Corrigendum to "Genetic diversity and iron metabolism of Staphylococcus hominis isolates originating from bovine quarter milk, rectal feces, and teat apices" (J. Dairy Sci. 105:9995-10006).

Staphylococcus chromogenes TA showed significantly lower growth under iron-deprived conditions, and adding an iron supplement (lactoferrin or ferritin) resulted in no improvement in growth; in contrast, growth of S. chromogenes IM was significantly recovered with ferritin iron supplementation. OnlyStaphylococcus hominis strains originating from quarter milk were able to significantly utilize ferritin as an iron source to reverse the growth inhibition caused by chelating agent 2,2'-bipyridyl in varying degrees. Both S. chromogenes strains (IM and TA) and all S. hominis strains were unable to significantly use lactoferrin as an iron source for growth recovery.

Comparison of non-aureus staphylococcal and mammaliicoccal species found in both composite milk and bulk-tank milk samples of dairy cows collected in tandem.

Non-aureus staphylococci and the closely related mammaliicoccal species (NASM) are the most common causes of bovine subclinical mastitis on modern dairy farms and are highly prevalent in bulk-tank milk. The purpose of this study was to determine the distribution of NASM in both composite cow milk (CCM) and bulk-tank milk (BTM) samples collected in tandem in commercial Flemish dairy herds and to estimate the origin of the different (subgroups of) NASM species present in BTM by applying strain typing (random amplification of polymorphic DNA or random amplified DNA [RAPD]). A single cross-sectional sampling was performed over 5 herds that volunteered to participate in the study. Composite cow milk samples (n = 356) were collected from all lactating cows (except those with clinical mastitis) during a milking in tandem with 6 BTM samples per herd sequentially collected immediately post that milking (n = 30). In total, 421 and 80 NASM isolates were recovered and identified by MALDI-TOF mass spectrometry from the CCM and BTM samples, respectively and a total of 21 and 12 different NASM species were identified from CCM and BTM samples, respectively. Staphylococcus cohnii was the most prevalent NASM species found in BTM followed by Staphylococcus haemolyticus, Staphylococcus epidermidis, Mammaliicoccus lentus, and Staphylococcus equorum, whereas from CCM samples the most common species were S. hemolyticus, S. cohnii, S. equorum, S. epidermidis, and Staphylococcus chromogenes. The prevalent NASM species in both CCM and BTM samples was distinct for each herd, corroborating other studies observing a herd-specific NASM microbiota. Random amplified DNA analysis was performed on 9 NASM species (S. chromogenes, S. epidermidis, S. haemolyticus, S. equorum, Mammaliicoccus sciuri, Staphylococcus xylosus, S. cohnii, Staphylococcus debuckii, and M. lentus) because these species were isolated from both sample types in a herd. The same RAPD types were found in both sample types for all NASM species selected for strain typing in varying degrees. When assessing the distribution of NASM species, differences within NASM species should be examined meaning a closer look should be taken at the strain level rather than at the species level only.

Genetic diversity and iron metabolism of Staphylococcus hominis isolates originating from bovine quarter milk, rectal feces, and teat apices.

Staphylococcus hominis, a member of the non-aureus staphylococci (NAS) group, is part of the human and animal microbiota. Although it has been isolated from multiple bovine-associated habitats, its relevance as a cause of bovine mastitis is currently not well described. To successfully colonize and proliferate in the bovine mammary gland, a bacterial species must be able to acquire iron from host iron-binding proteins. The aims of this study were (1) to assess the genetic diversity of S. hominis isolated from bovine quarter milk, rectal feces, and teat apices, and (2) to investigate the capacity of bovine S. hominis isolates belonging to these different habitats to utilize ferritin and lactoferrin as iron sources. To expand on an available collection of bovine S. hominis isolates (2 from quarter milk, 8 from rectal feces, and 19 from teat apices) from one commercial dairy herd, a subsequent single cross-sectional quarter milk sampling (n = 360) was performed on all lactating cows (n = 90) of the same herd. In total, 514 NAS isolates were recovered and identified by MALDI-TOF mass spectrometry; the 6 most prevalent NAS species were S. cohnii (33.9%), S. sciuri (16.7%), S. haemolyticus (16.3%), S. xylosus (9.6%), S. equorum (9.4%), and S. hominis (3.5%). A random amplified polymorphic DNA (RAPD) analysis was performed on 46 S. hominis isolates (19 from quarter milk, 8 from rectal feces, and 19 from teat apices). Eighteen distinct RAPD fingerprint groups were distinguished although we were unable to detect the presence of the same RAPD type in all 3 habitats. One S. hominis isolate of a distinct RAPD type unique to a specific habitat (8 from quarter milk, 3 from rectal feces, and 4 from teat apices) along with the quality control strain Staphylococcus aureus ATCC 25923 and 2 well-studied Staphylococcus chromogenes isolates ("IM" and "TA") were included in the phenotypical iron test. All isolates were grown in 4 types of media: iron-rich tryptic soy broth, iron-rich tryptic soy broth deferrated by 2,2'-bipyridyl, and deferrated tryptic soy broth supplemented with human recombinant lactoferrin or equine spleen-derived ferritin. The growth of the different strains was modified by the medium in which they were grown. Staphylococcus chromogenes TA showed significantly lower growth under iron-deprived conditions, and adding an iron supplement (lactoferrin or ferritin) resulted in no improvement in growth; in contrast, growth of S. chromogenes IM was significantly recovered with iron supplementation. Staphylococcus hominis strains from all 3 habitats were able to significantly utilize ferritin but not lactoferrin as an iron source to reverse the growth inhibition, in varying degrees, caused by the chelating agent 2,2'-bipyridyl.

Longitudinal study on the effects of intramammary infection with non-aureus staphylococci on udder health and milk production in dairy heifers.

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.

Milk losses and dynamics during perturbations in dairy cows differ with parity and lactation stage.

Milk yield dynamics during perturbations reflect how cows respond to challenges. This study investigated the characteristics of 62,406 perturbations from 16,604 lactation curves of dairy cows milked with an automated milking system at 50 Belgian, Dutch, and English farms. The unperturbed lactation curve representing the theoretical milk yield dynamics was estimated with an iterative procedure fitting a model on the daily milk yield data that was not part of a perturbation. Perturbations were defined as periods of at least 5 d of negative residuals having at least 1 day that the total daily milk production was below 80% of the estimated unperturbed lactation curve. Every perturbation was characterized and split in a development and a recovery phase. Based hereon, we calculated both the characteristics of the perturbation as a whole, and the duration, slopes, and milk losses in the phases separately. A 2-way ANOVA followed by a pairwise comparison of group means was carried out to detect differences between these characteristics in different lactation stages (early, mid-early, mid-late, and late) and parities (first, second, and third or higher). On average, 3.8 ± 1.9 (mean ± standard deviation) perturbations were detected per lactation in the first 305 d after calving, corresponding to an estimated 92.1 ± 135.8 kg of milk loss. Only 1% of the lactations had no perturbations. On average, 2.3 kg of milk was lost per day in the development phase, while the recovery phase corresponded to an average increase in milk production of 1.5 kg/d, and these phases lasted an average of 10.1 and 11.6 d, respectively. Perturbation characteristics were significantly different across parity and lactation stage groups, and early and mid-early perturbations in higher parities were found to be more severe with faster development rates, slower recovery rates, and higher milk losses. The method to characterize perturbations can be used for precision phenotyping purposes that look into the response of cows to challenges or that monitor applications (e.g., to evaluate the development and recovery of diseases and how these are affected by preventive actions or treatments).

Short communication: Barrier characteristics of 3 external teat sealants to prevent bacterial penetration under in vitro conditions using rubber calf-feeding nipples.

The main objective of this study was to evaluate the barrier characteristics of 3 external teat sealants for dry cows in preventing bacterial penetration by 3 common major mastitis pathogens (Escherichia coli, Staphylococcus aureus, and Streptococcus uberis) via a novel in vitro simulation model using rubber calf-feeding nipples. All feeding nipples were filled with a sterile cotton plug soaked in sterile broth heart infusion medium and were treated as follows: rubber teats 1 and 5 were sealed with Ubera Dry (Inovet, Arendonk, Belgium); rubber teats 2 and 6 were sealed with T-Hexx Dry (Huvepharma Livestock, St. Louis, MO); rubber teats 3 and 7 were sealed with Uddergold Dry (Ecolab Food and Beverage Division, St. Paul, MN); and rubber teats 4 and 8 remained unsealed and served as positive and negative controls, respectively. After the dips had dried, rubber teats 1 to 4 were immersed in a suspension of E. coli (experiment 1), Staph. aureus (experiment 2), or Strep. uberis (experiment 3; ≥1.5 × 108 cfu/mL) for 24 h, whereas rubber teats 5 to 8 were not exposed to the bacterial suspensions. All external teat sealants adhered well to the rubber teats. All cotton plugs collected from the teats that were not exposed to E. coli, Staph. aureus, or Strep. uberis (rubber teats 5 to 8) remained culture-negative, except for 1 (due to contamination). Of the rubber teats that were exposed to the major mastitis pathogens, all cotton plugs collected from the teats dipped with Ubera Dry and T-Hexx Dry remained culture-negative for the mastitis pathogen they were exposed to. The cotton plugs of the rubber teats that were sealed with Uddergold Dry and exposed to E. coli and Strep. uberis showed positive cultures for the respective bacteria, as demonstrated using strain-typing. The cotton plugs collected from the rubber teats that were not sealed with an external teat sealant and that served as positive controls became culture-positive for the mastitis pathogens they were exposed to. We conclude that Ubera Dry showed comparable and superior barrier performance against penetration of E. coli, Staph. aureus, and Strep. uberis compared with T-Hexx Dry and Uddergold Dry, respectively, under in vitro conditions using a novel in vitro simulation model. Although one should be aware that the method has not yet been validated to predict risk of intramammary infections, the proposed technique can be a meaningful starting point to evaluate and compare the barrier characteristics of external teat sealants in preventing bacterial penetration. A large-scale clinical trial is needed before any definite conclusions can be drawn as to the adherence, duration of adherence, barrier performance, and efficacy in protection against intramammary infections of the 3 external teat sealants under field conditions.

The effect of intramammary infection in early lactation with non-aureus staphylococci in general and Staphylococcus chromogenes specifically on quarter milk somatic cell count and quarter milk yield.

This longitudinal study aimed to evaluate the impact of subclinical intramammary infection (IMI) with non-aureus staphylococcal (NAS) species in the first 18 d in milk (DIM) on the quarter milk somatic cell count (qSCC) and quarter milk yield (qMY) during the first 4 mo of lactation in Holstein Friesian heifers. Quarter milk samples were collected from 82 heifers from 1 to 4 DIM until 130 DIM on a biweekly (14 d) basis for determination of the qSCC; qMY data were available through the automatic milking systems. The quarter samples collected on the first (1-4 DIM) and second (15-18 DIM) sampling days were used for bacteriological culturing to determine the IMI status. In this study, 324 quarters from 82 heifers were enrolled, of which 68 were NAS-infected at the first sampling day. Only 16 (23.5%) of these quarters were still NAS-infected at the second sampling day, demonstrating the high spontaneous cure rate of these infections shortly after calving; 9 of these 16 cases were infected with the same NAS species. Interestingly, none of the NAS-infected quarters at the first sampling day acquired a new infection with a major pathogen at the second sampling day, whereas 2.3% of the noninfected quarters did. All 102 isolates phenotypically identified as NAS were further identified to the species level. Staphylococcus chromogenes was the most prevalent species on the first (29.4% of all NAS) and second (52.9%) sampling days. Quarters infected with Staph. chromogenes at the first sampling day had a significantly higher qSCC in later lactation than noninfected quarters, whereas this was not true for quarters infected with all other NAS species (i.e., as a group of species). The average daily qMY in the first 4 mo of lactation did not differ between noninfected quarters and quarters infected with Staph. chromogenes or all other NAS species at the first sampling day. Persistently NAS species-infected quarters in the first 18 DIM (i.e., infected with the same NAS species on the first and second sampling days) had the highest qSCC later in lactation, followed by quarters with a new NAS IMI (i.e., noninfected at the first sampling day and infected with NAS at the second sampling day). The qSCC from transiently NAS species-infected quarters (i.e., not infected with the same NAS species at the second sampling day) was not significantly higher in later lactation compared with that in noninfected quarters. The IMI status of quarters in the first 18 DIM, combining culture results at 1 to 4 and 15 to 18 DIM (new, persistent, and transient IMI), was not significantly associated with daily qMY in the first 4 mo after calving. In general, NAS should be considered minor pathogens with no adverse effect on daily qMY in quarters of heifers infected in the first 18 DIM and with a high spontaneous cure rate. Staphylococcus chromogenes was the most prevalent species, causing an increase in qSCC comparable to the level of quarters infected with a major pathogen; Staph. chromogenes caused most infections that persisted through at least the first 18 DIM.

Distribution of non-aureus staphylococci from quarter milk, teat apices, and rectal feces of dairy cows, and their virulence potential.

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).

Incidence of milk leakage after dry-off in European dairy herds, related risk factors, and its role in new intramammary infections.

The incidence of milk leakage (ML) after dry-off (DO) and related risk factors was studied in 1,175 dairy cows from 41 commercial herds in 8 European countries: Belgium, Czech Republic, Denmark, France, Germany, Italy, the Netherlands, and Spain. Milk leakage was assessed twice for 30 s each during 3 visits at 20 to 24 h, 30 to 34 h, and 48 to 52 h after DO. Information related to dry-cow management and udder health was collected at herd and cow level, including individual somatic cell count (ISCC) from test-day controls and occurrence of clinical mastitis cases from DO until 30 d in lactation. Mixed-effect logistic regression analyses were used to identify possible risk factors for ML and to study the association between ML and new intramammary infections. Intramammary infections were defined as clinical mastitis cases during the dry period and in the first 30 d in lactation or a rise in ISCC from before to after the dry period (threshold: 200,000 cells/mL) or both. Milk leakage was observed in 24.5% of the cows between 20 and 52 h after DO, where the herd incidence varied between 0.0 and 77.8%. The reduction in number of milkings in the weeks before DO had statistically significant effect on the ML incidence. When the milking frequency was reduced from 3 times/d to 2 or maintained at twice a day, cows had 11 (95% CI = 3.43-35.46) or 9 (95% CI = 1.85-48.22) times higher odds of leaking milk, respectively, compared with cows where the milking frequency was reduced from twice to once a day. Also, the milk production 24 h before DO was associated with ML incidence. Hence, cows with a milk production between 13 and 21 L or above 21 L had 2.3 (95% CI = 1.48-3.53) and 3.1 (95% CI = 1.79-5.3) times higher odds of leaking milk, respectively, compared with cows with a milk production below 13 L. A higher ML incidence was present in the group of cows with an average ISCC in the last 3 mo before DO ≥200,000 cells/mL (odds ratio = 1.7; 95% CI = 1.13-2.41) compared with cows with an average ISCC <100,000 cells/mL. Quarters with ML tended to have 2.0 times higher odds of developing clinical mastitis compared with quarters not leaking milk. Cows with ML tended to have 1.5 times higher odds of intramammary infections (i.e., an increase of ISCC or clinical mastitis) compared with cows without ML.

The effect of mastitis management input and implementation of mastitis management on udder health, milk quality, and antimicrobial consumption in dairy herds.

The main objective of this study was to evaluate evolutions in herd-level antimicrobial consumption (AMC) and in udder health and milk quality parameters between herds that received mastitis management input on a regular basis (actively advised by the first author; referred to as intervention herds) and herds that did not (referred to as control herds). Strikingly, herds in the intervention group had a significantly higher prevalence of new intramammary infections compared with those in the control group. No significant differences were observed in the percentage of chronically infected cows, the bulk milk somatic cell count, and the bacterial and coliform count between the intervention and control herds, nor did the herd-level AMC differ between them. Furthermore, the level of mastitis management applied in each herd was assessed and scored [mastitis management score (MMS); higher is better], as was the level of implementation of different recommended mastitis management practices over time, expressed as the mastitis management implementation score (MMIS; higher is better). A large variation was observed in MMS and MMIS in the intervention herds (median = 16 and range = 12 to 22; median = 13 and range = -5 to 31, respectively) and the control herds (median = 16 and range = 9 to 22; median = 9 and range = -13 to 22, respectively). Also, intervention herds in which the herd veterinarian attended each herd visit executed by the first author had a higher MMS and MMIS (median = 20 and 24, respectively) compared with herds in which the veterinarian sometimes (median = 16 and 17, respectively) or never (median = 16.5 and 7.5, respectively) attended the herd visits. Further, the association between MMS or MMIS on one hand and udder health, milk quality, and the herd-level AMC over time on the other was studied using the data of both groups of herds. Better mastitis management was associated with a reduction in the consumption of antimicrobials that are critically important for human health over time and with lower bacterial counts and bulk milk somatic cell count. Better mastitis management can be helpful in obtaining better milk quality and more responsible use of critically important antimicrobials on dairy farms.

Evaluation of test-day milk somatic cell count information to predict intramammary infection with major pathogens in dairy cattle at drying off.

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.

Infection dynamics across the dry period using Dairy Herd Improvement somatic cell count data and its effect on cow performance in the subsequent lactation.

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 test-day 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.

Effect of intramammary infection with non-aureus staphylococci in early lactation in dairy heifers on quarter somatic cell count and quarter milk yield during the first 4 months of lactation.

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.

Non-aureus staphylococci in fecal samples of dairy cows: First report and phenotypic and genotypic characterization.

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 ß-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.

Antimicrobial consumption on dairy herds and its association with antimicrobial inhibition zone diameters of non-aureus staphylococci and Staphylococcus aureus isolated from subclinical mastitis.

The main objectives of this study were to quantify the consumption of antimicrobials on a convenience sample of dairy herds and to determine the association between herd-level antimicrobial consumption and inhibition zone diameters (IZD) of non-aureus staphylococci and Staphylococcus aureus isolates from subclinical mastitis cases. Also, the association between the IZD of non-aureus staphylococci and Staph. aureus isolates within a herd was studied. Antimicrobial consumption data on 56 Flemish dairy farms were obtained between 2013 and 2014 by so-called garbage can audits and expressed as antimicrobial treatment incidence (ATI), with the unit of ATI being the number of defined daily doses animal (DDDA) used per 1,000 cow-days. The average total ATI in adult dairy cattle for all active substances was 18.73 DDDA per 1,000 cow-days and ranged from 6.28 to 42.13 DDDA between herds. The ATI of critically important (for human health) antimicrobials was 6.91 DDDA per 1,000 cow-days; that is, 37% of total antimicrobial consumption. The average ATI for intramammary therapy of (sub)clinical mastitis, intramammary dry-cow therapy, and systemically administered therapy was 5.20, 6.70, and 6.73 DDDA, respectively. The IZD of 239 non-aureus staphylococci and 88 Staph. aureus isolates originating from milk samples from cows with subclinical mastitis collected on selected dairy herds were determined using Kirby-Bauer disk diffusion and ranged between 6 and 42 mm. Because only a limited number of clinical breakpoints (Clinical and Laboratory Standards Institute) and epidemiological cut-off values (European Committee on Antimicrobial Susceptibility Testing) are available for mastitis-causing bacteria in bovine, IZD were used as a proxy for antimicrobial resistance. Inhibition zone diameters of non-aureus staphylococci for cefquinome, a critically important ß-lactam antibiotic, were negatively associated with the ATI of critically important ß-lactam for systemically administered therapy and positively with the ATI for intramammary therapy of (sub)clinical mastitis of critically important ß-lactam antimicrobials. Only for neomycin was a positive association between the IZD of non-aureus staphylococci and Staph. aureus isolates within the same herd observed.

Coagulase-negative Staphylococcus species in bulk milk: Prevalence, distribution, and associated subgroup- and species-specific risk factors.

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 species-specific 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.

Immune response after an experimental intramammary challenge with killed Staphylococcus aureus in cows and heifers vaccinated and not vaccinated with Startvac, a polyvalent mastitis vaccine.

An experimental trial was conducted to explore the effect of vaccination with a polyvalent vaccine against mastitis (Startvac) on the early immune response after experimental intramammary challenge with a heterologous killed Staphylococcus aureus strain. The effect of vaccination on milk production, clinical signs, quarter milk somatic cell count, milk polymorphonuclear neutrophilic leukocyte (PMN) concentration and viability, the concentration of antigen-specific antibodies [slime associated antigenic complex (SAAC) and J5] and their IgG1 and IgG2 subtypes in both serum and whey, and the antigen-specific IFN-γ, IL-4, and IL-17 production by blood lymphocytes after in vitro stimulation with S. aureus and Escherichia coli extracts were determined. A cohort of 8 clinically healthy end-term cows and heifers were conveniently selected, of which half was vaccinated with Startvac at 45 and 10 d before the expected calving date and half served as nonvaccinated control animals. At 15 d in milk, 2 contralateral quarters of each of the 8 animals were challenged with 2×109 cfu/mL of the formaldehyde-killed S. aureusC195strain. The 2 other quarters were infused with phosphate-buffered saline and served as control quarters. The increase in both quarter milk somatic cell count and PMN concentration and the drop in milk production after S. aureus inoculation was less pronounced in the vaccinates than in the nonvaccinates, reflecting a less severe inflammatory response. No significant differences in PMN viability between vaccinates and nonvaccinates could be demonstrated. The serum SAAC- and J5-specific antibody concentration significantly increased across the dry period in the vaccinated animals only. The whey concentration of SAAC-specific antibodies was significantly higher in vaccinates than in nonvaccinates at both 15 and 17 d in milk, independent from the challenge status of the quarters. No significant differences in the whey J5-specific antibody concentration were observed. Vaccination with Startvac seems to primarily evoke a Th2 response for S. aureus characterized by a shift toward the IgG1 antibody subtype and accompanied by a less pronounced Th1 response. The type of response against E. coli was less clear, though a weak but significant shift toward the IgG2 antibody subtype after vaccination and high IFN-γ levels after in vitro stimulation suggest a Th1 response. The increased SAAC-specific antibody concentration in whey in vaccinates compared with nonvaccinates most probably triggers the opsonization of the inoculated S. aureus bacteria, resulting in a more efficient elimination of the bacteria from the mammary gland.

Evaluation of the composite milk somatic cell count as a predictor of intramammary infection in dairy cattle.

The objectives of this study were (1) to evaluate the test characteristics and predictive values of quarter-composite milk somatic cell count (quarter-cSCC) values based on either a single observation or the geometric mean of multiple recordings as a predictor of intramammary infection (IMI) in lactating dairy cows; and (2) to explore to what extent herd prevalence of IMI and cow factors such as parity and stage of lactation affect them. A total of 780 single-quarter milk samples were collected from 195 dairy cows for bacteriologic culture at a single cross-sectional herd screening performed at 21 different dairy herds as part of different research projects. Additionally, monthly quarter-cSCC milk samples at test day were available as part of the Dairy Herd Improvement program. Sensitivity (Se), specificity (Sp), positive predictive valu (PPV), and negative predictive value (NPV) were calculated to differentiate cows infected with any pathogen and cows infected with major pathogens from uninfected cows. Different threshold values for quarter-cSCC, ranging between 50,000 and 500,000 cells/mL, were evaluated for all animals in the study, as well as for high- and low-prevalence herds, heifers and multiparous cows, and cows in early, mid, and late lactation. The overall Se and Sp at a threshold of 200,000 cells/mL for a single quarter-cSCC observation obtained closest to the time of bacteriologic culture were 44.3 and 87.3%, respectively, for cows infected with any pathogen, and 65.1 and 73.0%, respectively, for cows infected with major pathogens. The overall PPV and NPV at a threshold of 200,000 cells/mL for a single quarter-cSCC observation obtained closest to the time of bacteriologic culture were 89.9 and 38.1%, respectively, for cows infected with any pathogen, and 40.6% and 88.1%, respectively, for cows infected with major pathogens. No major differences were observed between estimates of the test characteristics and predictive values of the quarter-cSCC criteria based on a single observation and the geometric mean of multiple observations. For IMI with any pathogen, the Se and PPV were higher in high-prevalence herds than in low-prevalence herds, particularly at thresholds of 50,000 and 100,000 cells/mL. For IMI with major pathogens, Sp was substantially higher in low-prevalence herds than in high-prevalence herds. Sensitivity was higher in multiparous cows than in heifers infected with any pathogen, more specifically at a threshold of 100,000 and 200,000 cells/mL. For cows in early and mid lactation infected with any pathogen, Sp was higher than for cows in late lactation using the single observation closest to the time of bacteriologic culture. The results suggest that the quarter-cSCC threshold value to select cows for bacteriologic culture to maximize the likelihood of finding the causative pathogen of IMI should depend on the group of pathogens one is interested in, the herd prevalence of subclinical mastitis, lactation stage, and the cow's parity.

Teat apex colonization with coagulase-negative Staphylococcus species before parturition: Distribution and species-specific risk factors.

Coagulase-negative staphylococci (CNS) are the main cause of bovine intramammary infections and are also abundantly present in extramammary habitats such as teat apices. Teat apex colonization (TAC) with CNS has already been explored in lactating dairy cows at the species level, whereas this is not true for dry cows and end-term heifers. Therefore, the aim of this observational study was to describe CNS TAC in nonlactating dairy cows and end-term heifers in Flemish dairy herds and to identify associated risk factors at the herd, cow, and quarter level. All CNS were molecularly identified to the species level using transfer RNA intergenic spacer PCR (tDNA-PCR) and sequencing of the 16S rRNA gene, allowing for species-specific statistical analyses using multivariable, multilevel logistic regression. Staphylococcus devriesei, Staphylococcus chromogenes, Staphylococcus haemolyticus, and Staphylococcus equorum were the most frequently isolated species. Staphylococcus chromogenes was the sole species colonizing teat apices of cows and heifers in all herds, whereas large between-herd differences were observed for the other species. Teat apices of red and white Holstein Friesians, of quarters dried off without an internal teat sealer, and swabbed in months with lower precipitation and higher ambient temperature were significantly more likely to be colonized by S. devriesei. Slightly dirty teat apices and teat apices swabbed in months with lower precipitation had higher odds of being colonized by S. chromogenes, whereas teat apices sampled in months with lower precipitation and higher ambient temperature were more likely to be colonized by S. haemolyticus. Dirty teat apices and teat apices swabbed in months with lower ambient temperature in combination with low precipitation had higher odds of being colonized by S. equorum. Diverse factors explaining CNS TAC, yet mostly related to humidity, ambient temperature, and hygiene, substantiate differences in epidemiological behavior and ecology between species.

Mastitis prevention and control practices and mastitis treatment strategies associated with the consumption of (critically important) antimicrobials on dairy herds in Flanders, Belgium.

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.