Physiological and pathological factors influencing bovine immunoglobulin G1 concentration in milk

Bovine immunoglobulin G1 concentration was determined by radial immunodiffusion in 349 milk samples of uninfected quarters, 95 of infected quarters, and 118 blood serum samples from 42 Holstein-Friesian cows taken at days 30, 150, and 270. In lactation, immunoglobulin G1 concentration in milk was not affected by immunoglobulin G1 concentration in blood serum or location of quarters. The immunoglobulin G1 concentrations increased at the end of lactation and in samples collected from cows beyond the third lactation. Uninfected quarters had a mean immunoglobulin G1 concentration of .46 mg/ml. This was less than means from quarters infected by minor or major pathogens. Quarter infection by Staphylococcus aureus resulted in an increase of immunoglobulin G1 concentration in blood serum (9.22 to 11.3 mg/ml). When Corynebacterium bovis was persistent throughout the lactation, immunoglobulin G1 concentration in blood serum was increased (11.26 mg/ml). There was no correlation between somatic cell count and immunoglobulin G1 concentration in uninfected quarters. There was a slight correlation between bovine serum albumin and immunoglobulin G1 concentration in identical quarters (.23). Infection of quarters increased in varying degrees the correlation between immunoglobulin G1 concentration and bovine serum albumin concentration or somatic cell count in milk.     

Effect of infection status on quarter milk production and composition following omitted milking

Sixteen cows in middle to late lactation were milked for 3.5 days at 12-h intervals except for a 24-h interval between third and fourth milkings. A cowside quarter milking unit was used. Quarters were classified by infection status. Milk chloride, lactose, somatic cell concentrations, N-acetyl-B-D-glucosaminidase activity, and cell differential counts were determined. Following the omitted milking, concentrations of milk chloride and somatic cells were elevated and lactose concentration reduced in infected quarters. In uninfected quarters, chloride concentration increased, and lactose concentration decreased after the 24-h interval. The milk N-acetyl-B-D-glucosaminidase activity was elevated only in quarters infected with major pathogens. Changes of milk secretion induced by an omitted milking are affected by infection status, and additional secretory cell damage in quarters infected with a major pathogen may result from an omitted milking.     

Physiological and pathological factors influencing bovine serum albumin content of milk

Concentrations of albumin from bovine blood serum were measured by radial immunodiffusion of 480 milk samples. Content in milk was not affected by content in serum, lactation number, or location of quarters. Bovine serum albumin concentrations in milk increased at the end of lactation (270 days) compared to the beginning (30 days) and at midlactation (150 days). Uninfected quarters had a mean concentration of serum albumin of .193 mg/ml. This was less than means for quarters infected by minor pathogens (.242 mg/ml) and by major pathogens (.284 mg/ml). Distributions of concentrations related to infection status, however, overlapped substantially. Somatic cell count was correlated .53 with concentrations of blood serum albumin in milk. About 32% of quarters infected by major pathogens had fewer than 500 x 10(3) cells/ml, whereas 47.5% of them had serum albumin content less than .2 mg/ml. For subclinical infections, concentration of serum albumin markedly increased when somatic cells were more than 1,000 x 10(3) cells/ml.     

Variation in milk protein concentrations associated with genetic polymorphism and environmental factors

Concentrations of alpha s-casein, beta-casein, kappa-casein, beta-lactoglobulin, alpha-lactalbumin, serum albumin, and immunoglobulin in milk from 1888 Holstein cows were determined monthly over the lactation period. Cows were phenotyped for genetic variants of alpha s1-casein, beta-casein, kappa-casein, and beta-lactoglobulin. Least squares analyses showed variations in individual proteins due to parity number, month of test, stage of lactation, somatic cell count, fat content, milk yield, and phenotypes of cows for milk proteins. beta-Casein declined and serum proteins increased with advancing age of cows. Concentration of individual proteins decreased during the first 2 to 3 mo in lactation and then increased as lactation progressed. alpha s1-Casein variants significantly affected concentrations of alpha s-casein (BC greater than BB greater than AB) and beta-lactoglobulin (AB greater than BB greater than BC). Variant B for beta-casein is associated with lower alpha s-casein, beta-lactoglobulin, immunoglobulins, and higher beta-casein and alpha-lactalbumin concentrations than variant A1, A2, or A3. Milk from BB kappa-casein, and BB beta-lactoglobulin cows contained more alpha s-casein, kappa-casein, and less beta-lactoglobulin than milk from AA cows for the two proteins. Concentrations of all proteins were negatively correlated with milk production. Increased somatic cell counts were associated with lower beta-casein and higher concentrations of other proteins. Fat content of milk was positively correlated with the three casein fractions and beta-lactoglobulin.     

Relationships between radioimmunoassays of alpha lactalbumin and prolactin in bovine skim milk

A radioimmunoassay developed for alpha-lactalbumin was sensitive between 5 and 140 ng alpha lactalbumin. Addition of increasing volumes of milk to assay tubes progressively decreased binding of iodine-125-labeled alpha-lactalbumin to the antisera in a manner which paralleled the binding curve generated by increasing concentrations of standard alpha-lactalbumin. The addition of 10, 20, 30, or 40 ng of alpha-lactalbumin to diluted milk samples gave 90, 100, 105, and 102% recoveries. Alpha-lactalbumin antisera did not crossreact with 1000 ng of bovine casein, blood serum albumin, beta-lactoglobulin, prolactin, or growth hormone. Milk from each of approximately 100 Holstein Friesian cows at different stages of lactation was sampled monthly for 12 mo. Concentrations of alpha-lactalbumin (1.63 mg/ml) and prolactin (24.9 ng/ml) in samples of skim milk collected in the 1st mo of lactation were greater than those in the remaining months of lactation. Monthly concentrations of alpha-lactalbumin and prolactin in skim milk did not change significantly during seasons of the year. The correlation between concentrations of prolactin and alpha-lactalbumin pooled within subclasses of month of lactation within month of year was .08 for 1125 pairs.     

Evaluation of somatic cell count thresholds to detect subclinical mastitis in Gyr cows

The objectives of this study were (1) to determine the sensitivity (Se) and specificity (Sp) of somatic cell count (SCC) thresholds to identify subclinical mastitis in Gyr cows caused by major and minor pathogens; (2) to study the effects of month of sampling, rear or front mammary quarters, herd, intramammary infection (IMI), and bacterial species on SCC at quarter level; and (3) to describe the prevalence of IMI in Gyr cows in commercial dairy herds. In total, 221 lactating Gyr cows from 3 commercial dairy farms were selected. Milk samples were collected from individual quarters once a month for 1 yr from all lactating cows for SCC and bacteriological analysis. Mammary quarters were considered the experimental units and the SCC results were log₁₀-transformed. Four SCC thresholds (100, 200, 300 and 400 × 10³ cells/mL) were used to determine Se and Sp to identify infected mammary quarters. The overall prevalence of IMI in quarter milk samples of Gyr cows was 49.8%, and the prevalence of minor pathogens was higher (31.9%) than that of major pathogens (17.8%). Quarter samples with microbial isolation presented higher SCC compared with negative samples. Sensitivity and Sp of selected SCC thresholds varied according to the group of pathogen (major and minor) involved in the IMI definition. Sensitivity increased and Sp decreased when mammary quarters with only major pathogens isolation were considered positive. The use of a single SCC analysis to classify quarters as uninfected or infected in Gyr cows may not be a useful test for this breed because Se and Sp of SCC at the studied thresholds were low. The occurrence of IMI and the bacterial species are the main factors responsible for SCC variation in mammary quarters of Gyr cows. Milk samples with major pathogens isolation elicited higher SCC than those with minor pathogens.     

Serum concentrations of the milk proteins alpha-lactalbumin and beta-lactoglobulin in pregnancy and lactation: correlations with milk and fat yields in dairy cattle.

Serum concentrations of alpha-lactalbumin and beta-lactoglobulin in first pregnancy, parturition, lactation, involution, and second parturition in 37 Holstein cattle were determined and used as an index of mammary status and in predicting milk yield. During first pregnancy, serum alpha-lactalbumin increased in the last 3 mo and reached a peak at parturition (approximately 1100 ng/ml). Changes in alpha-lactalbumin could not be described by a simple exponential equation, whereas changes in serum beta-lactoglobulin were described by a single exponential from second trimester until 4 wk prepartum and reached a peak at parturition (approximately 460 ng/ml). By 2 wk after parturition, alpha-lactalbumin had dropped to approximately 140 ng/ml, and beta-lactoglobulin dropped to approximately 25 ng/ml. In late lactation, alpha-lactalbumin was approximately 70 ng/ml and beta-lactoglobulin approximately 20 ng/ml. Short-term elevations were found after cessation of milking in both alpha-lactalbumin and beta-lactoglobulin in serum. The concentrations of alpha-lactalbumin and beta-lactoglobulin at second parturition were similar to those at first parturition with no differences found between parity. Both alpha-lactalbumin and beta-lactoglobulin in serum were functionally associated with mammary growth and development. In heifers late in pregnancy, both serum concentrations of alpha-lactalbumin and beta-lactoglobulin were positively correlated with mature equivalent milk and fat yields in the subsequent lactation. Serum beta-lactoglobulin concentrations at 16 wk prepartum in heifers were highly correlated with the sum of first and second lactation milk (r = .60) and fat (r = .60) yields. The potential value of using serum beta-lactoglobulin as an index for prescreening of heifers for lactation potential is discussed.     

Effect of subclinical intramammary infection on somatic cell counts and chemical composition of goats' milk

We investigated effects of subclinical intramammary infection (IMI) on milk somatic cell count (SCC) and milk composition in udder halves of dairy goats. A total of 35 mixed-age Alpine does (70 udder halves; approximately 55 kg body weight) were rotationally grazed on a mixture of vegetative forages (wheat/berseem clover, sudan grass and cowpeas). Milk samples for bacterial analysis and SCC were collected monthly from both halves from April to September, 2001. Across stages of lactation, 19-31% of udder halves became infected. The prevalence of IMI exhibited quadratic patterns through multi-peaked responses within each stage of lactation. Higher rates of IMI were observed during the early stage of lactation (19% in May) and in the late stage of lactation (31% in September). Coagulase negative Staphylococcus (CNS, 43.7%), Staph. aureus (35.4%), and Pseudomonas aeruginosa (12.4%) were the most prevalent pathogens. Within single-strain IMI, log SCC (6.24) was lower (P<0.01) for CNS than those derived from IMI by Staph. aureus (6.49), Ps. aeruginosa (6.53) or Serratia spp. (6.90). Infected udder halves had a higher average SCC (4761 v. 2259 x 10(3) cells/ml; P<0.01) than uninfected halves, but uninfected halves often had similar levels of SCC to infected halves. Daily average milk production was not significantly different between infected and non-infected goats and the relationship between IMI and SCC was not always correlated. Effective mastitis screening requires bacteriological culture since SCC was not highly correlated.     

Milk lactoferrin in heifers: Influence of health status and stage of lactation

The objective of the current study was to analyze the variations in lactoferrin (LF) concentrations in primiparous cows with intramammary infection and to study how the lactation stage affects these variations. In addition, we aimed to study the potential of the LF concentration in early lactation as a predictive factor for future infections. To accomplish this goal, a longitudinal analysis was performed for 96 primiparous cows. Milk samples were collected each month from individual quarters, and the LF concentration was determined for each sample. Criteria that included both somatic cell count (SCC) and a microbiological analysis were used to assess the health status of the quarters. Of the diseased quarters (SCC >200,000 or positive for pathogen isolation, or both), 62% corresponded to nonspecific mastitis (SCC >200,000 but microbiologically negative) and 25% corresponded to the category “presence of bacterial growth” (SCC <200,000 but microbiologically positive). Diseased quarters showed increased concentrations of LF compared with healthy quarters. However, this increase was greater during the first days of lactation compared with later periods. Kaplan-Meier analysis of time free of infection demonstrated that quarters with LF concentrations at early lactation (3–10 d in milk) greater than 0.1 mg/mL are more likely to become infected during the following lactation compared with quarters with lower LF concentrations in early lactation. The results support that LF plays a relevant role in combating intramammary infection, particularly during the first days of lactation. In addition, we present evidence of the potential use of LF as a predictive marker of future infections in the individual quarters of dairy heifers.     

Detection of mastitis pathogens by analysis of volatile bacterial metabolites

The ability to detect mastitis pathogens based on their volatile metabolites was studied. Milk samples from cows with clinical mastitis, caused by Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli were collected. In addition, samples from cows without clinical mastitis and with low somatic cell count (SCC) were collected for comparison. All mastitis samples were examined by using classical microbiological methods, followed by headspace analysis for volatile metabolites. Milk from culture-negative samples contained a lower number and amount of volatile components compared with cows with clinical mastitis. Because of variability between samples within a group, comparisons between pathogens were not sufficient for classification of the samples by univariate statistics. Therefore, an artificial neural network was trained to classify the pathogen in the milk samples based on the bacterial metabolites. The trained network differentiated milk from uninfected and infected quarters very well. When comparing pathogens, Staph. aureus produced a very different pattern of volatile metabolites compared with the other samples. Samples with coagulase-negative staphylococci and E. coli had enough dissimilarity with the other pathogens, making it possible to separate these 2 pathogens from each other and from the other samples. The 2 streptococcus species did not show significant differences between each other but could be identified as a different group from the other pathogens. Five groups can thus be identified based on the volatile bacterial metabolites: Staph. aureus, coagulase-negative staphylococci, streptococci (Strep. uberis and Strep. dysgalactiae as one group), E. coli, and uninfected quarters.     

Effect of parity, stage of lactation, and intramammary infection on concentration of somatic cells and cytoplasmic particles in goat milk

Aseptic foremilk samples (about 15 ml) were collected biweekly for four samplings and then monthly throughout lactation from 35 does in three herds on Dairy Herd Improvement test. Bacteriology, direct microscopic somatic cell counts, and cytospin differential cell counts were performed on all samples. Milk yield was obtained from monthly Dairy Herd Improvement records. Thirty-nine percent of udder halves were infected, and coagulase negative staphylococci were the most frequent isolates (201 of 205). Somatic cell counts were influenced by lactation number, stage of lactation, and intramammary infection. Also, infection of one udder half increased somatic cells in the corresponding uninfected mammary half of the same animal. Cytoplasmic particles were not affected by stage of lactation or by intramammary infection but were greater for goats in first lactation. Milk yield was influenced by lactation number, stage of lactation, and intramammary infection.     

Experimental challenge of bovine mammary glands with Enterococcus faecium during early and late lactation

Mammary glands of early and late lactation cows were challenged with Enterococcus faecium of bovine origin to determine in vivo pathogenicity and milk somatic cell count (SCC) responses. A total of 20 early lactation and 18 late lactation mammary glands were challenged. Two isolates highly adaptive and 2 isolates poorly adaptive for in vitro growth in mammary secretion were used as challenge strains of bacteria. Challenged quarters of early lactation cows were more susceptible to intramammary infection caused by E. faecium than those of late lactation cows. Intramammary challenge with isolates poorly adaptive for in vitro growth in mammary secretions resulted in 94.7% of quarters infected compared with 36.8% of the quarters infused with the isolates highly adaptive for in vitro growth in mammary secretions. Milk from quarters infused with the isolates poorly adaptive for in vitro growth had higher SCC and bacterial counts compared with quarters challenged with the isolates highly adaptive for in vitro growth. A stage of lactation effect within treatment groups was measured when milk SCC were compared between early and late lactation cows. Milk SCC in uninfused (negative control) quarters were lower in early lactation cows compared with late lactation cows. Conversely, in quarters infused with isolates poorly adaptive for in vitro growth, SCC were higher in early lactation cows compared with late lactation cows on d 2, 3, 4, 15, 16, and 17 postchallenge. In quarters infused with isolates highly adaptive for in vitro growth, SCC response did not differ between early and late lactation cows. In vitro growth of E. faecium in mammary secretion was inversely related to in vivo pathogenicity in the mammary glands of early and late lactation cows.     

Effects of prepartum intramammary antibiotic therapy on udder health, milk production, and reproductive performance in dairy heifers

Preparturient heifers (n = 561) from 9 herds in 6 US states and 1 Canadian province were enrolled in a study to test the hypothesis that prepartum intramammary therapy would cure existing intramammary infections (IMI) and lead to increased milk production, reduced linear somatic cell count (LSCC), and improved reproductive performance. Mammary secretions were collected 10 to 21 d before expected calving from each quarter. Heifers were then assigned by identification number to receive intramammary therapy consisting of infusion of one tube per mammary quarter of a lactating cow commercial antibiotic preparation containing cephapirin or to a nontreated control group. Overall, 34.1% of mammary quarters were infected with a mastitis pathogen before parturition and 63.4% of heifers had at least one mammary quarter infected. The coagulase-negative staphylococci (CNS) caused the majority (74.8%) of prepartum IMI. Coagulase-positive staphylococci, environmental streptococci, and coliforms accounted for 24.5% of prepartum infections. Treatment had a significant effect on the cure rate of infected mammary quarters. Mammary quarters that were infected prepartum and treated with antibiotics had a 59.5% efficacy of cure rate and the percentage reduction in heifers with IMI was 51.9. Control quarters had a spontaneous cure rate of 31.7%. Treatment did not significantly affect milk production or LSCC in the first 200 d of lactation; however, there was a significant treatment by herd interaction for milk production. Quarters cured of either CNS or major pathogens had a lower LSCC in the first 200 d of lactation. No significant effect on services per conception or days open between treatment and control groups was observed. This trial demonstrated that prepartum intramammary antibiotic therapy did reduce the number of heifer IMI postpartum. Milk production, LSCC, and reproductive performance during the first 200 d of the first lactation were not significantly affected by treatment. Given these results, use of prepartum intramammary antibiotic therapy in heifers as a universal strategy to increase milk production in first-lactation dairy cows may not be warranted.     

Milk composition and health status from mammary gland quarters adjacent to glands affected with naturally occurring clinical mastitis

Mammary gland quarters have usually been considered to be anatomically and physiologically independent, but some recent research has indicated more interdependence than previously reported. The objective of this study was to compare milk composition (fat, total protein, lactose, solids-not-fat, and chloride) and health status (somatic cell count, differential leukocyte count, and lactate dehydrogenase) of milk samples from unaffected mammary glands of an udder with a single clinically inflamed quarter to results of milk samples from healthy mammary glands of healthy cows. The study was designed as a prospective case control study with case and control cows matched by parity and days in milk. Cases were defined as cows (n = 59) experiencing clinical mastitis in a single mammary gland, and controls (n = 59) were defined as cows that had not experienced clinical mastitis during the current lactation. Quarter milk samples were collected from all mammary glands adjacent to clinically affected quarters of cases and from the same mammary glands of controls. Samples were used to assess concentration of chloride and lactate dehydrogenase, fat, total protein, solids-not-fat, somatic cell count, and differential leukocyte count. Microbiological analysis was also performed on milk samples obtained from clinically affected mammary glands (n = 59). Logistic regression models were used to assess possible associations among quarter somatic cell count (≥150,000 cells/mL) and quarter type (adjacent to case or control). Multivariate linear models were used to compare milk composition and health status between quarter types. A total of 170 quarters were enrolled per group. Milk obtained from adjacent quarters of cases contained a lesser concentration of total protein, lactose, and solids-not-fat, but had a greater concentration of fat and chloride. The somatic cell count, total leukocyte count, and absolute numbers of neutrophils, lymphocytes, and macrophages were all increased in milk obtained from adjacent quarters of case cows compared with milk obtained from quarters of control cows. The relative proportion of neutrophils was increased, whereas the proportion of macrophages was decreased in milk obtained from cases. Approximately 30% of milk samples obtained from adjacent quarters of cases had a somatic cell count ≥150,000 cells/mL compared with 12% of milk samples obtained from quarters of control cows. The position of the mammary gland was not associated with any outcomes. In conclusion, our results support previous research that indicates the immune response to intramammary infection in a single mammary gland quarter alters milk composition and health status throughout the udder.     

Fresh cow mastitis monitoring on day 3 postpartum and its relationship to subsequent milk production

The purpose was to determine the association of milk California Mastitis Test (CMT), somatic cell concentration (SCC), and milk differential cell count results on day 3 postcalving with subsequent lactation production and health events. On d 3 postcalving, the CMT was performed and quarter milk samples were collected from 130 dairy cows. Quarter SCC and milk differential cell counts were determined. Microbiology on duplicate quarter milk samples was used to determine the presence of intramammary infection by major or minor pathogens. Production measures obtained using Dairy Herd Improvement Association testing were 150-d standardized and summit milks. Milk culture results on a cow basis included 82 (63.1%) samples with no growth, 31 (23.9%) with major pathogens, and 17 (13.1%) with minor pathogens. Milk culture results comparing cows with no growth to those with any growth (major or minor pathogens) were not associated with statistically significant differences in milk production. Milk culture results comparing cows with major pathogens to those with no growth and minor pathogens combined were associated with statistically significant differences in 150 d milk. Milk production did not differ for cows with CMT results above and below a cut-off of trace, and for SCC results above and below cut-offs of 200,000, 300,000, and 400,000/mL, respectively. Statistically significant differences in milk production were found for cows above and below cut-offs for percentage neutrophils in milk and for absolute neutrophil counts. Associations were found for milk production and number of quarters (0, 1, 2, or 3 and 4 combined) above respective cut-offs for SCC, percentage neutrophils in milk, and absolute numbers of neutrophils in milk, but not for CMT. Milk production differed for cows experiencing any health event versus those with no health event. The most commonly recorded health event was clinical mastitis. Statistically significant associations were detected between health events and milk culture results, SCC, neutrophil percentage, and neutrophil absolute counts. Results of the present investigation indicate that milk monitoring on d 3 of lactation using milk neutrophil percentage or neutrophil absolute counts may be useful as an indication of subsequent milk production.     

Variation in milk somatic cells of heifers at first calving.

To evaluate variation in milk somatic cells, 24 primiparous cows (paired by calving date) were sampled during the first 75 d of lactation. Milk somatic cell counts were lowest at 9 to 10 wk. For differential cell counts in milk, only percentage of macrophages changed significantly during first 75 d (33% at 1 wk, 25% at 6 wk, and 34% at 11 wk). Epithelial cells were identified and ranged from 11 to 20% of total. For milk somatic cell count, variation between cows within pairs sampled contemporaneously was small (3 to 24%). However, variation between cows was much greater for the differential cell counts (46% of total for lymphocytes and 34% for epithelial cells). Of 1021 quarter foremilk samples, 26 were positive for major pathogens, but 326 were positive for various species. Prevalence of bacteria was significantly higher during first 10 d after calving. Rear quarters had significantly higher bacterial presence: 47% for left rear versus 21% for left front and 37% for right rear versus 24% for right front. Total milk somatic cell count after first calving appears to depend primarily on differences in temporary factors and is not a stable characteristic of individual cows. Proportions of the different somatic cell types in milk may vary consistently by cow in early first lactation.     

Association of coagulase-negative staphylococcal species,mammary quarter milk somatic cell count,and persistence of intramammary infection in dairy cattle

This study was conducted to evaluate the association between subclinical intramammary infection (IMI) with coagulase-negative staphylococci (CNS), mammary quarter milk somatic cell count (SCC), and persistence of IMI in dairy cattle. Convenience samples of CNS isolates harvested from milk samples of subclinically infected mammary quarters collected between 4 and 2 wk before drying-off, between 2 wk before drying-off and the day of drying-off, within 24 h after calving, between 1 and 2 wk after calving, and during lactation were evaluated. Isolates were obtained from the Canadian Bovine Mastitis Research Network culture bank and were identified to the species level using rpoB gene sequencing. Cow and quarter-level data were obtained from the Canadian Bovine Mastitis Research Network database and used for statistical analyses. In addition, for mammary quarters that had more than one isolation of the same CNS species at different time points, the isolates were evaluated using pulsed-field gel electrophoresis to identify persistent IMI. Milk SCC was compared between mammary quarters infected with different CNS species and to a cohort of uninfected mammary quarters. A total of 877 isolates from 643 mammary quarters of 555 cows on 89 Canadian dairy farms were identified to the species level. Twenty different species were identified, with Staphylococcus chromogenes being the most common species identified (48% of isolates), followed by Staphylococcus simulans (19%) and Staphylococcus xylosus (10%). Of the 20 species identified, only 9 species were found in persistently infected quarters. Milk SCC was significantly higher in the CNS-infected mammary quarters than in the uninfected control quarters for 8 of the 20 species studied. Also, mean SCC differed significantly between mammary quarters infected with different CNS species. Within a given species, a high degree of variability was noted in milk SCC. These data corroborate recent data from Europe with regard to the predominance of certain species of CNS (e.g., Staph. chromogenes). In addition, some species of CNS appear to have a greater effect on milk SCC. Finally, some CNS species are associated with persistent IMI suggesting that some species (e.g., Staph. chromogenes and Staph. simulans) are better host-adapted, whereas others may have an environmental reservoir.     

Elevated milk soluble CD14 in bovine mammary glands challenged with Escherichia coli lipopolysaccharide

The purpose of this study was to determine whether soluble CD14 (sCD14) in milk was affected by stage of lactation, milk somatic cell count (SCC), presence of bacteria, or lipopolysaccharide (LPS)-induced inflammation. Milk samples from 100 lactating cows (396 functional quarters) were assayed for sCD14 in milk to determine effects of stage of lactation, SCC, and intramammary infection. The concentration of sCD14 was highest in transitional milk (0 to 4 d postpartum) and in milk with high SCC (> 750,000 cells/ml). Most of the infected quarters (> 80%) were infected by coagulase-negative staphylococci and yeast. No difference was found between noninfected and infected quarters. One quarter of six healthy lactating cows was challenged with 100 microg LPS in order to study the kinetics of sCD14 during an LPS-induced inflammation. Milk samples were collected at various intervals until 72 h after injection. Rectal temperature, milk tumor necrosis factor-alpha, and interleukin-8 increased immediately after challenge. The increase in sCD14 paralleled the increase in SCC, peaked at 12 h, and started to decline after 24 h. Serum leakage, as characterized by the level of bovine serum albumin in milk, peaked at 4 h and then gradually decreased. All parameters remained at basal levels in control quarters throughout the study. In vitro experiments indicated that neutrophils released sCD14 in response to LPS in a dose-dependent manner. The results indicate that the concentration of sCD14 was significantly increased in milk after LPS challenge. The increase was not likely due to serum leakage. Instead, infiltrated neutrophils might be the main source of increased sCD14 in milk during inflammation.     

N-Acetyl-B-D-glucosaminidase in milk and blood plasma during dry and early postpartum periods

Milk and plasma N-acetyl-B-D-glucosaminidase activity was determined for cows during the dry and early postpartum periods. Milk samples were taken from individual quarters of 12 cows from 7 d preceding dry off until calving. Weigh jar milk samples were taken daily for 28 d postpartum from 9 of the 12 cows. Somatic cell concentration was also measured in the postpartum samples. N-Acetyl-B-D-glucosaminidase activity of mammary secretions was significantly elevated in the dry period. Activity in mammary secretions was significantly higher than blood plasma concentrations during the dry period, which suggests that the enzyme present in mammary secretions comes mainly from within the gland. Milk enzyme concentrations declined sharply by 4 d postpartum and gradually declined through 28 d postpartum. Activity was still slightly elevated at 28 d postpartum as compared with normal lactation. Greater daily variability was seen with somatic cells than with N-acetyl-B-D-glucosaminidase. However, somatic cells were more responsive to clinical infections postpartum, showing significant elevations in both clinical episodes. The enzyme was elevated in one clinical case, but relatively unchanged in the other. Plasma levels were constant throughout both trials.     

Mammary pathogens and their relationship to somatic cell count and milk yield losses in dairy ewes

A total of 9592 samples of half udder milk were collected monthly throughout lactation for bacteriological and somatic cell count (SCC) study from 1322 Churra ewe lactations from seven separate flocks enrolled in the recording scheme of the National Association of Spanish Churra Breeders in the Castile-Le6n region of Spain. Statistical analyses were carried out from a mixed model with random factor half udder or ewe for repeated measures. Test of significance of fixed effects of this mixed model showed significant effects of organisms, flock, parity, lactation stage, and birth type on SCC. Special reference must be made to novobiocin-sensitive coagulase-negative staphylococci, which represented more than 50% of the isolates and which elicited SCC geometric means of around 106/ml. In addition, the analysis of 4352 monthly test-day records for milk yield, SCC, and bacteriology showed that the ewes that were uninfected and infected by minor pathogens had the lowest SCC and the highest milk yields, whereas those infected by major pathogens had high SCC and milk yield losses between 8.8 and 10.1% according to the uni- or bilateral character of the infection. Finally, ewes infected by novobiocin-sensitive coagulase-negative staphylococci elicited SCC values similar to those of infections by major pathogens and milk yield losses ranging between those caused by minor and major pathogens. As a result, emphasis should be put on prevention of subclinical mastitis, particularly mastitis caused by novobiocin-sensitive coagulase-negative staphylococci in dairy sheep herds to improve microbiological and hygienic milk quality and to minimize losses in milk yield.