Field survey of clinical mastitis in low somatic cell count herds

Bovine mastitis: an evolving disease

Mastitis remains a major challenge to the worldwide dairy industry despite the widespread implementation of mastitis control strategies. The last forty years have seen a dramatic decrease in clinical mastitis incidence but this has been accompanied by a change in the relative and absolute importance of different pathogens. Escherichia coli and Streptococcus uberis are now the two most common causes of bovine mastitis and are an increasing problem in low somatic cell count herds. This paper reviews the changes in incidence and pattern of mastitis in the UK over the last four decades and discusses some of the possible explanations for these changes. It focuses in particular on apparent changes in the behaviour of E. coli and its ability to cause persistent intramammary infection; which may be as a result of bacterial adaptation or the unmasking of previously unrecognized patterns of pathogenesis. The prospects for novel approaches to mastitis control are discussed, as are the current and future challenges facing the industry.

Clinical bovine mastitis in Norway

A brief description of the Norwegian Health Card System for Cattle (NHCSC) is given. The incidence of clinical mastitis (CM) for dairy cows in Norway was determined using NHCSC data recorded from 1992 to 1995. Incidence density (ID) (which included repeated episodes of CM in the same cow) and various measures of risk were estimated. The ID for the entire study period, comprising almost 1.2 million cow-years, was 49 CM episodes per 100 cow-years at risk. Twenty-six percent of the cows with CM experienced at least two episodes of CM in 1 year. For the entire study period (1992-1995), the ID was 30 episodes per 100 cow-years at risk for acute CM (ACM). Annual risk of CM for fixed cohorts of cows that were at risk 1 January the particular year, as estimated by the actuarial method and accounting for the exact time of removal of culled cows, varied between 0.32 (1992) and 0.35 (1994 and 1995). Numerically similar risk estimates were found when using the density method for fixed cohorts. Lactational incidence risk for cows that calved in 1992-1994 varied between 0.32 and 0.34. In herds of a size greater than five cow-years, the crude ID of CM tended to decrease with increasing herd size. The ID of CM varied considerably between counties, and was higher in coastal areas than in inland areas.

Immunisation of dairy cattle with recombinant Streptococcus uberis GapC or a chimeric CAMP antigen confers protection against heterologous bacterial challenge

The gapC genes, encoding the cell surface-associated GapC proteins of S. uberis and S. agalactiae, have been cloned and sequenced. To identify potential vaccine candidates against S. uberis-induced bovine mastitis, lactating dairy cows were vaccinated with either (6 x His)GapC of S. uberis or S. dysgalactiae, or with a chimeric CAMP-factor antigen, CAMP-3. For 7 days following heterologous challenge with S. uberis, milk somatic cell counts were determined to assess differences in the severity of mastitis between vaccinates and an unvaccinated control group. Vaccination with S. uberis (6 x His)GapC or CAMP-3 resulted in a significant reduction in inflammation on several days post-challenge, most significantly for the former antigen. Inflammation was not reduced in S. dysgalactiae (6 x His)GapC vaccinates, suggesting that it does not confer cross-species protection.

The effect of pathogen-specific clinical mastitis on the lactation curve for somatic cell count

Data from 274 Dutch herds recording clinical mastitis (CM) over an 18-mo period were used to investigate the effect of pathogen-specific CM on the lactation curve for somatic cell count (SCC). Analyzed pathogens were Staphylococcus aureus, coagulase-negative staphylococci, Escherichia coli, Streptococcus dysgalactiae, Streptococcus uberis, other streptococci, and the culture-negative samples. The dataset contained 178,754 test-day records on SCC, recorded in 26,411 lactations of 21,525 cows of different parities. In lactations without both clinical and subclinical mastitis, SCC was high shortly after parturition, decreased to a minimum at 50 days in milk (DIM), and increased slowly toward the end of the lactation. Effects of CM on lactation curves for SCC differed among the pathogens isolated. Before a case of clinical E. coli mastitis occurred, SCC was close to the SCC of lactations without both clinical and subclinical mastitis, and after the case of CM had occurred, SCC returned rather quickly to a low level again. Similar curves were found for lactations with cases of CM associated with culture-negative samples. Before a case of clinical Staph. aureus mastitis occurred, average SCC was already high, and it remained high after the occurrence. Effects of CM associated with Strep. dysgalactiae, Strep. uberis, and other streptococci on the lactation curve for SCC were comparable. They showed a continuous increase in SCC until the case of pathogen-specific CM occurred, and afterwards SCC stayed at a higher level. Using SCC test-day records, these typical characteristics of each pathogen may be used to find more effective indicators of CM.

Risk of clinical mastitis in dairy herds with a high proportion of low individual milk somatic-cell counts

The relationships between the herd-somatic-cell count (SCC) pattern on a test day and the incidence of clinical mastitis in the subsequent period were studied by collecting health data and monthly records from 2 years (1995-1997) from 121 farms located in the west of France. A total of 980 herd-periods (from one test day to the following one) were analyzed. The outcome variable was the incidence density of clinical mastitis (ICM) within the herd-period. The herd-SCC pattern on a test day was described by cross-combining the proportions of cows with low SCC (<50,000 cells/ml) or with high SCC (>250,000 cells/ml). The relationship between herd-SCC pattern and subsequent ICM was assessed using a generalized linear mixed model. A sensitivity analysis evaluated the effect of different proportions of cows with low SCC on significance and magnitude of the relationship. Risk of clinical mastitis was expressed as a risk ratio (RR) in comparison to a moderate herd-SCC level (with low proportions of cows with low or high SCC). Median ICM was 0.38 cases per 365 cow-days at risk (first and third quartiles: 0 and 0.88). In the situations where few cows (<15%) had SCC>250,000 cells/ml, ICM was higher (RR>1.31) when the proportion of cows with low SCC exceeded 50% than in the reference situation. Risk ratios increased as the proportion of cows with low SCC increased from 40 to 60%. In the situations where the proportion of cows with SCC>250,000 cells/ml exceeded 15%, ICM was higher compared to the reference situation (whatever the proportion of low SCC). Risk ratios were also higher when the proportion of cows with low SCC were >40-60%, compared to the pattern with the proportion of cows with low SCC below 40%. Herd situations with a high proportion of cows with low SCC appeared to be at increased risk of clinical mastitis.

Antibiotic susceptibility patterns for environmental streptococci isolated from bovine mastitis in central California dairies

Environmental streptococci are frequently isolated from bovine mastitis in dairy cows with only limited information available on the antimicrobial susceptibility of these organisms. A total of 362 environmental streptococci isolated from cases of bovine mastitis from the central San Joaquin Valley of California over a 3-yr period were used in the study. Overall, 39.9% of the strains tested were Streptococcus uberis, 42.2% were Streptococcus dysgalactiae, and 11.1% were Enterococcus spp. The antimicrobial susceptibility for these organisms was determined for the following antimicrobial agents: penicillin, ampicillin, cephalothin, ceftiofur, penicillin + novobiocin, erythromycin, pirlimycin, tetracycline, and sulfadimethoxine. Results demonstrate substantial differences in the susceptibility patterns for the various organisms collectively referred to as the environmental streptococci. The MIC90 for penicillin was 0.06 microg/ml for 152 strains of S. dysgalactiae compared with 0.25 microg/ml for 133 strains of S. uberis. However, the Enterococcus spp. were the most resistant organisms tested. These data also indicate that the use of interpretive criteria based on human data may provide misleading results. In conclusion, these data confirm that the environmental streptococci are a diverse group of organisms comprised of several different genera and species and that identification of environmental streptococci to the species level is needed to appropriately modify control methods. Moreover, the use of the agar disk diffusion (Kirby-Bauer) susceptibility test for agents with human-based interpretive criteria is contraindicated, and these tests should only be performed with agents with mastitis specific interpretive criteria.

The effect of ascorbic acid and L-histidine therapy on acute mammary inflammation in dairy cattle

Ascorbic acid and L-histidine were investigated as antioxidant therapies for acute mammary inflammation. Mastitis was induced in eight nonpregnant Holstein cows by intramammary infusion of endotoxin. Treatments were administered in a 4 x 4 Latin square crossover design with 1-wk periods between challenges with endotoxin. Four individual treatments, control, ascorbic acid only, L-histidine only, and ascorbic acid plus L-histidine, were applied. Two doses of 25 g of ascorbic acid administered intravenously at 3- and 5-h postendotoxin challenge increased milk production recovery (9% higher, P < 0.02) and tended to reduce the extent of rumen stasis. Two doses of 25 g of L-histidine similarly administered decreased plasma antioxidant activities 5.5% (P < 0.05). However, ascorbic acid and L-histidine had no effects on rectal temperature, heart rate, respiratory rate, and dry matter intake. The data suggested that ascorbic acid provided some potential benefit for recovery from acute mammary inflammation in dairy cattle.

Immunity in the mammary gland

The ruminant mammary gland is an extremely important economic organ in that it provides a major nutrition source for a significant portion of the world's human population. The ruminant mammary gland is also responsible for providing protective immunity to neonates and for defending itself from invading pathogens. A wide array of humoral and cellular immune mechanisms are present in the mammary gland and actively participate in providing immunity to newborns and the mammary gland per se. The acute inflammatory response is essential in determining the outcome of intramammary challenge, and factors affecting innate and adaptive immunity in the context of mammary health are reviewed in detail. The ruminant mammary gland is also unique in that lymphocyte trafficking, which is essential to adaptive immunity, is shared with the peripheral immune system rather than the common mucosal immune system.

Escherichia coli induces apoptosis and proliferation of mammary cells

Mammary cell apoptosis and proliferation were assessed after injection of Escherichia coli into the left mammary quarters of six cows. Bacteriological analysis of foremilk samples revealed coliform infection in the injected quarters of four cows. Milk somatic cell counts increased in these quarters and peaked at 24 h after bacterial injection. Body temperature also increased, peaking at 12 h postinjection. The number of apoptotic cells was significantly higher in the mastitic tissue than in the uninfected control. Expression of Bax and interleukin-1beta converting enzyme increased in the mastitic tissue at 24 h and 72 h postinfection, whereas Bcl-2 expression decreased at 24 h but did not differ significantly from the control at 72 h postinfection. Induction of matrix metalloproteinase-9, stromelysin-1 and urokinase-type plasminogen activator was also observed in the mastitic tissue. Moreover, cell proliferation increased in the infected tissue. These results demonstrate that Escherichia coli-induced mastitis promotes apoptosis and cell proliferation.

Studies about the mechanism of internalization by mammary epithelial cells of Escherichia coli isolated from persistent bovine mastitis

The purpose of this study was to investigate the interaction between Escherichia coli and primary mammary epithelial cell cultures derived from cows with persistent intramammary infection (IMI). Two strains of E. coli, isolated from the milk of two different cows suffering from persistent E. coli IMI were tested for adhesion to and invasion of three primary mammary epithelial cell cultures derived from mammary biopsies of the two infected cows. Intracellular E. coli were detected during five days post infection in vitro. Both strains of E. coli adhered to and invaded monolayers of all three primary mammary epithelial cell cultures. One strain adhered less but invaded more than the other. Comparison with other mammary pathogens indicated that E. coli invaded the cells less efficiently than Staphylococcus aureus, about as efficiently as Streptococcus dysgalactiae and more efficiently than Streptococcus uberis. The mechanism of E. coli invasion was studied using the cytoskeleton disrupting agents colchicine and cytochalasin D. These compounds inhibited the invasion of E. coli. Invasion of E. coli could also be inhibited by the phosphokinase inhibitors genistein and staurosporin in a dose-dependent fashion. Phorbol-myristyl-acetate (PMA) had no effect on the invasion of E. coli. Histology of mammary tissue revealed chronic inflammatory changes in quarters that were persistently infected by E. coli. Intracellular bacteria were not detected in mammary tissue sections. Polymerase chain reaction (PCR) analysis suggested that the two strains of E. coli lacked genes encoding for bundle-forming pili (bfpA), intimin (eae) and translocated intimin receptor (tir), which are characteristic for enteropathogenic E. coli (EPEC).

Adaptation of Escherichia coli to the bovine mammary gland

Clinical mastitis in six Somerset dairy herds was monitored over a 12-month period. Escherichia coli was implicated in 34.7% of all clinical cases. Forty-one percent of all clinical E. coli mastitis cases occurred in just 2.2% of the population. A total of 23.9% of clinical E. coli cases occurred in quarters suffering recurrent cases of E. coli mastitis. The genotypes of strains involved in recurrent cases of clinical E. coli mastitis were compared by DNA fingerprinting with enterobacterial repetitive intergenic consensus primers. In 85.7% of cases of recurrent quarter E. coli mastitis, the same genotype was implicated as the cause of disease, suggesting persistence of the organism within the mammary environment. The same genotype as that in the original case was also implicated in 8.5% of recurrent cases occurring in different quarters of the same cow, suggesting spread between quarters. These findings challenge our current understanding of the epidemiology of E. coli mastitis and suggest that pathogen adaptation and host susceptibility may be playing a part in the changing pattern of clinical mastitis experienced in the modern dairy herd.

Analysis of an outbreak of Streptococcus uberis mastitis

An outbreak of Streptococcus uberis mastitis was described to gain insight into the dynamics of Strep. uberis infections at a herd level. Data were obtained from a longitudinal observational study on a commercial Dutch dairy farm with good udder health management. Quarter milk samples for bacteriological culture were routinely collected at 3-wk intervals from all lactating animals (n = 95 +/- 5). Additional samples were collected at calving, clinical mastitis, dry-off, and culling. During the 78-wk observation period, 54 Strep. uberis infections were observed. The majority of infections occurred during a 21-wk period that constituted the disease outbreak. The incidence rate was higher in quarters that had recovered from prior Strep. uberis infection than in quarters that had not experienced Strep. uberis infection before. The incidence rate of Strep. uberis infection did not differ between quarters that were infected with other pathogens compared with quarters that were not infected with other pathogens. The expected number of new Strep. uberis infections per 3-wk interval was described by means of a Poisson logistic regression model. Significant predictor variables in the model were the number of existing Strep. uberis infections in the preceding time interval (shedders), phase of the study (early phase vs. postoutbreak phase), and prior infection status of quarters with respect to Strep. uberis, but not infection status with respect to other pathogens. Results suggest that contagious transmission may have played a role in this outbreak of Strep. uberis mastitis.

Fecal shedding of coliform bacteria during the periparturient period in dairy cows

OBJECTIVE

To determine whether numbers of coliform bacteria in feces of dairy cattle changed during the periparturient period and whether fluctuations were associated with changes in dry-matter intake.

ANIMALS

12 healthy Holstein cows.

PROCEDURE

Fecal samples were collected on a semi-regular basis (i.e., 3 to 7 times/wk) beginning 4 to 6 weeks before the anticipated parturition date and continuing through the third day (5 cows) or second week (7 cows) after parturition, and total numbers of fecal coliform bacteria were determined. Daily feed intake of 7 cows was monitored.

RESULTS

For 11 cows, fecal coliform bacterial counts between 34 and 25 days prior to parturition were low and relatively constant (< 102 change in number of bacteria). Coliform bacteria were not detected in 4 to 8% of fecal samples from 10 cows. All cows had a 10(4) to 10(7) increase in number of colony forming units/g of feces near the time of parturition. Number of fecal coliform bacteria peaked within 7 days of parturition in 9 cows and within 12 days of parturition in 3. Number of fecal coliform bacteria was not correlated with feed intake.

CONCLUSIONS AND CLINICAL RELEVANCE

Cows may have large increases in fecal coliform bacteria count during the periparturient period; however, periparturient cows do not continually shed high numbers of coliform bacteria, and coliform bacteria may not always be detectable by conventional culture methods. Changes in fecal coliform bacteria count did not correlate with changes in dry-matter intake.

Clinical and laboratory findings in cases of toxic mastitis in cows in Northern Ireland

This paper describes the clinical and laboratory findings from 264 cases of toxic mastitis in cows in Northern Ireland between October 1995 and May 1997. Nearly all the cases occurred during the winter housing period, with 84 per cent occurring between November and March inclusive, and 30 per cent in March. Sixty per cent of the cases occurred within one month of calving, and 29 per cent within four days of calving. The most common clinical signs were lethargy (92 per cent), discoloured milk (90 per cent), anorexia (72 per cent), tachypnoea (23 per cent), diarrhoea (23 per cent), recumbency (18 per cent) and staggering (15 per cent). Severe pyrexia (18 per cent) and clinical dehydration (44 per cent) were relatively common findings. Pure growths of Escherichia coli were isolated from 50 per cent of the milk samples, but 11 per cent yielded no bacterial growth. In vitro sensitivity tests indicated that enrofloxacin was effective against 98 per cent of the bacteria isolated, and framycetin and amoxycillin/clavulanic acid against 91 per cent. Abnormally high blood urea levels were observed in 31 per cent of cases, high blood creatinine levels in 42 per cent, and severe leucopenia in 56 per cent. Of the cases which were followed up, 14 per cent died, 21 per cent were culled early and a further 22 per cent lost milk production from the affected quarter.

Adhesion and invasion of Escherichia coli from single and recurrent clinical cases of bovine mastitis in vitro

Seven strains of Escherichia coli, originating from clinical cases of bovine mastitis, and one Salmonella typhimurium control strain were tested for their ability to adhere to, and invade, bovine mammary epithelial cells (MAC-T cells) in vitro. Four of the seven strains were isolated from cows with chronic intramammary infections with recurrent episodes of clinical mastitis and three strains were isolated from single cases of clinical mastitis. Both adhesion and invasion of all strains were dose and time dependent. The four E. coli strains isolated from recurrent cases of clinical mastitis invaded twice as frequently as and three times faster than the strains isolated from single cases of clinical mastitis. By contrast, there was no difference in the amount or speed of adhesion between the two types of strains of E. coli. Adhesion and invasion curves of E. coli resembled a two-step chain reaction, where invasion was the rate-limiting step. Although adhesion and invasion of E. coli has not been demonstrated in vivo yet, the results of the present study may contribute to an understanding of the pathogenesis of chronic intramammary infections caused by E. coli.

Differential induction of complement fragment C5a and inflammatory cytokines during intramammary infections with Escherichia coli and Staphylococcus aureus

The prompt recruitment of neutrophils to the site of infection is essential for the defense of the bovine mammary gland against invading pathogens and is determinant for the outcome of the infection. Escherichia coli is known to induce clinical mastitis, characterized by an intense neutrophil recruitment leading to the eradication of the bacteria, whereas Staphylococcus aureus induces subclinical mastitis accompanied by a moderate neutrophil recruitment and the establishment of chronic mastitis. To elicit the neutrophil recruitment into the udder, inflammatory mediators must be produced after recognition of the invading pathogen. To our knowledge, those mediators have never been studied during S. aureus mastitis, although understanding of the neutrophil recruitment mechanisms could allow a better understanding of the differences in the pathogeneses elicited by E. coli and S. aureus. Therefore, we studied, at several time points, the accumulation of neutrophils and the presence of the chemoattractant complement fragment C5a and of the cytokines interleukin-1beta (IL-1beta), tumor necrosis factor alpha, and IL-8 in milk after inoculation of E. coli or S. aureus in lactating bovine udders. The low levels of C5a and the absence of cytokines in milk from S. aureus-infected cows, compared to the high levels found in milk from E. coli-infected animals, mirror the differences in the severities of the two inflammatory reactions. The cytokine deficit in milk after S. aureus inoculation in the lactating bovine mammary gland could contribute to the establishment of chronic mastitis. This result could help in the design of preventive or curative strategies against chronic mastitis.

Clinical mastitis in primiparous Holsteins: comparisons of bovine leukocyte adhesion deficiency carriers and noncarriers

The objective of this study was to determine the impact of bovine leukocyte adhesion deficiency on clinical mastitis incidence, severity, and duration in Holstein cows. Genomic DNA from milk of 847 Holstein cows in six Pennsylvania herds was used to determine bovine leukocyte adhesion deficiency genotypes (82 or 9.7% carriers). Data on clinical mastitis incidence, severity, duration, and pathogen involved were collected during first lactation for the project cows. One hundred ninety-four cows had one or more clinical mastitis episodes; milk samples from each quarter with clinical mastitis were collected at discovery of the episode and were cultured following National Mastitis Council recommendations. The overall incidence of clinical mastitis was significantly affected by sire and herd-year-season of calving. In addition, incidence of clinical mastitis tended to increase with age at first calving. Severity and duration of clinical mastitis were impacted by the pathogen involved. Incidence of clinical mastitis from all pathogens, from coagulase-negative staphylococci, and from coliform bacteria was not significantly related to bovine leukocyte adhesion deficiency status. Carriers tended to have lower rates of mastitis from streptococci other than Streptococcus agalactiae when compared with noncarriers, but this result should be interpreted with caution because of the low frequency of mastitis from the streptococci. Bovine leukocyte adhesion deficiency status was unrelated to severity or duration of clinical episodes. Bovine leukocyte adhesion deficiency carriers are probably similar to noncarriers in resistance to clinical mastitis.

Prevalence of clinical mastitis in 38 Waikato dairy herds in early lactation

AIM

To determine the prevalence of clinical mastitis in spring-calving dairy herds in the Waikato Region of New Zealand and to identify factors associated with variation in the prevalence of clinical mastitis between herds.

METHOD

A total of 799 quarters from 595 dairy cows from 38 dairy herds were diagnosed by herd owners as having clinical mastitis between 8 July and 21 August 1997. Quarters diagnosed with clinical mastitis were sampled for bacterial culture and somatic cell count, and the presence of clots in the milk and the presence of udder oedema were assessed by a technician or veterinarian.

RESULTS

Clinical mastitis was diagnosed in an average (+/-s.e.m.) of 9.9% (+/-0.8%, range 0.9-21.4%) of calved cows within the herds. Bacteria were not cultured from an average of 12.4 % (+/- 2.0%, range 0.0-45.5%) of cows and 22.3% (+/- 2.4%, range 0.0-54.0%) of quarters diagnosed as having clinical mastitis. There were significant differences between herds in the proportion of cows diagnosed with mastitis and in the proportion of clinical mastitis cases from which bacteria were not cultured. A decreased prevalence of clinical mastitis (p<0.001) was associated with an increased percentage of the herd treated with dry cow antibiotics. An increased prevalence of clinical mastitis (p<0.0001) was associated with both an increased percentage of cows treated in the previous season with lactating cow antibiotics and an increased percentage of heifers in the herd. Herds that were fed supplements before or during lactation had a higher prevalence of clinical mastitis than herds that were not fed supplements (p<0.001). An increased proportion of quarters diagnosed with clinical mastitis that did not culture bacteria was associated with an increased prevalence of clinical mastitis (p<0.001). The proportion of quarters that the technician or veterinarian found with evidence of clinical mastitis (i.e. a somatic cell count >500,000 cells/ml and the presence of either clots or udder oedema) within a herd was inversely related to the proportion of quarters within a herd from which no bacteria were isolated.

CONCLUSION

There was a large variation in the prevalence of clinical mastitis and in the proportion of clinical quarters from which no bacteria were grown between herds. Management factors such as the use of dry cow therapy, feeding regimes and heifer replacement rates all affected the prevalence of clinical mastitis. Herd owners appear to differ in the sensitivity and specificity of their diagnosis of clinical mastitis, with bacteria not isolated from up to 50% of quarters diagnosed with clinical mastitis in some herds. Improvements in the specificity of herd owner diagnosis of clinical mastitis may reduce the use of antibiotics for mastitis during lactation and hence may reduce the risk of antibiotic contamination of milk supplied for human consumption.

Management practices associated with the incidence rate of clinical mastitis

Risk factors for the incidence rate of clinical mastitis were studied in 274 Dutch dairy herds. Variables that were associated with resistance to disease were the feeding, housing, and milking machine factors. Variables that were associated with exposure were grazing, combined housing of dry cows and heifers, and calving area hygiene. Postmilking teat disinfection in herds with a low bulk milk somatic cell count and years of practicing dry cow therapy were positively associated with the incidence rate of clinical mastitis. Herds with a low bulk milk somatic cell count and in which postmilking teat disinfection was not used had lower incidence rates of clinical mastitis than did other herds. The incidence rate of clinical mastitis caused by Escherichia coli was mostly related to housing conditions, hygiene, and machine milking. The incidence rate of clinical mastitis caused by Staphylococcus aureus was mostly related to factors associated with bulk milk somatic cell count and factors that might be due to cause and effect reversal. A strong positive correlation existed between the incidence rate of clinical mastitis caused by Streptococcus dysgalactiae and the incidence rate of clinical mastitis caused by Staph. aureus. The incidence rate of clinical mastitis caused by Streptococcus dysgalactiae was related to nutrition, milking technique, and machine milking. The incidence rate of clinical mastitis caused by Streptococcus uberis was associated with factors related to housing, nutrition, and machine milking.

Recurrent clinical mastitis caused by Escherichia coli in dairy cows

In this study, the occurrence of persistent intramammary infections caused by Escherichia coli with recurrent episodes of clinical mastitis caused by E. coli are described for a cohort of 300 Dutch dairy herds. Calculations on the recurrent episodes were based on data collected by dairy farmers. The genotype of the E. coli strains was determined by means of a polymerase chain reaction using enterobacterial repetitive intergenic consensus (ERIC) primers, resulting in a DNA fingerprint. Quarters in which the same E. coli genotype was found were considered to be persistently infected. In 4.77% of all episodes of clinical mastitis caused by E. coli, persistent intramammary infections caused by the same E. coli genotype were found. Based on the occurrence of the same genotypes, we concluded that, in 2.98% of all episodes, transmission of E. coli strains among quarters within one cow might have occurred. In 13.04% of all episodes of clinical mastitis caused by E. coli in the study, different E. coli genotypes were isolated from recurrent episodes of clinical mastitis within the same cow, indicating that these cows were highly susceptible to recurrent intramammary infections caused by E. coli.

Loss in milk yield and related composition changes resulting from clinical mastitis in dairy cows

Relationships between clinical mastitis and milk yield and composition in dairy cows were reviewed. Requirements for inclusion were: data had to be collected after 1975; dependent variables for milk yield and milk composition had to be defined at the cow level; mastitis cases had to be defined by clinical signs, and at least 250 lactations had to be considered. Twenty studies dealing with milk-yield loss and, for four of them, also with related composition changes were selected. Study populations, design of data collection, and analysis methods differed widely between studies. As expected from these differences--but also due to structural-variation factors such as type of pathogen, animal and production level--estimates for milk-yield losses differed in average magnitude and pattern. Literature data regarding changes in milk-fat % and total-protein % changes were contradictory. Critiques of materials and methods allowed us to propose some final recommendations for values to be used as basic inputs in economic calculations of losses caused by mastitis.

Intramammary infections in primiparous Holsteins: heritabilities and comparisons of bovine leukocyte adhesion deficiency carriers and noncarriers

The objective of this study was to determine the impact of bovine leukocyte adhesion deficiency on intramammary infection (IMI) in Holstein cows at first calving. Quarter milk samples were collected between 3 d prepartum and 4 d postpartum from 756 Holstein cows in first lactation. These samples were frozen and subsequently cultured using National Mastitis Council recommendations. Sixty-eight carriers of bovine leukocyte adhesion deficiency were identified (9.0% of cows) from an additional milk sampling collected in early lactation. Binary variables (infected or uninfected) for each quarter were defined as dependent variables to evaluate IMI incidence from all bacterial species and major species groups: coliforms, coagulase-negative staphylococci, and streptococci other than Streptococcus agalactiae. The model included herd-season of calving, days in milk when samples were collected, age at calving, quarter, cow (random effect), and bovine leukocyte adhesion deficiency. Sire was included as a random effect (instead of cow), and bovine leukocyte adhesion deficiency was dropped from the model to estimate heritabilities. Heritabilities for IMI incidence from the various groups of organisms ranged from 0.02 to 0.66 (0.21 from all bacterial species). No differences were observed between carriers of bovine leukocyte adhesion deficiency and homozygous normal noncarriers for IMI from coliform, coagulase-negative staphylococci, streptococci other than Streptococcus agalactiae, or all bacterial species combined.

Effects of a core antigen vaccine against gram-negative bacteria on physiologic and yield parameters of dairy cows during late lactation and the dry period

The objective of the study was to assess the effects of a core antigen vaccine against Gram-negative bacteria on feed consumption, milk yield, somatic cell count, hematologic parameters, and milk progesterone concentrations for dairy cows in late lactation and the dry period. Sixty-eight multiparous Holstein cows from two farms were paired by days in milk and were randomly selected to receive either the vaccine or placebo. Cows received a secondary immunization with the same product (vaccine or placebo) 3 wk following the primary immunization. The physiologic and yield outcomes were measured prior to each immunization, at the time of each immunization, and for one or more periods following each immunization. No significant differences between vaccinated and placebo groups were detected for daily milk weight, daily feed intake, somatic cell score, rectal body temperature, or milk progesterone concentration (pregnant cows). Cows in the vaccinated group had significant elevations in total blood leukocyte counts following the secondary immunization, which was due to an increase in the neutrophil fraction 24 h postimmunization.

Management practices associated with low, medium, and high somatic cell counts in bulk milk

Management practices associated with bulk milk somatic cell counts (SCC) were studied for 201 dairy herds grouped into three categories according to bulk milk SCC. The cumulative production of fat-corrected milk over 305 d of lactation and category for bulk milk SCC were highly correlated; herds within the low category had the highest milk production. Differences in bulk milk SCC among the categories were well explained by the management practices studied. This correlation was not only true for the difference between the high (250,000 to 400,000) and low (< or = 150,000) categories for bulk milk SCC but also for the difference between the medium (150,000 to 250,000) and low categories and the high and medium categories. Management practices that are known to be important for herds in the high category for bulk milk SCC, such as dry cow treatment, milking technique, postmilking teat disinfection, and antibiotic treatment of clinical mastitis, were also found to be important in the explanation of the difference between herds in the medium and low categories for bulk milk SCC. More attention was paid to hygiene for herds in the low category than for herds in the medium or high category. Supplementation of the diet with minerals occurred more frequently for cows in the low category for bulk milk SCC than for cows in the medium and high categories.

Clinical, bacteriological and epidemiological aspects of clinical mastitis in Israeli dairy herds

A 4-year retrospective study was performed to determine the clinical, bacteriological and epidemiological aspects of acute clinical mastitis in seven Israeli dairy herds. A total of 1124 clinical mastitis cases were detected by abnormal changes in the milk and udder with concurrent decrease of at least 25% in daily milk production. A total of 1190 quarters were affected with clinical mastitis in 1089 cows. The rear quarters had a higher incidence risk (64.7% of quarter cases) than the front quarters. The annual herd-year-incidence varied from 4.2 to 126.8 cases/100 cows/year. The whole-lactation incidence risk (LIR) was 20.8 per 100 lactations. LIR increased from the first to fifth lactation and then decreased. Most clinical mastitis cases were associated with coliform bacteria (60.2% of cases), environmental streptococci (18.6%), coagulase-negative staphylococci (8.7%) and samples from which no bacterial growth was detected (8.1%). Most cases of clinical mastitis occurred in the early stages of lactation, with 51.4% of all cases, 52.3% of coliform cases and 54.6% of environmental streptococci mastitis cases occurring during the first 4 months of lactation. The median days in milk at diagnosis was 118 days. The incidence was lower in the dry summer months. The ratio of peak to low incidence was 1.62 with a calculated peak incidence in January.

Factors influencing adherence of Streptococcus dysgalactiae to bovine mammary epithelial cell monolayers

Factors that affected adherence of Streptococcus dysgalactiae to monolayers of primary bovine mammary epithelial cells and to a bovine mammary epithelial transformed cell line were evaluated. Cell culture medium inhibited more than 99% of binding of S. dysgalactiae to plastic and was as effective as several blocking agents in decreasing adventitious adherence of this organism to plastic. Adherence of two strains of S. dysgalactiae (UT516 and UT519) was higher to a transformed mammary epithelial cell line (2.85% and 0.83%, respectively) than to primary bovine mammary epithelial cells (0.45% and 0.52%, respectively). Measurement of the extent of bacterial adherence to cell monolayers showed that adherence was affected by inoculum size. This indicated that the process was mediated by saturable cell receptors and allowed selection of bacteria:epithelial cell ratios not approaching saturating conditions (< 1500:1). In addition, reduction of bacterial adherence by more than 90% following cell fixation indicated that cell surface proteins played a major role in this process. Delineation of bacterial and epithelial cell factors influencing adherence of S. dysgalactiae to mammary epithelial cell monolayers resulted in the development of an in vitro method for quantifying bacterial adherence to cell monolayers.

Potential virulence factors of Streptococcus dysgalactiae associated with bovine mastitis

Mastitis caused by environmental pathogens is a major problem that affects many well-managed dairy herds. Among the environmental pathogens, Streptococcus dysgalactiae is isolated frequently from intramammary infections during lactation and during the nonlactating period. In spite of its high prevalence, little is known about factors that contribute to the virulence of S. dysgalactiae. During the last decade, several cell-associated and extracellular factors of S. dysgalactiae have been identified; yet, the relative importance of these factors in the transmission and pathogenesis of mastitis caused by S. dysgalactiae has not been defined. Streptococcus dysgalactiae can interact with several plasma and extracellular host-derived proteins such as immunoglobulin G, albumin, fibronectin, fibrinogen, collagen, vitronectin, plasminogen, and alpha 2-macroglobulin. These interactions are mediated by bacterial surface proteins. This organism also produces hyaluronidase and fibrinolysin which may be involved in promoting dissemination of the organism into host tissue. Streptococcus dysgalactiae adheres to and is internalized by bovine mammary epithelial cells in vitro. Involvement of host cell kinases, intact microfilaments and de novo eukaryotic protein synthesis are required for internalization of S. dysgalactiae into bovine mammary epithelial cells; a process that appeared to occur by a receptor-mediated endocytosis mechanism. However, de novo bacterial protein synthesis was not required for epithelial cell internalization. Furthermore, S. dysgalactiae survived within mammary epithelial cells for extended periods of time without losing viability or damaging the eukaryotic cell. Further research on characterization of host-pathogen interactions that take place during the early stages of mammary gland infection will enhance our understanding of pathogenesis of intramammary infection which may contribute to development of methods to minimize production losses due to mastitis.

Risk factors for clinical mastitis in a random sample of dairy herds from the southern part of The Netherlands

The incidence of clinical mastitis in dairy cows was estimated in 171 randomly selected dairy herds from the southern part of The Netherlands. A total of 1103 quarter cases was reported. The mean annual incidence rate was 12.7 quarter cases/yr per 100 cows. The modeling incidence rate of clinical mastitis at the herd level indicated that a number of risk factors were associated with a higher rate of clinical mastitis: one or more cows that were leaking milk, one or more cows with trampled teats, no disinfection of the maternity area after calving, consistent use of post-milking teat disinfection, Red and White cattle (Meuse-Rhine-Yssel) as the predominant breed, and an annual bulk milk somatic cell count < 150,000 cells/ml. The following risk factors were associated with a higher rate of clinical mastitis caused by Escherichia coli: cows with trampled teats, no disinfection of the maternity area after calving, consistent use of post-milking teat disinfection, use of a thick layer of bedding in the stall, and the stripping of foremilk before cluster attachment. The following risk factors were associated with a higher rate of clinical mastitis caused by Staphylococcus aureus: Red and White cattle (Meuse-Rhine-Yssel) as the predominant breed, cows with trampled teats, the stripping of foremilk before cluster attachment, no regular disinfection of the stall, no regular replacement of stall bedding, and an annual bulk milk somatic cell count < 150,000 cells/ml.

Incidence of clinical mastitis in dairy herds grouped in three categories by bulk milk somatic cell counts

Incidence of clinical mastitis was studied in 274 herds grouped in three categories by bulk milk somatic cell count (SCC). Mean incidence rate of clinical mastitis was 0.278, 0.257, and 0.252 cases per 365 cow-days at risk in herds with low (< or = 150,000), medium (150,000 to 250,000), and high (250,000 to 400,000 cells/ml) bulk milk SCC, respectively. The incidence rate of clinical mastitis was not different among the three categories. Variance in the incidence of clinical mastitis among herds increased as bulk milk SCC decreased. Clinical mastitis caused by Gram-negative pathogens, such as Escherichia coli, Klebsiella spp., or Pseudomonas spp., occurred more often in herds with a low bulk milk SCC. Clinical mastitis caused by Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus agalactiae occurred more often in herds with a high bulk milk SCC. Systemic signs of illness caused by clinical mastitis occurred more often in herds with a low bulk milk SCC. Both overall culling rate and culling rate for clinical mastitis were not different among groups catergorized by bulk milk SCC. In herds with a high bulk milk SCC, however, more cows that produced milk with a high SCC were culled. In herds with a low bulk milk SCC, more cows were culled for teat lesions, milkability, udder shape, fertility, and character than were cows in herds with a high bulk milk SCC. In herds with a low bulk milk SCC, cows were also culled more for export and production reasons.

Response of Brazilian crossbred cows to varying doses of bovine somatotropin

The effect of n-methionyl bovine somatotropin (bST) on milk yield was evaluated in crossbred cows (40 1/2 Bos indicus x 1/2 Bos taurus and 18 1/4 B. indicus x 3/4 B. taurus) in Brazil. Cows were randomly assigned to treatments within stage of lactation [stage 1 = 56 to 100 d in milk (DIM); stage 2 = 101 to 199 DIM] and breed groups (1/2 vs. 1/4 B. indicus blood). Treatments were 250 or 500 mg of bST administered every 14 d. Cows in the control group did not receive bST or a placebo. Treated cows received bST injected subcutaneously in the postscapular region, alternating between the left and right sides. The 26-wk experiment consisted of 2 wk of pretreatment and 24 wk of treatment. Cows were housed in an open lot with regulated access to pasture. Cows were milked twice daily and scored for body condition at 2-wk intervals. Compared with controls, milk yield increased equally (22%) for cows receiving 250 or 500 mg of bST. Milk yield response to bST was higher and persisted longer during stage 1 of lactation than during stage 2 of lactation. No difference in response to bST was noted between cows with 1/2 or 1/4 B. indicus blood. Cows treated with 500 mg of bST tended to have more mastitis, but no other adverse health effects were observed. The potential use of 250-mg doses of bST at 14-d intervals in crossbred cattle in Brazil and other subtropical regions throughout the world is suggested, particularly before about 220 DIM.

Complement fragment C5a and inflammatory cytokines in neutrophil recruitment during intramammary infection with Escherichia coli

Generation of inflammatory mediators and leukocyte recruitment to infection at an epithelial surface were studied during Escherichia coli-induced mastitis. One uninfected gland of each of eight midlactation cows was challenged with only 30 CFU of E. coli McDonald strain 487, a serum-resistant isolate from a cow with mastitis. Bacteria grew logarithmically during the first 10 to 12 h after challenge, reaching concentrations of more than 10(5) CFU/ml with no detectable host response during this time. An intense inflammatory reaction began approximately 12 h after the challenge and was characterized by a breakdown in the blood-milk permeability barrier followed by pyrexia and a pronounced leukocytic influx. Coincident with the onset of mammary inflammation was the appearance of neutrophil chemotactic activity in the milk from infected glands. Factors able to upregulate CD18 expression on peripheral blood neutrophils also appeared in milk at this time. The lack of appearance of chemotactic and CD18-upregulating activities until 12 h after challenge indicated that delays in neutrophil recruitment resulted from an initial lack of bacterial recognition and inflammatory mediator production. Production of complement fragment C5a, tumor necrosis factor, and interleukin-1 (IL-1) occurred earlier than production of IL-6 or IL-8. The early and intense production of C5a indicates that this chemoattractant may be more important than IL-8 during the initial recruitment and activation of neutrophils to a developing E. coli infection.

Comparison of fluid and flunixin meglumine therapy in combination and individually in the treatment of toxic mastitis

During a three-year study, 54 cows with toxic mastitis were allocated randomly to one of three treatment groups (A, B and C). Each cow was re-examined within 24 hours of the initial examination, and, during this time, group A received fluid therapy (45 liters of intravenous isotonic electrolyte solution) and flunixin meglumine (2000 mg), group B received fluid therapy only, and group C received flunixin meglumine only. In addition all the cases were treated with parenteral and intramammary tetracyclines, oxytocin and calcium boroglucoanate. There was no significant difference in the rate of survival between the treatment groups and 29 of the cows (53.7 per cent, 95 per cent confidence interval of 39 to 67 per cent) survived.

Efficacy of cefquinome for treatment of cows with mastitis experimentally induced using Escherichia coli

The efficacy of intramuscularly and intramammarily administered cefquinome was evaluated in experimental Escherichia coli mastitis in dairy cows. Forty-seven multiparous, Israeli Holstein cows in early lactation that produced at least 25 L/d of milk were used, and 400 to 750 cfu of E. coli were infused into two healthy quarters of each cow. Cows were randomly assigned to one of the following treatment groups: 1) 75 mg of cefquinome administered intramammarily three times at 12-h intervals, 2) 75 mg of cefquinome administered intramammarily three times at 12-h intervals and 1 mg/kg of cefquinome administered intramuscularly two times at a 24-h interval, 3) 1 mg/kg of cefquinome administered intramuscularly two times at a 24-h interval, and 4) 75 mg of ampicillin and 200 mg of cloxacillin administered intramammarily three times at 12-h intervals. All cows developed typical signs of acute clinical mastitis by 12 to 16 h postinoculation. Parenteral cefquinome therapy, with or without intramammary cefquinome (groups 2 and 3), significantly improved clinical recovery and return to milk production. The bacteriological cure rates were considerably and significantly higher for cows in the groups treated with cefquinome than for cows in the group treated with ampicillin and cloxacillin. This study supported the efficacy of cefquinome in the treatment of clinical coliform mastitis in dairy cows.

Incidence of clinical mastitis in a random sample of dairy herds in the southern Netherlands

The incidence of clinical mastitis and distribution of pathogens in dairy cows was estimated in 171 randomly selected dairy herds in the southern Netherlands. A total of 1103 quarter cases were reported. The average annual incidence rate was 12.7 quarter cases per 100 cows per year. The most frequent isolates from clinical cases were Escherichia coli (16.9 per cent), Staphylococcus aureus (14.4 per cent), Streptococcus uberis (11.9 per cent) and Streptococcus dysgalactiae (8.9 per cent). Most cases were reported in early lactation: 25.4 per cent in the first month of lactation for all cows, and 39.1 per cent in the first month for first lactation cows. The rear quarters had a significantly higher incidence rate than the front quarters. Cows with an E coli infection showed more general clinical signs than cows infected with S aureus, S uberis and S dysgalactiae. A significantly higher incidence was observed in herds with a low (< 150,000 cells/ml) bulk milk somatic cell count than in herds with a count above 250,000 cells/ml.

The anti-inflammatory drugs phenylbutazone and dipyrone in the treatment of field cases of bovine mastitis

The efficacy of phenylbutazone vs. dipyrone for the treatment of acute clinical mastitis were compared in a clinical trial. All cows were treated with 20 g sulfadiazine and 4 g trimethoprim i.m. upon diagnosis and half dosage once daily thereafter. In addition, the NSAIDs treated cows received once daily either 4 g phenylbutazone or 20 g dipyrone i.m. for the duration of the antimicrobial therapy. In all treatment groups the major causative organisms were coliforms. Recovery rates for the controls, the phenylbutazone and dipyrone treatment groups were 81.8%, 89.4% and 86.6%, respectively. Recovery was evaluated by the logistic regression analysis, the odds ratios (OR) and their 95% confidence interval (CI) of treatment success for phenylbutazone and dipyrone treatments relative to the control treatment were calculated. Odds ratio of recovery was high for phenylbutazone (OR = 2.42; CI = 0.98-5.96; P = 0.054) as well as for dipyrone (OR = 1.71; CI = 0.98-3.00; P = 0.060), demonstrating a strong trend towards improved recovery in NSAID groups. The odds of treatment failure for the phenylbutazone group relative to the dipyrone group was 0.71 with 95% CI of 0.28-1.78. Clearly no significant difference could be demonstrated between phenylbutazone and dipyrone in this field trial.

The prevalence of mastitis in primiparous heifers in eleven Waikato dairy herds

The objective of the study was to determine the prevalence of mastitis among primiparous heifers at calving and at drying off in 11 Waikato dairy herds during the 1993-94 dairy production season. Duplicate quarter milk samples were collected aseptically from 458 heifers within 5 days after calving for bacteriological analysis. Mastitis was diagnosed in at least one quarter in 35.6% of these heifers. Coagulase-negative staphylococci were isolated from 21.8% of the heifers. The prevalence of coagulase-negative staphylococci varied between herds from 4.3% to 44.8%. Environmental streptococci caused mastitis in 12.2% of heifers, ranging from 5.6% to 24.1% between herds. Streptococcus uberus was the pathogen identified most frequently at calving and accounted for more than 90% of the streptococcal isolates. Staphylococcus aureus and coliforms were isolated from less than 1% of samples. Clinical mastitis was observed in 8.1% of heifers at calving; environmental streptococci were isolated from 67.6% of these clinical clinical cases. Only 2.8% of heifers developed clinical mastitis during lactation and environmental streptococci were isolated from 38.5% of these cases. The prevalence of mastitis among 428 of the heifers at drying off was 64.7%; a 1.8 fold increase during lactation. Corynebactetium bovis was isolated from 43% of heifers at drying off even though it was not isolated from any heifers at calving. During the season, the prevalence of Staphylococcus aureus mastitis increased to 2.8% while mastitis caused by environmental streptococci declined to 2.8%. The prevalence of environmental mastitis pathogens decreased during lactation while contagious pathogens increased in each of the 11 herds. Ineffective post-milking teat sanitation probably contributed to the increase in mastitis caused by contagious pathogens. Specific factors were not determined that affected the variation in prevalence between herds.

Environmental streptococcal intramammary infections of the bovine mammary gland

Characteristics of environmental streptococcal IMI were investigated over a 7-yr period for a herd in total confinement. A total of 374 new environmental streptococcal IMI was detected. Approximately 50.5% of IMI were new in the dry period, and 49.5% were new in lactation. The rate of new IMI was .00312 IMI/cow day during the dry period and .00054 IMI/cow day during lactation. The percentages of cows and quarters with an environmental streptococcal IMI present at calving were 10.6 and 3.2%, respectively. The percentage of heifers with an environmental streptococcal IMI at calving was similar to that for cows. The rate of new environmental streptococcal IMI was greater during the 1st mo of lactation than during the remainder of lactation. The rate of IMI during late lactation was higher for older cows than for either heifers or cows in second lactation. The rate of environmental streptococcal IMI during the dry period and during lactation was greatest during summer. The mean days of lactation that cows were infected for all IMI was 12.3 d. Approximately 41% of IMI had a duration of < 8 d. Stage of lactation, season of the year, and parity influenced the rate of new IMI.

Efficacy of a barrier teat dip containing .55% chlorhexidine for prevention of bovine mastitis

A natural exposure trial was conducted for 12 mo in a commercial herd of 125 lactating cows to compare the efficacy of an experimental barrier teat dip containing .55% chlorhexidine gluconate with the efficacy of a 1% iodophor for preventing new IMI and clinical mastitis. Teats of half of the cows were dipped in the experimental barrier product, and teats of the remaining half of the herd were dipped in the 1% iodophor product. Quarters dipped with the experimental barrier product had fewer new IMI caused by Escherichia coli, coagulase-negative staphylococci, or Gram-positive bacilli than did quarters dipped in the 1% iodophor. Incidence of new IMI caused by Serratia spp. and Pseudomonas spp. was greater for quarters dipped in the experimental barrier product than for quarters dipped in the 1% iodophor. Efficacy of the two teat dips against new IMI caused by Staphylococcus aureus, environmental streptococci, and Klebsiella spp. did not differ. Incidence of bacteriologically negative clinical cases of mastitis was greater in quarters dipped in the 1% iodophor than in quarters dipped in the experimental barrier product. Incidence of clinical mastitis cases caused by Staph. aureus, environmental streptococci, E. coli, Klebsiella spp., Serratia spp., and Pseudomonas spp. did not differ between treatment groups.

Mastitis of periparturient Holstein cattle: a phenotypic and genetic study

Environmental and genetic factors affecting somatic cell scores, clinical mastitis, and IMI by minor and major pathogens were studied on 137 periparturient Holstein cows selected for milk production. Environmental effects were obtained by generalized least squares and logistic regression. Genetic parameters were from BLUP and threshold animal models. Lactation number affected the number of quarters with clinical mastitis and the number of quarters infected with minor pathogens. The DIM affected somatic cell score and number of quarters infected with major pathogens. Heritabilities for all mastitis indicators averaged 10%, but differences occurred among the indicators. Correlations between breeding values of the number of quarters infected with minor pathogens and the number infected with major pathogens were antagonistic and statistically significant.

Efficacy of dry cow therapy and a Propionibacterium acnes product in herds with low somatic cell count

Dry cow therapy and a Propionibaterium acnes product were evaluated in four commercial herds with low SCC. Cows were randomly assigned within herds to treatment groups of approximately 90 cows receiving dry cow therapy, P. acnes, dry cow therapy plus P. acnes, or no treatment in a factorial arrangement. Each lactating quarter of cows that received dry cow therapy was infused via the teat duct with 300 mg of cephaprin at drying off. Cows that received P. acnes were infused intravenously with .4 mg of killed P. acnes at drying off, 7 to 10 d prepartum, and within 7 d after calving. A second prepartum injection of P. acnes immunostimulator was administered to cows that did not calve within 10 d after the first prepartum injection. Dry cow therapy enhanced bacteriological cures of IMI by Staphylococcus aureus and Corynebacterium bovis at drying off. Dry cow therapy reduced incidence of new IMI by environmental streptococci and C. bovis that originated during the dry period. Cows treated with P. acnes alone had a greater incidence of new IMI by Gram-negative bacilli originating during the dry period than did cows in the other treatment groups. Incidence of clinical mastitis at calving was greater for cows receiving no treatment than for cows receiving dry cow therapy, P. acnes, or dry cow therapy plus P. acnes.

Clinical mastitis in cows treated with sometribove (recombinant bovine somatotropin) and its relationship to milk yield

Effect of sometribove (methionyl bovine somatotropin) on mastitis in 15 full lactation trials (914 cows) in Europe and the US and 70 short-term studies (2697 cows) in eight countries was investigated. In full lactation studies, sometribove (500 mg/2 wk) was given for 252 d, commencing 60 d postpartum. Although herds varied considerably, incidence of clinical mastitis within a herd was similar for cows receiving control and sometribove treatments. Relative risk analyses indicated no treatment effect, and percentage of mastitis during treatment was similar for control and sometribove groups. A positive linear relationship existed between peak milk yield and mastitis incidence (percentage of cows contracting mastitis or cases per 100 cow days); sometribove treatment did not alter this relationship. Increases in mastitis related to milk yield increase from sometribove or related to genetic selection were similar. When expressed per unit of milk, mastitis incidence declined slightly as milk yield increased; this relationship was not altered by sometribove. No effect on clinical mastitis was observed in 70 commercial herds utilizing sometribove for 84 d. However, effects were significant for stage of lactation and milk yield. Overall, studies represented a wide range of research and commercial situations demonstrating that sometribove had no effect on incidence of clinical mastitis during the lactation of treatment. Furthermore, sometribove did not alter typical relationships between milk yield or herd factors and incidence of clinical mastitis.

Therapy of experimentally induced coliform mastitis with a Propionibacterium acnes product

The efficacy of a Propionibacterium acnes product for treatment of coliform mastitis was evaluated following intramammary infusion of Escherichia coli. Ten cows were injected intravenously with a product containing heat-killed P. acnes at 3 h, 3 d, and 7 d after bacterial challenge. Five cows served as untreated negative controls. Bacterial counts in milk, rectal temperatures, and milk SCC did not differ between treated cows and control cows. Intravenous infusion of P. acnes had no effect on milk production or DMI of treated cows compared with untreated controls. Therapy of experimentally induced coliform mastitis with a P. acnes product had no effect on severity or duration of clinical signs.

Factors affecting milk somatic cells and their role in health of the bovine mammary gland

Milk somatic cells play a protective role against infectious disease in the bovine mammary gland. Many genetic and environmental factors affect the number and kinds of leukocytes that account for the vast majority of somatic cells in milk. Neutrophils constitute the vast majority of somatic cells in mammary glands that are infected with mastitis pathogens. The recruitment of neutrophils into the infected mammary gland is a normal part of the cow's defense mechanisms that is very effective for eradicating the majority of infections that occur. For many reasons, milk production and milk quality are negatively impacted by the presence of inflammation in infected glands. Because of the negative effects of high SCC in milk, various approaches are needed to reduce milk SCC. In the future, genetic gains for milk quality and mastitis resistance may be made by removing bulls from breeding programs when their daughters are predisposed to high SCC.

Anti-inflammatory ketoprofen in the treatment of field cases of bovine mastitis

The efficacy of ketoprofen in the treatment of acute clinical mastitis was evaluated in a clinical trial comprising a non-blind controlled study and a blind, placebo-controlled study. All the cows were treated with 20 g sulphadiazine and 4 g trimethoprim intramuscularly upon diagnosis, and half the dosage was given once daily thereafter. In addition, the ketoprofen treatment groups received 2 g ketoprofen intramuscularly once daily for the duration of the antimicrobial therapy. Recovery rates for the non-blind contemporary controls and the blind placebo-controls were 83.7 per cent and 70.7 per cent, respectively. In the non-blind controlled ketoprofen and the placebo-controlled ketoprofen treatment groups, recovery rates were 94.7 per cent and 92.3 per cent, respectively. The odds ratio (OR) of recovery was significantly (P < or = 0.01) high in the placebo-controlled study (OR = 6.75, confidence interval [CI] = 1.45 to 31.4), and high but not significant in the non-blind controlled study (OR = 2.64, CI = 0.53 to 13.10). It was concluded that ketoprofen significantly improved recovery in clinical mastitis in dairy cows.