Endotoxin-induced bovine mastitis: arachidonic acid metabolites in milk and plasma and effect of flunixin meglumine

Arachidonic acid metabolites (AAM) were measured in milk and plasma during the course of acute endotoxin-induced mastitis in 12 lactating cows. Mastitis was induced by intramammary challenge exposure with 10 micrograms of Escherichia coli (026:B6) endotoxin. Endotoxin was injected into the teat cistern via the teat canal of a single randomly selected rear quarter of each cow. Concentrations of prostaglandin (PG) F2 alpha and thromboxane (Tx) B2 in fat-free unextracted milk and of 15-keto-13,14-dihydro-PGF2 alpha in plasma were measured by radioimmunoassay. Total production of AAM in milk was determined by measuring quarter milk production. The AAM were compared in 6 cows administered flunixin meglumine (1.1 mg/kg of body weight) and in 6 cows administered saline solution. Concentrations of TxB2 in milk were significantly (P less than 0.001) increased during the early course of acute mastitis in endotoxin-treated quarters of cows not administered flunixin meglumine. Peak concentrations of TxB2 in milk occurred at 8 hours after endotoxin inoculation. Flunixin meglumine treatment produced significant (P less than 0.05) reductions in milk TxB2 and plasma 15-keto-13,14-dihydro-PGF2 alpha concentrations. Concentrations of PGF2 alpha in milk and total PGF2 alpha and TxB2 production per quarter per milking were not significantly influenced by endotoxin challenge or by flunixin meglumine treatment.     

Prostaglandins and glutathione peroxidase in bovine mastitis

Prostaglandin (PG) levels in milk and plasma samples from mastitic cows were determined by radioimmunoassay and compared with erythrocyte glutathione peroxidase (GSH-Px) and other relevant parameters in milk and blood. The overall levels of PGE2, PGF2 alpha and thromboxane B2 (TXB2) in milk were two to four times higher than in blood plasma both in healthy and diseased animals (P less than 0.01). In mastitic milk the PG levels were 24 to 55 per cent and in blood plasma 41 to 95 per cent higher than in healthy animals. The changes were significant and largest for the PGF2 alpha values. In milk, the PG concentrations correlated with the markedly elevated cell count (r = 0.49 to 0.57), and TXB2 values also correlated with milk yield. In blood, PGE2 and PGF2 alpha correlated positively with serum albumin, and PGE2 also correlated with glutathione (GSH). PGE2 and PGF2 alpha correlated negatively with GSH-Px and gamma-glutamyl transferase. The substantial decline in GSH-Px in mastitic animals (P less than 0.01) may be related to changes in lipid peroxidation and PG formation. The possible implications of these findings in the treatment of mastitis are discussed.     

Acute phase response in naturally occurring coliform mastitis.

Changes in the activities of serum cytokines and in acute phase response were observed in dairy cows with naturally occurring coliform mastitis. Seven cows with severe mastitis showed systemic and mammary inflammatory response throughout the observation period, and 11 cows with mild mastitis recovered and were able to be milked within 3 days of onset of mastitis. Serum interleukin (IL)-I and tumor necrosis factor (TNF) activities were higher in the severe group than in the mild group at the first appearance of symptoms. Elevated IL-1 activity was evident in the severe group throughout the observation period. Serum alpha-1-acidglycoprotein (alpha1AG) concentration began to rise with the beginning of mastitis in the severe group, and peaked at 9 days. Serum haptoglobin (Hp) concentrations peaked at 3 days, and decreased gradually after 3 days in the severe group. These results showed that there are dynamic changes in serum IL-1 activity and in serum alpha1AG and Hp concentrations in cows with severe coliform mastitis.     

Role of eicosanoids, histamine, and serotonin in the pathogenesis of Klebsiella pneumoniae-induced bovine mastitis

By inoculating Klebsiella pneumoniae into the teat canals of mammary glands, coliform mastitis was induced experimentally in 6 lactating cows. Release of eicosanoids, histamine, and serotonin in plasma and milk was studied in response to 2 doses of K pneumoniae. A low dose (mean, 5,000 organisms/ml) was inoculated into cows 1 through 4, and a high dose (mean, 200,000 organisms/ml) was inoculated into cows 5 and 6. Milk and blood samples were collected before inoculation (0 hours), and hourly, from 3 to 24 hours after inoculation. Concentrations of prostaglandin F2 alpha (PGF2 alpha), prostaglandin E (PGE), thromboxane B2 (TxB2), histamine, and serotonin were measured in plasma and milk obtained from control (NaCl solution-inoculated) and infected quarters. Fluorometric analysis of milk from infected quarters revealed significantly increased histamine and serotonin concentrations regardless of the dose of K pneumoniae. The mean (+/- SEM) peak concentrations of histamine were significantly (P less than 0.01) increased from the preinoculation value of 44 (+/- 12) ng/ml to 312 (+/- 104) ng/ml in milk from infected quarters and 72 (+/- 24) ng/ml in milk from control quarters. The mean peak concentration of serotonin increased significantly from the preinoculation concentration of 436 (+/- 37) ng/ml to 1,754 (+/- 662) ng/ml and 4,867 (+/- 1,248) ng/ml in milk from control (P less than 0.02) and infected (P less than 0.001) quarters, respectively. However, serotonin concentration in milk from infected quarters was approximately 2.8 times greater than that in milk from control quarters. Concentrations of PGF2 alpha, PGE, and TxB2 in milk and plasma were evaluated by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)     

Controlling acute Escherichia coli mastitis during the periparturient period with recombinant bovine interferon gamma

The efficacy of recombinant bovine interferon (rBoIFN)-gamma against experimentally induced Escherichia coli mastitis during the periparturient period was investigated. Dairy cows intramammarily treated with rBoIFN-gamma 24 h before the E. coli challenge had fewer infected quarters, lower clinical scores, and infections of shorter duration when compared to placebo-treated animals. All rBoIFN-gamma treated cows survived the experimental E. coli challenge. However, placebo treated cows had a 42% mortality rate attributed to coliform mastitis within 3 days of the challenge. Results from this study suggest that intramammary infusion of rBoIFN-gamma can prevent the rapid, unrestricted growth of E. coli within the mammary gland and inhibit the subsequent development of an unlimited inflammatory response under experimental conditions. It is likely that controlling severe local inflammatory reactions may also decrease the pathological alterations to mammary parenchymal tissue that often accompanies acute coliform mastitis during the periparturient period. The potential for prophylactic treatment of perinatal dairy cows with rBoIFN-gamma to regulate the rate, severity, and duration of naturally occurring coliform mastitis during periods of heightened susceptibility is discussed.     

T-helper cells from naive to committed

An endotoxin-induced mastitis model was used to study permeability changes associated with increased milk matrix metalloproteinase (MMP) activity in early inflammation. One quarter of two cows was inoculated with endotoxin (Escherichia coli 055:B5). Blood, milk, and whey were collected before and repeatedly after inoculation for 48 h. The profile and amounts of gelatinolytic MMPs were determined by zymography; gelatinase A (72 kD MMP-2) and gelatinase B (92 kD MMP-9) were identified by Western immunoblotting. Bovine serum albumin (BSA) and trypsin inhibitor capacity (TIC) were used as markers of capillary permeability with parallel examination of neutrophil penetration from blood to milk. Five clinical E. coli mastitis milk samples and five milk samples from cows with healthy udders were analyzed to detect whether increased levels of gelatinolytic MMP-2 and MMP-9 have a role in naturally occurring mastitis with endotoxin involvement. Milk MMP levels increased 2h after the endotoxin challenge. Both MMP-2 and MMP-9 were involved in this early proteolytic event. These increased MMP levels are associated with increased capillary permeability, evidenced first by the penetration of small molecular weight proteins, such as BSA and TIC. Later, 6-12h post endotoxin inoculation, neutrophilic leucocytes also entered the site, as they require larger tissue damage in basal membrane and interstitial tissue structures than BSA and TIC to extravasate. In naturally occurring disease, increased MMP-2 and MMP-9 levels were detected in milk. Thus, gelatinases, especially MMP-2, are involved in the early degradation of the blood-milk barrier, which precedes the penetration of blood-derived cellular components into milk in endotoxin-induced mastitis. In the future, measuring MMP in milk/whey might be a useful tool for diagnosing early mastitis.     

Anti-inflammatory effects of intramammary infusions of glycyrrhizin in lactating cows with mastitis caused by coagulase-negative staphylococci

OBJECTIVE: To determine the anti-inflammatory effects of glycyrrhizin (GL) in lactating cows with mastitis attributable to naturally occurring infection with coagulase-negative staphylococci (CNS). ANIMALS: 12 lactating Holstein cows with mastitis attributable to infection with CNS and 2 healthy cows without mastitis. PROCEDURE: Clinical signs, number of bacteria in milk, somatic cell count (SCC) in milk, concentrations of alpha-lactalbumin and lactoferrin in milk, and concentration of histamine in milk were investigated before and after intramammary infusion of GL (6 cows) or antimicrobials (6 cows). Glands of 2 healthy cows were infused with staphylococcal enterotoxin; milk leukocytes were then harvested and incubated with various doses of GL. RESULTS: In cows infected with CNS that had a low bacterial concentration in milk, infusion of GL alone resulted in significant improvements in swelling, firmness of glands, and number of clots in milk, and it decreased the SCC, but not significantly. Percentage of neutrophils decreased significantly (to < 30%) by 2 days after infusion. Use of lactoferrin as a marker of inflammation in mammary glands revealed a decrease in concentrations, whereas use of alpha-lactalbumin as a marker of recovery for mammary glands revealed significant increases in concentrations in the GL-infused group. Accompanying these anti-inflammatory effects, a decrease in the concentration of histamine in milk was observed in the GL-infused group. Glycyrrhizin decreased histamine production by milk leukocytes in a concentration-dependent manner. CONCLUSIONS AND CLINICAL RELEVANCE: Infusion of GL may regulate intramammary inflammation through modulation of inflammatory mediators such as histamine.     

Efficacy of flunixin meglumine for the treatment of endotoxin-induced bovine mastitis

The clinical effect of flunixin meglumine administration was determined in cows with acute mastitis induced by intramammary administration of endotoxin. In 12 lactating cows, 10 micrograms of Escherichia coli 026:B6 endotoxin were administered via a teat cannula into the teat cistern of single randomly selected rear quarters. Cows were challenge exposed as pairs. One cow in each pair was administered parenteral flunixin meglumine (6 cows) and 1 cow per pair was administered saline solution (6 cows). Multiple doses (7) of 1.1 mg of flunixin meglumine/kg of body weight or saline solution were administered at 8-hour intervals beginning 2 hours after endotoxin. Cow and quarter clinical signs as well as milk somatic cell concentrations, bovine serum albumin, electrical conductivity, and milk production were determined before and for 14 days after endotoxin inoculation. Intramammary endotoxin produced signs characteristic of acute coliform mastitis. Quarter and systemic abnormalities occurred and milk production was reduced by approximately 50% at 12 hours after endotoxin. Flunixin meglumine therapy significantly (P less than or equal to 0.05) reduced rectal temperatures and quarter signs of inflammation and improved clinically graded depression when compared with these signs in saline solution-treated controls. Milk production and laboratory indicators of inflammation in milk were not significantly (P greater than 0.05) different for flunixin meglumine vs saline solution controls. The clinical response observed was consistent with the antipyretic, analgesic, and anti-inflammatory properties of flunixin meglumine.     

Serum amyloid A isoforms in serum and milk from cows with Staphylococcus aureus subclinical mastitis

Serum amyloid A proteins (SAA) are very sensitive acute phase proteins, displaying multiple isoforms in plasma and different body fluids. They are currently under investigation as biomarkers of diseases. The aim of the present study was to compare the concentration and isoform expression of SAA in serum and milk of cows with bacteriologically negative milk (control group) and naturally occurring Staphylococcus aureus (S. aureus) subclinical mastitis (subclinical mastitis group). Somatic cell count (SCC) and bacteriological analyses were performed to establish the control and subclinical mastitis group. SAA concentration was evaluated using a commercial ELISA kit, while expression of different isoforms (serum A-SAA and milk M-SAA3 isoforms) was visualized by denaturing isoelectrical focusing and immunoblotting. The SAA concentrations in sera and milk of cows in the subclinical mastitis group were three and 100 times higher than in those from the control group of cows, respectively. Cows in the subclinical mastitis group had more acidic SAA isoforms in serum with the most prominent one at pI 5.5. This isoform was not detected in sera from the control group. Milk samples in the subclinical mastitis group contained abundant highly alkaline M-SAA3 isoforms and most of the serum isoforms, except for that at pI 5.5. In the subclinical mastitis group SAA isoforms with equivalent pI as serum isoforms accounted for 20% of the total SAA concentration in milk. There were significant differences in the concentrations and isoform patterns of SAA in serum and milk between the control and subclinical mastitis groups of cows. Also, we demonstrated that serum SAA isoforms were not transferred to milk proportion to their plasma content.     

Modulation of arachidonic acid metabolism by bovine alveolar macrophages exposed to interferons and lipopolysaccharide

Stimulation of bovine alveolar macrophages with calcium ionophore A23187 resulted in marked production of leukotriene (LT)B4 and a lesser increase in thromboxane (TX)B2, whereas opsonized zymosan (OPZ) resulted in production of TXB2 and relatively small increases in LTB4 and prostaglandin (PG)F2 alpha. Alveolar macrophages incubated with recombinant bovine interferon-gamma or lipopolysaccharide, and subsequently stimulated with A23187 or OPZ, had altered arachidonic acid metabolism, producing markedly increased amounts of TXB2 and PGF2 alpha, and slightly increased LTB4. Incubation of alveolar macrophages with lipopolysaccharide had a more profound effect on the increased amounts of TXB2 and PGF2 alpha, observed in response to stimulation with A23187 or OPZ, than did incubation with interferon-gamma. Alveolar macrophages incubated with recombinant bovine interferon-alpha 1-1 also produced slightly increased amounts of LTB4 when stimulated with A23187 or OPZ. Altered arachidonic acid metabolism by alveolar macrophages exposed to interferons and lipopolysaccharide may contribute to the development of pulmonary inflammation, such as in the early stages of bacterial pneumonia following viral infections that induce interferon production.     

Elevated levels of tumor necrosis factor-α, (TNF-α) and interleukin-6 (IL-6) activities in the sera and milk of cows with naturally occurring coliform mastitis

The presence of tumor necrosis factor-α (tnf-α) and interleukin-6 (il-6) activities was determined in milk and serum of cows with naturally occurring coliform mastitis (cfm). tnf-α was detected in the sera from 26 of 32 cows with cfm. tnf-α levels were higher in the sera than in the milk. il-6 was high in the sera of surviving cfm animals, but was low in animals that died and in healthy controls. Furthermore, the mean level of il-6 was 20-fold higher in the milk than in the sera of mastitic cows. The level of il-6 in the serum was correlated to that in the milk in individual animals. The presence of il-6 and tnf-α in the sera appears to relate to severe clinical condition of cfm, in the milk whereas they may play a role in generating inflammation of the mammary gland.     

Immune response during the onset of coliform mastitis in dairy cows vaccinated with STARTVAC®

The immune response during the onset of coliform mastitis in vaccinated cows was investigated by measuring lactoferrin (LF), interleukin-8 ( IL-8), and interleukin-1β (IL-1β) concentrations and somatic cell counts in 28 milk samples at the onset of acute coliform mastitis (ACM) and 73 milk samples at the onset of peracute coliform mastitis (PCM). Vaccinated ACM, unvaccinated ACM, and vaccinated PCM showed significantly higher values for LF and IL-1β levels than unvaccinated PCM (p < .01). The IL-8 concentration was lower in vaccinated PCM than in unvaccinated PCM (p < .05). There was no significant difference in somatic cell counts for each parameter. There were no significant differences in the parameters between vaccinated and unvaccinated ACM cows, or vaccinated ACM and PCM cows. From the above results, it is suggested that mastitis vaccination improved the early immune response, particularly at the onset of PCM, and played a large role in host defense against the initial infection.     

Acute phase proteins in serum and milk from dairy cows with clinical mastitis

The serum concentrations of haptoglobin, serum amyloid A and alpha1 acid glycoprotein were determined in serum collected from healthy dairy cows and cows with clinical mastitis, graded as mild (clots in milk) or moderate (clots in milk and visible signs of inflammation in the mammary gland/s) to assess their relative diagnostic value in detecting the disease. The concentrations of haptoglobin and serum amyloid A were also measured in milk collected from infected and uninfected quarters. The concentrations of haptoglobin and serum amyloid A were higher in the serum and milk from the cows with mild or moderate mastitis. The diagnostic value of haptoglobin in differentiating between healthy animals and those with mastitis gave sensitivities and specificities of 82 per cent and 94 per cent respectively with serum and 86 per cent and 100 per cent with milk. The diagnostic value of serum amyloid A in differentiating between healthy animals and those with mastitis gave sensitivities and specificities of 83 per cent and 90 per cent with serum and 93 per cent and 100 per cent with milk. The diagnostic value of serum alpha1 acid glycoprotein in differentiating between healthy animals and those with mastitis gave sensitivities and specificities of 62 per cent and 91 per cent.     

Experimental infection of lactating bovine mammary glands with Streptococcus uberis in quarters colonized by Corynebacterium bovis

Twenty-seven quarters of 18 lactating dairy cows were inoculated intramammarily with 3.6 X 10(4) colony-forming units (CFU) of a strain of Streptococcus uberis isolated from a cow with clinical mastitis. Before quarters were inoculated, 22 were considered as naturally colonized with Corynebacterium bovis, and 5 were considered bacteriologically negative. Streptococcus uberis was isolated from all quarters within 2 days after inoculation, and all quarters developed clinical mastitis by 3 days after inoculation. Mastitis was acute, and most cows had increased rectal temperatures. The number of somatic cells increased significantly (P less than 0.05), and milk production decreased significantly. In many cows, rectal temperatures remained increased, and Str uberis was isolated from infected glands after intramammary and systemic antimicrobial treatments were given. A decreased number (110 CFU) of the same strain of Str uberis caused equally severe mastitis in 3 quarters colonized with C bovis and in 1 bacteriologically negative quarter in 2 cows. Streptococcus uberis was isolated from all inoculated quarters, and all quarters developed clinical mastitis by 2 days after inoculation. Two quarters colonized with C bovis and 2 bacteriologically negative quarters were inoculated once with 25 CFU and once with 240 CFU of a different strain of Str uberis (ATCC 27958). Streptococcus uberis was never isolated from inoculated quarters, and changes in milk yield or number of somatic cells were not observed.     

Endotoxin-induced bovine mastitis: immunoglobulins, phagocytosis, and effect of flunixin meglumine

Milk whey immunoglobulins (Ig) and phagocytosis of staphylococci by milk polymorphonuclear neutrophilic leukocytes (PMN) were measured in 12 cows (allotted to 6 pairs) during acute bovine mastitis induced by intramammary inoculation of endotoxin. Six of these cows (or 1 in each pair) were treated with flunixin meglumine and were compared with the others (given only saline solution). The endotoxin inoculation comprised 10 micrograms of Escherichia coli O26:B6 lipopolysaccharide injected into one of the rear quarters (mammae). Flunixin meglumine was administered parenterally at a dosage of 1.1 mg/kg every 8 hours (total of 7 doses) beginning at 2 hours after endotoxin was injected. Milk samples were obtained, and whey samples were prepared from each quarter of each cow 3 times before inoculation and at 2, 4, 8, 12, 24, 48, 72, 96, 120, 144, 168, and 336 hours after endotoxin was inoculated. Significant increases (P less than 0.05) in milk whey IgG1, IgG2, IgM, and IgA concentrations were observed in whey samples from endotoxin-inoculated quarters. Greatest relative increase was seen for IgG2. Increased whey Ig concentrations were not observed in quarters which were not inoculated with endotoxin. Concentrations of whey IgG1 and IgM in endotoxin-inoculated quarters were significantly (P less than 0.05) decreased in flunixin meglumine-treated cows, compared with those in saline solution-treated cows. Significant increases in phagocytosis of staphylococci by milk PMN were observed in whey samples from endotoxin-inoculated quarters. Significant differences in PMN phagocytosis were not found in whey samples from cows given flunixin meglumine when compared with whey samples from cows given saline solution.     

Kinetics of local and systemic isoforms of serum amyloid A in bovine mastitic milk

The aim of the present study was to characterise the serum amyloid A (SAA) response to intramammary inoculation of Escherichia coli and to examine the distribution of hepatically and extrahepatically produced SAA isoforms in plasma and milk from cows with mastitis. Milk and plasma SAA concentrations were determined before and after experimental induction of E. coli mastitis in six dairy cows. The milk SAA response was characterised by low or undetectable levels before inoculation, very rapid and large increases in concentration after inoculation, and rapid decline towards baseline levels after resolution of disease. In plasma from cows with experimentally induced E. coli mastitis, four hepatically derived SAA isoforms with apparent isoelectric point (pI) values of 5.8, 6.2, 6.8 and 7.4 were demonstrated by denaturing isoelectric focusing. In milk three highly alkaline isoforms with apparent pI values above 9.3 appeared 12 h post-inoculation. These isoforms were not present in any of the plasma samples, and it therefore seems likely that they were locally produced, tissue-specific isoforms. At 24-36 h post-inoculation one or more acidic isoforms corresponding to those found in plasma appeared in the milk samples. The isoforms demonstrated in plasma from cows with E. coli mastitis were also present in serum obtained from three cows with clinical Streptococcus uberis mastitis. In conclusion, experimentally induced E. coli mastitis is accompanied by a prominent SAA response. The results of the present study indicate that SAA accumulation in mastitic milk is the result of both local synthesis of SAA and of hepatically derived SAA gaining access to the milk due to increased permeability of the blood-milk barrier.     

Bacteremia associated with naturally occuring acute coliform mastitis in dairy cows

OBJECTIVE: To determine the incidence of bacteremia in dairy cows with naturally occurring acute coliform mastitis (ACM) with a wide range of disease severity. DESIGN: Cohort study. ANIMALS: 144 dairy cows with ACM from 6 herds. PROCEDURE: Cows were examined at time of identification of ACM (time 0) and classified as having mild, moderate, or severe mastitis on the basis of rectal temperature, hydration status, rumen contraction rate, and attitude. Cows were reexamined at 24 or 48 hours. Bacteriologic culturing of milk and blood (30 ml), CBC, and serum biochemical analysis were performed at each time point. Appropriate samples were obtained at a single point from herdmates without mastitis (controls) that were closely matched for lactation number and days since parturition. Blood culture results were compared among severity groups and controls by use of chi2 tests, as was outcome of an ACM episode for cows grouped by blood bacterial isolates. RESULTS: Bacteria were isolated from 52 blood samples from 46 of 144 (32%) cows with ACM, which was significantly more than control cows (11/156; 7.1%). Group-1 isolates (Escherichia coli, Pasteurella multocida, Mannheimia haemolytica, Klebsiella pneumoniae, Enterobacter agglomerans, and Salmonella enterica serotype Typhimurium) were identified in 20 of 144 (14%) cows with ACM and 0 of 156 control cows. Group-1 isolates were identified in 4.3, 9.1, and 42% of cows classified as having mild, moderate, and severe ACM, respectively. Escherichia coli and K pneumoniae milk and blood isolates obtained from the same cow were of the same genotype. Bacillus spp were identified in 21 of 144 (15%) cows with ACM, which was significantly more than control cows (3/156; 1.9%). Thirty-five percent of cows with a group-1 isolate died during the mastitis episode. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that bacteremia develops in a substantial proportion of cows with ACM. Classification of severity of disease is important for establishment of effective treatment protocols; parenteral antimicrobial treatment may be indicated in cows with ACM.     

Bovine mycoplasma mastitis from intramammary inoculation of small numbers of Mycoplasma bovis. I. Microbiology and pathology

Intrammary inoculation of 70 colony forming units (cfu) of Mycoplasma bovis into one quarter of four previously non-infected cows resulted in severe mastitis in inoculated and uninoculated quarters. Hematogenous spread of the infection was most likely, as mycoplasma was isolated from the peripheral blood of three of four cows and the milking machine was designed to prevent quarter to quarter communication of milk and air. The presence of large numbers of mycoplasma exceeding 10⁶ cfu/ml of milk preceded the onset of overt sero-purulent mastitis by 1–3 days. In general, the severity, duration of the infection and within cow spread of mastitis to adjacent quarters after the inoculation of 70 cfu was indistinguishable from naturally occurring mycoplasma mastitis.The pathology of the chronically infected quarters consisted of alveolar involution and moderate to severe mononuclear infiltration and an increase in interalveolar and loose connective tissue. The quarters of one cow resolving the infections at the time of slaughter were not as severely affected and contained numerous milk-producing alveoli and many alveoli with hyperplasia of the alveolar cells.     

A Histological Study of the Effects of Enzootic Abortion of Ewes Virus in the Lactating Bovine Mammary Gland

Inoculation of the udders of cows with the virus of enzootic abortion of ewes resulted in a severe acute mastitis. The mastitis was characterized clinically by pyrexia, anorexia, decreased milk production, swelling and marked alteration in the physical quality of the milk. The basic lesion was necrosis of alveolar and duct epithelial cells. Virus particles were demonstrated in all levels of the mammary gland three days after inoculation illustrating the rapid spread of the agent. Cells resembling Reed-Sternberg cells and similar to those seen in experimental mastitis produced by the virus of infectious bovine rhinotracheitis were seen in tissues collected six and nine days after inoculation.     

High milk neutrophil chemiluminescence limits the severity of bovine coliform mastitis

Polymorphonuclear neutrophil (PMN) function changes during mastitis. To investigate the contribution of milk PMN to the severity of Escherichia coli (E. coli) mastitis, chemiluminescence (CL) of blood and milk PMN and their efficiency to destroy coliform bacteria in the mammary gland were examined following the induction of E. coli mastitis in early lactating cows. To better assess and define the degree of mastitis severity, cows were classified as moderate and severe responders according to milk production loss in the non-infected quarters at post-infection hour (PIH) 48. There was an inverse relationship between pre-infection milk PMN CL and colony-forming units at PIH 6. In moderate cows, the pre-infection blood and milk PMN CL was approximately 2-fold higher than that of severe cows. The probability of severe response increased with decreasing pre-infection PMN CL. At the beginning of the infection blood and milk PMN CL was consistently higher, and milk PMN CL increased faster after infection in moderate cows. At PIH > 48 milk PMN CL in severe cows exceeded that of moderate cows. The somatic cell count (SCC) in moderate cows increased faster than colony-forming units, whereas in severe cows the results were reversed. The kinetics of CL activity for blood and milk PMN before and during the early phase of infection confirmed an impairment in PMN CL activity for severe responding cows. High pre-infection blood and milk PMN CL and the immediate increase of milk PMN CL and SCC after infection limited bacterial growth thereby facilitating the recovery of E. coli mastitis in moderate cows. Our study strengthens the idea that pre-existing milk PMN (a static part of the udder's immune defense) functions as a "cellular antibiotic" before and during infection, and low milk PMN CL is a risk factor for bovine coliform mastitis.