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Coagulase-negative staphylococci (CNS) are a group of bacteria classified as either minor mastitis pathogens or commensal microbiota. Recent research suggests species- and even strain-related epidemiological and genetic differences within the large CNS group. The current pilot study investigated in 2 experiments whether a mouse mastitis model validated for bovine Staphylococcus aureus can be used to explore further differences between CNS species and strains. In a first dose titration experiment, a low inoculum dose of S. aureus Newbould 305 (positive control) was compared with increasing inoculum doses of a Staphylococcus chromogenes strain originating from a chronic bovine intramammary infection to a sham-inoculated mammary glands (negative control). In contrast to the high bacterial growth following inoculation with S. aureus, S. chromogenes was retrieved in very low levels at 24 h postinduction (p.i.). In a second experiment, the inflammation inflicted by 3 CNS strains was studied in mice. The host immune response induced by the S. chromogenes intramammary strain was compared with the one induced by a Staphylococcus fleurettii strain originating from cow bedding sawdust and by a S. chromogenes strain originating from a teat apex of a heifer. As expected, at 28 and 48 h p.i., low bacterial growth and local neutrophil influx in the mammary gland were induced by all CNS strains. As hypothesized, bacterial growth p.i. was the lowest for S. fleurettii compared with that induced by the 2 S. chromogenes strains, and the overall immune response established by the 3 CNS strains was less pronounced compared with the one induced by S. aureus. Proinflammatory cytokine profiling revealed that S. aureus locally induced IL-6 and IL-1β but not TNF-α, whereas, overall, CNS-inoculated glands lacked a strong cytokine host response but also induced IL-1β locally. Compared with both other CNS strains, S. chromogenes from the teat apex inflicted a more variable IL-1β response characterized by a more intense local reaction in several mice. This pilot study suggests that an intraductal mouse model can mimic bovine CNS mastitis and has potential as a complementary in vivo tool for future CNS mastitis research. Furthermore, it indicates that epidemiologically different bovine CNS species or strains induce a differential host innate immune response in the murine mammary gland. [ABSTRACT FROM AUTHOR]

Heifer mastitis is a disease that potentially threatens production and udder health in the first and subsequent lactations. In general, coagulase-negative staphylococci (CNS) are the predominant cause of intramammary infection and subclinical mastitis in heifers around parturition, whereas Staphylococcus aureus and environmental pathogens cause a minority of the cases. Clinical heifer mastitis is typically caused by the major pathogens. The variation in proportions of causative pathogens between studies, herds, and countries is considerable. The magnitude of the effect of heifer mastitis on an individual animal is influenced by the form of mastitis (clinical versus subclinical), the virulence of the causative pathogen(s) (major versus minor pathogens), the time of onset of infection relative to calving, cure or persistence of the infection when milk production has started, and the host's immunity. Intramammary infection in early lactation caused by CNS does not generally have a negative effect on subsequent productivity. At the herd level, the impact will depend on the prevalence and incidence of the disease, the nature of the problem (clinical, subclinical, nonfunctional quarters), the causative pathogens involved (major versus minor pathogens), the ability of the animals to cope with the disease, and the response of the dairy manager to control the disease through management changes. Specific recommendations to prevent and control mastitis in late gestation in periparturient heifers are not part of the current National Mastitis Council mastitis and prevention program. Control and prevention is currently based on avoidance of inter-sucking among young stock, fly control, optimal nutrition, and implementation of hygiene control and comfort measures, especially around calving. More risk factors for subclinical and clinical heifer mastitis have been identified (e.g., season, location of herd, stage of pregnancy) although they do not lend themselves to the development of specific intervention strategies designed to prevent the disease. Pathogen-specific risk factors and associated control measures need to be identified due to the pathogen-related variation in epidemiology and effect on future performance. Prepartum intramammary treatment with antibiotics has been proposed as a simple and effective way of controlling heifer mastitis but positive long-lasting effects on somatic cell count and milk yield do not always occur, ruling out universal recommendation of this practice. Moreover, use of antibiotics in this manner is off-label and results in an increased risk of antibiotic residues in milk. Prepartum treatment can be implemented only as a short-term measure to assist in the control of a significant heifer mastitis problem under supervision of the herd veterinarian. When CNS are the major cause of intramammary infection in heifers, productivity is not affected, making prepartum treatment redundant and even unwanted. In conclusion, heifer mastitis can affect the profitability of dairy farming because of a potential long-term negative effect on udder health and milk production and an associated culling risk, specifically when major pathogens are involved. Prevention and control is not easy but is possible through changes in young stock and heifer management. However, the pathogenesis and epidemiology of the disease remain largely unknown and more pathogen-specific risk factors should be identified to optimize current prevention programs. [ABSTRACT FROM AUTHOR]

Abstract: Although many studies report coagulase-negative staphylococci (CNS) as the predominant cause of subclinical bovine mastitis, their epidemiology is poorly understood. In the current study, the genetic diversity within four CNS species frequently associated with bovine intramammary infections, Staphylococcus haemolyticus, S. simulans, S. chromogenes, and S. epidermidis, was determined. For epidemiological purposes, CNS genotypes recovered from bovine milk collected on six Flemish dairy farms were compared with those from the farm environment, and their distribution within the farms was investigated. Genetic diversity was assessed by two molecular typing techniques, amplification fragment length polymorphism (AFLP) and random amplification of polymorphic DNA (RAPD) analysis. Subtyping revealed the highest genetic heterogeneity among S. haemolyticus isolates. A large variety of genotypes was found among environmental isolates, of which several could be linked with intramammary infection, indicating that the environment could act as a potential source for infection. For S. simulans, various genotypes were found in the environment, but a link with IMI was less obvious. For S. epidermidis and S. chromogenes, genetic heterogeneity was limited and the sporadic isolates from environment displayed largely the same genotypes as those from milk. The higher clonality of the S. epidermidis and S. chromogenes isolates from milk suggests that specific genotypes probably disseminate within herds and are more udder-adapted. Environmental sources and cow-to-cow transmission both seem to be involved in the epidemiology of CNS, although their relative importance might substantially vary between species. [Copyright &y& Elsevier]

An abstract of the article "Antibiotic Susceptibility and Resistance of Staphylococcus Chromogenes From Bovine Mastitis," by B. Catry and colleagues is presented.

The main objectives of this study were to evaluate to what extent variations in herd-level antimicrobial consumption (AMC) can be explained by differences in management practices that are consistently effective in the prevention of (sub)clinical mastitis, on the one hand, and by differences in mastitis treatment strategies, on the other hand. Antimicrobial consumption data were obtained during 2012 and 2013 by "garbage can audits" and expressed as antimicrobial treatment incidences (ATI) for all compounds combined (total ATI) and for the critically important antimicrobials for human health separately. Data on mastitis prevention and control practices were obtained via face-to-face interviews performed during herd visits in March 2013. Some management practices and treatment strategies related to udder health were associated with the total AMC. However, the results demonstrated that implementing effective udder health management practices does not necessarily imply a low AMC and vice versa. Herds participating in a veterinary herd health management program and herds selectively drying off cows used fewer antimicrobials compared with herds not participating in such a program or applying blanket dry-cow therapy. Moreover, herds treating (some) (sub)clinical mastitis cases with intramammary homeopathic substances consumed fewer antimicrobials than herds not applying such homeopathic treatments. Besides these factors, no other direct association was found between effective udder health management practices on the one hand and AMC on the other hand. Also, the use of critically important antimicrobials was only associated with the way in which subclinical mastitis cases were treated. The latter indicates that the AMC of critically important antimicrobials is potentially driven by factors other than those included in this study such as those related to the "mindset" of the veterinarians and their farmers. Future research should therefore aim to unravel the reasoning of vets and their farmers behind the use of those critically important antimicrobials for the treatment of mastitis and other diseases. [ABSTRACT FROM AUTHOR]

Heifer mastitis is a well-known problem, with several pathogens being involved. Several generic risk factors associated with the likelihood of intramammary infections (IMI) in fresh dairy heifers have been identified before. Yet, a need exists to identify pathogen group-specific factors, as the effect of (groups of) pathogens on udder health and milk yield is different. The aim of the present study was to identify pathogen group-specific risk factors for IMI in heifers participating in a prepartum antimicrobial treatment trial, allowing us to test the hypothesis that different factors are of importance between treated and untreated control heifers as well. Data from a clinical trial in which end-term heifers were treated systemically (over 3 consecutive days) 2 wk before calving with penethamate hydriodide (n = 76) or remained untreated (n = 73), were available. Several potential risk factors at the herd, heifer, and quarter level were recorded in the first 3 d in milk. Quarters from untreated heifers supplemented with ≥4 mg of selenium/ d prepartum were significantly less likely to be infected with coagulase-negative staphylococci (CNS), whereas quarters were more likely to be infected with CNS when assistance during calving was needed. Udder edema before calving significantly decreased the odds of IMI with major pathogens. In treated heifers, no factors were detected that were associated with the likelihood of CNS IMI, whereas quarters from heifers were significantly more likely to be infected with major pathogens when they were housed in the calving pen more than 1 d and when they had been in contact with the lactating cows before calving. The risk factors for IMI that were identified in treated heifers were dif- ferent than those in untreated heifers, independent of the pathogen group that was considered. It looks as if [ABSTRACT FROM AUTHOR]

Prepartum intramammary treatment with antimicrobials of end-term dairy heifers has frequently been proposed as a practice to reduce the prevalence of intramammary infections (IMI) at calving. From a safety standpoint for both animal and administrator, systemic treatment is preferred. A clinical trial was conducted on heifers from 10 well-managed, commercial dairy farms with a low prevalence of heifer mastitis. The aim was to assess both the short- and long-term effects of a systemic prepartum therapy with penethamate hydriodide on udder health and milk production. Because it was hypothesized that some herds would benefit more from this treatment than others, specific herd-level information was collected before the start of the actual trial to screen for and explain potential herd-specific treatment effects. Further, the effect of treatment on antimicrobial susceptibility of staphylococcal isolates was monitored. End-term heifers were either treated systemically (over 3 consecutive days) 2 wk before expected calving date with penethamate hydriodide (n = 76) or remained untreated (n = 73). Systemic prepartum treatment of end-term heifers with penethamate hydriodide resulted in fewer IMI in early lactation. However, all 6 cases of clinical mastitis in early lactation occurred in the treatment group [Streptococcus uberis (n = 1), Cory- nebacterium bovis (n = 1), Staphylococcus aureus (n = 1); 1 sample was contaminated; 2 samples remained culture negative]. No long-term treatment effects (from 4 to 120 d in milk) on milk production, udder health, or culling hazard during later lactation were detected, although treated heifers belonging to herds classified as having low-yielding heifers out-produced the control heifers. Moreover, penicillin susceptibility of staphylococci isolated from milk samples of treated or control heifers did not differ. Herds with a low prevalence of heifer mastitis are not likely to benefit from prepartum systemic antimicrobial treatment of the end-term heifers. [ABSTRACT FROM AUTHOR]

In many parts of the world, coagulase-negative staphylococci (CNS) are the predominant cause of intramammary infections (IMI) in dairy cows and in water buffaloes, as well. A longitudinal field study was carried out on one well-managed dairy water buffalo herd to determine the prevalence and distribution of CNS and a recently described CNS-species, Staphylococcus rostri, in milk samples to explore its relevance for buffaloes' udder health throughout lactation, and to gain insight into the susceptibility of the latter species toward commonly used antimicrobials. Twice weekly quarter milk samples from a cohort of 11 lactating water buffaloes were collected over an 8-mo period. The CNS (n = 109; 76.2% of all culture-positive samples) were the predominant pathogens causing IMI, followed by Corynebacterium bovis (n = 11; 7.6%) and Streptococcus spp. (n = 9; 6.2%) other than Stretococcus uberis (n = 2; 1.4%). Thirty-seven hemolytic staphylococci suspected to be Staphylococcus aureus were further differentiated using transfer DNA-intergenic spacer-PCR and rpoB-gene sequencing because they were coagulasenegative. Thirty-three of those isolates were identified as Staph. rostri, whereas 2 others were identified as Staphylococcus epidermidis. None of the Staph. rostri isolates displayed resistance to the antimicrobial agents tested. Mean quarter milk somatic cell count (qSCC) of all samples collected throughout lactation was 20,970 cells/mL. The qSCC at sampling of quarters infected with Staph. rostri (34,466 cells/mL) and CNS other than Staph. rostri (34,813 cells/mL) were significantly higher than the qSCC of noninfected quarters (20,287 cells/mL), yet not significantly different from each other. These findings provide novel insight into the prevalence and distribution, antimicrobial susceptibility, and relevance of Staph. rostri compared with other CNS species causing IMI in water buffaloes. Further studies are needed to pinpoint the relevance, niches, and transmission routes of Staph. rostri, as well as other CNS in water buffaloes. [ABSTRACT FROM AUTHOR]

Mastitis is a prevalent disease in dairy cattle, and staphylococci are among the most common causative pathogens. Staphylococci can express resistance to a range of antimicrobials, of which methicillin resistance is of particular public health concern. Additionally, Staphylococcus aureus carries a variety of virulence factors, although less is understood about the virulence of non- aureus staphylococci (NAS). The aim of our study was to identify and characterize 3 collections of staphylococcal isolates from bovine milk samples regarding antimicrobial resistance, with emphasis on methicillin resistance, and their carriage of virulence genes typically displayed by Staph. aureus. A total of 272 staphylococcal isolates collected in Norway and Belgium in 2016 were included, distributed as follows: group 1, Norway, 100 isolates; group 2, Flanders, Belgium, 64 isolates; group 3, Wallonia, Belgium, 108 isolates. Species identification was performed by use of MALDI-TOF mass spectrometry. Phenotypic resistance was determined via disk diffusion, and PCR was used for detection of methicillin resistance genes, mecA and mecC , and virulence genes. Antimicrobial resistance was common in Staphylococcus epidermidis and Staphylococcus haemolyticus from all different groups, with resistance to trimethoprim-sulfonamide frequently occurring in Staph. epidermidis and Staph. haemolyticus as well as in Staph. aureus. Resistance to penicillin was most frequently observed in group 1. Ten Belgian isolates (1 from group 2, 9 from group 3) carried the methicillin resistance determinant mecA : 5 Staph. aureus from 2 different farms and 5 NAS from 3 different farms. Almost all Staph. aureus isolates were positive for at least 3 of the screened virulence genes, whereas, in total, only 8 NAS isolates harbored any of the same genes. Our study contributes to the continuous need for knowledge regarding staphylococci from food-producing animals as a basis for better understanding of occurrence of resistance and virulence traits in these bacteria. [ABSTRACT FROM AUTHOR]

We conducted a longitudinal study to evaluate the effect of non- aureus staphylococci (NAS) causing subclinical intramammary infections (IMI) on quarter milk somatic cell count (qSCC) and quarter milk yield (qMY). In total, 324 quarters of 82 Holstein Friesian heifers were followed from calving to 130 d in milk (DIM) and were sampled 10 times each at 14-d intervals. The IMI status of each quarter was determined based on bacterial culture results at the current and previous or next sampling day, or both. The qSCC was determined on each sampling day and the average qMY on sampling day was available through stored daily milk weight data in the management program of the automatic milking system. A transient IMI (tIMI) was defined as a case where a specific pathogen was isolated from a quarter on only one sampling day and not on the previous or next sampling day. When the same bacterial strain, as defined by random amplification of polymorphic DNA-PCR, was isolated from the same quarter on multiple sampling days, it was defined as a persistent IMI (pIMI) status on those sampling days; a pIMI episode was defined as the combination of multiple consecutive pIMI statuses with the same bacterial strain on different sampling days. During this study, 142 subclinical IMI with NAS occurred in 116 different quarters from 64 animals, yielding in total 304 NAS isolates belonging to 17 different species. The prevalence of NAS was highest in the first 4 DIM. Overall, the predominant species was Staphylococcus chromogenes (52% of the isolates), followed by S. epidermidis (9.2%), S. xylosus (8.2%), and S. equorum (5.9%). Staphylococcus chromogenes was the only species for which an effect on qSCC and qMY could be analyzed separately; the other NAS species were considered as a group because of their low prevalence. Eighteen out of 40 IMI (45%) caused by S. chromogenes persisted over at least 2 sampling days, whereas only 10 of 102 (9.8%) IMI caused by other NAS species persisted for at least 2 sampling days. The average duration of pIMI episodes was 110.4 d for S. chromogenes and 70 d for the other NAS species. Remarkably, 17 of the 18 pIMI episodes with S. chromogenes started within the first 18 DIM. The qSCC was highest in quarters having a pIMI with a major pathogen, followed by quarters having a pIMI with S. chromogenes , and a pIMI with other NAS. Transient IMI with other NAS or with a major pathogen caused a small but significantly higher qSCC, whereas the qSCC in quarters having a tIMI with S. chromogenes was not statistically different compared with noninfected quarters. No significant differences in qMY were observed between quarters having a pIMI or tIMI with S. chromogenes or with the other NAS species compared with noninfected quarters, despite the higher qSCC. Quarters having a pIMI with major pathogens showed significantly lower daily milk production. Surprisingly, quarters that cured from an IMI with S. chromogenes had a significantly lower qMY than noninfected quarters. [ABSTRACT FROM AUTHOR]

Non- aureus staphylococci (NAS) are predominantly isolated from bovine milk samples of quarters suffering from subclinical mastitis. They are also abundantly present on dairy cows' teat apices and can be recovered from bovine fecal samples, as recently described. Differences in ecology, epidemiology, effect on udder health, and virulence or protective traits have been reported among the species within this group. The objectives of this study were (1) to describe the species-specific distribution of NAS in 3 bovine-associated habitats, namely quarter milk, teat apices, and rectal feces, and (2) to evaluate the virulence potential of NAS by comparing their distribution in contrasting milk sample strata and the presence of selected virulence genes. A cross-sectional, systematic sampling procedure was followed in 8 dairy herds that participated in the local Dairy Herd Improvement program in Flanders, Belgium. Quarter milk samples (n = 573) were collected from 144 lactating cows in 8 herds. In 5 of the 8 herds, teat apex swabs (n = 192) were taken from 15 lactating cows, before and after milking, and from 18 dry cows. In the same 5 herds, rectal feces were sampled from 80 lactating cows (n = 80), taking into account that a cow could only serve as the source of one type of sample. In addition, milk samples of all clinical mastitis cases were continuously collected during the 1-yr study period from March 2017 to March 2018 in the 8 herds. In total, 1,676 Staphylococcus isolates were phenotypically identified and subjected to MALDI-TOF mass spectrometry. Thirty-three, 98, and 28% of all quarter milk, teat apex, and rectal fecal samples were NAS-positive, respectively, reaffirming the presence of NAS in rectal feces. The overall predominant species in the 3 habitats combined were Staphylococcus haemolyticus , Staphylococcus chromogenes , and Staphylococcus hominis. Four, 16, and 12% of the healthy quarters (quarter milk somatic cell count ≤50,000 cells/mL of milk), quarters with subclinical mastitis (quarter milk somatic cell count >50,000 cells/mL of milk), and quarters with clinical mastitis, respectively, were NAS-positive, suggesting that the potential to cause (mild) clinical mastitis is present among NAS. This was substantiated by comparing the presence of virulence genes of NAS isolates originating from contrasting milk sample strata (healthy quarters and quarters with clinical mastitis). [ABSTRACT FROM AUTHOR]

We analyzed a large number of immune response parameters from quarter milk samples with distinct bacteriological and quarter somatic cell count (qSCC) statuses. Furthermore, we sought to explore and identify displayed immune response patterns in milk samples from mammary glands with nonspecific mastitis. Thus, 92 quarter milk samples from 28 cows were stratified into 4 groups, as follows: (1) 49 culture-negative control quarters with a low qSCC (<1 × 105 cells/mL) from 19 dairy cows (so-called healthy quarters); (2) 15 culture-negative quarters with high qSCC (>2 × 105 cells/mL; so-called quarters with nonspecific mastitis) from 10 dairy cows; (3) 8 culture-positive quarters with low qSCC (noninflammatory quarters with low qSCC) from 5 dairy cows; and (4) 20 culture-positive quarters with high qSCC (so-called truly infected quarters) from 8 dairy cows. Using flow cytometry, we evaluated the percentage of milk neutrophils and their viability, intracellular reactive oxygen species production, phagocytosis, and the expression of CD62L, CD11b, and CD44 for each of the 4 quarter strata. Furthermore, the percentage of monocyte/macrophages, B cells, and T lymphocyte subsets were evaluated by flow cytometry. Milk samples from bacteriologically negative quarters (both with a low and elevated qSCC) had a lower qSCC than those with bacteriologically positive outcomes (both with a low and elevated qSCC). As expected, the healthy quarters showed the lowest percentage of neutrophils and also showed a higher percentage of milk monocytes/macrophages and lower percentage of T lymphocytes than truly infected quarters. The most prominent result of the present study is that quarters with nonspecific mastitis showed the highest percentage of milk CD4+ T lymphocytes. The healthy quarters had a lower percentage of apoptotic neutrophils than noninflammatory and truly infected quarters, although it did not differ from those from the quarters with nonspecific mastitis. Our study supports the role of differential cell counting in the diagnosis of mastitis, as the milk leukocyte populations markedly fluctuate under healthy and inflammatory conditions. Furthermore, an increase in milk CD4+ T cells was associated with nonspecific mastitis, suggesting an increase in this leukocyte subpopulation is correlated with low bacterial shedding. Our study allows us to go further in our understanding of mammary gland immunity, providing further insights on potential protective mammary gland immunity, which we hypothesize can open new avenues for the development of novel targets that can promote bovine udder health. [ABSTRACT FROM AUTHOR]

The aims of this study were to determine whether non- aureus staphylococci (NAS) are present in rectal feces of healthy dairy cows, and if so, to delineate species to which they belong and to study several phenotypic and genotypic traits as a first step toward determining the potential impact of fecal shedding of NAS on bovine udder health. Fecal samples were aseptically collected from the rectum of 25 randomly selected clinically healthy dairy cows in a commercial dairy herd using an automated milking system. Fecal NAS were isolated and then identified at the species level using transfer RNA-intergenic spacer PCR and sequencing of the 16S rRNA housekeeping gene. Strain typing was performed using random amplification of polymorphic DNA (RAPD)-PCR. The antimicrobial resistance profiles, biofilm formation, and growth and inhibitory characteristics of all NAS isolates were evaluated. Half of the cows were shedding NAS, resulting in 31 NAS isolates belonging to 11 different species. The most prevalent species were Staphylococcus rostri (23%, n = 7), Staphylococcus cohnii (16%, n = 5), and Staphylococcus haemolyticus (13%, n = 4) with all Staphylococcus agnetis , Staphylococcus chromogenes , and Staph. rostri isolates belonging to the same strain according to RAPD banding patterns. Acquired antimicrobial resistance was observed in 28 of the 31 NAS isolates, mainly due to β-lactamase production. Most of the isolates (84%, n = 27) had a weak biofilm-forming potential, but only 2 contained the bap gene. The ica and aap genes were not detected in any of the isolates. In vitro growth of Staphylococcus aureus and Streptococcus dysgalactiae was inhibited by Staph. agnetis isolates, and Staph. chromogenes isolates were able to inhibit the growth of Strep. dysgalactiae and Streptococcus uberis. All fecal isolates were able to grow when oxygen and iron were limitedly available, mimicking the growth conditions in the mammary gland. [ABSTRACT FROM AUTHOR]

A longitudinal study was conducted to assess to what extent intramammary infection (IMI) with non- aureus staphylococci (NAS) within the first 4 d after calving in dairy heifers affects quarter milk yield (qMY) and quarter milk somatic cell count (qSCC) during the first 4 mo of lactation. In total, 324 quarters from 82 Holstein Friesian heifers from 3 commercial dairy herds equipped with an automatic milking system were included and followed from calving up to 4 mo in lactation. The automatic milking system allowed us to precisely determine the daily qMY. A milk sample from each quarter was collected in early lactation (between 1 and 4 d in milk) for bacteriological culturing and measurement of the qSCC. Subsequently, milk samples were taken on a biweekly basis for measurement of the qSCC. The milk prolactin level in early lactation was measured, and the relation with NAS IMI was determined. Overall, NAS IMI in early lactation caused only a slight but significant increase in qSCC compared with milk from noninfected quarters during the first 4 mo in lactation, whereas no significant difference in daily qMY was present between NAS-infected and noninfected quarters. The milk prolactin level in early lactation did not differ between NAS-infected and noninfected quarters either. Our data suggest that IMI with NAS (as a group) present shortly after calving do not have an adverse effect on later production. The milk prolactin concentrations were not dissimilar between NAS-infected and noninfected quarters and thus cannot explain why NAS-infected quarters do not produce less than noninfected quarters. [ABSTRACT FROM AUTHOR]

The objectives of this study were (1) to determine the test characteristics and predictive values of cow-level milk somatic cell count (SCC) information from (multiple) test-day recordings before drying off to identify major-pathogen-infected cows at drying off; and (2) to explore to what extent (an estimate of) the herd prevalence of subclinical mastitis, milk yield level, and parity of the cows affects the estimates. In total, 550 cows from 15 commercial dairy herds with overall good udder health management were dried-off during a study period of 6 mo. Test-day SCC were available through milk recording and within 5 d before drying off cows were sampled for quarter-level bacteriological culturing serving as the gold standard. Sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) were calculated at different threshold values of SCC, ranging between 50,000 and 500,000 cells/mL, to detect major-pathogen-infected cows. At a commonly used threshold of 200,000 cells/mL, the Se and Sp of (a combination of) test-day SCC before drying off ranged between 37.6 and 57.6% and between 66.7 and 79.3%, respectively. Still, estimates were modified by the herd level prevalence of subclinical mastitis and the cow's milk yield and parity. For instance, at the 200,000 cells/mL threshold using the geometric mean SCC of the 3 last test-days, the overall Se, Sp, PPV, and NPV were 37.6, 79.3, 30.8, and 83.9%, respectively, whereas these were 27.8, 87.5, 21.7, and 90.6%, respectively, for heifers and 40.3, 73.5, 33.3, and 78.9%, respectively, for multiparous cows. In conclusion, test-day SCC records obtained via milk recording are reliable to detect dairy cows at drying off that are not infected with major pathogens as determined by bacteriological culture and could eventually facilitate implementation of selective dry cow therapy in commercial dairy herds. Because estimates of the herd-level prevalence of subclinical mastitis, milk yield level, and parity of the cows affect the estimates of the test characteristics and predictive values to some extent, one should consider taking these parameters into account when differentiating infected from uninfected cows based on SCC data. [ABSTRACT FROM AUTHOR]

In this study, we studied infection dynamics across the dry period using test-day somatic cell count (SCC) data from 739 Holstein cows from 33 randomly selected commercial dairy herds in Flanders, all of which applied blanket dry-cow therapy at dry-off. First, we determined infection dynamics, combining the last test-day SCC before dry-off and the first test-day SCC after calving. Next, we determined the effect of dry period infection dynamics, adjusting for the level of the second test-day SCC after calving, on the evolution of testday SCC and milk yield (MY) and on clinical mastitis and culling hazard in the subsequent lactation. Using an SCC threshold of 200,000 cells/mL, 12.6% of the cows considered healthy before dry-off acquired a new intramammary infection (IMI) across the dry period, whereas 66.9% of the cows considered infected before dry-off cured from IMI. Infection dynamics across the dry period significantly affect a cow’s SCC, clinical mastitis risk, and culling hazard in the subsequent lactation. Cows with a new IMI, a cured IMI, or a chronic IMI across the dry period had higher test-day SCC than healthy cows, and their test-day SCC evolved differently over time. This was not the case for test-day milk yield, for which no association with infection dynamics was detected. Furthermore, cows with a second test-day SCC <200,000 cells/mL had a lower test-day SCC in the remainder of the lactation than cows with a second test-day SCC ≥200,000 cells/mL, but this association was modified by infection dynamics across the dry period. The lowest test-day SCC in the remainder of the lactation was observed for cows that remained healthy across the dry period combined with a low (<200,000 cells/mL) second test-day SCC. Cows that cured from an IMI present at dry-off and cows with a chronic IMI across the dry period were more likely to develop clinical mastitis (hazard ratio = 2.22 and 2.89; 95% confidence interval = 1.45–3.43 and 1.60–5.20, respectively), and chronic IMI cows were more likely to be culled (hazard ratio = 3.68; 95% confidence interval = 1.64–8.20) in the subsequent lactation compared with healthy cows. This was not true for cows that became infected across the dry period. This study underlines the importance of good udder health management during lactation to prevent IMI at dry-off rather than curing infected cows during the dry period to ensure optimal udder health in the subsequent lactation. [ABSTRACT FROM AUTHOR]

Coagulase-negative staphylococci (CNS) have become the main pathogens causing bovine mastitis in recent years. A huge variation in species distribution among herds has been observed in several studies, emphasizing the need to identify subgroup- and speciesspecific herd-level factors to improve our understanding of the differences in ecological and epidemiological nature between species. The use of bulk milk samples enables the inclusion of a large(r) number of herds needed to identify herd-level risk factors and increases the likelihood of recovering enough isolates per species needed for conducting subgroup- and, eventually, species-specific analyses at the same time. This study aimed to describe the prevalence and distribution of CNS species in bulk milk samples and to identify associated subgroup- and species-specific herd-level factors. Ninety percent of all bulk milk samples yielded CNS. Staphylococcus equorum was the predominant species, followed by Staphylococcus haemolyticus and Staphylococcus epidermidis. A seasonal effect was observed for several CNS species. Bulk milk samples from herds with a loose-pack or a tiestall housing system were more likely to yield CNS species compared with herds with a freestall barn, except for S. epidermidis, Staphylococcus simulans, and Staphylococcus cohnii. In September, herds in which udders were clipped had lower odds of yielding Staphylococcus chromogenes, S. simulans, and Staphylococcus xylosus, the CNS species assumed to be most relevant for udder health, in their bulk milk than herds in which udder clipping was not practiced. Bulk milk of herds participating in a monthly veterinary udder health-monitoring program was more likely to yield these 3 CNS species. Herds always receiving their milk quality premium or predisinfecting teats before attachment of the milking cluster had lower odds of having S. equorum in their bulk milk. Herds not using a single dry cotton or paper towel for each cow during premilking udder preparation were more likely to have S. cohnii-positive bulk milk. Herds in which flushing with hot water or steam of the milking cluster after having milked a cow with a (sub)clinical mastitis was applied, were less likely to yield S. simulans, S. haemolyticus, and S. cohnii in their bulk milk. Always wearing gloves during milking decreased the odds of having Staphylococcus devriesei-positive bulk milk. Tap water from the public drinking system used as drinking water increased the odds of yielding S. simulans in the bulk milk. In conclusion, CNS are highly prevalent in bulk milk and might originate from the environment for some species (we hypothesize this is true for S. equorum or S. cohnii), or from within the udder (e.g., for S. simulans). Studies collecting bulk milk and quarter milk samples at the same time along with environmental samples are needed to determine the exact origin of the different (subgroups of) CNS species present in bulk milk using strain-typing techniques. [ABSTRACT FROM AUTHOR]

Despite the increasing knowledge of prevention and control strategies, bovine mastitis remains one of the most challenging diseases in the dairy industry. This study investigated the antimicrobial activity of 13 species of lactic acid bacteria (LAB), previously isolated from the honey crop of the honeybee, on several mastitis pathogens. The viable LAB were first reintroduced into a sterilized heather honey matrix. More than 20 different bovine mastitis isolates were tested against the mixture of the 13 LAB species in the honey medium using a dual-culture overlay assay. The mastitis isolates were identified through bacteriological culturing, followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Additionally, the mastitis isolates were subjected to antimicrobial susceptibility testing through disk diffusion. Growth of all tested mastitis pathogens, including the ones displaying antimicrobial resistance to one or more antimicrobial compounds, were inhibited to some extent by the honey and LAB combination. The antibacterial effect of these LAB opens up new perspectives on alternative treatment and prevention of bovine mastitis. [ABSTRACT FROM AUTHOR]

Coagulase-negative staphylococci (CNS) are frequently isolated from quarters with subclinical mastitis, teat apices, and the cows' environment. Virulence, ecology, epidemiological behavior, and effect on udder health vary between different CNS species. Staphylococcus chromogenes, Staph. simulans, and Staph. xylosus are frequently present in milk and have a more substantial effect on quarter milk somatic cell count than other species. Therefore, these species are considered the "more relevant" CNS. As species-specific factors associated with CNS intramammary infection (IMI) have not yet been identified and susceptibility for IMI differs between cows and quarters, this study aimed to identify predictors for CNS IMI at the cow and quarter level (some of them changing over time) with a specific focus on the aforementioned more relevant CNS. Precise data were available from a longitudinal study (3,052 observations from 344 quarters from 86 dairy cows belonging to 3 commercial dairy herds). All CNS were molecularly identified to the species level, and multivariable, multilevel logistic regression models taking into account the longitudinal nature of the data, were fit to study the likelihood of infection. Staphylococcus chromogenes, Staph. xylosus, and Staph. cohnii were the most frequently isolated species from CNS IMI in older cows, whereas Staph. chromogenes, Staph. xylosus, and Staph. simulans were the main species found in IMI in heifers. Quarters from heifers (as opposed to multiparous cows), from heifers and multiparous cows in third or fourth month in lactation (as opposed to early lactation, <60 d in milk), and with an increasing quarter milk SCC were more likely to be infected with the more relevant CNS species. Quarter milk SCC was identified as the sole statistically significant predictor for IMI with other CNS species, although the size of the effect was lower [odds ratio of 1.6 (1.4-1.9) vs. 2.1 (1.8-2.5)] than the effect for IMI with the more relevant CNS. As a strong herd effect was present, studying herd-level predictors is warranted. [ABSTRACT FROM AUTHOR]

Coagulase-negative staphylococci (CNS) are the most common bacteria involved in subclinical mastitis in dairy cows. Remarkably, CNS-infected dairy heifers produce more milk than uninfected heifers. Because the lactation hormone prolactin (PRL) is also involved in mammary gland immunity, we investigated the milk PRL response and the mammary quarter milk yield following experimental CNS challenge. Eight healthy Holstein-Friesian heifers in mid-lactation were experimentally infected using a split-udder design with 3 different CNS strains: one Staphylococcus fleurettii (from sawdust bedding) and 2 Staphylococcus chromogenes strains (one isolate from a teat apex, the other isolate from a chronic intramammary infection). Three mammary quarters per heifer were simultaneously inoculated with 1.0 x 106 cfu, whereas the remaining mammary quarter was infused with sterile phosphate-buffered saline, serving as a control. An existing radioimmunoassay was modified, validated, and used to measure PRL frozen-thawed milk at various time points until 78 h after challenge. The mean milk PRL level tended to be higher in the CNS-challenged mammary quarters compared with the control mammary quarters (7.56 and 6.85 ng/mL, respectively). The increase in PRL over time was significantly greater in the CNS-challenged mammary quarters than in the control mammary quarters. However, no difference was found in the PRL response when comparing each individual CNS strain with the control mammary quarters. The mean mammary quarter milk yield tended to be lower in the CNS-infected mammary quarters than in the control mammary quarters (1.73 and 1.98 kg per milking, respectively). The greatest milk loss occurred in the mammary quarters challenged with the intramammary strain of S. chromogenes. Future observational studies are needed to elucidate the relation between PRL, the milk yield, and the inflammatory condition, or infection status, of the mammary gland. [ABSTRACT FROM AUTHOR]