison to products containing cephalonium (10-week action) or cloxacillin alone (7-week action). METHODS: A total of 493 cows were selected from 6 spring-calving dairy herds in the Manawatu region of New Zealand, according to the criteria of the SAMM plan, to receive intramammary antibiotic therapy at the end of lactation (drying off). Cows were randomly allocated to receive 1 of the 3 dry-cow antibiotic products under investigation. Cows were examined twice during the dry period and twice daily during the first 10 days of their subsequent lactation for the presence of mastitis. Milk samples were collected from individual quarters at the time of drying off and at 7 and 28-35 days after calving, for determination of milk somatic cell counts (SCC). Bacteriology was carried out on milk samples taken from cows that developed mastitis during the first 10 days after calving. RESULTS: No cows developed mastitis during the dry period. Sixteen cows developed clinical mastitis within 10 days of calving; there was no difference in incidence between treatments. Streptococcus uberis was the most commonly isolated organism. Mean SCC on Day 7 were lower (p = 0.019) in cephalonium-treated quarters (189.9+/-28.4 x 10(3) cells/ml) than in cloxacillin-treated quarters (388.7+/-71.2 x 10(3) cells/ml); values in quarters receiving cloxacillin plus ampicillin were intermediate (252.0+/-47.0 x 10(3) cells/ml). SCC were similar between treatment groups on Day 28-35. CONCLUSIONS: The use of a combination of cloxacillin plus ampicillin was effective for the prevention of mastitis during the dry and peri-calving-periods in pastured dairy cattle.     

Efficacy of blanket treatment of cows and heifers with an internal teat sealant in reducing the risk of mastitis in dairy cattle calving on pasture

AIM: To evaluate the benefit of blanket treatment of all milking cows at drying-off and all replacement heifers one month prior to the planned start of mating with an internal teat sealant on the incidence of mastitis, and somatic cell counts (SCC), postpartum in a 650-cow herd with a mastitis incidence in early lactation of 15% in cows and 26% in heifers. METHODS: Prior to drying-off, lactating cattle were divided on the basis of SCC and mastitis history. Cattle with records of individual SCC >150,000 cells/ml or mastitis in the previous lactation were treated with a cloxacillin-based dry-cow therapy (DCT), while the remaining cattle received no antibiotics. Cattle in each of the two groups were then randomly assigned to receive either an internal teat sealant or no further treatment. Additionally, one month prior to the planned start of calving the rising 2-year-old heifers were also randomly assigned to receive either an internal teat sealant or no treatment. All clinical mastitis cases were recorded for the first 10 weeks after the start of calving, while SCC were measured on three occasions during the subsequent lactation. RESULTS: Data were available from 466 cows and 206 heifers; treatment with the internal teat sealant significantly reduced the incidence of mastitis in both groups. For cows, the reduced risk of mastitis due to treatment with the teat sealant was not significantly different between cows, which, based on their mastitis history, required dry-cow antibiotics and those which did not. There was no effect of teat sealant on the mean SCC of any group at any time-point. CONCLUSIONS: On this farm, treatment of all cows and heifers prior to parturition with an internal teat sealant significantly reduced the risk of clinical mastitis. The benefits of an internal teat sealant were the same when used in combination with antibiotics in cows with a history of mastitis as when used alone in cows with no such history. CLINICAL RELEVANCE: These data support the proposition that blanket treatment with an internal teat sealant of all cows due to enter the milking herd can be a useful method of mastitis control. They also suggest that combined therapy with dry-cow antibiotics and internal teat sealants can be beneficial under New Zealand conditions. More detailed research on more farms in more areas of New Zealand is required to confirm these suggestions.     

Prevalence of udder infections and mastitis in 50 California dairy herds

The California mastitis test (CMT) and bacteriologic culture were performed on samples of bulk-tank milk and cow-composite milk (n = 23,138 cows) from 50 California dairies, 19 of the 50 with known mastitis problems. Thirty-eight (76.0%) bulk-tank milk samples and 12,334 (53.3%) cows were positive by results of the CMT. Potential mastitis agents were isolated from 5,085 (22%) cows. Staphylococcus aureus was isolated from all 50 herds, Streptococcus agalactiae was isolated from 47 herds, and Mycoplasma sp was isolated from 24 herds. For cow-composite milk samples, the prevalences were 9.3% for Str agalactiae, 9.1% for S aureus, 0.9% for Mycoplasma sp, 1.2% for coliform bacteria, 0.9% for other streptococci, 0.8% for coagulase-negative staphylococci, and 1.3% for other organisms. The relative sensitivity and the relative specificity of the CMT performed on cow-composite milk samples were 83.4% and 55.2%, respectively, and the predictive value of positive CMT results was 34.2%.     

A comparison of the effect of short-acting and long-acting cloxacillin-based dry-cow therapy on somatic cell counts after calving in cows also given internal teat sealants

AIM: To compare, in cows treated with an internal teat sealant, the effect of short-acting and long-acting cloxacillin-based dry-cow therapy on somatic cell counts (SCC) after calving.

METHODS: Cows from a spring-calving, pasture-based dairy farm in the Manawatu-Whanganui region of New Zealand were randomly allocated to receive either a short-acting cloxacillin and ampicillin dry-cow therapy and internal teat sealant (n=291) or a long-acting cloxacillin and ampicillin dry-cow therapy and internal teat sealant (n=288) at the end of lactation. Cows were managed on-farm with routine husbandry procedures through the dry period and following calving. A multivariable logistic regression model was used to determine the association between length of action of dry-cow therapy and the proportion of cows with a SCC >150,000?cells/mL at the first herd test after calving.

RESULTS: Age of cow, mean SCC for the preceding season and interval from calving to the first post-calving herd test were all associated with the proportion of cows with an individual SCC >150,000?cells/mL at the first herd test (p<0.001) Treatment with the short-acting dry-cow therapy was not associated with decreased odds of cows having a SCC >150,000?cells/mL at the first herd test compared with treatment with long-acting dry-cow therapy (OR=0.724; 95% CI=0.40–1.30).

CONCLUSIONS AND CLINICAL RELEVANCE: In this herd, which routinely used internal teat sealants, the use of short-acting cloxacillin-based dry-cow therapy did not result in an increased proportion of cows with elevated SSC post-calving. This was a single farm, single year study but indicates that in this herd, changing from a long-acting to a short-acting antimicrobial may have no impact on the prevalence of subclinical mastitis.     

The prophylactic effect of a dry-cow antibiotic against Streptococcus uberis

The prophylactic use of a dry-cow antibiotic for reducing the incidence of mastitis due to Streptococcus uberis was studied in four seasonally calving dairy herds involving 378 cows. The treatment was a long-acting dry-cow antibiotic preparation administered immediately after the last milking of lactation. New intramammary infections were identified by comparing the bacteriological status of quarters at drying off with that after calving, or through manual udder palpation during the dry period. The administration of dry-cow antibiotic to uninfected quarters at drying off reduced the overall incidence of new infections with Streptococcus uberis from 12.3% for untreated quarters to 1.2% of quarters (p<0.01). The reduction was significant (p<0.01) for both dry-period and post-calving infections. The susceptibility of uninfected quarters to new infection by Streptococcus uberis appeared to be unrelated to the infection status of a cow at drying off. Clinical infections during the dry period were most prevalent (97%) in quarters identified as having open teat canals. Fewer open teat canals (p<0.05) were observed among antibiotic treated quarters over the first 4 weeks of the dry period. Treated quarters had a lower (p<0.05) incidence of new clinical infection during the ensuing lactation and lower somatic cell counts. This did not affect production levels of milk, milk fat or protein. The results clearly indicated a prophylactic benefit for the dry cow antibiotic treatment against new Streptococcus uberis infections during the dry period.     

The prophylactic effect of a dry-cow antibiotic against Streptococcus uberis

The prophylactic use of a dry-cow antibiotic for reducing the incidence of mastitis due to Streptococcus uberis was studied in four seasonally calving dairy herds involving 378 cows. The treatment was a long-acting dry-cow antibiotic preparation administered immediately after the last milking of lactation. New intramammary infections were identified by comparing the bacteriological status of quarters at drying off with that after calving, or through manual udder palpation during the dry period. The administration of dry-cow antibiotic to uninfected quarters at drying off reduced the overall incidence of new infections with Streptococcus uberis from 12.3% for untreated quarters to 1.2% of quarters (p<0.01). The reduction was significant (p<0.01) for both dry-period and post-calving infections. The susceptibility of uninfected quarters to new infection by Streptococcus uberis appeared to be unrelated to the infection status of a cow at drying off. Clinical infections during the dry period were most prevalent (97%) in quarters identified as having open teat canals. Fewer open teat canals (p<0.05) were observed among antibiotic treated quarters over the first 4 weeks of the dry period. Treated quarters had a lower (p<0.05) incidence of new clinical infection during the ensuing lactation and lower somatic cell counts. This did not affect production levels of milk, milk fat or protein. The results clearly indicated a prophylactic benefit for the dry cow antibiotic treatment against new Streptococcus uberis infections during the dry period.     

Incidence and types of clinical mastitis in dairy herds with high and low somatic cell counts

Eighteen dairy herds were studied, 12 with a 12-month Dairy Herd Improvement Association herd mean somatic cell count (SCC) less than or equal to 150,000 cells/ml (low SCC) and 6 with a 12-month mean SCC greater than 700,000 cells/ml (high SCC). At the outset of the study, quarter samples for bacteriologic culture were collected (in duplicate) from all quarters of all lactating cows (whole herd culture). Subsequently, quarter milk samples for culture from all cows with clinical mastitis were collected for a period of 6 months. In the herds with low SCC, results of whole herd culture revealed low prevalence of intramammary infection attributable to all major pathogens (less than 4% of all quarters). Prevalence of infection with Streptococcus agalactiae (22.2% of all quarters) and Staphylococcus aureus (6.6% of all quarters) was significantly (P less than 0.05) higher in the herds with high SCC. Mean incidence of clinical mastitis in the herds with low SCC was 4.23 infections/100 cows/month (range, 0.42 to 10.25 infections). In the herds with high SCC, mean incidence was 2.91 infections/100 cows/month (range, 1.33 to 3.92 infections). In the herds with low SCC, infection type, as mean percentage of total clinically infected quarters sampled for culture/herd, was 0.0%, 2.2%, 12.3%, 43.5%, and 28.6% for Str agalactiae, S aureus, streptococci other than Str agalactiae, coliforms, and organisms not isolated, respectively. Respective percentages for the herds with high SCC were 41.5%, 18.3%, 12.6%, 8.0%, and 8.8%. During the study period (from April through January), incidence of clinical mastitis and clinical mastitis caused by coliform bacteria were highest in July and August for herds with low SCC.(ABSTRACT TRUNCATED AT 250 WORDS)     

无乳链球菌毒力基因与耐药性的相关性研究进展

乳房炎是奶牛养殖业中最常见的一种疾病，会造成奶牛乳腺发炎肿胀，使产奶量大幅下降。作为一种多因素性疾病，奶牛乳房炎发病原因复杂，饲料污染、病原菌感染以及环境因素均可以导致乳房炎的发生。无乳链球菌（Streptococcus agalactiae）作为奶牛乳房炎的主要致病菌，常会造成乳腺组织的局部炎症，随着无乳链球菌分离率的增加以及抗菌药物的滥用，其对抗菌药物的耐药性逐步攀升，给临床治疗带来了一定的困难。此外，无乳链球菌能够定植于宿主体内，破坏宿主的免疫系统，而其自身毒力因子会引起宿主机体疾病的产生。随着相关研究的深入，发现毒力与耐药性本身互为关联，耐药性的增强以不同的方式影响毒力，表明了耐药性与毒力因子之间存在着一定的相关性。笔者主要回顾了国内外链球菌以及其他细菌毒力基因与耐药性之间相关性的研究进展，从无乳链球菌毒力因子及耐药性等多种角度入手，分析了无乳链球菌的毒力机制以及毒力基因，并对近5年国内不同地区无乳链球菌耐药性进行统计，从细菌种类、环境和相关机制对链球菌的毒力和耐药性之间的关系展开综述，以期为无乳链球菌所引起的临床症状筛选出合理的抗菌药物并对毒力基因与耐药性的相关性研究提供理论参考。     

The prevalence of mastitis in primiparous heifers in eleven Waikato dairy herds

The objective of the study was to determine the prevalence of mastitis among primiparous heifers at calving and at drying off in 11 Waikato dairy herds during the 1993-94 dairy production season. Duplicate quarter milk samples were collected aseptically from 458 heifers within 5 days after calving for bacteriological analysis. Mastitis was diagnosed in at least one quarter in 35.6% of these heifers. Coagulase-negative staphylococci were isolated from 21.8% of the heifers. The prevalence of coagulase-negative staphylococci varied between herds from 4.3% to 44.8%. Environmental streptococci caused mastitis in 12.2% of heifers, ranging from 5.6% to 24.1% between herds. Streptococcus uberus was the pathogen identified most frequently at calving and accounted for more than 90% of the streptococcal isolates. Staphylococcus aureus and coliforms were isolated from less than 1% of samples. Clinical mastitis was observed in 8.1% of heifers at calving; environmental streptococci were isolated from 67.6% of these clinical clinical cases. Only 2.8% of heifers developed clinical mastitis during lactation and environmental streptococci were isolated from 38.5% of these cases. The prevalence of mastitis among 428 of the heifers at drying off was 64.7%; a 1.8 fold increase during lactation. Corynebactetium bovis was isolated from 43% of heifers at drying off even though it was not isolated from any heifers at calving. During the season, the prevalence of Staphylococcus aureus mastitis increased to 2.8% while mastitis caused by environmental streptococci declined to 2.8%. The prevalence of environmental mastitis pathogens decreased during lactation while contagious pathogens increased in each of the 11 herds. Ineffective post-milking teat sanitation probably contributed to the increase in mastitis caused by contagious pathogens. Specific factors were not determined that affected the variation in prevalence between herds.     

Intramammary infections and risk factors for clinical mastitis in herds with low somatic cell counts in bulk milk

Ten herds with low somatic cell counts in bulk milk had an incidence of clinical mastitis of only 2.2 per 100 cows whereas 10 other herds with similarly low cell counts had an incidence of 53.6 per 100 cows. The major pathogens in the herds with a high incidence were Escherichia coli, Streptococcus uberis, Staphylococcus aureus and the coagulase-negative staphylococci. The percentage of uninfected quarters in the herds with a high incidence of clinical mastitis was 21.4 per cent compared with 12.2 per cent in the herds with a low incidence of clinical mastitis. The prevalence of coagulase-negative staphylococci, Corynebacterium bovis and Micrococcus species was higher in the herds with a low incidence of clinical mastitis. There was a significant linear relationship between the percentage of uninfected quarters and the incidence of clinical mastitis in the herds with a high incidence of clinical mastitis. In herds with a low incidence of clinical mastitis significantly less teat disinfection after milking was practised. The results suggest that infections with minor pathogens tend to protect cows against mastitis, and that teat disinfection after milking may increase the percentage of uninfected quarters and lead to an increased risk of clinical mastitis in herds with low somatic cell counts in bulk milk.     

THE NEW SOUTH WALES MASTITIS CONTROL PROGRAM

SUMMARY A mastitis control program based on teat dipping and dry cow therapy was evaluated in 35 herds over a 3 year period. The incidence of subclinical mastitis as detected by the Rapid Mastitis Test (RMT) fell from 34% to 12% quarters positive, a reduction of 65%. Clinical mastitis was reduced from 37 clinical cases per 100 cows in the first 3 month period to 12 clinical cases per 100 cows in the last 3 month period, a reduction of 68%. Variations in response to the program in the reduction of subclinical and clinical mastitis are discussed and the results compared with similar trials conducted overseas. The Modified Whiteside Test was used on bulk milk samples from the control herds and these results were significantly correlated with the prevalence of subclinical mastitis assessed by RMT individual quarters.