Identification of potential sources of Staphylococcus aureus in herds with mastitis problems

Staphylococcus aureus is a common udder pathogen of dairy cows that often causes herd problems. Various mastitis control programs have been used to combat the problem but have not always been efficient in preventing new Staph. aureus infections, indicating the presence of possible sources of infection other than those traditionally considered. Therefore, the aim of the study was to identify potential sources of infection relevant for Staph. aureus mastitis within 5 dairy herds with udder health problems caused by Staph. aureus. Samples were collected from milk of lactating cows, from body sites, and from the environment of lactating cows, dry cows, late pregnant heifers, young heifers 4 to 12 mo old, and heifer calves 0 to 3 mo old. Isolates of Staph. aureus were identified and compared using pulsed-field gel electrophoresis. Four to 7 unique Staph. aureus pulsotypes were found within each herd, with one strain predominating in milk in each herd. The milk pulsotypes were also frequently isolated in body samples, especially on hock skin, and in the immediate environment of lactating cows, and were sometimes found in other animal groups, especially in dry cows and heifer calves 0 to 3 mo old. The prevalence of Staph. aureus in milk and other types of samples varied markedly between herds. Staphylococcus aureus isolates with genotypes indistinguishable from those found in milk also dominated in extra-mammary sites within the dairy herds studied, and hock skin was identified as an important reservoir of Staph. aureus. The results contribute new knowledge necessary to improve strategies for udder health control in herds.     

Short communication: Staphylococcus aureus isolated from colostrum of dairy heifers represent a closely related group exhibiting highly homogeneous genomic and antimicrobial resistance features

In heifers, intramammary infections caused by Staphylococcus aureus affect milk production and udder health in the first and subsequent lactations, and can lead to premature culling. Not much is known about Staph. aureus isolated from heifers and it is also unclear whether or not these strains are readily transmitted between heifers and lactating herd mates. In this study, we compared phenotypic characteristics, spa types, and DNA microarray virulence and resistance gene profiles of Staph. aureus isolates obtained from colostrum samples of dairy heifers with isolates obtained from lactating cows. Our objective was to (1) characterize Staph. aureus strains associated with mastitis in heifers and (2) determine relatedness of Staph. aureus strains from heifers and lactating cows to provide data on transmission. We analyzed colostrum samples of 501 heifers and milk samples of 68 lactating cows within the same herd, isolating 48 and 9 Staph. aureus isolates, respectively. Staphylococcus aureus strains from heifers, lactating herd mates, and an unrelated collection of 78 strains from bovine mastitis milk of mature cows were compared. With 1 exception each, characterization of all strains from heifers and lactating cows in the same herd yielded highly similar phenotypic and genotypic results. The strains were Staphaurex latex agglutination test negative (Oxoid AG, Basel, Switzerland) and belonged to agr type II, CC705, and spa types tbl 2645 and t12926. They were susceptible to all antimicrobial agents tested. In contrast, the strains from mature cows in other herds were spread across different clonal complexes, spa types, and SplitsTree clusters (http://www.splitstree.org/), thus displaying a far higher degree of heterogeneity. We conclude that strains isolated from colostrum of heifers and mastitis milk of lactating cows in the same herd feature highly similar phenotypic and genomic characteristics, suggesting persistence of the organism during the first and potentially subsequent lactations or transmission between heifers and mature herd mates.     

Streptococcus dysgalactiae isolates at calving and lactation performance within the same lactation

The objective of the study was to investigate the association between early lactation Streptococcus dysgalactiae isolates and milk yield, somatic cell count (SCC), clinical mastitis, and culling in the same lactation. The 178 commercial dairy herds were randomly placed into 3 penicillin- or penicillin-dihydrostreptomycin-based dry-cow treatments and 3 different postmilking teat disinfection groups—negative control, iodine, or external teat sealant. All cows were sampled in early lactation, and Strep. dysgalactiae-positive and culture-negative cows were followed throughout the remainder of the lactation. Mixed models, including repeated measurements, with test-day observation as dependent variable, were used to compare milk yield, SCC, and available milk quality variables throughout the remaining lactation. Survival analyses, using a positive frailty model to account for any herd random effects, were used to estimate the hazard ratio for clinical mastitis and culling. Streptococcus dysgalactiae-positive cows had a significantly higher SCC throughout the lactation compared to culture-negative cows. For primiparous or multiparous cows, respectively, the differences in the geometric mean SCC between Strep. dysgalactiae-positive and culture-negative cows was 197,000 or 280,000 cells/mL at the beginning of the lactation, 24,000 or 46,000 cells/mL in mid lactation, and 39,000 or 111,000 cells/mL at the end of the lactation. Streptococcus dysgalactiae-positive primiparous or multiparous cows produced 334 or 246 kg less milk, respectively, during a 305-d lactation compared with culture-negative cows. Compared with culture-negative cows, the hazard ratios for clinical mastitis in Strep. dysgalactiae-positive cows were 2.3 (1.9 to 2.9) and 1.6 (1.3 to 2.0) for culling. For cows with both Strep. dysgalactiae and Staphylococcus aureus isolates, the hazard ratio for culling significantly increased to 2.5 (1.9 to 3.2).     

Elimination of selected mastitis pathogens during the dry period

We aimed to evaluate the elimination of 4 different mastitis pathogens, Streptococcus agalactiae, Mycoplasma bovis, Staphylococcus aureus, and Streptococcus uberis, from infected udder quarters during the dry period using quantitative PCR. The second purpose of this study was to evaluate the association between milk haptoglobin (Hp) concentration and the presence of udder pathogens (Strep. agalactiae, Staph. aureus, M. bovis, and Strep. uberis) in udder quarter milk samples before and after dry period. Aseptic udder quarter milk samples (n = 1,001) were collected from 133 dairy cows at dry off and at the first milking after calving from 1 large dairy herd. Bacterial DNA of Strep. agalactiae, Staph. aureus, Strep. uberis, and M. bovis in the udder quarter milk samples was identified with commercial quantitative PCR analysis Mastitis 4B (DNA Diagnostic A/S, Risskov, Denmark). Milk Hp concentration (mg/L) was measured from udder quarter milk samples. The elimination rates during the dry period for M. bovis, Staph. aureus, Strep. agalactiae, and Strep. uberis were 86.7, 93.6, 96.2, and 100.0%, respectively. The new IMI rate was 3.0% for M. bovis, 2.9% for Staph. aureus, 2.4% for Strep. agalactiae, and 3.1% for Strep. uberis. The milk Hp concentration was significantly higher in udder quarter milk samples with blood and in samples positive for Strep. agalactiae at dry off and for Staph. aureus postcalving. Elevated milk Hp concentration was not associated with the presence of M. bovis in the udder quarter milk samples. In conclusion, elimination of Staph. aureus, Strep. agalactiae, and Strep. uberis during the dry period was high; the elimination of M. bovis from infected udder quarters was lower, but probably spontaneous. Additionally, milk Hp concentration may be used as a marker for udder inflammation when combined with the bacteriological results at dry off and postpartum.     

Retrospective cohort study of management procedures associated with dairy herd-level eradication of Streptococcus agalactiae in the Danish surveillance program

The aim of this observational retrospective cohort study was to identify management procedures that are associated with herd-level eradication of Streptococcus agalactiae in dairy herds. The objective was to compare herds that recovered from Strep. agalactiae with herds that remained infected with Strep. agalactiae on the basis of specific management procedures. Data from the Danish surveillance program for Strep. agalactiae, where all milk delivering dairy herds are tested yearly, were used to identify study herds. One hundred ninety-six herds that were classified in the program as infected with Strep. agalactiae, in both January 2013 and January 2014, were identified as study herds. These were followed until January 2017. One hundred forty-four herds remained infected every year until January 2017. Forty-six herds recovered from Strep. agalactiae after January 2014 (were tested negative continuously after January 2015, January 2016, or January 2017 and remained noninfected in the program from recovery until January 2017). Herd characteristics and management procedures were obtained through the Danish Cattle Database. Herd characteristics included herd size, yield, milking system, and bulk milk somatic cell count (SCC). Management procedures included the proportion of cows culled within 100 d after calving due to mastitis, the extent of diagnoses relative to the extent of mastitis treatments, the proportion of cows treated for mastitis during lactation, the proportion of cows treated for mastitis early in lactation, the proportion of cows treated at dry-off, and the median length of the dry period for cows receiving dry cow treatment. All variables were calculated on herd level. Multivariable logistic regression was used to analyze the association between herd infection status and management procedures. A higher proportion of culling due to mastitis within 100 d from calving was associated with a higher probability of herd-level recovery from Strep. agalactiae in herds with conventional milking system. For example, herds with conventional milking, a bulk milk SCC of 260,000 cells/mL, and 10% early culling due to mastitis had a recovery probability of 0.13, whereas similar herds with 20% early culling due to mastitis had a recovery probability of 0.15. A higher proportion of mastitis treatments within 250 d postcalving was associated with a higher probability of herd-level recovery for herds with a relatively high bulk milk SCC. For example, herds with conventional milking, a bulk milk SCC of 260,000 cells/mL, and 10% lactational mastitis treatments had a recovery probability of 0.12, whereas similar herds with 20% lactational mastitis treatments had a recovery probability of 0.15. Herds with a low bulk milk SCC (<220,000 cells/mL) combined with a low proportion of lactational treatments (<0.2) had a relatively high probability of herd-level recovery (>0.2). Additional variables, including the proportion of dry cow treatments, were not associated with herd-level recovery from Strep. agalactiae.     

Relationships between milk culture results and treatment for clinical mastitis or culling in Norwegian dairy cattle

In quarter milk samples from 2,492 randomly sampled cows that were selected without regard to their current or previous udder health status, the relationships between the following outcome variables were studied: treatment of clinical mastitis; the joint event of either treatment or culling for mastitis; culling for all reasons; culling specifically for mastitis; and the covariates of positive milk culture for Staphylococcus aureus, Streptococcus spp., and coagulase-negative Staphylococcus spp., or other pathogens, or of negative culture for mastitis pathogens. Microbiological diagnoses were assigned at the cow level, and altogether 3,075 diagnoses were related to the outcome variables. The relation between the absence of pathogens and rich (>1,500 cfu/mL of milk) or sparse (≤1,500 cfu/mL of milk) growth of Staph. aureus were also assessed separately for each outcome variable. The hazard of treatment of clinical mastitis was greater for cows diagnosed with Staph. aureus compared with cows with no pathogens in all analyses. Cows with sparse growth of Staph. aureus upon microbiological analysis were more likely to be treated for clinical mastitis, and cows with rich growth of the bacteria experienced a higher overall risk of culling when the models adjusted for cow composite milk somatic cell count. No difference between rich and sparse growth of Staph. aureus was found when mastitis was defined as the joint event of either culling for mastitis or treatment of clinical mastitis, and when the relationship with culling specifically for mastitis was assessed. The combined outcome of treatment and culling for mastitis was related to a positive diagnosis of Strep. spp. after cow composite milk somatic cell count was omitted from the model. Presence of Streptococcus spp. was also related to culling specifically for mastitis, whereas culling for all reasons and treatment of clinical mastitis was not related to a positive culture of Strep. spp. Presence of coagulase-negative Staph. spp. or other pathogens was not associated with either of the outcome variables.     

Analysis of an outbreak of Streptococcus uberis mastitis

An outbreak of Streptococcus uberis mastitis was described to gain insight into the dynamics of Strep. uberis infections at a herd level. Data were obtained from a longitudinal observational study on a commercial Dutch dairy farm with good udder health management. Quarter milk samples for bacteriological culture were routinely collected at 3-wk intervals from all lactating animals (n = 95 +/- 5). Additional samples were collected at calving, clinical mastitis, dry-off, and culling. During the 78-wk observation period, 54 Strep. uberis infections were observed. The majority of infections occurred during a 21-wk period that constituted the disease outbreak. The incidence rate was higher in quarters that had recovered from prior Strep. uberis infection than in quarters that had not experienced Strep. uberis infection before. The incidence rate of Strep. uberis infection did not differ between quarters that were infected with other pathogens compared with quarters that were not infected with other pathogens. The expected number of new Strep. uberis infections per 3-wk interval was described by means of a Poisson logistic regression model. Significant predictor variables in the model were the number of existing Strep. uberis infections in the preceding time interval (shedders), phase of the study (early phase vs. postoutbreak phase), and prior infection status of quarters with respect to Strep. uberis, but not infection status with respect to other pathogens. Results suggest that contagious transmission may have played a role in this outbreak of Strep. uberis mastitis.     

Effect of enhanced hygiene on transmission of Staphylococcus aureus,Streptococcus agalactiae,and Streptococcus dysgalactiae in dairy herds with automatic milking systems

The objective of the study was to evaluate the effect of hygiene measures in automatic milking units on the transmission of 3 mastitis pathogens considered to be mainly or partly transmitted from cow to cow during milking events. Two studies were conducted as within-herd experimental trials in 2 Danish commercial dairy herds (A and B) with automatic milking systems. Interventions to enhance hygiene were implemented on the automatic milking units. The 2 studies evaluated separate interventions. In herd A, the hygiene interventions were manual wash with the Lely foam unit and adjustments on the brush-mediated teat cleaning procedure. In herd B, the hygiene intervention included automatic disinfection spray on the upper surface of the brush motor and daily change of brushes. Composite milk samples were collected longitudinally at 3- or 4-wk intervals from all lactating cows. Additional milk samples were taken from cows entering or leaving the study groups. Milk samples were analyzed with quantitative PCR. A hidden Markov model implemented within a Bayesian framework was used to estimate the transmission probability. For analysis, 701 samples from 156 cows were used for herd A, and 1,349 samples from 390 cows were used for herd B. In the intervention group in herd B, transmission of Streptococcus agalactiae was reduced to 19% (95% posterior credibility interval: 0.00–64%) of the transmission in the control group, whereas transmission of Streptococcus dysgalactiae was reduced to 17% (95% posterior credibility interval: 0.00–85%) of transmission in the control group. This suggests that automatic spray on the upper surface of the brush motor with disinfectant along with daily change of brushes collectively reduced transmission of Strep. agalactiae and Strep. dysgalactiae. Results on Staphylococcus aureus in herd B and results on manual foam cleaning and brush-mediated teat cleaning adjustments in herd A were inconclusive.     

Short communication: Antimicrobial efficacy of intramammary treatment with a novel biphenomycin compound against Staphylococcus aureus, Streptococcus uberis, and Escherichia coli-induced mouse mastitis

Bovine mastitis undermines udder health, jeopardizes milk production, and entails prohibitive costs, estimated at $2 billion per year in the dairy industry of the United States. Despite intensive research, the dairy industry has not managed to eradicate the 3 major bovine mastitis-inducing pathogens: Staphylococcus aureus, Streptococcus uberis, and Escherichia coli. In this study, the antimicrobial efficacy of a newly formulated biphenomycin compound (AIC102827) was assessed against intramammary Staph. aureus, Strep. uberis, and E. coli infections, using an experimental mouse mastitis model. Based on its effective and protective doses, AIC102827 applied into the mammary gland was most efficient to treat Staph. aureus, but also adequately reduced growth of Strep. uberis or E. coli, indicating its potential as a broad-spectrum candidate to treat staphylococcal, streptococcal, and coliform mastitis in dairy cattle.     

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

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

Short communication: Streptococcus species isolated from mastitis milk samples in Germany and their resistance to antimicrobial agents

Mastitis is one of the most frequent infectious diseases in dairy cattle and is a reason for antimicrobial drug usage in dairy cows. The bacteria involved in bovine mastitis are mainly Streptococcus spp., Staphylococcus spp., and coliforms. The aim of this study was to determine antimicrobial resistance among Streptococcus spp. isolated from bovine mastitis milk. Antimicrobial resistance in Strep. uberis (n = 227), Strep. dysgalactiae (n = 49), and Strep. agalactiae (n = 3) was determined for 9 antimicrobial agents using the broth microdilution method in accordance with Clinical and Laboratory Standards Institute recommendations. Of all Streptococcus spp., 13% were multidrug resistant. The rate of multidrug resistance was higher among Strep. uberis (15%) than among Strep. dysgalactiae (6%) and Strep. agalactiae (0%). Resistance to tetracycline was the most common, followed by resistance to erythromycin, pirlimycin, and gentamicin. Resistance rates were higher on farms with more than 80 cows compared with those with fewer than 20 cows. β-Lactams should remain the drugs of choice in the treatment of streptococcal mastitis. The slightly elevated minimum inhibitory concentrations determined for these antibiotics may indicate, however, the emergence of resistant streptococci. To identify such changes in susceptibility as early as possible, antimicrobial resistance in streptococci should be surveyed regularly.     

Postcalving udder health and productivity in cows approaching dry-off with intramammary infections caused by non-aureus Staphylococcus,Aerococcus, Enterococcus,Lactococcus, and Streptococcus species

The objective of this prospective cohort study was to explore associations between intramammary infection (IMI) in late-lactation cows and postcalving udder health and productivity. Cows (n = 2,763) from 74 US dairy herds were recruited as part of a previously published cross-sectional study of bedding management and IMI in late-lactation cows. Each herd was visited twice for sampling. At each visit, aseptic quarter milk samples were collected from 20 cows approaching dry-off (>180 d pregnant), which were cultured using standard bacteriological methods and MALDI-TOF for identification of isolates. Quarter-level culture results were used to establish cow-level IMI status at enrollment. Cows were followed from enrollment until 120 d in milk (DIM) in the subsequent lactation. Herd records were used to establish whether subjects experienced clinical mastitis or removal from the herd, and DHIA test-day data were used to record subclinical mastitis events (somatic cell count >200,000 cells/mL) and milk yield (kg/d) during the follow-up period. Cox regression and generalized estimating equations were used to evaluate the associations between IMI and the outcome of interest. The presence of late-lactation IMI caused by major pathogens was positively associated with postcalving clinical mastitis [hazard ratio = 1.5, 95% confidence interval (CI): 1.2, 2.0] and subclinical mastitis (risk ratio = 1.5, 95% CI: 1.3, 1.9). Species within the non-aureus Staphylococcus (NAS) group varied in their associations with postcalving udder health, with some species being associated with increases in clinical and subclinical mastitis in the subsequent lactation. Late-lactation IMI caused by Streptococcus and Streptococcus (Strep)-like organisms, other than Aerococcus spp. (i.e., Enterococcus, Lactococcus, and Streptococcus spp.) were associated with increases in postcalving clinical and subclinical mastitis. Test-day milk yield from 1 to 120 DIM was lower (?0.9 kg, 95% CI: ?1.6, ?0.3) in late-lactation cows with any IMI compared with cows without IMI. No associations were detected between IMI in late lactation and risk for postcalving removal from the herd within the first 120 DIM. Effect estimates reported in this study may be less than the underlying quarter-level effect size for IMI at dry-off and postcalving clinical and subclinical mastitis, because of the use of late-lactation IMI as a proxy for IMI at dry-off and the use of cow-level exposure and outcome measurements. Furthermore, the large number of models run in this study (n = 94) increases the chance of identifying chance associations. Therefore, confirmatory studies should be conducted. We conclude that IMI in late lactation may increase risk of clinical and subclinical mastitis in the subsequent lactation. The relationship between IMI and postcalving health and productivity is likely to vary among pathogens, with Staphylococcus aureus, Streptococcus spp., Enterococcus spp., and Lactococcus spp. being the most important pathogens identified in the current study.     

A cohort study of the effect of Streptococcus agalactiae on milk yield and somatic cell count in Norwegian dairy cows

The primary objective of the present study was to estimate the effect of Streptococcus agalactiae intramammary infection on milk production and somatic cell count (SCC) in Norwegian dairy cows. A secondary objective was to assess differences in the effect of common Strep. agalactiae sequence types (ST) found in Norwegian dairy herds. We performed a cohort study combining registry data with sequence-type data from Strep. agalactiae isolates. Herds in which Strep. agalactiae had been detected in individual animals (bacteriological culture or quantitative PCR) between 2012 and 2015 were included. We accessed monthly test-day milk yield records for the entire period to compare milk yield and SCC between cows that were Strep. agalactiae positive and all other cows, within each herd. The study sample consisted of 150 herds, 15,757 cows, 30,850 lactations, and 204,126 test days. We evaluated the effects of Strep. agalactiae on test-day milk yield and SCC using mixed linear regression models, controlling for clustering by herd, cow, and lactation. Multilocus sequence typing of Strep. agalactiae was available for isolates from 86 herds. Additional models were fit to a subset of herds (n = 59) in which ST1, ST23, ST103, and ST196 had been found, to compare the effects of ST on milk production and SCC. In the period 3 to 2 mo before diagnosis, Strep. agalactiae-positive cows produced an average of 1.3 kg more DIM-adjusted milk/d than their negative herd mates. At the time of diagnosis, production was on average 0.13 kg less DIM-adjusted milk/d in Strep. agalactiae-positive cows than in negative cows; 2 to 3 mo after diagnosis, they produced 1.24 kg less DIM-adjusted milk/d than negative cows. Losses persisted for the rest of the investigated period. Cows with ST23, ST103, and ST196 followed a similar pattern as the overall analysis with respect to milk production, whereas ST1-affected cows produced similar amounts of milk before diagnosis as the negative cows. Cows with ST1 experienced the largest milk loss 1 to 2 mo after diagnosis but then recovered to some extent; for cows with ST103, the severe milk loss persisted for the rest of the investigation period. The cow-associated ST103 elicited a lower response in peak SCC compared with ST23, ST103, and ST196. The results indicate an effect of Strep. agalactiae on milk production and SCC. Production was lowest 2 to 3 mo after a positive sample. Peak SCC was reached the month before diagnosis, with notable differences between sequence types.     

The effect of season on somatic cell count and the incidence of clinical mastitis

Bulk milk somatic cell count (BMSCC), individual cow somatic cell count (ICSCC), and incidence rate of clinical mastitis (IRCM) are all udder health parameters. So far, no studies have been reported on the effect of season on BMSCC, IRCM, and ICSCC in the same herds and period over multiple years. The objectives of this study were to determine the seasonal pattern over a 4-yr period of 1) BMSCC, 2) elevated ICSCC, 3) IRCM, and 4) pathogen-specific IRCM. Bulk milk somatic cell count, ICSCC, and pathogen-specific clinical mastitis data were recorded in 300 Dutch dairy farms. For the analyses of BMSCC, ICSCC, and IRCM, a mixed, a transitional, and a discrete time survival analysis model were used, respectively. Sine and cosine were included in the models to investigate seasonal patterns in the data. For all parameters, a seasonal effect was present. Bulk milk somatic cell count peaked in August to September in all 4 years. The probability of cows getting or maintaining a high ICSCC was highest in August and May, respectively. Older and late-lactation cows were more likely to develop or maintain a high ICSCC. Incidence rate of clinical mastitis was highest in December to January, except for Streptococcus uberis IRCM, which was highest in August. Totally confined herds had a higher Escherichia coli IRCM in summer than in winter. Compared with the major mastitis pathogens, the seasonal differences in IRCM were smaller for the minor pathogens. Distinguishing between Strep. uberis, Streptococcus dysgalactiae, Streptococcus agalactiae, and other streptococci is essential when identifying Streptococcus spp. because each of them has a unique epidemiology. Streptococcus uberis IRCM seemed to be associated with being on pasture, whereas E. coli IRCM was more housing-related.     

Short communication: Outbreak of Nocardia neocaledoniensis mastitis in an Italian dairy herd

Nocardia spp. are an uncommon cause of mastitis, and outbreaks have typically been reported in dairy farms with poor hygienic and management conditions. The outbreak described herein involved a dairy farm with 43 lactating cows that, after a long period with low bulk milk somatic cell counts (<180,000 cells/mL), experienced an increasing incidence of clinical mastitis with bulk milk somatic cell counts greater than 300,000 cells/mL. Fifteen mastitic quarters milk samples from 9 dairy cows were found to be infected by a member of the genus Nocardia, as identified on the basis of selected phenotypic and chemotaxonomic characteristics. The isolates were confirmed as Nocardia neocaledoniensis by 16S rDNA gene sequencing. Average quarter milk somatic cell count for infected udders was 863,057 cells/mL, significantly greater than the average value in noninfected quarters (189,710 cells/mL).     

Pathogen-specific production losses in bovine mastitis

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

Detection of Clinical Mastitis with the Help of a Thermal Camera

Increasing dairy farm size and increase in automation in livestock production require that new methods are used to monitor animal health. In this study, a thermal camera was tested for its capacity to detect clinical mastitis. Mastitis was experimentally induced in 6 cows with 10 μg of Escherichia coli lipopolysaccharide (LPS). The LPS was infused into the left forequarter of each cow, and the right forequarters served as controls. Clinical examination for systemic and local signs and sampling for indicators of inflammation in milk were carried out before morning and evening milking throughout the 5-d experimental period and more frequently on the challenge day. Thermal images of experimental and control quarters were taken at each sampling time from lateral and medial angles. The first signs of clinical mastitis were noted in all cows 2 h postchallenge and included changes in general appearance of the cows and local clinical signs in the affected udder quarter. Rectal temperature, milk somatic cell count, and electrical conductivity were increased 4 h postchallenge and milk N-acetyl-β-D-glucosaminidase activity 8 h postchallenge. The thermal camera was successful in detecting the 1 to 1.5°C temperature change on udder skin associated with clinical mastitis in all cows because temperature of the udder skin of the experimental and control quarters increased in line with the rectal temperature. Yet, local signs on the udder were seen before the rise in udder skin and body temperature. The udder represents a sensitive site for detection of any febrile disease using a noninvasive method. A thermal camera mounted in a milking or feeding parlor could detect temperature changes associated with clinical mastitis or other diseases in a dairy herd.     

Quarter and cow risk factors associated with the occurrence of clinical mastitis in dairy cows in the United Kingdom

Quarter and cow risk factors associated with the development of clinical mastitis (CM) during lactation were investigated during a 12-mo longitudinal study on 8 commercial Holstein-Friesian dairy farms in the southwest of England. The individual risk factors studied on 1,677 cows included assessments of udder and leg hygiene, teat-end callosity, and hyperkeratosis; body condition score; and measurements of monthly milk quality and yield. Several outcome variables for CM were used for statistical analysis, which included use of generalized linear mixed models. Significant covariates associated with an increased risk of CM were increasing parity, decreasing month of lactation, cows with very dirty udders, and quarters with only very severe hyperkeratosis of the teat-end. Thin and moderate smooth teat-end callosity scores were not associated with an increased risk for CM. Cows that recorded a somatic cell count >199,000 cells/mL and a milk protein percentage <3.2 at the first milk recording after calving were significantly more likely to develop CM after the first 30 d of lactation. There was no association between cow body condition score and incidence of CM. Of the cases of CM available for culture, 171 (26.7%) were confirmed as being caused by Escherichia coli and 121 (18.9%) confirmed as being caused by Streptococcus uberis. Quarters with moderate and very severe hyperkeratosis of the teat-end were at significantly increased risk of clinical E. coli mastitis before the next visit. Quarters with very severe hyperkeratosis of the teat-end were significantly more likely to develop clinical Strep. uberis mastitis before the next visit. There were strong trends within the data to suggest an association between very dirty udders (an increased risk of clinical E. coli mastitis) and teat-ends with no callosity ring present (an increased risk of clinical Strep. uberis mastitis). These results highlight the importance of individual quarter- and cow-level risk factors in determining the risk of CM associated with environmental pathogens during lactation.     

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

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

Short communication: Molecular characteristics,antimicrobial susceptibility,and pathogenicity of clinical Nocardia cyriacigeorgica isolates from an outbreak of bovine mastitis

The occurrence of nocardial mastitis, mostly in the context of outbreaks, has been reported in many countries. However, there is a paucity of reports regarding detailed characterization of Nocardia cyriacigeorgica from bovine mastitis. Thus, herein we report characteristics, antimicrobial susceptibility patterns, molecular identification, and pathogenicity of N. cyriacigeorgica isolated from an outbreak of clinical mastitis in a dairy herd in northern China. A total of 182 (80.2%) lactating cows had clinical mastitis with severe inflammation and firmness of the udder, reduced milk production, and anorexia, with no apparent clinical response to common antibiotics. Out of 22 mastitic milk samples submitted to our laboratory, 12 N. cyriacigeorgica were isolated and characterized using standard microbiological analysis, 16S rRNA gene sequencing, random amplified polymorphic DNA PCR analysis, biochemical assays, and antibiotic susceptibility testing. Additionally, in vivo experiments were done to determine pathogenicity of these clinical mastitis isolates. All isolates were resistant to ampicillin, amoxicillin-clavulanic acid, ciprofloxacin, minocycline, rifampicin, and aminoglycosides (type VI pattern). Additionally, intramammary inoculation of mice with N. cyriacigeorgica caused chronic inflammatory changes, including hyperemia, edema, and infiltration of lymphocytes and neutrophils, as well as hyperplasia of lymph nodules in mammary glands. Therefore, we concluded that N. cyriacigeorgica was involved in the current outbreak of mastitis. To our best knowledge, this is the first report to characterize N. cyriacigeorgica isolated from cases of bovine mastitis in China.