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.     

Risk factors associated with BMSCC greater than 200 000 cells/ml in dairy herds in southern Chile

A cross-sectional survey of 523 dairy farms in the south of Chile was carried out to quantify risk factors associated with bulk-milk somatic-cell count (BMSCC) >200 x 10(3)cells/ml.Questionnaires followed by one reminder were sent to 3710 dairy farms via the 11 milk-processing plants that they supplied in October 1998. The response proportion was 14.1%. The median BMSCC was 289 x 10(3) cells/ml (range: 74 x 10(3) to 1800 x 10(3)cells/ml). The median herd size was 70 cows (range: 7-616); herd size was not associated with BMSCC. The annual milk yield of 33.2% of the herds was <4000 l and 53.4% had an annual milk yield of 4 x 10(3) to 6 x 10(3) l. Clinical-mastitis records were kept by 55.3% of the farmers. Seventy-six percent of the farmers (377/499) reported <10 clinical cases of mastitis in the year prior to the questionnaire.Logistic multiple regression indicated that BMSCC >200 x 10(3)cells/ml was more likely when foremilking was practised, and when cows were collected in a yard before milking. BMSCC was less likely to be >200 x 10(3)cells/ml when teats were washed with water containing disinfectant compared with plain water; when the udder and teats were always checked before milking compared with, sometimes or never; when cows with mastitis were milked first compared with any other ordering, and when farmers recorded individual-cow somatic-cell count (ICSCC) compared with when ICSCC was not recorded.     

Normal somatic cell count and subclinical mastitis in Murrah buffaloes

This study was conducted to investigate the normal somatic cell count (SCC) and to define subclinical mastitis in Murrah buffaloes. Data were collected from 60 clinically normal buffaloes stationed at five farms of Chitwan Nepal and Buffalo Research Center, Hissar, India. Somatic cell count was measured using the Newman-Lampert staining technique. The upper limit of SCC was determined >or=200 000/ml of milk based on the mean +/- 2SD of a total SCC. Abnormal data of the SCC was repeatedly removed, which lie beyond the values of more than mean + 2SD until all the data come to lie within (mean + 2SD). Averages of SCC of right front and right hind quarters were significantly higher than left front and left hind quarters. Nearly 94% of California mastitis test (CMT) negative quarters were having somatic cells >or=200 000/ml. The mean SCC of CMT positive quarter was significantly higher (P < 0.01) than CMT negative quarters. Subclinical mastitis was diagnosed on the basis of samples with SCCs >or=200 000/ml with positive bacterial cultures. Subclinical mastitis was found in 21.7% buffaloes and 8% of the quarter foremilk samples. Neutrophil counts were significantly higher in subclinical mastitis milk.     

Intramammary treatment of clinical mastitis of dairy cows with a combination of lincomycin and neomycin, or penicillin and dihydrostreptomycin

AIM: To compare clinical and bacteriological cure rates of clinical mastitis following treatment with intramammary preparations containing either lincomycin and neomycin or penicillin and dihydrostreptomycin. METHODS: Cases of clinical mastitis were sourced from four seasonal-calving dairy herds in the central Waikato region of New Zealand during the first 120 days of lactation. Affected quarters were infused three times at 12 h intervals with either 333 mg lincomycin plus 100 mg neomycin (lin/neo; 197 glands),or 1,000 mg penicillin plus 500 mg dihydrostreptomycin (pen/DHS; 207 glands). Milk samples were collected for bacteriology from each quarter immediately before and approximately 21 days after initiation of treatment. Additionally, a composite milk sample from each cow was collected, on average, 54 days after enrolment for assessment of milk yield, composition and somatic cell count (SCC). The probability of bacterial cure was initially analysed using Chi-squared analysis, and factors that were associated (p<0.2) were offered to a reverse stepwise logistic regression model. Continuous variables (e.g. milk solids production and log10 SCC) were analysed using general linear models. RESULTS: A total of 404 quarters diagnosed with clinical mastitis, from 282 cows in the first 120 days of lactation, were included. Streptococcus uberis, coagulase-negative staphylococci and Staphylococcus aureus were isolated from 56.5%, 18.8% and 10.0% of the bacteriologically positive quarters. There was no difference in the bacteriological cure rate (76.7% vs 76.7%, OR=0.94; p>0.8), the log10 SCC (2.1, SE 0.1, vs 2.0, SE 0.1; p>0.3) or milk production (1.2, SE 0.1, vs 1.2, SE 0.1, kg milksolids/cow/day; p>0.7) between lin/neo vs pen/DHS treatments, respectively. However, the proportion of cows re-treated following initial treatment was higher for the lin/neo compared to pen/DHS-treated group (16.3% vs 5.2%, OR=3.46; p<0.05). CONCLUSIONS: No difference in bacteriological cure rate, milk production or SCC was evident between lin/neo and pen/DHS intramammary treatments for clinical mastitis in dairy cows during the first 120 days of lactation. KEYWORDS: Dairy cow, mastitis, intramammary, antibiotic, treatment, somatic cell count.     

The detection of mastitis in individual quarters using electrical conductivity or somatic cell concentration

In this investigation electrical conductivity (EC) and somatic cell concentration (SCC) were compared in 3 herds for their ability to correctly identify the infection status of quarters. For EC, thresholds of 6.0 and 6.8 mS/cm were used and comparisons were made between quarters within each cow. The method of comparison between quarters was the same as that described by the manufacturers of the AHI Mastitis Detector. For SCC a threshold of 500 x 10(3) cells/ml was used. For both EC and SCC considerable variation was found between herds for sensitivity (the proportion of quarters infected with a major pathogen and detected as abnormal), and specificity (the proportion of quarters free from infection and detected as normal). The mean sensitivity and specificity of EC for the three herds was 49% and 79% respectively, whereas for SCC the means were 71% and 81% respectively. The variation in sensitivity and specificity of EC between herds was attributed to differences in the distribution of EC for quarters of similar infection status. It was concluded that these differences in herd EC precluded the use of pre-determined EC thresholds which were applicable for detecting mastitis in all herds.     

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)     

Effect of abraded intramammary device on outcome in lactating cows after challenge exposure with Streptococcus uberis

Intramammary devices (IMD) were abraded with medium-grade emery cloth or were left smooth. One IMD of each type was inserted into a mammary quarter of each of 5 lactating cows. The remaining 2 quarters served as controls. Quarter foremilk, bucket milk, and stripping milk samples were collected for 3 consecutive days at 2 weeks after IMD insertion, and milk somatic cell counts (SCC) were determined. Milk samples also were collected immediately after and 0.5, 1, 2, 4, 6, 8, and 11 hours after milking. All quarters were challenge exposed with 250 colony-forming units of Streptococcus uberis at 2 months after IMD insertion. Foremilk and stripping milk samples were collected for bacteriologic culture and SCC at the next 10 milkings. Mean foremilk, bucket milk, and stripping milk SCC (X 10(6) cells/ml) were 0.18, 0.07, and 0.91, respectively, for quarters with abraded IMD; 0.06, 0.05, and 0.43, respectively, for quarters with smooth IMD; and 0.03, 0.03, and 0.15, respectively, for control quarters. Mean SCC after milking (X 10(6) cells/ml) for the various intervals were 0.70, 1.29, 0.70, 0.97, 1.15, 1.17, 0.77, and 0.85 for quarters with abraded IMD; 0.43, 0.62, 0.61, 0.45, 0.64, 0.60, 0.31, and 0.26 for quarters with smooth IMD; and 0.15, 0.24, 0.15, 0.19, 0.15, 0.15, 0.14 and 0.06 for control quarters. After challenge exposure, 2 of 5 of the quarters with abraded IMD, 4 of 5 of the quarters with smooth IMD, and 8 of 9 control quarters became infected. Results indicated that abraded IMD increased SCC in stripping milk to concentrations that provided 60% protection against challenge exposure with S uberis.     

Skeletal myonecrosis in a cat

In this investigation electrical conductivity (EC) and somatic cell concentration (SCC) were compared in 3 herds for their ability to correctly identify the infection status of quarters. For EC, thresholds of 6.0 and 6.8 mS/cm were used and comparisons were made between quarters within each cow. The method of comparison between quarters was the same as that described by the manufacturers of the AHI Mastitis Detector. For SCC a threshold of 500 × 10³ cells/ml was used.

For both EC and SCC considerable variation was found between herds for sensitivity (the proportion of quarters infected with a major pathogen and detected as abnormal), and specificity (the proportion of quarters free from infection and detected as normal). The mean sensitivity and specificity of EC for the three herds was 49% and 79% respectively, whereas for SCC the means were 71% and 81% respectively.

The variation in sensitivity and specificity of EC between herds was attributed to differences in the distribution of EC for quarters of similar infection status. It was concluded that these differences in herd EC precluded the use of pre-determined EC thresholds which were applicable for detecting mastitis in all herds.     

The use of Markov chain Monte Carlo for analysis of correlated binary data: patterns of somatic cells in milk and the risk of clinical mastitis in dairy cows

Two analytical approaches were used to investigate the relationship between somatic cell concentrations in monthly quarter milk samples and subsequent, naturally occurring clinical mastitis in three dairy herds. Firstly, cows with clinical mastitis were selected and a conventional matched analysis was used to compare affected and unaffected quarters of the same cow. The second analysis included all cows, and in order to overcome potential bias associated with the correlation structure, a hierarchical Bayesian generalised linear mixed model was specified. A Markov chain Monte Carlo (MCMC) approach, that is Gibbs sampling, was used to estimate parameters.

The results of both the matched analysis and the hierarchical modelling suggested that quarters with a somatic cell count (SCC) in the range 41,000–100,000 cells/ml had a lower risk of clinical mastitis during the next month than quarters <41,000 cell/ml. Quarters with an SCC >200,000 cells/ml were at the greatest risk of clinical mastitis in the next month. There was a reduced risk of clinical mastitis between 1 and 2 months later in quarters with an SCC of 81,000–150,000 cells/ml compared with quarters below this level. The hierarchical modelling analysis identified a further reduced risk of clinical mastitis between 2 and 3 months later in quarters with an SCC 61,000–150,000 cells/ml, compared to other quarters.

We conclude that low concentrations of somatic cells in milk are associated with increased risk of clinical mastitis, and that high concentrations are indicative of pre-existing immunological mobilisation against infection. The variation in risk between quarters of affected cows suggests that local quarter immunological events, rather than solely whole cow factors, have an important influence on the risk of clinical mastitis. MCMC proved a useful tool for estimating parameters in a hierarchical Bernoulli model. Model construction and an approach to assessing goodness of model fit are described.     

Prevalence of pathogens causing subclinical mastitis in 15 dairy herds in the Republic of Ireland

: Milk samples from 285 cows in 15 dairy herds were collected for bacteriological analysis. Cows were selected on the basis of a somatic cell count (SCC) exceeding 200,000 cells per ml at the three most recent milk recordings prior to sampling. Staphylococcus aureus and Streptococcus uberis were the predominant isolates accounting for 21% (n = 61) and 19% (n = 53) of isolates, respectively. Streptococcus uberis was more frequently isolated from split-calving herds than from spring-calving herds and this difference was statistically significant (P < 0.005). Herds with suboptimal housing had a significantly greater prevalence of S. uberis than did herds where housing was adequate (P < 0.005). The isolation rates for S. aureus was significantly greater in herds where parlour hygiene was suboptimal (P < 0.05).     

On distinguishing cause and consequence: do high somatic cell counts lead to lower milk yield or does high milk yield lead to lower somatic cell count?

Researchers have reported that as milk yield increases composite milk somatic cell count (SCC) is diluted in cattle with no intramammary infection (IMI) and as a consequence, estimates of SCC from high yields are lower than estimates of SCC from low yields in dairy cows without an IMI. To date, estimates of reduced milk yield associated with high SCC because of intramammary infection have not been adjusted for any dilution of SCC. Ignoring dilution is therefore likely to lead to an overestimate of reduction in yield with increasing SCC. This paper investigates scenarios of the possible impact of dilution and inflammation on the association between somatic cell count and yield. The data used to investigate this relationship come from 8373 monthly records of milk yield and composite somatic cell count, together with incidence of clinical mastitis, which were recorded on 850 cows from five dairy cattle farms in Gloucestershire, UK. Two sets of models were used to investigate dilution and inflammation using two-level hierarchical models. The first set of models was used to estimate the linear (dilution) and log10-linear (inflammation) impact of SCC on the outcome variable milk yield. Five general linear models with increasing inclusion of higher test day SCC values were run. The cumulative categories were test day SCC values of up to and inclusive of 30, 50, 100, 200 and 400x10(3)cells/ml. Linear and log linear SCC influences on milk yield were estimated. At low SCC values the linear SCC predictor was dominant, while at higher values the log linear predictor was dominant. Up to 100x10(3)cells/ml there was mostly a slightly negative linear relationship between SCC and yield, potentially indicating a dilution effect. In the second set of models, three approaches to adjust milk loss for dilution were compared with an unadjusted model. In general, dilution-adjusted SCC values fitted the data better and resulted in a slightly lower milk loss per SCC category compared with unadjusted SCC. In all models with a dilution term there was a significant reduction in yield with SCC>200x10(3)cells/ml.     

Skin sensitivity to tuberculins in cattle vaccinated against Johne's disease

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 × 10³ cells/ml) than in cloxacillin-treated quarters (388.7 ± 71.2 x 10³ cells/ml); values in quarters receiving cloxacillin plus ampicillin were intermediate (252.0 ± 47.0 × 10³ 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.     

Bactericidal activity of macrophages against Streptococcus uberis is different in mammary gland secretions of lactating and drying off cows

The aim of this study was to compare the ability of milk macrophages and macrophages from the mammary gland secretions during the mid-dry period for their interaction with the mastitis-causing Streptococcus uberis. We also aimed to determine if S. uberis induced the release of the cytokine tumour necrosis alpha (TNF-alpha) and the bactericidal moiety nitric oxide (NO) from milk macrophages of lactating cows and macrophages from the mammary gland secretions at the mid-dry period. Macrophages were isolated from the mammary gland secretions of cows during the mid-lactation or mid-dry period, and compared with blood monocytes for their interaction with the important mastitis-causing pathogen S. uberis. When infected in vitro with S. uberis, milk macrophages from lactating cows with S. uberis released modest amounts of the cytokine tumour necrosis factor alpha (TNF-alpha) (139 pg/ml) and the bactericidal moiety nitric oxide (NO) (3-4 microM of nitrite). Blood monocytes from lactating cows released significantly higher amounts of TNF-alpha (345 +/- 143 pg/ml) and NO (7 +/- 2 microM of nitrite) after interaction with S. uberis, compared to milk macrophages (P < 0.01 for both TNF-alpha and NO). Stimulation of blood monocytes with the cytokine interferon-gamma (IFN-gamma) enhanced significantly the release of NO and TNF-alpha, but IFN-gamma did not significantly enhance the production of NO and TNF-alpha by milk macrophages from lactating cows. Milk macrophages from all lactating cows failed to kill S. uberis efficiently, and this lack of killing was unaffected by prior treatment with gamma interferon (IFN-gamma) (P > 0.05). Rather, S. uberis multiplied significantly inside infected milk macrophages from lactating cows, with a two-fold increase in bacterial numbers at 2 h post-infection. Milk macrophages from lactating cows were able however, to kill a significant proportion (50-60%, P < 0.01) of phagocytosed Staphylococcus aureus. Blood monocytes from all cows were found to exert significant bactericidal activity against S. uberis. There were no significant differences in the bactericidal activity of milk macrophages obtained from lactating cows with low somatic cell counts (SCC; < 10(5) ml(-1)) compared with those with a mildly elevated SCC (> 10(5) ml(-1)) (P > 0.05). In contrast, mammary gland secretion macrophages isolated from the same cows in the mid-dry period killed a significant proportion of phagocytosed S. uberis (50-65% of ingested S. uberis killed, P < 0.01) although cytokine production in response to in vitro bacterial infection was low. We conclude that the bactericidal activity of mammary gland secretion macrophages against a virulent strain of S. uberis is low during the lactation period. In addition, our data indicate that S. uberis is not a strong inducer of NO and TNF-alpha in macrophages from the milk or mammary gland secretions of cows during the drying off period. Finally, IFN-gamma does not activate milk macrophages or macrophages from cows during the lactating period or mammary gland secretions during the drying off period.     

Experimentally induced Staphylococcus aureus mastitis in selenium-deficient and selenium-supplemented dairy cows

Ten Holstein cows were fed a selenium-deficient (SeD) diet containing 0.04 mg of Se/kg of dry matter for 3 months before and throughout their first lactation. A selenium-supplemented (SeS) group of 10 cows was fed an additional 2 mg of Se/head/d to increase dietary Se concentration of the dry matter to approximately 0.14 mg/kg of body weight. An intracisternal challenge exposure of 40 to 60 colony-forming units (CFU) of Staphylococcus aureus was administered into 1 or 2 quarters of the udder of each trial cow at about the twenty-second week of lactation. Blood Se concentration (micrograms/ml +/- SEM) at the time of challenge exposure was 0.035 +/- 0.002 in SeD and 0.139 +/- 0.006 in SeS cows. Infections were established in 14/16 of the challenge-exposed quarters in SeD and 16/19 of the challenge-exposed quarters in SeS cows. The infection in 1 quarter of each Se group cleared without treatment by the end of the 8-week trial period. Log10 peak bacterial concentrations in milk from infected SeD quarters (5.04 +/- 0.25 CFU/ml) were higher (P less than 0.05) than those of infected SeS quarters (4.40 +/- 0.12 CFU/ml). Log10 peak somatic cell count (SCC) in milk from infected SeD quarters (7.18 +/- 0.08 cells/ml) did not differ from that of SeS quarters (7.17 +/- 0.05 cells/ml). Peak bacterial concentrations were attained sooner (P less than 0.05) in SeD quarters (9.5 +/- 4.0 days) than in SeS quarters (20.7 +/- 3.1 days). Similarly, peak SCC were reached earlier (P less than 0.05) in SeD (4.3 +/- 1.1 days) than in SeS quarters (13.3 +/- 3.8 days).(ABSTRACT TRUNCATED AT 250 WORDS)     

An outbreak of Streptococcus canis mastitis in a dairy herd in Israel

CASE HISTORY: An increase in the bulk somatic cell count (BSCC) of up to 1,000 x 103 cells/ml occurred in a dairy herd in Israel at the end of 2001 and beginning of 2002. CLINICAL FINDINGS: Bacteriological examination of milk from 69 cows revealed a high prevalence of Streptococcus group G bacteria, identified as S. canis, affecting 38% of cows and 20% of all quarters. Isolates were sensitive to cephalothin and moderately sensitive to penicillin G. Infected cows were separated from the herd, treated with intramammary antibiotics, milked last, and strict hygiene practices were introduced to the milking routine. The pathogen was cleared from the herd and BSCC decreased to 250-350 x 103 cells/ml after 6 months. DIAGNOSIS: Streptococcus canis mastitis. CLINICAL RELEVANCE: Streptococcus canis infection may cause subclinical mastitis and high bulk SCC in dairy herds and be resolved by treatment with intramammary antibiotics and the introduction of strict hygiene practices.     

Prevalence and herd-level risk factors for intramammary infection with coagulase-negative staphylococci in Dutch dairy herds

In this study, the prevalence of intramammary infection (IMI) with coagulase-negative staphylococci (CNS) in The Netherlands was estimated on 49 randomly selected herds with at least 40 lactating cows. In total, 4220 quarter milk samples were collected. The prevalence of CNS IMI in The Netherlands was estimated at 10.8% at quarter level and 34.4% at cow level, making it the most frequently isolated group of pathogens. Fourteen species of CNS were identified; the most frequently isolated species was Staphylococcus chromogenes (30.3%) followed by Staphylococcus epidermidis (12.9%) and Staphylococcus capitis (11.0%). Prevalence of CNS IMI was higher in heifers compared to older cows. Geometric mean quarter SCC of CNS-positive quarters was 109,000 cells/ml, which was approximately twice as high as culture-negative quarters. Quarters infected with S. chromogenes, S. capitis and Staphylococcus xylosus had a higher SCC (P<0.05) than culture-negative quarters, while quarters that were culture-positive for S. epidermidis and Staphylococcus hyicus tended to have a higher SCC than culture-negative quarters. An increased prevalence of CNS IMI was associated with the herd-level variables source of drinking water not being tap water, housing of dry cows in one group instead of multiple groups, measurement of cow SCC every month, udder health monitoring by the veterinarian, pasturing during outdoor season, percentage of stalls contaminated with milk, and BMSCC>250,000 cells/ml. Although a causal relation between these factors and prevalence of CNS is not proven and for some factors not even likely, knowledge of the associations found may be helpful when approaching CNS problems on dairy farms.     

Milk leucocyte population patterns in bovine udder infection of different aetiology

This study compared the different leucocyte populations in milk from udders infected with different mastitic pathogens and in different stages of infection. Milk samples were collected from quarters free of intramammary infection, acutely infected with Escherichia coli or Staphylococcus aureus and chronically infected with S. aureus, coagulase-negative staphylococci (CNS) or Streptococcus dysgalactiae. Udder bacteriological status was confirmed after three consecutive bacteriological examinations from weekly quarter milk samples. At the time of the trial, milk samples were tested for somatic cell count (SCC) and differential cell count by both light microscopy (LM) and flow cytometry. Monoclonal antibody (mAb) CD11a/CD18 was used in order to differentiate between leucocytes and epithelial cells when tested by flow cytometry. Udder quarters free of intramammary infection had a mean SCC lower than 107 x 10(3) cells/ml in which the epithelial cells were the main cell type followed by polymorphonuclear cells (PMNs), while macrophages and lymphocytes had a lower concentration. Only 56% of the cells were labelled with the mAb anti-CD11a/CD18. In either acute E. coli- or S. aureus-infected quarters, SCC were significantly higher (P < 0.0001) than in samples from the time of inoculation, with over 90% of the cells labelled with the mAb anti-CD11a/CD18. The main cell type was neutrophils. In chronically infected cows, differences in SCC and in leucocyte patterns were found between infecting pathogens as well as between quarters harbouring the same pathogen. In all the chronically infected quarters, SCC was significantly higher (P < 0.05) than in uninfected ones. The distribution of the leucocyte patterns in the quarters infected with S. dysgalactiae did not differ from that in quarters with acute infection with both E. coli and S. aureus. In the cows chronically infected with S. aureus or CNS, the proportion of PMN was higher but not significantly different from quarters free of intramammary infection, while epithelial cells were significantly lower (P < 0.05). The T lymphocytes bearing CD4+ or CD8+ were significantly higher in quarters chronically infected with S. aureus than in quarters free of intramammary infection and in quarters acutely infected with either E. coli or S. aureus. In all samples B cells were negligible.     

Immune cell differentiation in mammary gland tissues and milk of cows chronically infected with Staphylococcus aureus

This study identifies and compares the distribution of mononuclear cells in the mammary gland tissues and milk of healthy and chronically infected with Staphylococcus aureus cows. Somatic cell counts (SCCs) during the 3 months before the study were > 1 x 10(6) cell/ml in the infected quarters and < 1 x 10(5) cell/ml in the infection-free quarters. Immediately after slaughter, samples from the tissues above the gland cistern and supra-mammary lymph node were collected. No histological differences were found between the supra-mammary lymph nodes of the healthy and infected udders, and both appeared normal. In the milk of the healthy infection-free mammary glands, SCC was < 50,000 cells/ml) while epithelial cells were the predominant type. The percentage of CD18+ was low than 45%, of which over three-quarters were polymorphonuclear (PMN), and less than one- quarter were mononuclear cells. The later comprised CD4+ or CD8+ T-lymphocytes, macrophages (Mo) but not B-cells. In the tissues, there were few CD18+ leukocytes, and most of the cells were T-lymphocytes. The number of B-lymphocytes bearing CD21+ was similar to that of CD8+ and were localized in the connective tissue as clusters of 2-5 cells, mainly in areas with no alveoli, or as single cell having a dendritic like form. The number of Mos was negligible. In the milk of the infected glands, SCC exceeded 700,000 cells/ml, of which > 95% were CD18+ positive. The distribution of the leukocytes had two patterns: one presented (> 80%) of PMN cells and a small number of mononuclear cells; the second had less than 50% PMN and many mononuclear cells. The CD8+ cells in these infected sections were observed throughout the mammary epithelial cells (MEc) around the alveoli and in the alveolar lumen (AL). The numbers and the location of CD21+ B-lymphocytes were similar to those in the infection-free mammary glands. The number of CD5+ positive cells was lower than T and B- cells combined and were located throughout the mammary epithelial cells, around the alveoli and within the connective tissue. Mo numbers were high in most of those infected quarters, and were localized around the connective tissue and within the AL.     

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.     

Risk factors for intramammary infections and relationship with somatic-cell counts in Italian dairy goats

Routine examination of milk was performed on five herds of lactating goats in northern Italy as part of a milk quality-monitoring program in the year 2000. As part of the study, aseptic samples of foremilk were collected monthly from both half udders during the entire lactation for 305 goats, resulting in a total of 4571 samples. The samples were tested with cytological and bacteriological analyses to evaluate the relationship between mammary infections and somatic-cell count (SCC; Fossomatic (TM) method). Prevalence of intramammary infection (IMI) was 40.2% (n = 1837) of all udder-half samples examined. The most-prevalent mastitis agents were coagulase-negative Staphylococci (CNS), 80% (n = 1474 udder-half samples); within this group, Staphylococcus epidermidis was the most-prevalent species (38%). Other prevalence were Staphylococcus aureus 6% (n = 112 udder-half samples) and environmental pathogens 14% of infected udder-half samples (n = 251) with a diverse mixture of species, none of which had a frequency of >4%. Enterococcus faecalis was the most-frequently isolated among this group. Neither Salmonella spp. nor Listeria monocytogenes were detected. The risk (sample level) of infection differed across herds, parities, and stage of lactation according to results from logistic multiple regression. Infection was more common among goats in third and fourth parities and during the later stages of lactation. Of the 2734 samples from uninfected udder halves, the mean log₂ SCC was 3.9 cell/ml; of the 1837 bacteriological positive samples, the mean log₂ SCC was 5.6 cell/ml. According to results from a linear mixed model, concentrations of somatic cells tended to increase with increasing age and days in milk and with the presence of bacteria. Infection with S. aureus was associated with the highest SCS.