Histological response of the bovine mammary gland to intramammary devices.

Histologic response of the bovine mammary gland to presence of three intramammary device models (abraded, star, or grooved) was studied in 12 lactating cows. Uninfected quarters fitted with devices exhibited greater leukocyte infiltration into teat and gland cistem linings as well as into mammary parenchyma adjacent to the gland cistem compared with unfitted control quarters. Cytologic alterations to cistem linings in device-fitted quarters ranged from degeneration and sloughing of surface cells of the double-layered epithelium to hyperplasia, stratification, and keratin formation. In uninfected quarters, quantification of mammary parenchymal components showed no differences among models for percentages of epithelium, but percentage of lumen was lowest and stroma highest for the star intramammary device model, suggesting reduced secretory activity or mammary involution in response to these intramammary devices. Presence of bacterial infection amplified the histologic responses to all devices. Leukocyte infiltration remained greater in device-fitted quarters compared with controls but was elevated over uninfected quarters for all treatments. Likewise, hyperplasia, stratification, and keratin formation of the cistem epithelial lining were more frequently observed in infected quarters. Among models in infected quarters, percentage of lumen was lowest and stroma highest in quarters fitted with abraded devices. In most cases, presence of infection masked any effect of devices on mammary parenchymal components. Plaque formation was observed on all models and tended to be thicker on those retrieved from infected quarters. Electron microscopic examination showed that plaque was composed of leukocytes, cell debris, keratin, and amorphous material. Results demonstrated that most intramammary device models were successful in stimulating leukocytosis into the gland, and tissues from fitted quarters displayed alterations to cisternal linings; however, quarters fitted with these devices exhibited reduced secretory activity.     

Pathology of Staphylococcus aureus mastitis during lactogenesis: relationships with bovine mammary structure and function

Pathological alterations of mammary parenchymal tissue from 5 dairy cows with Staphylococcus aureus mastitis were studied. Tissue from infected quarters exhibited less synthetic and secretory ability during lactogenesis, as indicated by lower percentages of luminal area, but higher percentages of stromal area compared with control tissue. Ultrastructural analysis of alveolar epithelium demonstrated decreased numbers of organelles associated with milk synthesis and secretion. Mammary secretion from 12 additional cows confirmed the loss of secretory potential in infected quarters as concentrations of alpha-lactalbumin were lower during the first 14 d of lactation compared with concentrations from controls. Higher concentrations of serum alpha-lactalbumin from cows with Staphylococcus aureus mastitis suggest leakage of mammary secretion through gaps left by damaged or sloughed alveolar epithelium. Macrophages and lymphocytes were observed frequently in large gaps between basal plasma membrane of secretory cells and the basal lamina which may contribute to epithelial damage. Ability of neutrophils and macrophages to phagocytize staphylococci may have been compromised in the prelactating gland due to the indiscriminate ingestion of accumulated fat and casein.     

Efficacy of a cephapirin dry cow product for treatment of experimentally induced Staphylococcus aureus mastitis in heifers.

A dry cow product containing 300 mg of cephapirin benzathine was evaluated in pregnant and nonpregnant Jersey heifers for its effect on experimentally induced Staphylococcus aureus mastitis. Cephapirin was detectable in mammary secretion of nonpregnant heifers for up to 5 wk and in tissue for 1 wk after intramammary infusion. Staphylococcus aureus was not detectable in tissue and secretion of treated quarters at 1 and 3 wk but was not eliminated from two quarters of one heifer tested at 6 wk posttreatment. Histologic evaluation of mammary tissue from nonpregnant heifers revealed significant differences in leukocytosis between uninfected and S. aureus-infected quarters but no differences in epithelium, lumen, and stroma, indicating no difference in secretion potential or glandular development. Twenty-five pregnant Jersey heifers were experimentally infected in two quarters with S. aureus 12 to 14 wk prepartum. After 1 to 3 wk, 13 heifers were infused in 21 S. aureus-infected quarters with a commercial cephapirin dry cow product. Nine infected quarters were left untreated. All treated quarters were bacteriologically negative both at calving and through 2 mo after calving. Of the 9 infected quarters not treated prepartum, 1 spontaneously cured and 2 became non-functional. The remaining quarters were treated at calving with a commercial cephapirin lactating cow product. Of these, 3 cured and 3 failed to resolve.     

Treatment of Staphylococcus aureus mastitis with penicillin and novobiocin: antibiotic concentrations and bacteriologic status in milk and mammary tissue

Cows with Staphylococcus aureus mastitis received either one or two intramammary infusions containing 100,000 U penicillin G and 150 mg novobiocin. Milk and tissue samples were obtained from each quarter. Peak mean penicillin and novobiocin concentrations from antibiotic-positive tissue samples were .013 U/mg and .06 microgram/mg, respectively, for quarters treated once. Quarters treated twice had peak mean penicillin and novobiocin concentrations of .057 U/mg and .06 microgram/mg, respectively. Viable Staphylococcus aureus were isolated intermittently from milk and tissue samples of quarters positive for penicillin and novobiocin for both treatment groups. Histological analysis of mammary parenchyma demonstrated marked decreases in luminal area and increases in connective tissue area and leukocyte infiltration in S. aureus-infected quarters compared with uninfected controls, suggesting that reduction in milk collecting space and presence of inflammatory changes may be responsible for poor drug distribution.     

Influence of prepartum pirlimycin hydrochloride or penicillin-novobiocin therapy on mastitis in heifers during early lactation

A study was conducted in 2 dairy research herds to determine whether prepartum therapy of heifer mammary glands with penicillin-novobiocin or pirlimycin hydrochloride was effective for reducing the percentage of heifers and mammary quarters infected with mastitis pathogens during early lactation. Almost 96% of Jersey heifers (67 of 70) and 71.3% of quarters (199 of 279) were infected 14 d before expected calving. Of the quarters infected at 14 d before expected parturition, 75% (54 of 72) were uninfected following treatment with penicillin-novobiocin; 87% (61 of 70) were uninfected following treatment with pirlimycin, and 56% (32 of 57) were uninfected in the untreated negative control group. The majority of intramammary infections in Jersey heifers were due to coagulase-negative staphylococci (61%), Streptococcus species, primarily Streptococcus uberis (19%), and Staphylococcus aureus (8%). Almost 73% of Holstein heifers (40 of 55) and 34.3% of mammary quarters (73 of 213) were infected 14 d before expected calving. Of the quarters infected at 14 d before expected parturition, 76% (19 of 25) were uninfected following treatment with penicillin-novobiocin; 59% (17 of 29) were uninfected following treatment with pirlimycin, and 26% (5 of 19) were uninfected in the untreated negative control group. The majority of intramammary infections in Holstein heifers were due to coagulase-negative staphylococci (44%) and Staph. aureus (30%). In both herds, the bacteriological cure rate was significantly higher in heifer mammary glands treated with penicillin-novobiocin or pirlimycin hydrochloride than in untreated controls. Prepartum therapy of heifer mammary glands with penicillin-novobiocin or pirlimycin hydrochloride significantly reduced the percentage of heifers and quarters infected with mastitis pathogens during early lactation.     

Histological tissue structure alterations resulting from Staphylococcus aureus intramammary infection in heifer mammary glands hormonally induced to rapidly grow and develop

Intramammary infections (IMI) are common in nonlactating dairy cattle and are expected to impair mammary growth and development and reduce future milk production. The objective of this study was to histologically evaluate how IMI alter tissue structure in growing and developing heifer mammary glands. A total of 18 nonpregnant, nonlactating heifers between 11 and 14 mo of age were used in the present study. Heifers received daily supraphysiological injections of estradiol and progesterone for 14 d to stimulate rapid mammary growth and development. One-quarter of each heifer was subsequently infused with Staphylococcus aureus (CHALL) while a second quarter served as an uninfected control (UNINF). Heifers were randomly selected and euthanized either the last day of hormonal injections to observe IMI effects on mammary gland growth (GRO), or 13 d post-injections, to observe IMI effects on mammary development (DEV). Mammary tissues were collected from the center and edge parenchymal regions of each mammary gland for morphometric tissue area evaluation. For GRO tissues, CHALL quarters had less epithelial tissue area and marginally more intralobular stroma tissue area than UNINF quarters. Tissue areas occupied by luminal space, extralobular stroma, adipose, and lobular tissue were similar. For DEV tissues, area occupied by epithelium, luminal space, intralobular stroma, and extralobular stroma did not differ between quarter treatments, but UNINF quarters had more adipose tissue area and marginally less lobular area than CHALL quarters. Results indicate that IMI in growing and developing mammary glands reduces mammary epithelial growth and alters mammary gland development by impairing epithelial branching into the mammary fat pad. Taken together, these tissue changes before calving may have adverse effects on milk production. Therefore, an important focus should be placed on improving udder health in replacement heifers through management strategies that mitigate the deleterious effects of IMI and promote the positive development of the mammary gland.     

Effect of naturally occurring coagulase-negative staphylococci infections on new infections by mastitis pathogens in the bovine

Microbiological data from 1123 uninfected quarters and 216 quarters with preexisting coagulase-negative staphylococci infections were analyzed to determine the influence of infection status on subsequent new infection rate. Overall, prevalence of new infections in uninfected quarters was approximately two times that in quarters already harboring a coagulase-negative Staphylococcus infection. New infections by coagulase-negative staphylococci were greater in uninfected quarters than in quarters with preexisting coagulase-negative staphylococci infections. However, no differences were observed between uninfected and infected quarters in number of new infections by major pathogens (Staphylococcus aureus, streptococci, and coliforms). No differences were observed in uninfected or coagulase-negative Staphylococcus-infected quarters in infections with minor pathogens compared with major pathogens. The influence of individual coagulase-negative Staphylococcus species on new infections was also analyzed. However, numbers of existing infections by Staphylococcus species other than Staphylococcus chromogenes were limited. Therefore, the protective capacity of each coagulase-negative Staphylococcus species was difficult to assess. Overall, a significant restriction of bacterial invasion was observed in quarters with a preexisting infection. These results suggest that quarters harboring a coagulase-negative Staphylococcus infection suppress colonization of the mammary gland by mastitis-causing pathogens.     

Prevalence of intramammary infection and teat canal colonization in unbred and primigravid dairy heifers.

Teat canal keratin (n = 461) and mammary gland secretions (n = 370) were collected from 31 unbred and 85 primigravid Jersey heifers from one research and three commercial dairy herds. Of 97 heifers from which secretion samples were obtained, 96.9% had intramammary infections and 29% showed clinical symptoms. Seventy-five percent of quarters were infected. Staphylococcus aureus were isolated from 36 (37.1%) heifers and 55 (14.9%) quarters. One hundred and eight (93.1%) heifers and 326 (70.7%) quarters had teat canals colonized with mastitis pathogens. Staphylococcus aureus were isolated from teat canal keratin samples from 36 (31%) heifers and 57 (12.3%) quarters. The three most common species isolated from secretion and teat canal keratin samples were Staphylococcus chromogenes, Staphylococcus hyicus, and S. aureus. Secretions from infected (n = 240) and uninfected (n = 85) quarters had SCC of 13.6 X 10(6)/ml and 5.7 X 10(6)/ml. Macrophages were the most numerous cell type in secretions of infected and uninfected quarters. Quarters with teat canal colonization, but with no intramammary infections, exhibited higher SCC in secretion (9.3 X 10(6)/ml) than quarters without both teat canal colonizations and intramammary infections (4.9 X 10(6)/ml). Data indicated that intramammary infections and teat canal colonizations were more prevalent and SCC higher than previously realized in dairy heifers.     

Determination of milk and mammary tissue concentrations of ceftiofur after intramammary and intramuscular therapy

Twenty-five Staphylococcus aureus strains isolated from bovine mastitis were tested for their susceptibility to ceftiofur. Zone diameter for 30 micrograms disks averaged 39 mm, and minimum inhibitory concentrations ranged from .5 to 1 microgram/ml. Tissue and milk concentrations were determined from biopsy and quarter milk samples collected from eight cows treated with either intramammary infusion of 100 or 200 mg of ceftiofur, one or two intramuscular injections of 500 mg of ceftiofur, or combination therapy of intramammary infusion coupled with intramuscular injection. Three additional cows received two intramammary infusions of 200 mg of cephapirin at 24-h intervals. Intramuscular injections of ceftiofur resulted in tissue and milk concentrations below detectable limits. Staphylococcus aureus was not eliminated from infected mammary glands by infusion of 100 mg of ceftiofur or by injection of 500 mg of ceftiofur by 48 h after treatment. Combination therapy of 100 mg of ceftiofur infused and 500 mg injected reduced S. aureus numbers in milk and tissue markedly, as did infusion of 200 mg of ceftiofur. Cows receiving intramammary infusion of 200 mg of ceftiofur (two doses at 24-h intervals) had highest concentrations in milk (450 micrograms/ml at 4 and 6 h) and in tissue (.08 microgram/mg at 30 h). These concentrations are similar to those obtained with two 200-mg doses of cephapirin at 24-h intervals. Histologic analysis of mammary parenchymal tissues showed that combination therapy resulted in higher percentages of alveolar luminal area and lower percentages of interalveolar stroma compared with infusion or injection alone. Histology of quarters receiving combination therapy was not different from that of quarters receiving cephapirin infusion alone.     

Functional activity of neutrophils from bovine mammary glands infected with Staphylococcus aureus

To test the effect of Staphylococcus aureus infection on mammary neutrophil function, intramammary neutrophils from S. aureus-infected quarters (n = 8), from adjacent uninfected quarters (n = 8) of S. aureus-infected cows, and from quarters (n = 8) of uninfected cows were collected and incubated with S. aureus in vitro. Mean percent neutrophils phagocytizing, number S. aureus per neutrophil, and log10 viable phagocytized S. aureus/ml were: 53.2, 6.4, and 4.72. Differences in function of neutrophils collected from infected and uninfected quarters were not statistically significant. Results indicate that function of neutrophils from S. aureus-infected quarters is similar to function of neutrophils from uninfected quarters.     

Rate of environmental mastitis in quarters infected with Corynebacterium bovis and Staphylococcus species

Rates of environmental streptococcal and coliform intramammary infections were compared among quarters uninfected and infected with either Corynebacterium bovis or Staphylococcus species. Rate of environmental streptococcal intramammary infections was 3.9 times greater in C. bovis-infected quarters than in uninfected quarters. Rate of environmental streptococcal infections was 2.6 times greater in quarters infected with Staphylococcus species than in uninfected quarters. Rate of coliform intramammary infections did not differ among quarters with differing bacteriological infection statuses. Quarters infected with either C. bovis or Staphylococcus species had higher milk SCC than did uninfected quarters. Intramammary infection with either Corynebacterium bovis or Staphylococcus species did not protect quarters against coliform infection. Rate of environmental streptococcal infections was enhanced in quarters infected with either C. bovis or Staphylococcus species.     

Diagnosis of Staphylococcus aureus intramammary infection by detection of specific antibody titer in milk.

The diagnostic value of the determination of Staphylococcus aureus antibody titer in milk as a method for identification of mammary quarters with S. aureus IMI was evaluated. Ten cows with a history of S. aureus IMI and 9 cows with no history of S. aureus IMI were sampled daily for 10 d. Quarter and composite milk samples were collected and processed by standard methods for concentration of S. aureus, S. aureus antibody titer (percentage of positive laboratory control), and SCC (cells per milliliter). Microbiologic culture identified 13 S. aureus-infected quarters from the 10 cows with a history of S. aureus IMI. Only 2 of the 130 samples (1.5%) from these infected quarters had undetectable concentrations of S. aureus. Antibody titers in milk from infected quarters of infected cows were below the previously established level considered to be indicative of IMI in 6 of 130 samples (4.6%). Four samples from infected quarters of infected cows had titers considered to be in the suspect range. The sensitivity of the antibody test was 83% (13% SE) when the suspect samples were included and 86% (12% SE) when they were not. Milk from uninfected quarters of cows with S. aureus IMI tended to have S. aureus antibody titers greater than the test's positive control, which would suggest that the quarters were infected with S. aureus. Antibody titer was below the infection threshold level in all pooled samples of uninfected cows, suggesting that the test correctly identified all cows free of S. aureus IMI.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histological response of bovine mammary tissue to an intracisternal bead device

Placement of an intracisternal bead device into teat cisterns of dairy cows at drying off was studied. Histological analysis of teat cisternal tissues from quarters fitted with devices demonstrated significant elevation in leukocyte infiltration and hypertrophy of the epithelial lining. Tissue changes ranged from degeneration and sloughing of surface cells of double-layered epithelia to marked thickening and lysis of cisternal epithelium, leaving only the basement membrane intact. Quantification of mammary parenchymal components from quarters fitted with devices demonstrated no differences in percentage area occupied by alveolar epithelium, lumen, and intraalveolar stroma from unfitted control quarters. However, quantification of leukocyte numbers demonstrated slightly greater leukocytosis into tissues of quarters fitted with devices in comparison with controls. Devices were successful in stimulating a localized leukocytosis into teat cisternal tissues, which may serve to amplify the leukocyte response to mastitis-causing organisms once they penetrate the teat duct.     

Protective effect of Staphylococcus chromogenes infection against Staphylococcus aureus infection in the lactating bovine mammary gland

The susceptibility of uninfected or Staphylococcus chromogenes-infected quarters to challenge with Staphylococcus aureus was measured. Seventeen S. chromogenes-infected quarters were challenged by infusion of S. aureus into the teat sinus; 47% (8 of 17) became infected and all 18 uninfected quarters challenged similarly with S. aureus became infected. No differences in daily milk yield were seen between uninfected quarters and S. chromogenes-infected quarters prior to S. aureus infusion. Postinfusion, milk yield for S. aureus-infected, S. chromogenes-infected, and S. chromogenes- and S. aureus-infected quarters differed. Somatic cell counts were elevated in S. chromogenes-infected quarters compared with uninfected quarters prior to S. aureus infusion. Somatic cell counts were not different between S. aureus- and S. chromogenes- and S. aureus-infected quarters postinfusion, but were different for S. chromogenes-infected quarters. Chloride concentrations in S. chromogenes- and S. aureus-infected quarters were different from either S. aureus-infected or S. chromogenes-infected quarters. Staphylococcus aureus colony forming units in quarters with preexisting S. chromogenes infections were lower than S. aureus colony-forming units in previously uninfected quarters. Possible protective mechanisms induced by S. chromogenes against superinfection by S. aureus are discussed.     

Cellular proliferation and apoptosis in Staphylococcus aureus–infected heifer mammary glands experiencing rapid mammary gland growth

Intramammary infections in nonlactating mammary glands are common and can occur during periods of rapid mammary epithelial cell (MEC) accumulation, which may ultimately reduce total MEC numbers. Reduced MEC numbers, resulting from impaired MEC proliferation and increased cellular apoptosis, are expected to reduce future milk yields. The objective of this study was to measure the degree of cellular proliferation and apoptosis in the epithelial and stromal compartment of uninfected and Staphylococcus aureus–infected mammary glands hormonally induced to grow rapidly. Nonpregnant heifers (n = 8) between 11 and 14 mo of age were administered supraphysiological injections of estradiol and progesterone for 14 d. One mammary gland of each heifer was randomly selected and infused with Staph. aureus (CHALL) while another mammary gland was designated as an uninfected control on d 8 of injections. Mammary tissues were collected on the last day of hormonal injections from center and edge parenchymal regions and subject to proliferation assessment via Ki-67 staining and apoptotic assessment via terminal deoxynucleotidyl transferase dUTP nick-end labeling. Differences in cellular proliferation between CHALL and uninfected control quarters were not apparent, but proliferation of MEC was marginally greater in edge parenchyma than in center parenchyma. Coincidently, CHALL quarters experienced a greater percentage of apoptotic MEC and lower percentage of stromal cells undergoing apoptosis than uninfected control quarters. This study also provides the first insight into the mechanisms that allow the mammary fat pad to be replaced by expanding mammary epithelium as edge parenchyma contained a greater percentage of apoptotic stromal cells than center parenchyma. When taken together, these data suggest that Staph. aureus intramammary infection impairs mammary epithelial growth through reductions in MEC number and by preventing its expansion into the mammary fat pad. These factors during periods of rapid mammary growth are expected to impair first lactation milk yield.     

Influence of Staphylococcus aureus strain-type on mammary quarter milk somatic cell count and N-acetyl-beta-D-glucosaminidase activity in cattle from eight dairies

The hypothesis tested was that there are differences in pathogenicity between strains of Staphylococcus aureus that cause bovine mastitis. Mammary quarter milk somatic cell count (SCC) and N-acetyl-beta-D-glucosaminidase (NAGase) activity were used as indicators of the pathogenicity of different strains of S. aureus that infect the bovine udder. Eight commercial dairy herds with a history of S. aureus in bulk tank milk cultures were studied. Initially, composite foremilk samples were collected from all lactating cattle in each herd and cultured for staphylococci. Subsequently, all cows with a coagulase-positive staphylococcal intramammary infection (IMI) at the initial sampling that were still present in the herd of origin had individual mammary quarter foremilk samples collected. Coagulase-positive staphylococcal isolates were confirmed as S. aureus using a commercial biotyping system. Staphylococcus aureus isolates were strain-typed using pulsed-field gel electrophoresis. Mammary quarter milk SCC and N-acetyl-beta-D-glucosaminidase activity were determined for each cow. The difference in mean somatic cell count and mean NAGase activity for mammary quarters infected with the same strain of S. aureus and for uninfected quarters on the same cow was calculated. One-way analysis of variance was used to assess differences between strains within a herd. Overall, no significant differences were found between strains, suggesting that the degree of udder parenchymal injury induced by S. aureus IMI is in general significantly affected by factors other than strain type.     

Leukocytic infiltration of bovine mammary parenchymal tissue in response to Corynebacterium bovis colonization

Morphological changes and local leukocyte response to prolonged Corynebacterium bovis colonization were studied in lactating bovine mammary glands. Morphometric analysis of parenchymal tissue demonstrated no adverse effects of colonization on the synthetic and secretory activity of mammary epithelium. Numbers of macrophages, lymphocytes, and plasma cells were higher in tissue from C. bovis-colonized quarters. However, there were no differences in numbers of neutrophils between colonized and uninfected quarters. Results suggest persistent C. bovis colonization may elicit effector cell populations in lactating mammary tissue where leukocyte concentrations tend to be lower.     

Characteristics of mammary secretions collected from infected and uninfected primigravid dairy heifer mammary glands

Intramammary infections (IMI) in primigravid dairy heifers can affect mammary growth and development, which can reduce first-lactation milk yield. Detection of IMI in heifers most often involves the use of culture-based methods that are not often used in production dairy settings given their labor- and time-consuming nature. The objective of this study was to determine whether mammary secretion somatic cell count (SCC) and viscosity were associated with the infection status of primigravid heifer mammary glands. A total of 270 heifers from a single farm were used, selected based on the farmer's willingness to participate. The study was conducted from June to October 2020. Mammary secretion samples were aseptically collected from a randomly selected quarter of each heifer at 75 d prepartum (75PP), and another quarter of each heifer was sampled at 35 d prepartum (35PP). The remaining 2 quarters of each heifer were not examined. Mammary secretion samples underwent bacteriological examination to determine IMI status and quantitative SCC measurement and were also assessed for secretion viscosity based on visual observation. Prevalence of IMI was 26% (69/270) and 28% (71/255) at 75 and 35 d prepartum, respectively. Uninfected secretion samples had 133.2 [95% confidence interval (CI): 16.8 to >999.9] times greater odds to be thick compared with samples infected with a major pathogen, and 14.4 (95% CI: 8.5 to 24.1) times greater odds to be thick compared with samples infected with non-aureus staphylococci (NAS). The mean secretion SCC of uninfected quarters (6.04 ± 0.03 log₁₀ cells/mL) was significantly lower than that of secretions collected from quarters infected with Staphylococcus chromogenes (6.34 ± 0.04 log₁₀ cells/mL), other NAS species (6.28 ± 0.10 log₁₀ cells/mL), or a major pathogen (6.73 ± 0.08 log₁₀ cells/mL). These results indicate that mammary secretion viscosity and SCC measurement may be useful tools in identifying primigravid heifer quarters with IMI. The ability to evaluate viscosity at time of sampling may be a useful strategy that could be incorporated into interventions designed to diminish the negative effects of prepartum IMI on lactational performance.     

Effect of a biological response modifier on expression of growth factors and cellular proliferation at drying off

Agents that increase natural protective mechanisms have been proposed for the prevention and treatment of intramammary infections. Staphylococcus aureus is a major pathogen causing primarily subclinical chronic mastitis that responds poorly to antibiotic therapy. The objectives of this study were to describe the effects of a single intramammary infusion of a lipopolysaccharide-based biological response modifier (BRM) on mammary epithelial cellular proliferation and expression of insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) in uninfected and Staph. aureus-infected bovine mammary glands during involution. Three groups of 12 cows, 6 Staph. aureus-infected and 6 uninfected, were infused with BRM or placebo in 2 mammary quarters and killed at 7, 14, and 21 d of involution. The proportion of infected quarters, mammary cell proliferation, and IGF-I and VEGF expression were evaluated. Biological response modifier treatment decreased the proportion of Staph. aureus-infected mammary quarters at 7 d of involution, but a similar number of isolations were observed at 14 and 21 d of involution in either treated or control quarters. The percentage of proliferating mammary epithelial cells was higher in infected than uninfected quarters at every observation period, irrespective of the treatment administered, whereas uninfected BRM-treated quarters showed increased cell proliferation at 7 d of involution. Insulin-like growth factor-I expression in uninfected quarters was not affected by treatment and showed a decrease at 21 d of involution. Expression of IGF-I was greater in infected than uninfected quarters at every observation period, irrespective of the treatment received. Expression of VEGF was greater in BRM-treated uninfected quarters at 7 d of involution compared with controls. In infected quarters, VEGF expression was lowest in BRM-treated quarters at 7 d of involution and increased throughout the observation period. Conversely, untreated infected quarters showed the highest VEGF expression at 7 d and decreased at 21 d of involution. Mammary cell proliferation and expression of IGF-I and VEGF were increased in Staph. aureus-infected quarters. Increased mammary cell proliferation and VEGF expression were observed in BRM-treated quarters during the first week of involution.     

Shedding pattern of Staphylococcus aureus from bovine intramammary infections

Twenty-one quarters of seven cows were experimentally infected with Staphylococcus aureus (ATCC 29740) to study the shedding pattern in quarter milk samples. Of 991 consecutive quarter milk samples collected from infected quarters during the trial, 745 were positive for S. aureus by bacteriological culture. The sensitivity of a single quarter milk sample to determine infection status of a quarter was 74.5% based on the mean of each gland's recovery pattern. Sensitivity of bacterial culture increased to 94% and 98% by including a second and a third consecutive sample. Because S. aureus is shed in a cyclical manner from mammary glands, consecutive samples would be advisable for accurate diagnosis of infected quarters.