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.

In vitro fluence rate effects in photodynamic reactions with AIPcS4 as sensitizer

It has been shown previously that the efficiency of photodynamic therapy (PDT) both in vivo and in vitro is dependent on fluence rate. In this study, different in vitro experiments showed that tetrasulfonated aluminum phthalocyanine (AIPcS4) is more efficient in photosensitization if the light is delivered at low fluence rate. Erythrocyte damage, virus inactivation and photooxidation of reduced glutathione (GSH) and histidine were all enhanced if light was delivered at 100 W/m2 as compared to 500 W/m2. Bleaching did not occur under these conditions. Oxygen depletion, shown to be important in fluence rate effects observed in vivo, does not seem to be involved. On theoretical grounds saturation of the triplet state is not likely under these conditions. A possible explantation for the observed fluence rate effects might be found in different reaction pathways, that are favored under high or low fluence rate illuminations. These reactions might involve uni- or bimolecular reactions of intermediate products, resulting in less efficiency at higher fluence rate. It proves to be important, under all circumstances, to monitor fluence rate, because a change in fluence rate, even with similar total fluences, might influence photobiological results in an unexpected way.

Intrauterine transfusions affect fetal T-cell immunity

Intrauterine transfusion (IUT) therapy is the treatment of choice in severe hemolytic disease of the fetus. This treatment automatically implies the introduction of alloantigens in the fetal circulation, which might potentially influence the unprimed fetal immune system. The present study provides evidence that the fetal immune system is indeed prone to modulations of the T-cell receptor BV (TCRBV) repertoire as a result of IUT treatment. Most notably, IUT therapy affects the composition of the CD4+ repertoire, whereas this effect may be obscured in the CD8+ subset. The CD8+ subset was found to be influenced by alterations of the TCRBV repertoire both in IUT patients and controls, suggesting that modulations in this subset could be the result of developmental influences. A more detailed analysis on the composition of the individual TCRBV families was performed by evaluating the distribution of the complementarity determining region 3 (CDR3) size lengths of [32P]-radiolabeled TCRBV transcripts. Using this technique, referred to as spectratyping, only marginal changes were observed in the CD4+ and CD8+ subset during the course of treatment and gestational development of both IUT-treated patients and controls. Therefore, the alterations in the overall TCRBV repertoire were of a quantitative rather than a qualitative nature. To evaluate whether the observed alterations in TCRBV usage-frequencies were a reflection of an allo-reactive response, a primed lymphocyte test (PLT) was performed in 3 IUT-treated patients. We observed that IUT, performed as early as 23 weeks of gestation, may induce the establishment of memory T cells against the IUT donor. However, there was no association between the observed changes in TCRBV repertoire and the magnitude of the secondary allo-reactive response.

Estimation of interdependence among quarters of the bovine udder with subclinical mastitis and implications for analysis

Interdependency among udder quarters with subclinical mastitis was evaluated on 150 farms using a total of 35,828 udder quarters. The occurrence of high somatic cell count (SCC) (> 250,000 cells/ml) in 0, 3, and 4 quarters occurred at a higher rate than would be expected based on independence of the quarters. For all bacterial species, intramammary infection in 0, 2, 3, or 4 quarters of the same cow occurred at a higher rate than would be expected based on independence of the quarters. Intramammary infection and high SCC were found less often in front quarters than in rear quarters. High SCC and intramammary infection occurred more often in right front quarters than in left front quarters. High SCC in diagonal quarters occurred at a lower rate than expected. Corynebacterium bovis, Streptococcus agalactiae, and Staphylococcus aureus had the highest intraclass correlation within herd. Streptococcus uberis had a very low intraclass correlation within herd. The intraclass correlation within cow for the natural logarithm of SCC was 0.47. Corynebacterium bovis and Strep. agalactiae had the highest intraclass correlation within cow, and Streptococcus dysgalactiae had the lowest. Analytical methods were proposed to manage the problem of interdependence and its effect on the design or evaluation of field studies on subclinical mastitis.

Metabolism of acetate in rat brain neurons, astrocytes and cocultures: metabolic interactions between neurons and glia cells, monitored by NMR spectroscopy

The existence of metabolic compartmentation is generally accepted for the brain because of the specific differences in glial and neuronal metabolism. Extracellularly supplied acetate is believed to serve as a substrate only for glia cells, but not for neurons. To further test this hypothesis, primary rat brain cultures of neurons, astrocytes, and cocultures of both cell types were used to investigate the metabolic fate of [2-13C]acetate by means of nuclear magnetic resonance (NMR) spectroscopy. Acetate was metabolized by both cell types, neurons and astrocytes in culture. While glutamine was the main product of glial metabolism, labelled glutamate and aspartate were detected in neuron cultures. Astrocytes and neurons in cocultures showed a very different picture, which is similar to results obtained from brain slices, or in vivo studies. The analysis of the isotopomer pattern of glutamate and glutamine confirm an active glutamate-glutamine-cycle between neurons and astrocytes in cocultures. Furthermore, the analysis of unlabelled metabolites revealed a metabolic coupling of hypotaurine and taurine metabolism in astrocytes and neurons, which provides both cell types with one of the most important organic osmolytes.

The mago nashi gene is required for the polarisation of the oocyte and the formation of perpendicular axes in Drosophila

BACKGROUND

Drosophila axis formation requires a series of inductive interactions between the oocyte and the somatic follicle cells. Early in oogenesis, Gurken protein, a member of the transforming growth factor alpha family, is produced by the oocyte to induce the adiacent follicle cells to adopt a posterior cell fate. These cells subsequently send an unidentified signal back to the oocyte to induce the formation of a polarised microtubule array that defines the anterior-posterior axis. The polarised microtubules also direct the movement of the nucleus and gurken mRNA from the posterior to the anterior of the oocyte, where Gurken signals a second time to induce the dorsal follicle cells, thereby polarising the dorsal-ventral axis.

RESULTS

In addition to its previously described role in the localisation of oskar mRNA, the mago nashi gene is required in the germ line for the transduction of the polarising signal from the posterior follicle cells. Using a new in vivo marker for microtubules, we show that mago nashi mutant oocytes develop a symmetric microtubule cytoskeleton that leads to the transient localisation of bicoid mRNA to both poles. Furthermore, the oocyte nucleus often fails to migrate to the anterior, causing the second Gurken signal to be sent in the same direction as the first. This results in a novel phenotype in which the anterior of the egg is ventralised and the posterior dorsalised, demonstrating that the migration of the oocyte nucleus determines the relative orientation of the two principal axes of Drosophila. The mago nashi gene is highly conserved from plants to animals, and encodes a protein that is predominantly localised to nuclei.

CONCLUSIONS

The mago nashi gene plays two essential roles in Drosophila axis formation: it is required downstream of the signal from the posterior follicle cells for the polarisation of the oocyte microtubule cytoskeleton, and has a second, independent role in the localisation of oskar mRNA to the posterior of the oocyte.

The growth arresting effect of human immunoglobulin for intravenous use is mediated by antibodies recognizing membrane glycolipids

Intravenous human IgG (IVIg) given to patients with autoimmune disorders can result in significant clinical improvement in some patients. The mechanism(s) by which IVIg induces these improvements is(are) not known. We have previously shown that IVIg inhibited the proliferation of peripheral blood lymphocytes in allogeneic mixed lymphocyte reactions and of autonomously growing human and mouse cell lines. In an effort to identify the antigen(s) to which the human IgG binds, the human B cell line JY, whose proliferation was inhibited by IVIg, was incubated with IVIg, washed extensively with PBS, and lysed. Human IgG from these lysates was purified by protein A-Sepharose (IVIgJY). IVIgJY binds to and inhibits the proliferation of JY cells and of peripheral blood lymphocytes stimulated in a MLR at a 1000- to 10,000-fold lower concentration compared to IVIg. IVIgJY was analyzed on a 5-15% gradient SDS/PAGE and only immunoglobulin heavy- and light-chain (run under reducing conditions) proteins were detected. Immunoprecipitation experiments from JY cell lysates with IVIgJY indicated that this IgG did not bind to a protein epitope. Thin-layer immunoblot experiments showed that the IVIgJY binds to glycolipids expressed by JY cells and lymphocytes. Furthermore, evidence is presented indicating that antiglycolipid antibodies are involved in IVIg-induced growth inhibition.

[Thrombotic thrombocytopenic purpura in 13 Dutch centres: treatment and longterm follow-up]

OBJECTIVE

Analysis of the incidence, treatment modalities and disease course of thrombotic thrombocytopenic purpura (TTP) in the Netherlands.

DESIGN

Retrospective follow-up study.

SETTING

13 centres in the Netherlands.

METHODS

Regarding all patients admitted between 1-1-1979 and 1-1-1992 to one of 13 Dutch haematological centres, in whom the diagnosis of TTP was made for the first time, information was gathered from the medical records and from the patients own physicians on patient characteristics at presentation and the occurrence of relapse or death. The follow-up period tended on 1-4-1995.

RESULTS

A total of 65 patients with newly diagnosed TTP were identified: 0.34 per 1,000,000 persons a year (95% confidence interval (95%-CI): 0.26-0.45), increasing to 0.83 in the last year of the study. Forty-six (95%) patients were treated with fresh frozen plasma: 18 (28%) by plasma infusion and 44 (68%) by plasma exchange; 48 (74%) (additionally) received corticosteroids. All 52 patients (80%) who survived the first four weeks after admission reached complete remission. Twelve patients with relapsing TTP underwent splenectomy in remission. The 5-year survival rate was 77% (95% CI: 66-87) and the 5-year relapse-free survival rate 38% (95% CI: 25-52). Cardiac symptoms, severe thrombocytopenia and a high serum LDH were risk factors for acute mortality, but no risk factors for relapse or late-occurring death could be identified.

CONCLUSION

TTP is a rare disease which is increasingly being recognized. Plasma exchange and corticosteroids are the most frequently used therapies. The disease has a high mortality rate in the acute phase of the disease.

The effect of discontinuation of postmilking teat disinfection in low somatic cell count herds. II. Dynamics of intramammary infections

Results of a 20 month split-udder trial on the effect of discontinuation of postmilking teat disinfection on intramammary infections (IMI) with major and minor pathogens in seven dairy herds with a low somatic cell count are described. The incidence of Escherichia coli IMI was found to be significantly lower, whereas the incidence of IMI with Staphylococcus aureus and minor pathogens was significantly higher in quarters for which postmilking teat disinfection was discontinued than in disinfected quarters. It was concluded that discontinuation of postmilking teat disinfection decreased the incidence of E. coli IMI, accompanied by a, from a practical point of view, acceptable rise in somatic cell count. However, the possible increase in the incidence of S. aureus IMI calls for careful monitoring of the dynamics of IMI with contagious pathogens, when postmilking teat disinfection is discontinued in an attempt to reduce E. coli mastitis.

Shelf-life of photodynamically sterilized red cell concentrates with various numbers of white cells

BACKGROUND

Phthalocyanines are useful sensitizers for the photodynamic sterilization of red cell concentrates. The use of the phthalocyanine Pc4 (HOSiPcOSi(CH3)2(CH2)3N(CH3)2) and red light is very efficient in killing various viruses. The addition of scavengers of Type I photodynamic reactions and the use of cremophor to deliver Pc4 give protection to the red cells.

STUDY DESIGN AND METHODS

Various red cell components, either white cell-enriched, buffy coat-removed, or white cell-reduced, have been used to study the effect of photodynamic treatment with Pc4 on hemoglobin and potassium leakage and on ATP and glucose levels after prolonged storage.

RESULTS

After treatment, storage interval-dependent damage to the red cells could be observed. In components with 26 x 10(9) white cells per L, virus inactivation was less efficient than that in components with no or 2 x 10(9) white cells per L. Similarly, red cells were less affected by the treatment in components with a large number of white cells. Pretreatment storage and use within 1 week after photodynamic treatment induce less damage to the red cells at the moment of transfusion.

CONCLUSION

Various improvements in the treatment protocol may ultimately lead to the implementation of photodynamic treatment in transfusion practice. In this respect, the white cell content of the red cell concentrates should be taken into account.

The effect of discontinuation of postmilking teat disinfection in low somatic cell count herds. I. Incidence of clinical mastitis

Results are described of a split-udder trial on the effect of discontinuation of postmilking teat disinfection on the incidence of clinical mastitis in seven dairy herds with a low bulk milk somatic cell count and a high incidence of clinical mastitis. Overall incidence of clinical mastitis was non-significantly lower (18%), whereas the incidence of the most prevalent pathogen associated with clinical mastitis, Escherichia coli, was significantly lower in quarters for which postmilking teat disinfection was discontinued. We concluded that discontinuation of postmilking teat disinfection may decrease the incidence of clinical Escherichia coli mastitis in herds for which standard mastitis prevention measures are executed adequately, bulk milk somatic cell count is low, and incidence of clinical mastitis is high. However, because an increase in intramammary infections with contagious pathogens may occur, care is recommended when advising discontinuation of postmilking teat disinfection.

Alterations in cord blood leukocyte subsets of patients with severe hemolytic disease after intrauterine transfusion therapy

OBJECTIVES

The aim of this study was to compare, at delivery, the cord blood mononuclear cells of infants with severe hemolytic disease who received intrauterine transfusion (IUT) therapy with the cord blood mononuclear cells of healthy nonimmunized control neonates.

STUDY DESIGN

The expression of leukocyte markers on CBMNC of 14 IUT-treated and 18 control neonates was analyzed by means of a panel of well-defined monoclonal antibodies and flow cytometry.

RESULTS

Patients with severe hemolytic disease requiring IUT treatment displayed significant altered expression of some leukocyte markers when compared with control subjects. The circulating CD34+ progenitor cells were significantly increased in comparison with cord blood of nonimmunized neonates. IUT-treated patients also showed a statistically significant decrease in natural killer (NK) cell associated markers (CD16, CD57, and CD69), which correlated with a lower expression of CD56. In these patients an increased expression of CD3/CD45RO and CD3/CD5 was also noted. Although these latter alterations were statistically significant in a single-parameter analysis, the significance disappeared after multi-parameter analysis because of a loss of statistical power.

CONCLUSIONS

Compared with nonimmunized healthy newborn infants, patients who underwent IUT also exhibited a down-regulation of NK cells and NK cell associated markers, as well as increased numbers of CD34+ progenitor cells.

Modulation of the T cell compartment by blood transfusion. Effect on cytotoxic and helper T lymphocyte precursor frequencies and T cell receptor Vbeta usage

Recent data suggest that the favorable effect of pretransplant blood transfusion (BT) on transplant outcome depends on the HLA match. HLA-DR or haplotype shared transfusions lead to transplantation tolerance, and HLA-mismatched BT leads to immunization. The immunological mechanism involved is still unknown. To investigate the effect of HLA compatibility between blood donor and recipient on the T cell compartment, we determined the frequency of cytotoxic and helper T cell precursors specific for blood donor cells (n=20) and the T cell receptor Vbeta (TCRBV) repertoire of the CD4- and CD8-positive peripheral blood mononuclear cells before, at 2 weeks after, and at more than 10 weeks after BT (n=10). Patients had received one transfusion of a nonstored (<24 hr after withdrawal) erythrocyte concentrate without buffy coat containing on average 6x10(8) leukocytes. Eight patients shared an HLA-B and -DR antigen, nine patients shared one HLA-DR antigen, and three patients shared no HLA class II antigens with the blood donor. All patients showed a significant increase in both cytotoxic and helper T cell precursor frequencies against the blood donor 2 weeks after BT. In most patients, the frequencies reached pretransfusion levels again long after BT. In 5 of 10 patients, an expansion of one or more TCRBV families was observed in either the CD4 or CD8 compartment. This study demonstrates that BT, irrespective of the degree of HLA matching, induces activation of the T cell compartment. The degree of sharing of HLA antigens was not correlated with quantitative changes in cytotoxic T lymphocyte precursor or helper T lymphocyte precursor frequencies, or changes induced in the TCRBV repertoire. Cytotoxic and helper T lymphocyte precursor frequencies and TCRBV repertoire determined after BT do not give an indication for a state of tolerance prior to transplantation.

Immunomodulation and remyelination: two aspects of human polyclonal immunoglobulin treatment in immune mediated neuropathies?

Intravenous immunoglobulin is used in inflammatory demyelinating diseases of the peripheral as well as the central nervous system. It is not known which mechanism(s) accounts for the beneficial effect observed in these diseases. The immunomodulatory effects of IVIg in two different models of T and B cell activation were investigated. IVIg inhibited a predominantly cellular immune response of the Th 1 type, which was partially reversed by addition of Th 1 cytokines. In contrast, in a model, which leads to B cell differentiation and antibody production, a synergistic stimulatory effect of IVIg and Th2 cytokines was observed. The ability of IVIg to interfere with cell proliferation and to manipulate the Th1/Th2 profile will have consequences for the induction, character, and amplification of an immune response. Apart from the immunomodulatory effects, evidence shows that IVIg promote remyelination not only by abrogation of the auto-immune attack but also by an effect on glial cells. We showed that IVIg induce growth arrest of normal human fibroblasts and Schwann cells. In fibroblasts this growth arrest is accompanied by upregulation of GAS-3/PMP-22 mRNA. The implications of this finding are discussed. Further studies in human Schwann cells are imperative to prove the hypothesis that IVIg directly stimulates remyelination.

Primary targets for photoinactivation of vesicular stomatitis virus by AIPcS4 or Pc4 and red light

Phthalocyanines are useful sensitizers for the photodynamic sterilization of red blood cell concentrates. The mechanism of photoinactivation of lipid-enveloped viruses is not completely understood. Vesicular stomatitis virus (VSV) was used as a model virus to study the primary targets of photoinactivation by aluminum phthalocyanine tetrasulfonate (AIPcS4) or silicon phthalocyanine HOSiPcOSi(CH3)2(CH2)3N(CH3)2 (Pc4) and red light. Inactivation conditions for VSV in buffer were determined using an end point dilution assay, and viral RNA synthesis in host cells was measured to determine the loss of infectivity in a direct way. The very rapid decrease in the viral RNA synthesis after photodynamic treatment was correlated with respect to different potential primary targets that are involved in different steps of the viral replication cycle. Damage to the viral proteins, induced by treatment with AIPcS4 or Pc4 and analyzed by gel electrophoresis, could not account for the observed loss of infectivity. Binding of VSV to host cells was only slightly impaired after photodynamic treatment with both sensitizers and could therefore not be responsible for the rapid decrease in viral RNA synthesis in cells. A very strong inhibition of viral RNA polymerase activity after treatment with AIPcS4 and red light was detectable using an in vitro assay. This decrease correlated well with the loss of infectivity, indicating that either the RNA or the viral RNA polymerase is the primary target for photoinactivation of VSV with AIPcS4. Treatment with Pc4 did not cause inhibition of viral RNA polymerase activity to an extent that could account for the observed very rapid loss of infectivity. It was therefore concluded that neither the viral proteins nor the binding to the host cells nor the RNA or RNA polymerase are the primary targets for photoinactivation of VSV by Pc4.

Interactions of triethyltin-chloride (TET) with the energy metabolism of cultured rat brain astrocytes: studies by multinuclear magnetic resonance spectroscopy

The effect of triethyltin-chloride (TET), a highly neurotoxic compound, on the cellular metabolism of rat brain astrocytes in vitro was examined by nuclear magnetic resonance (NMR) spectroscopy. 5-week-old cultures were exposed to TET (0.2-40 microM) either for (1) acute (3h), (2) 24 h, or (3) chronic treatment (8 d). Cells were labeled with 1-(13)C-glucose, cell extracts were prepared and 31P, 1H, and 13C spectra were analyzed. Cytotoxic effects of TET were assessed by vital dye uptake assay using neutral red (NR) and by exclusion of trypan blue (TB). Cells were examined ultrastructurally by electron microscopy. The data show that the major target of TET at concentrations already causing morphological effects on cultured astrocytes is not the energy metabolism, but that TET rather alters the intracellular concentrations of organic osmolytes, such as myo-inositol, taurine and hypotaurine, which are part of the control of ion and volume regulation and osmotic balance in astrocytes.

Transfusion of red cells is associated with increased incidence of bacterial infection after colorectal surgery: a prospective study

BACKGROUND

Several studies suggest that perioperative blood transfusion is a major independent risk factor for postoperative bacterial infections. Transfusion-induced immunosuppression is thought to mediate this effect.

STUDY DESIGN AND METHODS

In a randomized clinical trial comprising 697 patients with colorectal cancer, the relationship between two types of red cell components (buffy coat-depleted packed red cells and white cell-reduced [filtered] packed red cells) and postoperative bacterial infections was analyzed.

RESULTS

Both types of red cells appeared to be associated with a greater incidence of postoperative infection than was no transfusion (39 vs. 24%, p < 0.01). A dose-response relationship could be demonstrated: the corrected relative risk was 1.6 for 1 to 3 units of red cells and 3.6 for more than 3 units. Multivariate analyses identified the transfusion of red cells and tumor location as the only significant independent risk factors for postoperative bacterial infection.

CONCLUSION

Because allogeneic white cells, plasma, microaggregates, citrate, and platelets could be ruled out as risk factors for transfusion-associated postoperative infections, it is hypothesized that the transfusion of red cells is a potentially detrimental factor that transiently impairs the clearance of bacteria by phagocytic cells.

[Immunological effects of erythrocyte and leukocyte transfusion. Work Group Blood Group Serology of the Medical Advisory Commission of the College for Blood Transfusion of the Netherlands Red Cross]

Immunological consequences of blood transfusion are less well-known than infectious complications although they occur more frequently. In many cases the effects in individual patients are hardly visible although fatal transfusion reactions may occur: Transfusion of red cells may induce acute or delayed haemolytic transfusion reactions. Transfusion of leukocytes may suppress the function of the immune system of the recipient (with consequences for immune tolerance in transplant patients, cancer surveillance and the occurrence of postoperative infections) but also may induce graft versus host disease.

Preinfection in vitro chemotaxis, phagocytosis, oxidative burst, and expression of CD11/CD18 receptors and their predictive capacity on the outcome of mastitis induced in dairy cows with Escherichia coli

Four to 6 wk after parturition, 12 cows in second, fourth, or fifth lactation were experimentally infected in one gland with Escherichia coli. The capacity of chemotaxis, phagocytosis, oxidative burst, and expression of CD11/CD18 receptors to predict the severity of IMI was measured. Bacterial counts in the infected quarter, expressed as area under the curve, and residual milk production in the uninfected quarters were compared to determine severity of the infection. Although these two outcome parameters were highly negatively correlated, regression models with preinfection tests for leukocyte function fitted best with bacterial counts as an outcome parameter. Of the preinfection tests for leukocyte function, chemotaxis best predicted the outcome of the IMI that had been experimentally induced by E. coli. The number of circulating peripheral leukocytes just prior to inoculation was used to predict 52 and 45% of the severity of IMI for bacterial counts and residual milk production, respectively. As a categorical variable, parity predicted 75 and 56% of the severity of IMI expressed as bacterial counts and residual milk production, respectively. Because of the strong effect of parity on the outcome of the experimentally induced mastitis, analysis was performed to discriminate between second parity cows and older cows. Significant differences were found for the number of circulating peripheral leukocytes and for the expression of CD11b/CD18 and CD11c/CD18 receptors between younger and older cows.

Effect of natural infection with minor pathogens on susceptibility to natural infection with major pathogens in the bovine mammary gland

OBJECTIVE

To evaluate the effect of natural udder infection with minor pathogens on subsequent natural infection with major pathogens.

SAMPLE POPULATION

7 dairy herds with low bulk milk somatic cell count.

PROCEDURE

During a 20-month prospective study, milk samples were collected from diary cows at regular intervals and from quarters with clinical signs of mastitis. Incidence of intramammary infection was calculated in uninfected quarters and in quarters infected with minor pathogens. A within-cow, matched case-control analysis was used to evaluate the effect of minor pathogens on subsequent infection with major pathogens.

RESULTS

Quarters infected with minor pathogens had higher somatic cell count than did uninfected quarters. In quarters infected with Corynebacterium bovis, the rate of infection with major pathogens was lower, whereas in quarters infected with coagulase-negative Micrococcaceae, the rate of infection with major pathogens was higher than that in uninfected quarters. From the within-cow comparison, it appeared that, in quarters infected with minor pathogens, infection with major pathogens was significantly lower than that in comparable control quarters not infected with minor pathogens.

CONCLUSIONS

Minor pathogens have a protective effect against infection with major pathogens. The protective effect of C bovis against subsequent infection with major pathogens appears to be greater than the effect of coagulase-negative Micrococcaceae.