Intramammary infections and risk factors in freshly calved heifers in Swedish dairy herds.

Subclinical mastitis can be common among freshly calved heifers (FCH), but the prevalence differs between herds, possibly due to variation in risk factors. The aims of this observational study were to identify differences in occurrence of intramammary infection (IMI) in FCH between herds with documented good or poorer first-parity udder health based on cow somatic cell count (CSCC) in early lactation, and to study herd differences in animal factors important for udder health, such as udder and hock skin lesions and animal cleanliness. Three groups of herds were included: those with high proportions of FCH with low CSCC (≤75,000 cells/mL) at the first 2 milk recordings after calving (LL), herds with high proportions of FCH with high CSCC (>100,000 cells/mL) at the first and low CSCC at the second recording (HL), and herds with high proportions of FCH with high CSCC at both recordings (HH). Thirty-nine herds (13 LL, 11 HL, 15 HH) were visited 3 times during a 12-mo period for observation of cleanliness and hock lesions, and sampling of udder and teat skin using swab cloths of milk-fed calves, early-pregnant heifers, and late-pregnant heifers. In 25 (9 LL, 9 HL, 7 HH) udder quarter samples from colostrum and milk on d 3 to 4 after calving were taken by the farmers from FCH during one year. The farmers also provided information on calving (individual or group), use of restraint and oxytocin at milking, and presence of teat and udder skin lesions. Bacterial growth in swab samples and quarter samples was investigated by culturing, and a selection of isolates was genotyped using whole-genome sequencing. Cleanliness, hock and udder skin lesions other than udder-thigh dermatitis, and growth of bacteria in swab samples did not differ between herd groups. It was more common that FCH from LL herds, compared with FCH in HH and HL herds, calved in a group of animals. Use of restraint at milking was more common in LL herds than in HH herds, whereas presence of udder-thigh dermatitis was lowest in LL herds. Specific infection was found in 14% of 5,593 quarter samples from 722 FCH. The most common IMI was Staphylococcus chromogenes. Growth of Staphylococcus simulans was more common in HH than in LL and HL herds. In colostrum samples, Staphylococcus haemolyticus was more common in HL and HH than in LL herds. The proportion of quarters with the same specific infection at both samplings was higher in HH than in LL herds and tended to be higher in HH than in HL herds. The proportion of quarters with Staph. chromogenes IMI at both samplings tended to differ between herd groups and was highest in HH herds. Whole-genome sequencing found the same sequence type of Staph. chromogenes and Staphylococcus aureus in both samples in almost all quarters with the same infection at both samplings. The differences in IMI between herd groups were in line with the higher somatic cell count in HH herds. The reasons for the predominance of Staph. chromogenes IMI in FCH need further studies.

Genotypic characterization of Staphylococcus chromogenes and Staphylococcus simulans from Swedish cases of bovine subclinical mastitis.

Staphylococcus chromogenes and Staphylococcus simulans are commonly found in intramammary infections (IMI) associated with bovine subclinical mastitis, but little is known about genotypic variation and relatedness within species. This includes knowledge about genes encoding antimicrobial resistance (AMR) and potential virulence factors (pVF). The aim of this study was therefore to investigate these aspects by whole-genome sequencing of milk isolates from Swedish dairy cows with subclinical mastitis in an observational study. We also wanted to study if specific genotypes were associated with persistent IMI and the inflammatory response at udder quarter level. In total, 105 and 118 isolates of S. chromogenes and S. simulans, respectively, were included. Isolates were characterized using a 7-locus multilocus sequence typing (7-MLST), core genome analysis and in-silico analysis of AMR and pVF genes. Forty-seven sequence types (ST) and 7 core genome clusters of S. chromogenes were identified, and the most common ST were ST-6 and ST-109, both belonging to cluster VII. A 7-locus MLST scheme for S. simulans was not available, but 3 core genome clusters and 5 subclusters were described. Overall, substantial variation in ST and clusters among cows and herds were found in both species. Some ST of S. chromogenes were found in several herds, indicating spread between herds. Moreover, within-herd spread of the same genotype was observed for both species. Only a few AMR genes [blaZ, strpS194, vga(A)] were detected in a limited number of isolates, with the exception of blaZ coding for ß-lactamase, which was identified in 22% of the isolates of S. chromogenes with ST-19, ST-102, and ST-103 more commonly carrying this gene compared with other ST. However, the blaZ gene was not identified in S. simulans. The average total number of pVF detected per isolate was similar in S. chromogenes (n = 30) and S. simulans (n = 33), but some variation in total numbers and presence of specific pVF or functional groups of pVF, was shown between ST/clusters within species. Differences in inflammatory response and potentially in persistent IMI at udder quarter level were found between S. chromogenes subtypes but not between S. simulans subtypes. In conclusion, the results from the present study generates new insight into the epidemiology of bovine S. chromogenes and S. simulans IMI, which can have implications for future prevention and antimicrobial treatment of infections related to these species.

Risk and success factors for good udder health of early lactation primiparous dairy cows.

We compared the management and housing of dairy heifers from calf to calving in herds that were very successful versus less successful in preventing mastitis in early lactation primiparous cows. This retrospective observational study included 170 Swedish dairy herds. Eligible herds were identified from the Swedish official milk recording scheme (SOMRS). Each herd had at least 60 cows per year, production data from 3 consecutive years, and at least 10 primiparous cows per year with their first milk recording 5 to 35 d after calving and their second milk recording 20 to 40 d after the first milk recording. In each herd, primiparous cows with a low (≤75,000 cells/mL) cow somatic cell count (CSCC) at both the first and second milk recording were categorized as low-low (LL); those with a high (>100,000 cells/mL) CSCC at both recordings were categorized as high-high (HH). Cows with high CSCC at the first recording and low at the second were categorized as high-low (HL). The annual proportions of LL, HL, and HH cows within each herd were calculated. Herds with an above-median proportion of LL, HL, or HH cows during the first year of a 3-yr selection period, and above the third quartile proportion of LL, HL, or HH cows, respectively, during the second and third year were identified. These herds (LL herds, n = 129; HL herds, n = 92; HH herds, n = 139) were contacted until a maximum of 60 herds per category had agreed to participate. Field technicians/veterinarians visited each herd once in the mid to late indoor season to collect data on housing and management of the heifers from birth to calving. Additional data were retrieved from the SOMRS. Associations between herd category (LL, HL, or HH) and variables collected were analyzed in 8 multivariable multinomial logistic regression submodels covering herd characteristics, milk-fed calves, heifers in early pregnancy, heifers in late pregnancy, calving and colostrum period, miscellaneous factors, summarized heifer housing data, and general health, culling, and fertility data. A final multivariable model was built from the results of the submodels and univariable analyses. The final model showed that having a standard operating procedure for colostrum feeding was more common in LL and HL herds than in HH herds; the mean bulk milk SCC and overall culling rate due to udder health was higher in HH herds than in LL and HL herds; and automatic milking was less common in LL herds than in HL and HH herds. Several herd and management variables differed between herd categories in the submodels. In conclusion, we identified several success factors for herds with good udder health among early lactation primiparous cows. This knowledge can be used to improve preventive measures in dairy herds to ensure sustainable and economic milk production.

Longitudinal study of Staphylococcus aureus genotypes isolated from bovine clinical mastitis.

Bovine clinical mastitis is an important problem for the dairy industry, and Staphylococcus aureus is a common mastitis-causing pathogen in many countries. Detailed knowledge on genetic variation of Staph. aureus strains within the bovine population, including changes over time, can be useful for mastitis control programs, because severity of disease and effects on milk production are at least partly strain-associated. Therefore, the major aim of this study was to compare sequence types of Staph. aureus isolated from cases of bovine clinical mastitis from 2002 to 2003 with sequence types of a more recent set of isolates collected from 2013 to 2018, using core genome multi-locus sequence typing (cgMLST). We also wanted to compare antibiotic resistance genes of isolates from the 2 sets, to identify changes that may have occurred over time in the Staph. aureus population. A total of 157 isolates of Staph. aureus, almost equally distributed between the 2 time periods, were subjected to high-throughput sequencing and cgMLST. The results showed that the most prevalent sequence types found among the 2002 to 2003 isolates belonged to the clonal complexes CC97, CC133, and CC151, and that those complexes still dominated among the isolates from 2013 to 2018. However, a population shift from CC133 to CC97 and CC151 over time was observed. Likewise, no important differences in prevalence of antibiotic resistance genes were found between the 2 sets of isolates. As expected, genes belonging to the major facilitator superfamily of transporter proteins, and multidrug and toxic compound extrusion transporters, were very common. Moreover, several genes and mutations conferring resistance to fosfomycin were present, but not in CC97 isolates. The ß-lactamase gene blaZ was found in only 3 out of 81 isolates from 2002 to 2003 and 1 out of 76 isolates in 2013 to 2018. In conclusion, the results indicate that mastitis-associated Staph. aureus strains circulating among dairy cows in Sweden exhibit a remarkable genotypic persistence over a time frame of close to 15 yr.

Incidence of udder cleft dermatitis (UCD) in dairy cows and risk factors for transitions to UCD.

Udder cleft dermatitis (UCD) is a common skin condition in Swedish dairy cows, affecting the anterior parts of the udder. The main objective of this study was to investigate incidence rate and duration of UCD in a 1-yr longitudinal study. Other objectives were to investigate risk factors for transitions from being healthy to having mild or severe UCD, and from having mild UCD to having severe UCD, and associations between UCD and clinical mastitis, somatic cell count (SCC) and hock lesions. Seven herds were included in the study and visited 9 times each at 6-wk intervals. At the visits, mild and severe UCD lesions, hock lesions, udder conformation traits, and hygiene scores were registered for each cow milked in the milking parlor. Information on breed, parity, days in milk (DIM), results from test milkings (milk production, SCC, and urea level), and veterinary treatments was also obtained. A UCD case was defined as one or several consecutive observations of UCD. The incidence and duration of UCD were described. Mixed-effect logistic regression models were used to analyze associations between potential risk factors and transitions to any type of UCD. Separate risk factor analyses were performed for transitions to mild and severe UCD. Associations with SCC, mastitis, and hock lesions were also analyzed with mixed-effect logistic regression models. The mean overall incidence of new UCD cases for all visits and herds was 0.5 cases per cow-year at risk. Risk factors associated with a higher risk of a transition to any type of UCD and mild UCD were breed (Swedish Red vs. Swedish Holstein), an indentation or fold at the fore udder attachment, and increasing DIM. In addition, a low milk urea level was associated with a lower risk of transition to any type of and mild UCD. Cows with previous mild UCD and high-yielding cows had increased risk for a transition to severe UCD. Cows that had an observed transition to severe UCD had an increased risk of veterinary-treated clinical mastitis within 6 wk after the UCD observation. No associations were found between UCD and SCC or hock lesions. The median observed duration of a UCD case was 12 wk, but most cases did not have an observed start or end during the study period. The observed duration of cases including severe UCD was longer than for cases involving only mild UCD. The high incidence and often long duration of UCD emphasize the need for preventive measures and treatment strategies.

Udder health of early-lactation primiparous dairy cows based on somatic cell count categories.

The aims were to investigate the prevalence of intramammary infection in early-lactation primiparous dairy cows (PC) in Sweden using milk recording cow composite somatic cell count (CSCC) categories based on classification of CSCC at the first 2 milk recordings after calving as low or high using cut-offs indicating intramammary infection. We also wanted to evaluate if herd-specific patterns in CSCC categories among PC can be identified to indicate success and problem herds as well as cow-level associations between CSCC categories and breed and sire, and herd-level associations between CSCC categories and herd size, milk production, production system, milking system, and year. A total of 1,597 dairy herds were included. Inclusion criteria were enrolment in the Swedish official milk recording scheme and having production data from at least 10 PC per year during 2014, 2015, and 2016. Herd (size, SCC, milk production, production system, milking system) and cow (breed, lactation number, calving date, CSCC, milk production) data were collected from the Swedish official milk recording scheme. Each PC was assigned a CSCC category (low-low, low-high, high-high, high-low, or inconclusive) based on the CSCC at the first 2 milk recordings using the following cut-offs. At each milk recording a CSCC ≤75,000 cells/mL was considered low and a CSCC >100,000 cells/mL was considered high, whereas a CSCC in between those values was considered inconclusive. Associations between CSCC categories and breed or sire of the PC were analyzed using multivariable multinomial logistic regression models. Associations at herd level between number of PC in a CSCC category and herd variables were analyzed using multivariable Poisson or negative binomial regression models. The annual proportions of CSCC categories for all PC were 51.3%, 5.5%, 15.5%, 13.7%, and 14.0% for the low-low, low-high, high-low, high-high, and inconclusive categories, respectively. The distribution of CSCC categories varied markedly between herds. Overall, the median herd prevalence was 50.2 to 54.2% and 11.7 to 13.2% per year for the low-low and high-high categories, respectively. At cow level, both breed and sire were significantly associated with CSCC categories, showing for example that a higher proportion of Jersey PC were categorized as high-high compared with Swedish Holstein (SH) and Swedish Red (SR) PC, and that PC of certain SH and SR sires more often were categorized as low-low or high-high cows than PC of other sires within each breed. All herd factors, except conventional and organic production, were significantly associated with the proportion of PC in a CSCC category at herd level. For example, the proportion of PC in the low-low category was significantly lower in larger herds (≥80 cows) compared with smaller herds (<80 cows) and significantly lower in automatic milking system herds than in herds with other milking systems, but significantly higher in herds with higher milk production. Overall, the results indicate a substantial need for prevention of subclinical mastitis in early-lactation PC as only 50% of these cows had low CSCC at both milk recordings after calving. Moreover, we conclude that CSCC categories may be a useful tool for identifying success and problem herds.

Prevalence and risk factors for udder cleft dermatitis in dairy cattle.

Udder cleft dermatitis (UCD) is a skin lesion in dairy cattle mostly located at the anterior junction between the udder and the abdominal wall or between the front quarters. Relatively little is known about causative factors for UCD, and few studies have investigated prevalence and risk factors of UCD. Therefore, the aim of this study was to investigate the prevalence of UCD in a random sample of dairy herds with freestalls and milking parlors in a county of Sweden. Thirty dairy herds participated in the study. Each herd was visited once at milking, when every third cow was investigated for presence of UCD. Associations between UCD and milk production, breed, parity, days in milk, claw health, and udder health on the herd and cow levels were also investigated. In addition, a case-control study was performed in 6 herds with a high prevalence of UCD to investigate associations between udder conformation or mange and UCD. Udder cleft dermatitis was found in 18.4% of the 1,084 cows included in the study. The within-herd cow prevalence varied between zero and 39%, with an average of 18.5%. Risk factors for UCD at the herd level were a high proportion of Swedish Red cows and a high production level. At the cow level, breed, parity, and production level were identified as risk factors. The highest risk of having UCD was found in high-producing Swedish Red cows that had calved at least 3 times. Veterinary-treated clinical mastitis was associated with UCD, but cow composite somatic cell count was not. A strong anterior udder attachment was a protective factor, but signs of mange had no association with UCD. The primary cause of UCD is still unclear, and more research is needed to identify the best ways to prevent the development of this animal welfare problem.

Status of vitamins E and A and ß-carotene and health in organic dairy cows fed a diet without synthetic vitamins.

Synthetic vitamin supplementation is not consistent with organic production, so it is important to investigate whether dairy cows can maintain their health and production without synthetic vitamins being added to their diet. In basic dairy cow diets, provitamin A (ß-carotene) and vitamin E are mainly found in pasture and in grass and legume silages, but the concentrations are highly variable. This study compared the vitamin status and health of cows without synthetic vitamin supplementation (NSV group) with control cows (CON group) fed synthetic vitamins according to Swedish recommendations (600 IU of vitamin E and 80,000 IU of vitamin A per cow per day) to investigate whether dairy cows can fulfill their requirements of vitamins A and E without supplementation with synthetic vitamins. Vitamin concentrations in blood plasma and milk, health, fertility, milk yield, and milk composition were measured in Swedish Holstein cows (n=28) during 2 complete lactations. All cows were fed a 100% organic diet containing grass-legume silage, cold-pressed rapeseed cake, peas, cereal grains, and minerals. Blood samples were collected from each cow 3 wk before expected calving, at calving, and 3 wk, 3 to 5 mo, and 7 to 9 mo after calving. Samples of colostrum were taken and milk samples were collected 4d after calving and at the same time as the 3 blood samplings after calving. The only difference in vitamin status between groups was found in colostrum in yr 1, when CON cows tended to have a higher concentration of α-tocopherol, and their ß-carotene concentration was higher compared with NSV cows. The NSV cows tended to have more cases of mastitis than CON cows in yr 2. Within the NSV group, fewer cows were healthy and more cases of mastitis were observed in yr 2 than in yr 1. The groups did not differ in production parameters. In conclusion, the vitamin status in blood and milk of the studied cows indicated that cows in organic dairy production can fulfill their requirements of vitamins A and E without any supplementation of synthetic vitamins, except at the time around calving, when the requirements are high. However, the impaired health of NSV cows in yr 2 may indicate a long-term negative health effect in cows fed no synthetic vitamins.

Associations of udder-health indicators with cow factors and with intramammary infection in dairy cows.

The objective of this study was to investigate if and how cow factors and intramammary infection (IMI) are associated with 4 different udder-health indicators in dairy cows as a first step in investigating whether the diagnostic performance of these indicators can be improved. The investigated indicators were somatic cell count (SCC), lactate dehydrogenase (LDH), N-acetyl-ß-d-glucosaminidase (NAGase), and alkaline phosphatase (AP) measured in milk. In this cross-sectional study, approximately 1,000 cows from 25 dairy herds were sampled for bacteriology (quarter milk samples) during 3 consecutive days: the day before test milking, at the day of test milking, and at the day after test milking. The whole-udder test milking sample was analyzed for milk composition, SCC, LDH, NAGase, and AP. Cow data (parity, breed, milk yield, percentage of milk fat and protein, milk urea concentration, and days in milk from the sampled test milking) were collected from the Swedish milk-recording scheme. Of the sampled cows 485 were considered IMI negative and were used in multivariable mixed-effect linear regression models to investigate associations between cow factors and the udder-health indicators. A second modeling including all cows, both IMI negative and IMI positive (256 cows), was also performed. The results showed that all udder-health indicators were affected by cow factors but that different cow factors were associated with different indicators. Intramammary-infection status was significantly associated with all udder-health indicators except AP. Parity and milk urea concentration were the only cow factors associated with all indicators in all models. The significant cow factors explained 23% of the variation in SCC and >30% of the variation in LDH, NAGase, and AP in IMI-negative cows, showing that LDH, NAGase, and AP are more affected than SCC by cow factors. The IMI status explained 23% of the variation in SCC in the model with all cows but only 7% of the variation in LDH and 2% of the variation in NAGase, indicating that SCC has the best potential as a diagnostic tool in finding cows with IMI. However, further studies are needed to investigate whether the diagnostic properties of these udder-health indicators will improve with adjustment according to their associations with different cow factors when used as a diagnostic tool for finding cows with IMI.

An improved method to culture Staphylococcus aureus from bovine milk.

Staphylococcus aureus is an important udder pathogen often associated with subclinical mastitis in dairy cows. Identification of Staph. aureus-positive udder quarters and cows is an important part of control programs to reduce spread of Staph. aureus within and between dairy herds. Therefore, accurate and easy-to-perform culturing methods of Staph. aureus in milk are needed. In the present study, 8 methods for isolation of Staph. aureus in bovine milk samples were investigated. The methods involved different culturing volumes, enrichment, incubation, and freezing processes as well as sedimentation and use of the Mastistrip cassette (SVA, Uppsala, Sweden). Three different sets of milk samples were collected, and 6, 5, and 4 methods were used in each subset of samples. Our results indicate an increased probability of detecting Staph. aureus in milk samples when a simple incubation step (37 degrees C for 18 h) without additives was included before culturing. Using this incubation method, the number of Staph. aureus-positive udder quarters and cows increased by 50 and 29%, respectively, compared with using the standard method of direct culturing of 10 microL of milk. The improved method may be especially useful for detection of low concentrations of Staph. aureus in milk; for example, when screening herds for Staph. aureus.

Short communication: relationships between α-lactalbumin and quality traits in bulk milk.

The main objective of this study was to investigate whether the α-lactalbumin (α-LA) content of bulk milk is related with some known inflammatory markers and milk quality traits. An additional objective was to study whether combining α-LA, haptoglobin (Hp), and serum amyloid A (SAA) in an acute phase index (API) could be useful as an alternative marker for bulk milk quality. For the dairy industry, it is of great importance to receive high quality bulk milk for manufacture of liquid milk and dairy products. The somatic cell count (SCC) is currently used as an indirect marker for bulk milk quality, but because it is somewhat insensitive and unspecific, interest exists in alternative markers. Bulk milk samples were analyzed for α-LA, SCC, polymorphonuclear leukocyte count, Hp, SAA, fat, lactose, total protein and casein contents, casein number, protein composition, proteolysis, and coagulating properties. No significant differences were found in SCC, polymorphonuclear leukocyte count, Hp, or SAA between milk samples containing low, medium, or high concentrations of α-LA. Differences between α-LA groups were, however, found in some milk quality traits because high α-LA concentration was related to low concentrations of α(S1)-, α(S2)-, and ß-caseins and high concentrations of lactose and ß-lactoglobulin. A high API was related to low lactose content and casein number. Samples with high SCC contained less casein and had a lower casein number than milk with a low SCC, and proteolysis was significantly higher in high SCC milk than in low SCC milk. Neither α-LA nor API proved to be a better marker than SCC for the quality traits investigated, and α-LA was not considered to be a useful inflammatory marker in bulk milk.

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

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

Microbial aetiology of acute clinical mastitis and agent-specific risk factors.

A nation wide study on the microbial aetiology of cases of acute clinical mastitis in Swedish dairy cows was conducted with the aim to investigate changes in the microbial panorama compared to a previous study performed 1994-1995. Another aim was to investigate some agent-specific environmental and individual risk factors. Milk samples were collected from 987 udder quarter cases from 829 cows during six 2-month periods from May 2002 to April 2003, and data on risk factors and demography were collected at sampling by means of a questionnaire. In total, 1056 bacteriological diagnoses were made. The most frequently isolated bacterial species was Staphylococcus aureus constituting 21.3% of the diagnoses, followed by Escherichia coli (15.9%), Streptococcus dysgalactiae (15.6%), Streptococcus uberis (11.1%), coagulase-negative staphylococci (6.2%), Arcanobacterium pyogenes (6.1%) and Klebsiella spp. (4.2%). Samples with no growth or contamination constituted 10.6% and 4.5% of the diagnoses, respectively. A major shift in the panorama of udder pathogens was not observed compared to the survey in 1994-1995. Isolation of Klebsiella spp. was strongly associated with the use of sawdust as bedding material. On the other hand, using sawdust as bedding reduced the risk of isolating S. uberis relative to using straw or peat. The risk of isolating E. coli increased with increasing milk yield and was higher in loose housing systems than in tie stalls. Isolation of S. aureus was associated with tie stalls, and A. pyogenes with low yielding cows and teat lesions. S. dysgalactiae infections were also associated with teat lesions.

Management practices associated with udder health of first-parity dairy cows in early lactation.

This study aimed at investigating associations between management routines including feeding, housing, and milking around calving, and udder health of first-parity cows in early lactation in Swedish large, high producing, low bulk-milk somatic cell count (SCC) dairy herds housed in free stalls. Seventy-two dairy herds participated and data concerning 1189 first-parity cows calving during the study period (October 2005-January 2006) was collected. Multivariable regression analysis were performed with three different outcomes; within-herd number of first-parity cows veterinary treated for clinical mastitis at days -10 to 60 after calving, within-herd number of first-parity cows with a SCC> or =200,000cells/mL at first test-day, and SCC of first-parity cows at first test-day. Cow factors significantly associated with good udder health of first-parity cows (few cases of clinical mastitis and or low SCC) were being of the Swedish Red breed, having a high milk yield at first test-day, and a milk-urea > or =5mmol/L at first test-day. Herd factors significantly associated with good udder health were having mattresses as flooring in the cubicles in the lactating cow housing, and to house the first-parity cows in tie stalls 1 month before calving. Cow factors significantly associated with poor udder health of first-parity cows were having a milk-urea <4mmol/L at first test-day. Herd factors significantly associated with poor udder health of first-parity cows were feeding first-parity cows sugar-beet pulp or corn silage, and to give silage from a different batch to pregnant heifers than to lactating cows. Moreover, to have sawdust or shavings in the calving pen, to be moved from the calving pen > or =2 days after calving, to milk first-parity cows at the calving site instead of in the parlor, and to rinse, clean or disinfect milking units before a first-parity cow was milked were also significantly associated with poor udder health of first-parity cows. The results indicate that different control measures must be taken depending on the nature of the udder health problem.

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

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

Supplementation of RRR-alpha-tocopheryl acetate to periparturient dairy cows in commercial herds with high mastitis incidence.

Dietary vitamin E supplementation of dairy cows around calving has been associated with improved udder health. However, few studies have been performed in Europe and in commercial dairy herds. Therefore, the main aim of the study was to evaluate whether extra daily dietary supplementation of 1,610 mg of alpha-tocopherol, in the form of RRR-alpha-tocopheryl acetate, to dairy cows around calving could improve the udder health in commercial herds with a high incidence of veterinary-treated clinical mastitis. In addition, the effects of supplementation on other cow diseases, fertility, milk production, culling, and stillbirth were also studied. Cows in 21 herds in southeast Sweden were assigned to 1 of 2 groups, 1) daily supplementation with 1,610 mg of RRR-alpha-tocopherol from 4 wk before to 2 wk after calving (n = 196), or 2) no extra supplementation (n = 203), on top of the normal diet containing average vitamin E supplementation (on average, 386, 664, and 957 mg/d to cows at 1 mo prior to calving, at calving, and at 15 d after calving, respectively). Multivariable generalized linear mixed models were used for statistical analyses of the effects of supplementation on the cumulative incidence risk of veterinary-treated clinical mastitis and of veterinary-treated diseases other than mastitis within 1 and 2 mo after calving, culling (due to udder health or other reasons) within 2 and 9 mo after calving, the risk of stillbirth or calf death within 24 h after calving, time from calving to first insemination, number of inseminations per service period, and cow composite natural logarithm of somatic cell count and daily milk production at the first monthly testing after calving. A significant effect of supplementation was observed only for stillbirth or calf death within 24 h after birth, which was significantly lower in the supplemented group. The reasons for this finding require further study.

Metabolism and udder health at dry-off in cows of different breeds and production levels.

The effects of milk yield at dry-off (DO), different calving intervals (CI; 12 and 15 mo) and breed on metabolism and udder health were studied in 56 primiparous and multiparous cows of the Swedish Red and White (SRB) and Swedish Holstein (SH) breeds. The cows were dried off 55 +/- 5 d prior to expected parturition. They were fed 4 kg of DM as silage and wheat straw ad libitum for 5 d, and were milked in the morning of d 2 and 5. Depending on their daily milk yield, the cows were divided into 3 numerically equal groups on 2 d during the week prior to DO: low (LY; 5.0 to 11.4 kg of milk/d, n = 19), medium (MY; 11.5 to 17.7 kg of milk/d, n = 19), and high (HY; 17.8 to 29.5 kg of milk/d, n = 18). The plasma cortisol concentration increased during DO only in MY and HY cows. Plasma nonesterified fatty acids increased during DO in all groups, but the maximum nonesterified fatty acid concentration was related to the milk yield prior to DO. The plasma glucose level during the DO period was not significantly affected by yield, but the insulin concentration decreased after DO, with a more pronounced drop in the HY group. The CI 15-mo group had a higher glucose level and tended to have a higher insulin level in plasma than the CI 12-mo group before DO. They also had a higher body condition than the CI 12-mo group. The results indicate that the CI 15-mo cows had a more positive nutrient balance. There were no effects of CI on milk production or composition during DO. The SRB and SH breeds did not differ in any of the measured plasma parameters or milk production. However, the lower somatic cell counts in SRB than in SH observed before and during DO, as well as after parturition, were attributed to being an effect of breed. The proportion of cows with intramammary infections (IMI) was significantly lower just after calving in the LY group than in the other yield groups. At 2 and 3 wk after DO, significantly fewer cows in the LY group had open teat canals compared with the HY and MY groups, respectively, but teat-end condition did not differ between yield groups. The yield before DO did not significantly influence the somatic cell counts during the first 4 wk after parturition or the presence of IMI 4 wk after parturition. We concluded that in the present study, higher milk yield prior to DO gave rise to a more pronounced metabolic response and a higher risk of contracting IMI during the dry period, at calving, or both, but yield at DO did not have any long-term effects on udder health. A prolonged CI did not facilitate a rapid decrease in milk production. The SRB and SH breeds responded equally in decreasing the milk production during DO, but the SRB breed had lower somatic cell counts.

Effects of housing, management, and health of dairy heifers on first-lactation udder health in southwest Sweden.

Data on health, management, and housing from birth to first calving were collected for 2,126 heifers on semi-monthly visits made by project veterinarians to 107 dairy herds from southwest Sweden. Additional data were obtained from the official milk- and health-recording program. Factors associated with incidence of veterinarian-treated clinical mastitis (VTCM) in the period 7 d before (d -7) to 30 d after first calving and of elevated cow composite somatic cell count (SCC, > or =200,000 cells/mL) at first test milking after first calving, respectively, were investigated using a 2-level (animal and herd) logistic regression analysis after initial screening by univariate analyses. The incidence risk of VTCM during the complete first lactation (305 d) was 10.8%. Ten percent of the diseased animals had more than 1 case of VTCM and 51% of total cases occurred from -7 to 30 d postcalving. The incidence rate of VTCM during the complete first 305-d lactation was 1.13 cases per 100 cow-mo. In total, 18.1% of the animals had elevated SCC at first test milking (mean 21 d) after calving. Veterinarian-treated clinical mastitis at -7 to 30 d postcalving was associated with higher overall incidence of mastitis in the herd and with reproductive disorders (i.e., retained placenta, endometritis, pyometra, dystocia, or twin birth). The risk of elevated SCC increased with increasing percentage of cows in the herd that, some time during the year, had had an increased udder disease score (chronically increased SCC). Other factors associated with increased risk of elevated SCC were increasing amounts of concentrates fed to 11- to 16-mo-old heifers, moving to confined housing the day of calving instead of earlier, and use of restraint measures at milking. In addition, growth rate from birth to weaning, and several feed-related variables (e.g., amount of concentrates and type of roughage given) were associated with VTCM at -7 to 30 d post-calving or elevated SCC at first test milking in the univariate analyses.

Changes in blood and milk lymphocyte sub-populations during acute and chronic phases of Staphylococcus aureus induced bovine mastitis.

Staphylococcus aureus (S. aureus) often causes long-lasting chronic sub-clinical udder infections in dairy cows. To investigate if this can be due to a negative impact of S. aureus on lymphocytes important for the immune defence, alterations in proportions and expression intensity of CD4+, CD8+, WC1+, B and IL-2R+ lymphocytes was studied in blood and milk, as S. aureus mastitis developed from acute clinical to chronic sub-clinical form. Six healthy dairy cows were inoculated with S. aureus in one udder quarter per cow, and one quarter per cow acted as an uninfected control. Blood samples, and milk samples from infected and non-infected quarters were collected before infection and for five weeks after infection. All infected quarters developed acute clinical mastitis, of which five turned into chronic sub-clinical mastitis. In infected quarters, the proportions of all lymphocyte sub-sets, except WC1+ cells, differed in acute phase compared to pre-infection, while the dominant finding in the chronic phase was increased expression intensities per cell. An impact on blood lymphocytes and milk lymphocytes in non-infected quarters also occurred, mainly during the chronic phase. The most prominent finding was the increased proportion and expression of B-lymphocytes in blood, infected and non-infected quarters during chronic sub-clinical mastitis. As S. aureus can invade and survive intracellularly, a preferential stimulation of B-cells, suggesting development of a humoral response, may not be sufficient to eliminate intracellular bacteria, which could explain the persistence of the infection.

Sensitivity and specificity of PCR analysis and bacteriological culture of milk samples for identification of intramammary infections in dairy cows using latent class analysis.

Real-time PCR analysis of milk samples is a fast method to identify intramammary infections (IMI) in dairy cows, and has the potential to be used for routine analysis of test milking composite milk samples. However, the results of the PCR analysis can be difficult to interpret. The objective of this study was to compare the sensitivity (Se) and specificity (Sp) of PCR analysis of composite milk samples, and conventional bacteriological culturing (BC) of quarter milk samples, when used to identify cows with IMI. The comparisons were performed for IMI with four common udder pathogens; Staphylococcus aureus (S aureus), Streptococcus dysgalactiae (Str dysgalactiae), Str uberis and coagulase negative staphylococci (CoNS). The Se and Sp of real-time PCR (SePCR; SpPCR) and BC (SeBC; SpBC) was simultaneously estimated using latent class analysis (LCA), studying one pathogen at the time. Milk samples from 970 dairy cows from 25 herds were included. Aseptically collected quarter milk samples taken at the day before test milking (TM), at the day of TM, and at the day after TM, were analyzed using BC. Non-aseptically collected composite milk samples taken at the day of TM were analyzed using PCR. Moreover, the composite milk somatic cell count (SCC) was recorded and summarized by diagnostic test and bacterial finding. LCA was first performed using only test results from samples taken at the day of TM, but in a second analysis BC results from the three consecutive samplings, interpreted in parallel, were included. The SePCR was significantly higher than the SeBC for S aureus, Str dysgalactiae and CoNS in the first analysis, but only for CoNS in the second analysis. The SpPCR was significantly lower than the SpBC for Str dysgalactiae and CoNS. In conclusion, using PCR analysis of composite milk samples, as a diagnostic tool for identifying cows with IMI increased the Se for all the pathogens investigated (although not always significantly), while Sp in general remained on a similar level, compared to BC of quarter milk samples. The use of repeated quarter milk sampling improved the SeBC, making the results of PCR analysis and BC more similar. However, the SCC of cows with IMI according to BC was higher than for cows with IMI according to PCR, suggesting that some of the cows with IMI according to PCR did not have an active inflammation. Hence, extra caution is needed when decisions about treatment of IMI are based on PCR.