Staphylococcal Intramammary Infections Research Articles

Association between species-specific staphylococcal intramammary infections and milk somatic cell score over time in dairy goats

Numerous factors affect milk somatic cell score (SCS) in dairy goats including physiologic factors such as stage of lactation, and pathological factors such as bacterial intramammary infection (IMI), e.g. staphylococcal IMI. The association between IMI and udder inflammation and especially differences in the inflammatory response between the different staphylococcal species are yet to be identified. The objectives of this study were to use data from a recently published longitudinal study that characterized IMI status over time to evaluate the species-specific effect of staphylococcal IMI on udder half-level milk SCS, and to evaluate the effect of time since IMI diagnosis on this relationship. Half-level milk samples for culture and determination of SCS were collected from 171 goats starting within 10 days in milk (DIM), and then at various intervals until ≥ 120 DIM. A mixed linear model was used to assess the effect of species-specific staphylococcal IMI on SCS, accounting for confounding by lentivirus infection, parity, DIM, and the contralateral half IMI status, and for repeated measurements within udder half and for clustering of halves within goat. A second model was used to evaluate the effect of time since first IMI diagnosis and its interaction with staphylococcal IMI status on the relationship between staphylococcal IMI status and SCS. Lentivirus seropositivity and contralateral half IMI status were associated with SCS. Staphylococcal IMI status was associated with SCS, with differences between species. Staphyloccocus caprae, Staphylococcus epidermidis, Staphylococcus simulans, and Staphylococcus xylosus were associated with higher SCS than a number of other species. Time since first diagnosis did not modify the relationship between IMI status and SCS.

Evaluation of efficacy of a biofilm-embedded bacteria-based vaccine against staphylococcal mastitis in sheep—A randomized, placebo-controlled field study

Our objective was to evaluate the efficacy of a vaccine against staphylococcal mastitis in 5 dairy sheep farms, with 316 ewes in the vaccinated (V) group and 307 in the control (C) group studied throughout a lactation period. Two administrations of the vaccine were performed during the last stage of gestation of ewes. Starting 15 d after lambing and at monthly intervals thereafter, up to 9 milk samplings were performed for bacteriological and cytological examinations. Staphylococcal isolates recovered were examined for biofilm formation. Blood samples were collected for measurement of IgG poly-N-acetylglucosamine-specific antibodies. The most frequently isolated bacteria were staphylococci: 56.4 and 76.1%, respectively, of total isolates recovered from ewes of group V and C, respectively; staphylococci as causal agents of mastitis were isolated less frequently from V (5.3%) than in ewes in C (10.3%). Among mastitis-associated staphylococcal isolates recovered from V ewes, a smaller proportion was biofilm-forming than among ones from C: 53.2% versus 74.9% of isolates; biofilm-forming staphylococci as causal agents of mastitis were isolated less frequently from ewes in group V (2.3%) than in ewes in group C (6.0%). Anti-poly-N-acetylglucosamine-specific antibody values increased in V ewes and were higher than in C; a greater proportion of ewes with low antibody titers developed staphylococcal mastitis (41.4%) than of V ewes with high antibody titers (17.0%). Incidence risk of mastitis, staphylococcal mastitis, and biofilm-associated staphylococcal mastitis was smaller in V than in C: 36.7, 17.1, and 8.0% versus 44.3, 30.9, and 18.9%, respectively. The first case of staphylococcal mastitis occurred later in V than in C: third versus second sampling point. Overall, efficacy of the vaccine was 44.6% for staphylococcal mastitis, 57.7% for biofilm-associated staphylococcal mastitis, 33.1% for staphylococcal intramammary infection, and 51.5% for biofilm-associated staphylococcal intramammary infection. Nevertheless, vaccination should not be the only means for controlling mastitis; other udder health management measures should be included therein to improve control of the infection.

Persistence of coagulase negative staphylococcal intramammary infections in dairy goats.

The objectives of the research described here were to describe the persistence of intramammary infections (IMI) caused by coagulase negative staphylococci (CNS) in goats using strain-typing, and to evaluate the relationship between species-specific CNS IMI and somatic cell score (SCS) at the udder-half level. Udder-half milk samples were collected from all 909 lactating goats (1817 halves; 1 blind half) in a single herd. Milk samples were cultured on Columbia blood agar, and 220 goats with at least one half yielding a single colony type CNS were enrolled for two additional half-level samplings at approximately 1-month intervals. Isolates were identified to the species level by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry or PCR amplification and partial sequencing of tuf or rpoB. An IMI was defined as persistent when ≥1 follow-up sample yielded the same species and strain as on Day 0 based on pulsed-field gel electrophoresis. A generalised mixed linear model was used to evaluate the odds of persistence as a function of CNS species. A mixed linear model was used to evaluate the relationship between IMI status on a given day and SCS. Among 192 IMI, 69.8% were persistent based on species and strain-type. Staphylococcus simulans IMI had higher odds of persistence than Staphylococcus arlettae IMI. In primiparous goats, Staphylococcus epidermidis IMI was associated with higher SCS than S. arlettae, Staphylococcus xylosus and 'other CNS' IMI. The differences detected in the present study between CNS species, with regard to persistence of IMI and association with SCS, highlight the need to study CNS at the species and strain level to understand the pathogenicity and epidemiology of CNS in goats.

Staphylococcal intramammary infection dynamics and the relationship with milk quality parameters in dairy goats over the dry period

The objectives of this study were (1) to report the rates of new intramammary infection (IMI) and spontaneous IMI cure over the dry period in 3 dairy goat herds; (2) to evaluate the factors predicting infection dynamics over the dry period; and (3) to define milk quality parameter thresholds that predict infection dynamics over the dry period. Two consecutive udder-half milk samples were collected 10 to 14 d apart before dry-off from 288 goats in 3 herds, and 2 consecutive udder-half samples were collected 7 to 14 d apart in the following lactation, with the first sample being collected ≤10 d in milk, from 200 of the same goats. In 2 of the herds, udder-half milk samples were also collected at the same time points (n = 312 halves; 157 goats) for measurement of milk quality parameters. Standard aerobic culture of milk samples was performed for the detection of mastitis pathogens. To rule out the presence of Mycoplasma spp. IMI, milk samples were also cultured on modified Hayflick medium. Non-Mycoplasma isolates were speciated using MALDI-TOF mass spectrometry. Staphylococcal isolates, when not identified by MALDI-TOF, were speciated using partial gene sequence analysis of rpoB or tuf. When >1 sample from an udder half yielded the same species, available isolates from the first and last positive samples for that species were strain-typed using pulsed-field gel electrophoresis. Incidence of new IMI and cure rate were computed. Generalized linear mixed regression models were built to evaluate the associations between new IMI and pre-dry somatic cell score (SCS), between IMI persistence and half-level SCS, and between IMI persistence and pre-dry IMI species. Thresholds for pre-dry SCS and lactose concentration were computed to predict IMI persistence. Overall, 12.6% (48/380) of halves had a persistent IMI. Cumulative incidence of new IMI over the dry period was 13.2%, and cure rate was 52.0%. Pre-dry SCS was not associated with odds of new IMI or IMI persistence. Pre-dry IMI species was not associated with odds of persistence. Lactose concentration was not associated with odds of persistence. Regardless of culture data, the optimal pre-dry SCS threshold to detect IMI that would persist into the next lactation was 8.7, with sensitivity and specificity of 50 and 73.8%, respectively. Further studies on the effect of control measures on species-specific incidence and cure rates during the dry period are warranted.

Longitudinal microbiological evaluation of subclinical non-aureus staphylococcal intramammary infections in a lentivirus-infected dairy goat herd

The objectives of this study were to 1) correlate pre-partum teat skin colonization with non-aureus staphylococcal (NAS) intramammary infection (IMI) in early lactation, and 2) evaluate infection dynamics of subclinical NAS IMI in goats during lactation in a small ruminant lentivirus-infected herd. Pre-partum teat skin swabs (41 goats, 82 halves) and post-partum half-level milk samples (106 goats, 203 halves) were collected at various intervals starting at ≤10 days in milk (DIM) until ≥120 DIM. Teat skin colonization and IMI were defined by culture and strain-typing. The association between the pre-kidding udder-half teat skin sample status and early lactation IMI status for a given species was investigated using McNemar’s exact test or logistic regression. Time to IMI elimination and time to new IMI were evaluated by discrete-time survival analysis. Halves with S. caprae isolated from teat skin prior to kidding had increased odds of S. caprae IMI ≤ 10 DIM. Time to IMI elimination varied as a function of NAS species. Intramammary infections detected >10 DIM had a higher hazard of elimination (hazard ratio [HR] 5.6, 95% CI 2.8–11.2) than IMI detected ≤10 DIM. The presence of an IMI in the contralateral half was associated with a higher hazard of new IMI (HR 2.1, 95% CI 1.3–3.4) in an uninfected half. Further studies on interventional strategies targeting early IMI and IMI caused by persistent species are warranted.

Use of MALDI-TOF to characterize staphylococcal intramammary infections in dairy goats

The most common pathogens causing intramammary infections (IMI) in dairy goats are staphylococci. Gene sequencing has been the reference method for identification of staphylococcal species, but MALDI-TOF mass spectrometry could represent a rapid and cost-effective alternative method. The objectives were to evaluate the typeability and accuracy of partial gene sequencing and MALDI-TOF for identifying staphylococci isolated from caprine milk samples, and to evaluate the relationship between staphylococcal species IMI, milk somatic cell score (SCS), and milk yield (MY). A composite (goat-level) milk sample was collected from all 940 lactating goats in a single herd. Dairy Herd Information Association test-day data for parity, days in milk, SCS, and MY were retrieved from Dairy Herd Information Association records. Milk samples were cultured on Columbia blood agar, and isolates from samples that yielded a single colony type of a presumptively identified Staphylococcus spp. were identified by PCR amplification and partial sequencing of rpoB, tuf, or 16S-rRNA, and MALDI-TOF. Mixed linear models were used to evaluate the relationship between staphylococcal IMI, SCS, and MY. The goat-level prevalence of staphylococcal IMI based on isolation of a single colony type was 24.4% (213/874). Seventeen goats had a contaminated sample. Among the remaining goats (n = 857), the most common species causing single colony-type IMI were Staphylococcus simulans (7.9%), Staphylococcus xylosus (3.5%), Staphylococcus caprae (3.6%), Staphylococcus chromogenes (2.9%), and Staphylococcus epidermidis (2.2%). The typeability of staphylococcal isolates with partial housekeeping gene sequence analysis (rpoB, complemented by tuf and 16S as needed) was 97.7%. The typeability and accuracy of MALDI-TOF were 84 and 100%, respectively. Overall, only Staphylococcus chromogenes IMI was associated with a higher SCS than goats with no growth. After adjusting for parity and stage of lactation, staphylococcal IMI status was not significantly associated with MY. For the staphylococci isolated from goats in this herd, MALDI-TOF proved an accurate method of speciation with a relatively high typeability. An association between staphylococcal IMI, SCS, and MY was not defined using goat-level data with the exception of S. chromogenes IMI, which was associated with a higher SCS than goats with no growth.

071 Potential body site reservoirs for coagulase negative staphylococcal intramammary infection in heifers

071 Potential body site reservoirs for coagulase negative staphylococcal intramammary infection in heifers

Moving towards the immunodiagnosis of staphylococcal intramammary infections.

Bovine mastitis is the primary disease of dairy cattle that has a great impact on the dairy industry. It is estimated that worldwide economic losses due to mastitis range between US$82 and US$131 per cow/year. A fast and efficient diagnosis of the disease remains a major bottleneck that directly influences the speed with which treatment decisions and management are undertaken. Microbiological culture remains the gold standard in the identification of bacteria that cause mastitis, but the method has inherent limitations, such as a delay in obtaining results and cost, and requires special care during the collection and processing of the sample. For this reason, multiple groups have devoted efforts to develop alternative methods that, preferably, can be easily accomplished in the field. The specificity of the antigen-antibody reaction has enabled the emergence of major diagnostic methods used in clinical practice, such as immunoassays, which have significant advantages in terms of speed, sensitivity, specificity, and portability. Commercially, immunodiagnostics have been used in the detection of various diseases in cattle. However, in several cases, only a presumptive diagnosis can be made, which requires confirmation using culture-based methods. This review discusses the immunological-based assays developed since the 1990s for the detection of Staphylococcus aureus, which is considered the primary pathogen of contagious bovine mastitis. Although no ideal antigens ensure the accurate performance of tests and the costs need to be reduced to allow for good market competitiveness, immunoassays, particularly lateral flow immunoassay and immunoagglutination, have emerged as promising tests to be used in the field.

Efficacy of vaccination on Staphylococcus aureus and coagulase-negative staphylococci intramammary infection dynamics in 2 dairy herds

The aim of this study was to evaluate vaccine efficacy of a commercial vaccine (Startvac, Hipra Spain) aimed at reducing intramammary infections (IMI) with Staphylococcus aureus and coagulase-negative staphylococci under field conditions. During the 21-mo duration of the study, 1,156 lactations from 809 cows were enrolled in 2 herds. During the first phase of the trial, all cows that were due to calve were vaccinated until approximately 50% of cows in the milking herd were vaccinated (at ~6mo). At that point, when 50% vaccination coverage was reached, cows that were due to calve were randomly assigned to be vaccinated or left as negative controls. Cure rate, rate of new infection, prevalence, and duration of infections were analyzed. Vaccination resulted in a moderate reduction in incidence of new staphylococcal IMI and a more pronounced reduction in duration of IMI associated with reduction of the basic reproduction ratio of Staph. aureus by approximately 45% and of coagulase-negative staphylococci by approximately 35%. The utilization of vaccine in combination with other infection-control procedures, such as excellent milking procedures, treatment, segregation, and culling of known infected cattle, will result in an important reduction in incidence and duration of intramammary staphylococcal infections.

Persistence of staphylococcal species and genotypes in the bovine udder

Staphylococci are a major cause of intramammary infections (IMI) in ruminants. The main aim of this study was to investigate staphylococcal IMI in dairy cattle with emphasis on persistence and distribution of staphylococcal species and genotypes. With a sampling interval of 4–8 weeks, over a year, 4030 samples from 206 cows in 4 herds were collected. Coagulase-negative staphylococci (CNS) and Staphylococcus aureus were detected in 13.2% and 4.2% of the samples, respectively. Selected CNS isolates from quarter milk samples were identified to species level using sodA sequencing. Staphylococcus chromogenes (32%) and Staphylococcus simulans (25%) predominated. The proportion of S. chromogenes was greater in primiparous (52%) than in multiparous cows (12%), while the opposite was the case for Staphylococcus epidermidis (6% and 21%, respectively). Isolates from possibly persistent IMI were selected for pulsed-field gel electrophoresis (PFGE). Six staphylococcal species were found to cause persistent IMI; S. aureus, S. chromogenes, S. simulans, S. epidermidis, Staphylococcus haemolyticus and Staphylococcus warneri. It was shown that several pulsotypes (PTs) within each species were associated with persistent infections, but only a few were spread and caused persistent IMI in multiple cows within a herd. Of special interest was the observation that only one, or a few, strains of each species caused persistent IMI in multiple cows within a same herd. This indicates strain differences with respect to transmissibility and pathogenicity.

Genetic variations in immunoglobulin G3 and association with staphylococcal intra-mammary infections in cattle and buffaloes

Animals (n = 152) suffering with mastitis were used to study association between immunoglobulin G3 (IgG3) genotypes and staphylococcal mastitis. Thus, animals (affected and unaffected) were evaluated using PCR-RFLP. Restriction digestion of amplicons of IgG3 using BstYI showed allele A and, genotypes AC, AB and AA predominated in Karan Fries, Sahiwal and Murrah, respectively. HphI digestion revealed allele A and, genotypes AC and AB in higher frequency in animals of first group of all the breeds. Additionally, genotypes associated with mastitic infection showed predominance of AB (BstYI) in unaffected animals of Sahiwal and Murrah; whereas AC and AA were observed in affected group only. Genotype AB (HphI) was prevalent in unaffected and AC in affected animals of Karan Fries and Sahiwal. In Murrah, AC was common in affected and unaffected animal; while AB remained in affected category. Identified genotypes associated with determinants of SpA gene of S. aureus strains revealed the significant outcome. For example AB (BstYI) was found to be correalted with SpA ≤ 7R; whereas with SpA > 7R in Karan Fries. Genotypes AA and AB were more favorably associated with SpA ≤ 7R and AB with the SpA > 7R in Sahiwal cattle. The genotype AB seemed influenced (100%) with SpA > 7R and AC in SpA ≤ 7R in cases of Murrah. Similarly, AA (HphI) in Karan Fries was more likely to be correlated with SpA ≤ 7R, while AC with SpA > 7R. Overall, the molecular analysis revealed that IgG3 gene could be use for selection of animals against mastitis. However, further investigations on IgG3 needed to aid in identify disease- resistant animal.

Effect of systemic antibacterial administration during prepartum period on coagulase negative Staphylococcal intramammary infection in Holstein Heifers

Summary A total of 183 coagulase negative Staphylococcal infected quarters and 64 uninfected quarters were randomly allotted to 4 experimental groups: infected quarters that did not receive any treatment (positive control group; n = 60); infected quarters that received Tylosin (n = 61) or Cefquinome (n = 62) and also uninfected quarters that did not receive any treatment were considered as negative control group (n = 64). Treated heifers received Tylosin or Cefquinome 10 to 14 days before the expected calving date. The bacteriological cure rate based on sampling obtained 3 days after calving was significantly higher (P<0.01) in mammary glands treated with systemic Tylosin (85.3%) than in the positive control group and mammary glands treated with systemic Cefquinome (69.4%). At the same time Tylosin treated heifers had significantly lower (P<0.01) somatic cell count scores compared to the positive control and Cefquinome groups. With the exception of one heifer that calved 8 days earlier than the expected calving date, there was no detectable antibiotic residues in the milk of the treated heifers on the 3rd day of lactation.

Efficacy of vaccination against staphylococcal mastitis: A review and new data

Infection of the heifer mammary gland with common mastitis pathogens, particularly staphylococci, prior to calving is well documented. Efforts to eliminate pre-partum intramammary infections (IMI) in heifers have focused primarily on intramammary antibiotic therapy shortly before or at the time of calving. Few studies have evaluated vaccination of heifers against staphylococcal mastitis. The objectives of the present study were to evaluate the efficacy of a commercially available Staphylococcus aureus bacterin in protecting against staphylococcal IMI ( S. aureus and coagulase-negative staphylococci (CNS)), to study the effect of vaccination on milk SCC, and to evaluate the milk antibody isotype response to vaccination using a lactating cow model. Ninety Holstein–Friesian lactating dairy cows of various parities were systematically assigned to a vaccinated ( n = 44) or control ( n = 46) group. Vaccinates received two 5 ml doses of the bacterin 14 days apart starting on day 0. Quarter milk samples for bacterial culture were collected prior to each vaccination and approximately monthly thereafter for 6 months. Composite milk samples were collected on days 0, 14, 28, 49 and 70 for IgA, IgG 1, IgG 2, and IgM determinations and somatic cell count. No animals in either group developed a new S. aureus IMI after vaccination. The numbers of mammary quarters that developed a new CNS IMI, time to new CNS IMI, milk somatic cell count, and milk antibody isotype sample-to-positive ratio did not significantly differ between groups ( P > 0.05). In a herd with a 3% prevalence of S. aureus IMI and a 30% prevalence of CNS IMI, the vaccine did not reduce the new staphylococcal IMI rate. There may be insufficient vaccine-induced opsonizing antibody in milk to facilitate phagocytosis and clearance of staphylococci from the mammary gland.

Epidemiological Study of Non‐contagious Intramammary Infections in Nine Commercial Dairy Herds following a Staphylococcus aureus Control Programme

Changes in prevalence in intramammary infection, by pathogen type, in herds applying a stringent contagious mastitis control programme was studied. Enrollment of 1651 lactating cows and collection of milk samples was made in this ancillary study to a cohort study of the dynamics of mastitis prevalence after adoption of a strict contagious mastitis control programme that targeted the elimination of mastitis caused by Staphylococcus aureus. Nine commercial dairies in Italy were used. Aseptic collection of milk samples from all lactating cows was performed at the time of enrollment, from all cows within 7-14 days of entering the lactating herd after the date of enrollment, and from all lactating cows at 2, 4, 7, 10 and 14 months after the date of enrollment. Prevalence of intramammary infection by pathogen type was determined from culture of milk samples. Application of the strict contagious mastitis programme did not lead to an increased risk of non-contagious mastitis. The risk of coliform, environmental streptococcal and coagulase-negative staphylococcal intramammary infections decreased after adoption of the programme. The data reported herein indicate that the overall risk for any intramammary infections decreases with adoption of a strict contagious mastitis programme, and that such a programme therefore does not necessarily lead to an increase in environmental mastitis.

Influence of Staphylococcus aureus Strain-type on Mammary Quarter Milk Somatic Cell Count and N-acetyl-β-D-glucosaminidase Activity in Cattle from Eight Dairies

The hypothesis tested was that there are differences in pathogenicity between strains of Staphylococcus aureus that cause bovine mastitis. Mammary quarter milk somatic cell count (SCC) and N-acetyl-β-D-glucosaminidase (NAGase) activity were used as indicators of the pathogenicity of different strains of S. aureus that infect the bovine udder. Eight commercial dairy herds with a history of S. aureus in bulk tank milk cultures were studied. Initially, composite foremilk samples were collected from all lactating cattle in each herd and cultured for staphylococci. Subsequently, all cows with a coagulase-positive staphylococcal intramammary infection (IMI) at the initial sampling that were still present in the herd of origin had individual mammary quarter foremilk samples collected. Coagulase-positive staphylococcal isolates were confirmed as S. aureus using a commercial biotyping system. Staphylococcus aureus isolates were strain-typed using pulsedfield gel electrophoresis. Mammary quarter milk SCC and N-acetyl-β-D-glucosaminidase activity were determined for each cow. The difference in mean somatic cell count and mean NAGase activity for mammary quarters infected with the same strain of S. aureus and for uninfected quarters on the same cow was calculated. One-way analysis of variance was used to assess differences between strains within a herd. Overall, no significant differences were found between strains, suggesting that the degree of udder parenchymal injury induced by S. aureus IMI is in general significantly affected by factors other than strain type.

Coagulase-negative staphylococcal intramammary infections in cows and heifers during the nonlactating and periparturient periods.

Coagulase-negative staphylococci (CNS) are isolated frequently from unbred and primigravid heifers and from lactating and nonlactating dairy cows. The importance of CNS intramammary infections that occur during the nonlactating period has not been adequately delineated. Mammary secretions from udders infected with CNS during early lactation and the nonlactating period have increased somatic cell counts, CNS have been isolated in mammary secretions from cows with clinical mastitis, and a few studies have indicated that CNS infected mammary glands produced significantly less milk during lactation than uninfected mammary glands. In addition, mammary glands of postpubertal heifers infected with CNS were not as well developed as uninfected mammary glands. Consequently, CNS intramammary infections in heifers and cows during the nonlactating period could impair mammary gland growth and development and ultimately influence mammary function during lactation resulting in decreased lactational performance. Some CNS IMI detected in heifers and multiparous cows at calving do not persist into early lactation. Postmilking teat disinfection with an effective germicide and antibiotic therapy during the nonlactating period markedly reduces the prevalence of CNS in dairy herds. Methods of controlling CNS infections in primigravid heifers based on prepartum intramammary antibiotic therapy have been developed, and results have shown that prepartum antibiotic therapy is very effective against CNS and other mastitis pathogens as well. Additional research is required to determine the influence of CNS infections that occur during the nonlactating period on milk yield in the subsequent lactation.

Comparison of the effects of local and systemic dry cow therapy for staphylococcal mastitis control

The therapeutic effects of systemic injections of enrofloxacin ortylosin and intramammary infusions of an ointment containing naficillin, penicillin and dihydrostreptomycin were compared in the dry period against staphylococcal intramammary infection (IMI) in a large Holstein dairy herd. The frequency of IMI was 26.7% and samples were all negative for Mycoplasma spp. At the time of treatment, the prevalence of staphylococcal IMI in the three groups: (1) enrofloxacin (EN), (2) tylosin (TY) and (3) naficillin, penicillin and dihydrostreptomycin (DC) were 29.8%, 28.5% and 21.7%, respectively. The difference between the three figures were not statistically significant ( P = 0.17). The cure rates in the EN, TY and DC groups were 85.2%, 77.4% and 92.3%, respectively, which were also not significantly different ( p = 0.15). New infection rates in EN, TY and DC groups, after treatment, were 6.1%, 7.5% and 4.4%, respectively, showing no statistically significant difference between the three groups ( P = 0.46). We concluded that systemic dry cow therapy using enrofloxacin or tylosin can be an alternative to the conventional local method for elimination of staphylococcal IMI during the dry period, although, local dry cow therapy (using partially inserted cannulas) is still the most effective method when considering IMI at calving.

Risk factors associated with herd-group milk somatic cell count and prevalence of coagulase-positive staphylococcal intramammary infections

Fifty nine dairy herds enrolled in the Washington State Dairy Herd Improvement Association Milk Somatic Cell Count Program were split into low and high cell-count groups. Low herds had the lowest percentage of cows with linear-score somatic cell count (SCC) >4 and high herds had the highest percentage of cows with linear-score SCC >4. An estimate of prevalence of intramammary infections was made from aseptically-collected milk samples. Logistic regression analysis was used to construct models that would best describe the combination of management factors that best classified herds into high and low SCC groups. Similarly, stepwise linear regression analysis was used to determine management-factor combinations which would best describe herd prevalence of coagulase-positive staphylococcal intramammary infection. A subset of 75 variables was used in models and was from an initial set of more than 250 management factors. Variables from the initial set that were deemed to have a direct effect on mastitis and to be under management control were screened using univariate tests. Those variables found to be either significantly associated with herd SCC-group status and/or prevalence of intramammary infection by coagulase-positive staphylococci were used in the modeling procedures. Additionally, interactions were tested in the models and some variables commonly associated with mastitis control were included as forced variables in these models. Factors which were most likely associated with low-somatic-cell herds were: (1) milking cows with clinical mastitis last; (2) disinfecting the teat ends prior to administration of intramammary antibiotic therapy; and (3) having drier cow bedding. A model containing these three factors classified 87.9% of the herds into the correct group. Factors which described a reduction in the prevalence of intramammary infections with coagulase-positive staphylococci were: (1) disinfection of teat end prior to therapy administration; (2) applying disinfectant solution to the teat after milking (teat dip); and (3) cleaning the milking-system regulator frequently. These three factors were associated with decrease in coagulase positive staphylococcal intramammary infections of 27%, 9%, and 9%, respectively, and in combination described 36.6% of the herd-to-herd variation in infection prevalence by this pathogen.

Dynamics and Significance of Coagulase-Negative Staphylococcal Intramammary Infections

Cows (n = 139) were sampled within 17 d postpartum and monthly thereafter to examine dynamics of mammary infections and relationships between infection status, milk yield, SCC, NAGase activity, and chloride concentration. Forty-eight and 67% of cows and 19.5 and 30.5% of quarters were infected at first test and lactation end, respectively, with 51% of all infections present at first test.Coagulase-negative staphylococci accounted for 67 and 65% of first test and total infections with 85% persisting to lactation end. Animals with coagulase-negative staphylococci infections had significantly elevated quarter SCC and NAGase activity and a decrease of 821kg mature equivalent lactation milk production compared with uninfected animals.Clinical cases with no bacterial isolation or major pathogen infections were associated with significant elevations in bucket and quarter milk SCC, NAGase activity, chloride concentration in quarters, and a decrease of 1153kg mature equivalent lactation milk production as compared with uninfected animals.Correlations between milk production and ln SCC and ln NAGase and between ln SCC and ln NAGase were −.15, −.25, and .55 (−.23, −.28, and .41 for first lactation only).