Relationship among blood indicators of lipomobilization and hepatic function during early lactation in high-yielding dairy cows

Blood indicators are used as a tool to diagnose metabolic disorders. The present work was conducted to study the relationships among blood indicators of lipomobilization and hepatic function in high-yielding dairy cows. Two groups of Holstein cows were studied: 27 early lactation cows and 14 mid lactation cows from four different herds with similar husbandry characteristics in Galicia, Spain. Blood samples were obtained to measure beta-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA), triglycerides (TG), and the activity of aspartate transaminase (AST) and gamma-glutamyl transferase. Cows in early lactation had higher levels of BHB and NEFA than mid lactation cows. High lipomobilization (NEFA > 400 µmol/L) was detected in 67% and 7% of early lactation and mid lactation cows, respectively, while subclinical ketosis (BHB > 1.2 mmol/L) was detected in 41% and 28% of the early lactation and lactation cows, respectively. TG concentrations were low in all cows suffering subclinical ketosis and in 61% of the cows with high lipomobilization. During early lactation, 30% of cows suffered hepatic lipidosis as detected by levels of AST. Compromised hepatic function was observed in early lactation cows as shown by lower concentrations of glucose, total protein, and urea.     

Subclinical ketosis: prevalence and associations with production and disease.

Cows in 32 southern Ontario Holstein herds were monitored for subclinical ketosis for a period of two and one half years. Milk samples were routinely collected and the level of milk ketone bodies determined by the use of a commercial nitroprusside based test powder (reactions scored as negative, +1 or +2). Approximately 92% of positive reactions were observed in the first 65 days of lactation and for that time period the prevalence of ketosis was 12.1%. Based on this prevalence, the minimum possible duration of subclinical ketosis would be 7.9 days and the minimum possible lactational incidence rate would be 12.1%. The prevalence during the first 65 days of lactation in individual herds ranged from 0 to 33.9%. Subclinical ketosis was more likely to be found in cows experiencing metritis than in unaffected cows. Detection of elevated levels of milk ketones also indicated that the cow had a significantly higher risk of having clinical ketosis, metritis or cystic ovaries diagnosed within the following four days. Milk ketone scores of +1 and +2 were found to be associated with a reduction in daily milk production of 1.0 and 1.4 kg of milk respectively.     

The consequences of risk-based surveillance: Developing output-based standards for surveillance to demonstrate freedom from disease

Risk factors associated with high or low long-term incidence of displaced abomasum (DA) or clinical ketosis were studied in 60 Swedish dairy herds, using multivariable logistic regression modelling. Forty high-incidence herds were included as cases and 20 low-incidence herds as controls. Incidence rates were calculated based on veterinary records of clinical diagnoses. During the 3-year period preceding the herd classification, herds with a high incidence had a disease incidence of DA or clinical ketosis above the 3rd quartile in a national database for disease recordings. Control herds had no cows with DA or clinical ketosis. All herds were visited during the housing period and herdsmen were interviewed about management routines, housing, feeding, milk yield, and herd health. Target groups were heifers in late gestation, dry cows, and cows in early lactation. Univariable logistic regression was used to screen for factors associated with being a high-incidence herd. A multivariable logistic regression model was built using stepwise regression. A higher maximum daily milk yield in multiparous cows and a large herd size (p = 0.054 and p = 0.066, respectively) tended to be associated with being a high-incidence herd. Not cleaning the heifer feeding platform daily increased the odds of having a high-incidence herd twelvefold (p < 0.01). Keeping cows in only one group in the dry period increased the odds of having a high incidence herd eightfold (p = 0.03). Herd size was confounded with housing system. Housing system was therefore added to the final logistic regression model. In conclusion, a large herd size, a high maximum daily milk yield, keeping dry cows in one group, and not cleaning the feeding platform daily appear to be important risk factors for a high incidence of DA or clinical ketosis in Swedish dairy herds. These results confirm the importance of housing, management and feeding in the prevention of metabolic disorders in dairy cows around parturition and in early lactation.     

Prevalence of subclinical ketosis in dairy cattle in the Southwestern Iran and detection of cutoff point for NEFA and glucose concentrations for diagnosis of subclinical ketosis

Subclinical ketosis (SCK) is simply a condition marked by increased levels of circulating ketone bodies without the presence of the clinical signs of ketosis. Subclinical ketosis can cause economic losses through decreased milk production and association with preparturient diseases. Limited information is available regarding the prevalence of SCK in dairy herds in Southwestern Iran. The objectives of this study were (i) determination of the cutoff point of nonesterified fatty acids (NEFAs) and glucose concentrations for diagnosis of SCK using receiver operating characteristic (ROC) analysis, and (ii) determination of prevalence of subclinical ketosis in apparently healthy dairy cattle in Southwestern Iran. From October to December 2009, a total of 100 clinically healthy multiparous Holstein cows (3-8 years old) were randomly selected from 16 dairy herds around Kazerun, Fars Province, Iran. The cows had two-six lactations, with body weight ranging from 500 to 650 kg. Blood samples for each cow were taken at 2, 4 and 6 weeks post parturition and 3-4h after the morning feeding. The optimal cutoff point was set, by the ROC method, to >0.26 mmol/L for NEFA, and < 2.26 mmol/L for glucose with corresponding 82.54% sensitivity and 91.89% specificity for NEFA and 44.44% sensitivity and 78.38% specificity for glucose. Cows with BHB concentrations higher than 1200 μmol/L were classified as having SCK. In 2, 4 and 6 weeks post parturition 63%, 68% and 59% of the tested cows were subclinically ketotic. Overall, 97% of tested cows (97/100) were considered subclinically ketotic in at least one sample period. Thirty percent of tested cows (30/100) suffered from subclinical ketosis in all of the 2, 4 and 6 weeks postpartum. The results suggest that, a cut-off point of 0.26 mmol/L for NEFA concentrations can be used during early lactation for diagnosis of subclinical ketosis and making management decisions for prevention and treatment. Glucose cannot be a good criterion for diagnosis of SCK and it does not appear to be useful for monitoring subclinical ketosis.     

Disease, production and culling in Holstein-Friesian cows I. The data

A two-and-a-half-year study was undertaken in 32 commercial dairy herds within a 50-mile radius of Guelph, Ontario, in order to provide a comprehensive evaluation of relationships amongst diseases, production parameters and risk of removal in Holstein-Friesian cows. Diseases consisted of common clinical diseases as well as two subclinical diseases (mastitis and ketosis).

The data set consisted of a total of 2875 lactation records from 2008 cows. The means and standard deviations of some of the production parameters were: age 4.9 ± 2.5 year, breed class average for milk 140 ± 26 BCM units, milk production per day of life 18.0 ± 3.8 kg and days to conception 118 ± 60 days. Lactational incidence rates of the more common diseases were: reproductive tract infections 0.182, mastitis 0.168, cystic ovaries 0.104, subclinical ketosis 0.096, retained placenta 0.086 and ketosis 0.074. The average lactation mean log somatic cell count was 179 000 cells/ml. The times postpartum to the first diagnosis of all disease conditions are presented.     

Prevalence of bovine ketosis in relation to number and stage of lactation

The prevalence of bovine ketosis as distributed among various selected subgroups of 504 Ayrshire and Friesian cows was studied during the indoor-housing season 1978–1979 in western and eastern parts of Finland. Special attention was paid to variation by lactation number. Also the differences in prevalence at various phases of lactation and at the end of pregnancy were investigated. The whole blood concentration of acetoacetate (AA concn) was analysed and used as a measure of subclinical and clinical bovine ketosis. AA cocns below 0.35 mmol/1, between 0.36 mmol/1 and 1.05 mmol/1 and over 1.05 mmol/1 were considered to indicate normal, subclinal and clinical ketotic stages, respectively. The prevalence of clinical ketosis in cows during 3 post-calving months was 13 %. The percentage of subclinical ketosis was 34. The prevalence of clinical ketosis was 3 %, 7 %, 20 %, 22 % and 13 % at the first, second, third, fourth and fifth, or sixth and later calving, respectively, and the frequency of subclinical ketosis 31 %, 41 %, 35 %, 32 % and 32 %, respectively. No case of ketosis was found in 54 cows at the end phase of pregnancy and only one during the first postcalving week. Only 2 cows (4 %) had the AA concn at a clinically ketotic level during the 65th—92nd postcalving days, 16 %, 17 % and 16 % during the 8th—21st, 22nd—42nd and 43rd—64th postcalving days, respectively.Key words: acetoacetate blood concentration, prevalence of bovine ketosis, lactation number, stage of lactation     

An epidemiological and genetic study on registered diseases in Finnish Ayrshire cattle. II. Reproductive disorders

The epidemiology and genetic variability of the most common reproductive diseases were examined. The data set consisted of the lactation records of 70,775 Finnish Ayrshire dairy cows. Each cow was under observation for 2 days before for 305 days after calving. Lactation incidence rates (%) were: dystocia (DYST) 0.9, retained placenta (RTPL) 4.5, metritis (METR) 2.3, anoestrus and suboe&trus (ESTR) 5.2, and ovulatory dysfunction (CYST) 7.0. These diseases formed 33 % of all first treatmetns by veterinarians during farm visits. The occurrence of DYST, RTPL and METR was lowest in parity 2. ESTR decreased and CYST increased with parity. Cows calving during the dark season (September-February) had a higher risk of ESTR, METR and CYST (odds ratios (OR) 2.2–1.1) and a lower risk of RTPL (OR 0.9) than those calving during the light season (March-August). The increase in herd milk yield was positively associated with the occurrence of reproductive disorders. The cows with a history of parturient paresis had a higher risk of contracting CYST, RTPL and METR (OR 6.6–1.8), the cows with retained placenta of contracting metritis (OR 5.1), the cows with metritis of contracting ESTR and CYST (OR 1.5–1.7), the cows with mastitis of contracting METR and ESTR (OR 2.0–1.3) and the cows with ketosis of contracting METR, ESTR and CYST (OR 2.7–1.6). Heretabilities were determined for 5 diseases and for infertility in general. Heritability estimates for parity 2 were: DYST 2 %, RTPL 3 %, METR 7 %, ESTR 12 %, CYST 12 %, and infertility in general 5 %. Heritability for calving interval was 5 % in parity 1 and 6 % in parity 2.     

乌兰察布市泌乳奶牛亚临床酮病的调查研究

试验选取内蒙古乌兰察布市489头泌乳奶牛,通过对尿中和乳中酮体采用酮粉法检测进行奶牛亚临床酮病的监测与分析。结果表明,乌兰察布市泌乳奶牛亚临床酮病发病率为10.63%;第1和第2个泌乳月亚临床酮病发病率明显高于第3个及以上泌乳月;各胎次亚临床酮病发病率以3～5胎最高;日产奶量在30kg以上亚临床酮病发病率显著高于日产奶量在30kg以下奶牛;养殖小区以及规模户饲养奶牛的亚临床酮病发生率较高。     

Standard and lead feeding of dairy cowsAlimentation standard et alimentation renforcée des vaches laitièresStandardfütterung und fütterung nach dem “ead feeding system” bei milchkühen

Standard feeding means that the amount of feed offered is regulated according to actual requirement, with special reference to energy. Lead feeding indicates liberal supply during early lactation in order to challenge the cows for high peak yield. The lead feeding, in contrast to standard feeding rigidly practised, allows the cow to express its yield potential during the critical period of early lactation. Adjusted standard feeding may, however, be practised in a more flexible way by ad libitum feeding of forages, lead feeding during early lactation and with individual rationing of concentrates throughout.Adjusted standard feeding requires individual recordings of milk yield at intervals and qualitative judgement of the roughage available. Such a system is described and discussed.Adjusted standard feeding, flexibly practised seems most applicable for the small farm situation. By using a computerized system for diet calculation combined with adequate techniques for individual milk recordings and concentrate feeding, the system may be feasible even for larger herds.Adjusted standard feeding, as described, stresses the significance of high forage consumption together with efficient use of concentrates, high efficiency overall, and positive effect on ketosis and infertility.     

Associations of sole ulcer at claw trimming with reproductive performance, udder health, milk yield, and culling in Swedish dairy cattle

The association between sole ulcer found at routine claw trimming 2–6 months after calving and reproductive, health and productive traits in the same lactation, was investigated in an observational study of 2368 dairy cows in 102 Swedish herds. The data were analysed by mixed multivariable linear-, logistic- and Poisson-regression modelling at the cow level, accounting for clustering within herd. Associations were found between sole ulcer and first-service conception risk in the first study year (OR 0.59), calving interval (2% longer), treatment for anoestrus (OR 1.61), and 305-day milk yield (479 kg ECM higher). No associations could be shown between sole ulcer and first-service conception risk in the second study year, the number of services per conception, clinical mastitis, high milk somatic-cell counts or culling.     

Subclinical ketosis in dairy cows

Subclinical ketosis is defined as a preclinical stage of ketosis. The peak prevalence of subclinical ketosis occurs during the fourth week of lactation. Herd-related factors, breed, parity, and season are other important determinants. Subclinical ketosis can be revealed by determining levels of plasma glucose, plasma NEFA and blood, and milk or urine ketone body concentration. There are theoretical and practical advantages of using milk ketone bodies. Most authors are agreed on approximate lower and upper borderlines for subclinical ketosis. The risk of an outbreak of clinical symptoms has been evaluated by some authors. Most authors have found significant negative relationships between energy balance and ketone body concentration. Some disagreement may be attributable to the fact that the diets used in different experiments can have different glucogenic potential, even if the energy content is the same. This affects the relationship between energy balance and ketone body concentration, as the ketone body level is influenced by both the energy balance and plasma glucose. Feeding silage with high butyric acid content increases the risk of subclinical ketosis. There are indications that cows with the highest milk yield directly after calving are at greatest risk for developing ketosis. Increased ketone body level secondarily reduces milk production, a decrease that has been quantified by some authors. Subclinical ketosis causes delayed reproductive functions return to normal after calving, increased intervals from calving to first and last service, and an increased frequency of ovarian cysts. The routine determination of milk acetone levels in control programs can be used to evaluate the status of individual cows, to indicate the energy feeding in early lactation at a herd level, and to evaluate sires for breeding. The heritability and the tendency toward a positive genetic correlation between milk acetone and milk yield have also been discussed, as have aspects of nutritional prevention. Factors such as energy- and protein-rich roughage, tasty high-energy concentrates, suitable feeding during the dry period, and division of the concentrates into at least four meals are considered to be important.     

Persistent fecal Salmonella shedding in five dairy herds

OBJECTIVE: To monitor patterns of Salmonella fecal shedding in naturally infected dairy herds, determine the association between fecal shedding and individual animal production measures, and evaluate potential risk factors for shedding of Salmonella organisms among cattle in dairy herds. DESIGN: Longitudinal study. SAMPLE POPULATION: 5 Ohio dairy herds. PROCEDURE: For 3 herds, fecal samples were collected from all mature cows and unweaned calves 7 times during an 18-month period. For the remaining 2 herds, fecal samples were collected from 50 lactating cows 6 times during a 12-month period. Individual animal production records for 3 herds were used to examine associations between individual fecal Salmonella shedding status and 305-day mature-equivalent milk production, somatic cell count, milk fat content, and milk protein content. Multivariable logistic regression was used to test for associations between fecal shedding status and breed, lactation status, lactation number, and duration of lactation. RESULTS: None of the adult animals had clinical signs of salmonellosis, but prevalence of fecal Salmonella shedding at individual collection times ranged from 0 to 99% for cows and from 0 to 67% for unweaned calves. Mature cows were more likely to be shedding Salmonella organisms than were unweaned calves. Within herds, lactation status and duration of lactation for individual animals were associated with Salmonella shedding status. Salmonella fecal shedding status was not associated with individual cow production measures. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that subclinical fecal Salmonella shedding can persist in dairy herds for up to 18 months with no measurable effects on health or production of individual cows.     

Disease frequencies in dairy cows in Sweden. IV. ketosis

An epidemiologic study of ketosis in dairy cows in Sweden covering approximately 125 000 calvings in 1268 herds is presented and various risk factors identified.The Swedish Red and White breed (SRB) had a higher incidence of ketosis than the Swedish Friesian breed (SLB). A positive report of parturient paresis, alone or in combination with a positive report of retained placenta increased the risk of ketosis in SRB cows. Simultaneous reports of parturient paresis and retained placenta increased the risk of ketosis in SLB cows. Tied cows of both breeds with pasture had a decreased risk during the months of pasture. The incidence of ketosis decreased with herd size, and tied zero-grazing cows had a higher incidence than loose-housed cows.Cows reported positive once for ketosis had an increased risk in subsequent calvings but no increased risk of removal during lactation.     

Use of test day milk fat and milk protein to detect subclinical ketosis in dairy cattle in Ontario.

Serum beta-hydroxybutyrate (BHB) levels were determined for 1333 dairy cows in various stages of lactation and parity on 93 dairy farms in Ontario. The data were collected in a cross-sectional manner, as part of the 1992 Ontario Dairy Monitoring and Analysis Program. The median serum BHB was 536 mumol/L for all cows, with a range of 0 to 5801 mumol/L. When subclinical ketosis was defined as a serum BHB level of 1200 mumol/L or higher, the prevalence of ketosis for cows in early lactation (< 65 days in milk (DIM)) was 14.1%. Prevalences for mid lactation (65-149 DIM), late lactation (> 149 DIM), and dry cows were 5.3%, 3.2%, and 1.6%, respectively. The mean serum BHB was significantly higher in the early group compared with each of the other 3 groups (P < 0.05). There was a trend of increasing prevalence with increasing parity across all stages of lactation. Only the difference between the parity-1 group and the parity-4 and greater group was statistically significant (P < 0.05). Both test-day fat percent and test-day protein percent were significantly associated with subclinical ketosis. However, test-day fat percent and test-day protein percent, used alone or in combination, were not useful screening tests for identifying cows with subclinical ketosis.     

Blood parameters in Swedish dairy herds with high or low incidence of displaced abomasum or ketosis

Sixty dairy herds were studied to investigate the association between long-term incidence of displaced abomasum and clinical ketosis and body condition score and blood profiles, including parameters estimating energy metabolism and hepatic lipidosis in the periparturient period and early lactation. Blood samples were taken around parturition and in early lactation from cows without apparent clinical symptoms of metabolic disorders. A difference in metabolism between high and low incidence herds was shown post-partum by a lower metabolic index (the revised Quantitative Insulin Sensitivity Check Index, RQUICKI), and tendencies for higher concentrations of glucose, insulin and non-esterified fatty acids in the high incidence herds. High incidence herds had more cows and produced on average 1400kg energy-corrected milk per cow per year more than the low incidence herds. No differences were found in parameters reflecting liver cell damage. In the first 3weeks post-partum the RQUICKI was a more sensitive marker of herds with a high incidence of displaced abomasum and clinical ketosis than any of the individual parameters, but further research is needed before practical applications of the RQUICKI can be foreseen.     

Disease frequencies of tied zero-grazing dairy cows and of dairy cows on pasture during summer and tied during winter

Disease frequencies of Swedish Red and White Breed (SRB) and Swedish Friesian Breed (SLB) in tied herds with zero-grazing management system and in tied herds with pasture periods are presented. Incidences are compared both with respect to season and between the two systems. Figures are given for accidents and nine different diseases.In zero-grazing cows no seasonal difference could be demonstrated except for a higher risk of ketosis and tramped teat during wintertime for SRB.Cows of both breeds kept on pasture had lower risks of dystocia, ketosis, mastitis and tramped test during this period, but an increased risk of accidents and inflammation of the hoof(s). SRB cows also had higher risks of retained placenta, parturient paresis and non-inflammatory diseases of the hoof(s) during pasture period.Comparison of year-round incidence in the two management systems revealed a higher risk of retained placenta in zero-grazing cows of both breeds and higher risk or parturient paresis in zero-grazing SRB cows. The risk of accidents was decreased in zero-grazing cows of both breeds.The relative risks of tramped teat, mastitis and diseases of the hoof(s) varied depending on the herd size distribution of the control group. Increased risk of mastitis in zero-grazing cows of both breeds and of tramped teat in zero-grazing SLB cows was found when comparing with cows from a group of mainly smaller herds with pasture feeding during summer. However, comparison with cows from a group of herds with the same herd size distribution as zero-grazing cows revealed decreased risk of tramped teat, mastitis and inflammation of the hoof(s) in zero-grazing SRB cows and decreased risk of diseases of the hoof(s) in zero-grazing SLB cows.     

Risk factors for post-partum anoestrus in Charolais beef cows in France

Data from 248 Charolais cows from 20 herds of the Puisaye region (Yonne, France) were collected during winter 1991–1992 to investigate risk factors affecting post-partum anoestrus. Blood was collected 60 days after calving; diagnosis of cyclicity was established by progesterone radioimmunoassay. Herd variables were housing type, lighting of herd accomodation, use of nutritional flushing and nutritional variables (protein and energy before and after calving), and individual variables were parity, ease of calving, body-condition score and body weight at calving and at Day 60, exposure to bulls and calving period. Sixty days post-partum, 62.1% of cows were cyclic. Logistic regression was used to calculate odds ratio (OR). A random effects model was used to take into account the two levels of variables (animal and herd). Although it was defined subjectively, lighting was the only significant herd-level risk factor. Odds of anoestrus were higher in dark than in light accomodation (OR = 6.2, CI 1.2–33.3). Primiparous cows had a higher anoestrus risk than multiparous cows (OR = 10.2, CI 2.9–36.5). Compared with light cows, heavy or medium weight cows at calving had a lower anoestrus risk (OR = 0.25, CI 0.07–0.91, and OR = 0.20, CI 0.07–0.61, respectively.     

Associations of Neospora caninum seropositivity with gestation number and pregnancy outcome in Danish dairy herds.

The prevalence and distribution of seropositivity towards the protozoan parasite Neospora caninum were studied in single blood samples from 1561 cows from 31 Danish dairy herds. Blood samples were analysed by an indirect enzyme-linked immunoassay and an indirect fluorescent-antibody test. Seroprevalence in 15 herds with previous abortions assigned to neosporosis ranged from 1% to 58%, with a mean frequency of 22%. In eight out of 16 herds without a history of N. caninum related abortions, no seroreactors were found. In the remaining eight herds, the seroprevalence ranged from 6% to 59%. The prevalence and distribution of seropositivity, gestation number prior to sampling, and breed were related to abortions and perinatal deaths using a random-effects logistic-regression model. Abortion risk was significantly increased in seropositive animals (OR=3) and in 2nd-gestation cows (OR=3). Perinatal death was significantly influenced by gestation number and breed, but not by serostatus. Reproductive performance and culling risk of cows were not affected by serostatus. Seropositivity increased with “age” (i.e. gestation number) (P=0.02). In open cows, seropositivity tended to decrease with distance from calving (P=0.05). The proportion of seropositive pregnant cows increased with trimester (P=0.02).     

Ketosis treatment and milk yield in dairy cows related to milk acetoacetate levels

Milk yield and milk acetoacetate (M-acac) were measured weekly for the first 6 weeks of lactation in 5 herds with a ketosis problem. Ketosis treatments and the corresponding ketotest score, were also recorded. The treatment rate was highest 7-16 days after calving. Most of these early cases were associated with low ketone levels in milk, whereas the treatment rate for cows with high ketone levels was highest 17-31 days after calving. Nearly half of the treated cows were low-ketone animals. They were classified as ketosis cases in the cow health card records, although probably suffering from other post partum disturbances in many instances. About 40% of the cows with high ketone levels recovered spontaneously. Reduction in milk yield associated with peak M-acac levels was transient and moderate. It was concluded that health card statistics overestimates the severity of the ketosis problem in Norway.     

Udder health and risk factors for subclinical mastitis in organic dairy farms in Switzerland

A study was performed in 1997 to estimate the prevalence and to investigate the etiology of subclinical mastitis in Swiss dairy herds managed under guidelines of controlled organic farming. It was planned as a longitudinal study over a period of 1 year and included a stratified random sample of 152 certified organic farms and 1907 cows. Two farm visits (the first from June to October when cows were on pasture, the second from January to March when cows were confined to barns) were performed on each farm. At each visit, farm management and individual-cow data (with emphasis on milking procedures and udder sanitation) were recorded. California mastitis tests (CMTs) were performed on each udder quarter of all cows in lactation. Milk samples with CMT >1+ were submitted for somatic cell counting (SCC), bacteriological examination and to test for antibiotic susceptibility. The SCC and germ-cell counts of monthly bulk-tank milk samples were available through Dairy Inspection and Advisory Services and milk production data of 567 herd-book cows were available from breeding associations. Possible individual and environmental predictors of subclinical mastitis were identified using logistic models adjusted for clustering of the data at herd and cow levels. Data were analyzed separately for cows from 7 to 100 and from 101 to 305 days post partum. Prevalences of subclinical mastitis at the quarter level were 21.2% for lactation period 7–100 days and 34.5% for 101–305 days post partum. The geometric mean SCC in bulk-tank milk samples was 85.6×10³ cells/ml. Samples at 7–100 and 101–305 days post partum were positive for Staphylococcus aureus in 16.0 and 7.4%, for coagulase-negative Staphylococci in 51.5 and 50.6%, for Streptococcus agalactiae in 0.0 and 0.8%, for other Streptococci in 19.4 and 15.6%, for E. coli in 1.0 and 0.4%, and for Corynebacterium bovis in 25.7 and 45.1%, respectively. Risks of subclinical mastitis increased significantly with increasing days post partum and advancing age of cow. Cows that were sampled when staying in alpine dairies had considerably higher risks of subclinical mastitis than cows staying in home barns. Significantly lower risks of subclinical mastitis were observed in farms where CMT was performed regularly as a control measure. Bacteria in milk from cows with mastitis exhibited antibiotic resistance at a comparable frequency as found previously in conventional farms.