The Decline of Small Practice in Colorectal Surgery: Practice Consolidation From 2015-2022

INTRODUCTION

Physicians have gravitated toward larger group practice arrangements in recent years. However, consolidation trends in colorectal surgery have yet to be well described. Our objective was to assess current trends in practice consolidation within colorectal surgery and evaluate underlying demographic trends including age, gender, and geography.

METHODS

We performed a retrospective cross-sectional study using the Center for Medicare Services National Downloadable File from 2015 to 2022. Colorectal surgeons were categorized by practice size and by region, gender, and age.

RESULTS

From 2015 to 2022, the number of colorectal surgeons in the United States increased from 1369 to 1621 (+18.4%), while the practices with which they were affiliated remained relatively stable (693-721, +4.0%). The proportion of colorectal surgeons in groups of 1-2 members fell from 18.9% to 10.7%. Conversely, those in groups of 500+ members grew from 26.5% to 45.2% (linear trend P < 0.001). The midwest region demonstrated the highest degree of consolidation. Affiliations with group practices of 500+ members saw large increases from both female and male surgeons (+148.9% and +86.9%, respectively). New surgeons joining the field since 2015 overwhelmingly practice in larger groups (5.3% in groups of 1-2, 50.1% in groups of 500+).

CONCLUSIONS

Colorectal surgeons are shifting toward larger practice affiliations. Although this change is happening across all demographic groups, it appears unevenly distributed across geography, gender, and age. New surgeons are preferentially joining large group practices.

Comparing Changes in Medicare Reimbursement for Radiation Oncology and Medical Oncology (2010-2020)

PURPOSE/OBJECTIVE(S)

A recent study found that radiation oncology (RO) has seen significant declines in Medicare reimbursement (MCR) from 2010-2019. While it is presumed that other cancer subspecialties have seen decreasing MCR, to our knowledge, there are no studies directly comparing changes in MCR between RO and other oncology subspecialties. In this study, we analyze changes in MCR from 2010-2020 for both RO and medical oncology. We hypothesized that the declines in MCR will be similar between the two fields.

MATERIALS/METHODS

The publicly available Physician/Supplier Procedure Summary (PSPS) database was used for all years from 2010-2020. All reimbursement for providers with primary provider codes 92 (RO) and 83 and 90 (heme/onc and medical oncology, respectively) were analyzed. For the 150 most highly-reimbursed HCPCS codes for each specialty in 2010, the total allowed charge for each code was corrected for inflation and then divided by the number of submitted claims to calculate average MCR per code for each year. For each code and each specialty, the 2020 billing frequency was multiplied by the calculated average reimbursement per claim in a given year to calculate what the reimbursement would have been in that year using 2020 dollars and utilization rates (projected reimbursement). The projected reimbursement was summed for all HCPCS codes in each year for each specialty to calculate an aggregate MCR for that specialty for that year. This aggregate MCR was then compared with the actual 2020 reimbursement for that basket of codes to calculate the change in MCR over time.

RESULTS

Both medical and radiation oncology saw decreases in projected vs. actual MCR from 2010-2020 for this basket of services (Table). Adjusting for inflation and utilization, RO MCR declined by $0.7 billion (B) (-29.0%) from 2010 to 2020 and by $0.2B (-10.5%) from 2015 to 2020 while medical oncology MCR declined by $0.8B (-14.7%) from 2010-2020 and by $0.4B (-6.6%) from 2015-2020. The average decrease per year in projected vs. actual reimbursement for RO was 2.9% (2010 to 2015) and 1.05% (2015 to 2020) and for medical oncology was 1.5% (2010-2015) and 0.7% (2015-2020), respectively.

CONCLUSION

Adjusting for inflation, Medicare reimbursement for a large array of services has declined for both medical oncology and RO from 2010 - 2020. Contrary to our hypothesis, RO reported a 97% greater relative decline in reimbursement compared with medical oncology from 2010 - 2020. Significant decreases in reimbursement to both fields and their potential implications on patient care and access to care should be considered by policymakers while shifting towards an episode-based Alternative Payment Model and when considering further cuts to Medicare reimbursement.

Effect of Dose to the Heart and Cardiac Substructures on Cardiac Toxicity after Breast Cancer Radiation

PURPOSE/OBJECTIVE(S)

Pre-existing cardiovascular disease, chemotherapy, and higher mean heart dose are known risk factors for cardiac toxicity after breast radiation therapy. However, the relationship between cardiac substructure radiation exposure and toxicity is not well understood. We hypothesized that mean heart dose is a surrogate for global cardiac radiation exposure but that more specific dosimetric thresholds for the heart and its substructures could be identified, which could be used to guide radiation planning for breast cancer patients in the future.

MATERIALS/METHODS

In this cohort study, all breast cancer patients who received curative intent breast or chest wall radiotherapy at a single high-volume institution in 2014 and 2017 were included (n = 841). Baseline characteristics included hormone therapy, chemotherapy, menopausal status, diabetes, dyslipidemia, pre-existing cardiac toxicity, and age at diagnosis. Outcomes included any cardiac toxicity, arrhythmia, cardiomyopathy, ischemia, valvular, pericardial disease, and death. The heart and substructures, including left ventricle, right ventricle, left atrium, right atrium, aortic valve, pulmonic valve, mitral valve, tricuspid valve, and left anterior descending artery, were delineated on the simulation CT for each patient. Dosimetric variables, including mean dose, max dose, and V1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, and 70 Gy for the heart and substructures (in cc) were extracted. For each dosimetric variable, multivariable logistic regression was performed using baseline covariates in addition to the single dosimetric variable. Patients with missing data values were excluded. Results were combined and False Discovery Rate p-value correction was performed.

RESULTS

Multiple cardiac substructure dosimetric variables were associated with increased risk of mortality on multivariable analysis (p < 0.05). For left atrium and right atrium, V2, 3, 4, and 5 Gy were all significant. For right ventricle, mean dose, V1, 2, 3, 4, 5, 10, 15, 20, 25, 30, and 35 Gy were significant. For mitral valve, mean dose, max dose, V3, 4, and 5 Gy were significant. For tricuspid valve, mean dose was significant. For aortic valve, max dose, mean dose, V4, and V5 Gy were significant. For the whole heart, V1, 2, 3, 4, 5, 10, 15, 20, 25, 30, and 35 Gy were significant.

CONCLUSION

We have identified multiple dosimetric variables for the heart and its substructures which were associated with increased risk of mortality after breast cancer radiation. In fact, for certain structures, there were multiple exposure thresholds which showed increased risk of toxicity, highlighting the complex relationship between substructure dose and outcomes. Further study into these relationships will identify the most critical cardiac substructure constraints that could be used in radiation treatment planning.

Benchmarking the Radiation Oncology Alternative Payment Model: Changes in Medicare Reimbursement for 16 Common Radiation Therapy Treatment Courses

Radiation oncology (RO) has seen declines in Medicare reimbursement (MCR) in the past decade under the current fee-for-service model. Although studies have explored decline in reimbursement at a per-code level, to our knowledge there are no recent studies analyzing changes in MCR over time for common RO treatment courses. By analyzing changes in MCR for common treatment courses, our study had 3 objectives: (1) to provide practitioners and policymakers with estimates of recent reimbursement changes for common treatment courses; (2) to provide an estimate of how reimbursement will change in the future under the current fee-for-service model if current trends continue; and (3) to provide a baseline for treatment episodes in the event that the episode-based Radiation Oncology Alternative Payment Model is eventually implemented. Specifically, we quantified inflation- and utilization-adjusted changes in reimbursement for 16 common radiation therapy (RT) treatment courses from 2010 to 2020. Centers for Medicare & Medicaid Services Physician/Supplier Procedure Summary databases were used to obtain reimbursement for all RO procedures in 2010, 2015, and 2020 for free-standing facilities. Inflation-adjusted average reimbursement (AR) per billing instance was calculated for each Healthcare Common Procedure Coding System code using 2020 dollars. For each year, the billing frequency of each code was multiplied by the AR per code. Results were summed per RT course per year, and AR for RT courses were compared. Sixteen common RO courses for head and neck, breast, prostate, lung, and palliative RT were analyzed. AR decreased for all 16 courses from 2010 to 2020. From 2015 to 2020, the only course that increased in AR was palliative 2-dimensional 10-fraction 30 Gy, which increased by 0.4%. Courses using intensity modulated RT saw the largest AR decline from 2010 to 2020, ranging from 38% to 39%. We report significant declines in reimbursement from 2010 to 2020 for common RO courses, with the largest declines for intensity modulated RT. Policymakers should consider the significant cuts to reimbursement that have already occurred when considering future reimbursement adjustment under the current fee-for-service model or when considering mandatory adoption of a new payment system with further cuts and the negative effect of such cuts on quality and access to care.

Current trends in U.S. general surgery practice consolidation

BACKGROUND

Consolidation of physician practices is well-documented in recent years, yet minimal data exist regarding consolidation in general surgery. This study evaluates current trends in general surgery practice consolidation.

METHODS

Data were obtained through the CMS Physician Compare database. Surgeons and practices were categorized by size, and trends were analyzed using the Cochran-Armitage test. Data were stratified by US region.

RESULTS

From 2012 to 2020, practicing general surgeons increased from 20,044 to 20,637 (+3%). Unique general surgery practices declined from 8178 to 6489 (-21%). The percentage of surgeons in practices of 1 or 2 declined from 19% to 12%, while surgeons in groups of 500 or more grew from 20% to 31%. Tests for trends towards consolidation at both the individual surgeon and unique practice levels were significant (p < .001). The Midwest region demonstrated the highest degree of consolidation.

CONCLUSION

Consistent with trends in medicine overall, general surgery is experiencing substantial practice consolidation.

Orthopaedic Group Practice Size Is Increasing

PURPOSE

To analyze recent trends in orthopaedic surgery consolidation and quantify these changes temporally and geographically from 2012 to 2020.

METHODS

We performed a retrospective cross-sectional analysis of orthopaedic surgeon practice size in the United States using 2012 and 2020 data obtained from the Physician Compare database.

RESULTS

Although we observed an increase from 21,216 unique orthopaedic surgeons in 2012 to 21,553 in 2020 (1.6% increase), the number of practices experienced a large decrease from 7,299 practices in 2012 to 5,829 in 2020 (20.1% decrease). The proportion of orthopaedic surgeons working in solo practices decreased from 13.2% (2,790) in 2012 to 7.4% (1,595) in 2020, and the proportion of orthopaedic surgeons working in groups sized 2 to 24 decreased from 35.3% (7,482) in 2012 to 22.2% (4,775) in 2020. In contrast, groups sized 25 to 99 have grown from 20.7% (4,387) of all orthopaedic surgeons to 23.4% (5,048) in 2020. Groups sized 100 to 499 have increased from 16.9% (3,593) in 2012 to 24.1% (5,190) in 2020, whereas groups sized 500 or greater have grown from 14% (2,964) in 2012 to 22.9% (4,945) in 2020. The number of unique group practices showed a significant decrease in the number of solo groups, which comprised 43.8% (3,200) of the total number of individual practices in 2012, decreasing to 32% (1,886) in 2020. All other groups increased in number and proportionally from 2012 to 2020.

CONCLUSIONS

This study shows that over the period from 2012 to 2020, there has been a substantial trend of orthopaedic surgeons shifting to increasing practice sizes, potentially indicating that more orthopaedic surgeons are working for large health care organizations rather than small independent practices.

CLINICAL RELEVANCE

The impact of these changes should be examined to determine large-scale effects on patient care, payment models, access, and outcomes, along with physician compensation, lifestyle, and satisfaction.

Effects of various starch feeding regimens on responses of dairy cows to intramammary lipopolysaccharide infusion

Endotoxin tolerance (ET) can develop in mammals that have been challenged repeatedly with sublethal amounts of lipopolysaccharide (LPS). Previous research has shown that subclinical ruminal acidosis can increase circulating concentrations of LPS. We investigated whether ET would develop in Holstein cows that were subjected to chronic subacute ruminal acidosis (SARA) or acute SARA followed by intramammary infusion of LPS. Twenty-four cows, both primiparous and multiparous, were assigned to 8 blocks of 3 cows. Cows within blocks were randomly assigned to 1 of 3 treatments: (1) control (diet DM was 24% starch and 35% NDF), (2) high starch (formulated to induce chronic milk fat depression with 29% starch and 32% NDF), and (3) acidosis (designed to cause acute bouts of milk fat depression by short-term feeding of a diet with 32% starch, some of which came from wheat grain, and 30% NDF). Cows on the control and high-starch treatments were fed their respective diets throughout the 24-d trial. The acidosis cows were fed the control diet during most of the experiment, except during two 2-d bouts (d 10 and 11 and 17 and 18 of the experiment) in which a high-starch diet was fed. Cows on the high-starch and acidosis treatments produced milk fat with an altered fatty acid profile indicative of SARA (e.g., increased concentrations of specific trans, and odd-, and branched-chain fatty acids), but only cows on the high-starch treatment had milk fat depression. Concentrations of serum amyloid A were elevated in cows on the acidosis treatment, but did not differ between control and high-starch cows. On d 20 of the experiment, all cows were given an intramammary infusion of 10 µg of LPS into 1 mammary quarter 3h after morning milking. Milk yield and DMI decreased the day of the infusion, but the response was not affected by dietary treatment. No systemic indicators of ET were observed among treatments, but evidence of an ET response at the local level of the mammary gland was observed. Cows fed the control diet had higher concentrations of serum amyloid A in milk 12 and 24h postinfusion than did cows fed the high-starch diet and higher concentrations than cows on the acidosis treatment at 12h postinfusion. Our data suggest cows that experienced varying degrees of SARA (based on altered milk fatty acid profile) and subsequent experimental endotoxin mastitis experienced a blunted inflammatory response at the level of the mammary gland, but not a systemic reduction in some inflammatory mediators.

Activity and milk compositional changes following experimentally induced Streptococcus uberis bovine mastitis

Milk constituents and physical activity of cows experimentally infected with Streptococcus uberis mastitis were compared with those of uninfected cows. Twelve late-lactation Holsteins cows were paired based on milk production and parity. One cow in each pair was experimentally infected in the right front mammary gland with Strep. uberis. The remaining cow in each pair served as an uninfected control. Real-time analyses of milk constituents provided fat, protein, and lactose percentages at each milking. Pedometers were placed on the left front leg of all cows and activity was measured. Intramammary infections with Strep. uberis reduced milk yield in experimental cows by approximately 1.6kg/d in the first week after challenge compared with control cows. Lactose percentage in milk was reduced on d 3, 4, 5, and 6 after challenge in treatment cows compared with controls. Percentages of fat and protein in milk did not differ between infected and uninfected cows the week after infections were induced. Total steps per day were reduced and minutes resting per day were increased the week after experimental challenge in infected cows compared with control cows. The number of resting bouts did not differ between infected and uninfected cows. Changes in percentage of lactose in milk and animal activity caused by experimentally induced Strep. uberis mastitis were detected by the automated milk analyzer and pedometer systems.

Short communication: Bacterial counts in recycled manure solids bedding replaced daily or deep packed in freestalls

An experiment was conducted to compare bacterial counts of mastitis pathogens in deep-packed manure solids bedding with those in manure solids bedding replaced daily from mattresses. Eighteen Holstein cows were housed in 1 pen with 18 stalls. One row of 9 stalls was equipped with mattresses topped with bedding. The back one-third of these stalls toward the alleyway was covered in 25 mm of recycled manure solids, which was removed daily for the next 6 d and replaced with bedding from the brisket board and lunge space areas of stalls. The second row of 9 stalls was bedded for 3 wk with 100 to 150 mm of deep-pack recycled manure bedding from which only fecal matter was removed daily. After 3 wk, bedding treatments were changed between rows in a switchback design. Mean total gram-negative bacterial counts did not differ between treatments throughout the experiment. Coliform and Klebsiella spp. bacterial counts were lower in daily replaced bedding compared with deep pack across the experiment and on each of d 0, 1, 2, and 6. Streptococcal counts were reduced in daily replacement stalls compared with deep-pack stalls on d 0 and greater in daily replacement stalls compared with deep-pack stalls on d 1, 2, and 6. Daily replacement of recycled manure bedding from the back one-third of the stalls appeared to be an effective approach to reducing exposure to coliforms, specifically Klebsiella, but not streptococci. However, bacterial counts in bedding from both treatments were elevated throughout the trial and resulted in considerable risk for exposure to teats and development of intramammary infections.

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.

Isolation and activity of Xenorhabdus antimicrobial compounds against the plant pathogens Erwinia amylovora and Phytophthora nicotianae

AIMS

Broad-spectrum antibiotics produced by symbiotic bacteria [entomopathogenic bacterium (EPB)] of entomopathogenic nematodes keep monoxenic conditions in insect cadavers in soil. This study evaluated antibiotics produced by EPB for their potential to control plant pathogenic bacteria and oomycetes.

METHODS AND RESULTS

Entomopathogenic bacterium produce antibiotics effective against the fire blight bacterium Erwinia amylovora, including streptomycin resistant strains, and were as effective in phytotron experiments as kasugamycin or streptomycin. Xenorhabdus budapestensis and X. szentirmaii antibiotics inhibited colony formation and mycelial growth of Phytophthora nicotianae. From X. budapestensis, an arginine-rich fraction (bicornutin) was adsorbed by Amberlite((R)) XAD 1180, and eluted with methanol : 1 n HCI (99 : 1). Bicornutin inactivated zoospores, and inhibited germination and colony formation of cystospores at <<25 ppm. An UV-active molecule (bicornutin-A, MW = 826), separated by HPLC and thin-layer chromatography, was identified as a novel hexa-peptide : RLRRRX.

CONCLUSIONS

Xenorhabdus budapestensis produces metabolites with strong antibacterial and cytotoxic activity. Individual compounds can be isolated, identified and patented, but their full antimicrobial potential may be multiplied by synergic interactions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Active compounds of two new Xenorhabdus species might control plant diseases caused by pathogens of great importance to agriculture such as Erw. amylovora and P. nicotianae.

Genomic typing of enterococci isolated from bovine mammary glands and environmental sources

Enterococcal isolates (n = 102) from various sources of bovine origin on 1 farm were characterized using pulsed field gel electrophoresis analysis of SmaI restriction patterns. Isolates originated from feed samples (n = 6), bedding samples (n = 15), and bovine quarter-milk samples (n = 81). Isolates collected from milk samples included those from high-somatic cell count cows (n = 42), postpartum milk samples (n = 16), and clinical mastitis samples (n = 23). Species evaluated included Enterococcus faecium (n = 68), Enterococcus casseliflavus (n = 29), and Enterococcus faecalis (n = 5). A total of 20 clusters representing 44 isolates were detected when a similarity cut-off level of 75% was applied to interpret the pulsed field gel electrophoresis results. Fifteen of the clusters contained only isolates from milk samples. Four clusters contained isolates from bedding and milk samples. One cluster contained only isolates from feed samples. Clusters comprised of a single species represented 17 of the 20 total clusters. These results suggest enterococci from bovine origin were genetically diverse, whereas a limited number of isolates from various sources appeared to cluster together.

Xenorhabdus antibiotics: a comparative analysis and potential utility for controlling mastitis caused by bacteria

AIMS

The role of antibiotics produced by bacterial symbionts of entomopathogenic nematodes is to suppress growth of microbes in the soil environment. These antibiotics are active against Gram-positive and Gram-negative bacteria, and were tested against mastitis isolates from dairy cows.

METHODS AND RESULTS

Two bioassays were adapted for Xenorhabdus antibiotics; an overlay method on agar plates, and serially diluted, cell-free, Xenorhabdus cultures. The antimicrobial activities of the liquid cultures of 13 strains from five Xenorhabdus species were further evaluated. Antimicrobial activities of the type strains of X. nematophila, X. budapestensis and X. szentirmaii were tested on mastitis isolates of Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae with both bioassays. A previously reported antibiotic from X. nematophila, nematophin, was synthesized in three steps from tryptamine and 4-methyl-2-oxovaleric acid sodium salt.

CONCLUSIONS

The antibiotics of all three Xenorhabdus strains were powerful in either bioassay, but the sensitivity of the isolates differed from each other. While Kl. pneumoniae was the least susceptible, Staph. aureus had the highest sensitivity to each Xenorhabdus strain. Xenorhabdus szentirmaii and X. budapestensis were more potent antibiotic producers than X. nematophila, and raceme nematophin was ineffective against all mastitis isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results indicate that Xenorhabdus antibiotics are effective against mastitis isolates and should be further evaluated for their potential in mastitis control or prevention.

In Vitro Growth of Enterococci of Bovine Origin in Bovine Mammary Secretions from Various Stages of Lactation

In vitro growth responses of Enterococcus faecium and Enterococcus faecalis were tested in cell-free, fat-free bovine mammary secretions. Mammary secretions were collected during the dry period, and during early, late, and extended lactation. Sixty-three enterococcal isolates from aseptically collected bovine quarter milk samples and bedding samples from a commercial dairy herd were tested. Isolates from bovine quarter milk samples originated from mammary glands with clinical mastitis, cows with composite somatic cell score >4, postpartum milk samples, or from routine milk samples submitted to a mastitis diagnostic laboratory. Source of enterococcal isolates and the species significantly contribute to the ability of organisms to multiply in mammary secretions from various stages of lactation. Isolates collected from milk samples of the commercial herd and isolates from milk submitted to a mastitis diagnostic lab did not display enhanced growth in mammary secretions compared with isolates from bedding. Growth responses of E. faecalis were greater than those for E. faecium in secretions collected during the dry period, late lactation, and extended lactation. Bacterial growth did not differ between enterococcal species in mammary secretion collected from cows in early lactation. Differences in bacterial growth between E. faecalis and E. faecium in mammary secretions may indicate differences between species in susceptibility of mammary glands during the lactation cycle.

Effects of Dietary Vitamin C on Neutrophil Function and Responses to Intramammary Infusion of Lipopolysaccharide in Periparturient Dairy Cows

Neutrophil function and the severity and incidence of mastitis in dairy cows is related to the intake of many antioxidant nutrients. Because vitamin C is the major water-soluble antioxidant in mammals, we examined the effect of dietary vitamin C on neutrophil function and responses to intramammary infusion of lipopolysaccahride (LPS) in periparturient dairy cows. At 2 wk before anticipated calving, Holstein cows were fed diets that provided 0 (16 cows) or 30 (15 cows) g/d of supplemental vitamin C (phosphorylated ascorbic acid). Treatments continued until 7 d after cows received an infusion of 10 microg of LPS into one quarter of the mammary gland (on average, this occurred 32 d postcalving). Supplementation of vitamin C increased plasma concentrations of vitamin C at calving, but no differences were observed in samples taken 24 h postinfusion. Concentrations of vitamin C in milk (24 h postinfusion) and in neutrophils (calving and 24 h postinfusion) were not affected by treatment, but vitamin C concentrations in neutrophils isolated from milk were about 3 times greater than concentrations in blood neutrophils. The LPS infusion did not alter concentrations of vitamin C in plasma or milk, suggesting that the LPS model did not produce the same effects as a bacterial infection of the mammary gland with respect to antioxidant effects. Supplemental vitamin C had no effect on neutrophil phagocytosis or bacterial kill. Dietary vitamin C reduced the milk somatic cell count but did not affect the febrile response or milk production following LPS infusion.

Bacterial Counts in Organic Materials Used as Free-Stall Bedding Following Treatment with a Commercial Conditioner

An acidic conditioner was tested in recycled manure and sawdust used as free-stall bedding to determine the effect on bacterial counts of common environmental mastitis pathogens. Free stalls were bedded with 10 kg of either kiln-dried sawdust or recycled manure per stall. All bedding was removed and fresh bedding was applied every 7 d. Approximately 1 kg of commercial bedding conditioner containing 93% sodium hydrosulfate (wt/wt) was spread evenly over bedding in the back one-third of each treated stall. Control bedding received no treatment. Cows were bedded on the same material for 3 consecutive weeks. After 3 wk on a bedding treatment, cows remained in the same pens and bedding treatments were changed between rows within pens in a switchback design. The addition of bedding conditioner to sawdust reduced gram-negative bacterial, coliform, Klebsiella spp., and streptococcal counts immediately after application and 1 d after application. Bacterial counts did not differ between treated and untreated sawdust on d 2 and 6 after the conditioner treatment. Each bacterial count measured was reduced in recycled manure immediately after application. Gram-negative bacterial and streptococcal counts were reduced in treated recycled manure compared with untreated recycled manure on d 1 after conditioner was applied. Bacterial counts did not differ between treated and untreated recycled manure bedding on d 2 and 6 after application in free stalls. The antibacterial activity of the conditioner was related to the pH of the bedding and was diminished by d 2 after application in both bedding types.

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.

Comparison of bacteria populations in clean and recycled sand used for bedding in dairy facilities

Bedding samples were collected twice from commercial dairy free-stall facilities that used recycled sand and clean sand in both the summer and winter. Collection began on the day sand was taken from the pile (d 0) and placed in the free stalls, and continued for 5 to 7 additional days. The number of colonies per gram of bedding of gram-negative bacteria, coliforms, Streptococcus spp., and Klebsiella spp. were estimated for each sand sample as well as amounts of dry and organic matter. Clean sand (CS) and recycled sand (RS) had the same bacterial counts when compared at any sampling time. The mean counts of bacterial populations did vary over the course of the study in both CS and RS. There was a significant increase in bacterial counts from d 0 to d 1 for gram-negative bacteria, coliforms, and Streptococcus spp. in both winter and summer. Counts of gram-negative bacteria, coliforms, Klebsiella spp., and Streptococcus spp. did not differ from d 1 to 7 in the winter. Total counts of gram-negative bacteria did not differ from d 1 to 7 in the summer. On d 1 in the summer, coliform counts were lower than at d 5 to 7, and Klebsiella spp. counts were lower than on d 3 to 7. Streptococcus spp. counts were high on d 1 and were constant through d 7 in both winter and summer trials. The number of coliform and Klebsiella spp. in both CS and RS was below the threshold thought to cause mastitis during the sampling times. The number of Streptococcus spp. was high in both CS and RS during the sampling periods. Other management factors need to be identified to decrease the number of Streptococcus spp. in bedding. Recycled sand had a higher organic matter and lower dry matter compared with CS in winter and summer. The results for this study were obtained from multiple herd comparisons, and herd was a significant effect suggesting that different management systems influence the number and types of bacteria in both CS and RS.

Effect of selenium source on selenium status, neutrophil function, and response to intramammary endotoxin challenge of dairy cows

The effects of feeding dry and early lactation dairy cows diets with selenate or selenized yeast (Se-yeast) on concentrations of Se in serum, milk, and newborn calves, neutrophil function, and inflammatory response were determined. At 60 d before anticipated calving until approximately 30 d in milk (DIM), cows were fed diets that contained 0.3 mg of supplemental Se/kg of DM from sodium selenate or Se-yeast. Diets also contained 0.2% supplemental S (as sulfate) because it has been shown to reduce absorption of Se by dairy cows. The concentration of Se in serum at calving and 28 DIM was about 1.4 times greater for cows fed Se-yeast than for those fed selenate. Serum concentrations decreased 45 and 23% from dry-off to calving for cows fed selenate or Se-yeast, respectively. Selenium concentrations in serum from newborn calves were also about 1.4 times greater when the dams were fed Se-yeast. Concentrations of Se in colostrum and milk were about 1.8 times greater when cows were fed Se-yeast. Blood neutrophils were isolated from cows at 28 DIM and were used in an in vitro kill assay. Selenium treatment did not affect bacterial kill or the percentage of neutrophils that phagocytized bacteria. At approximately 28 DIM, one quarter from each cow was infused with a solution containing endotoxin. Peak body temperature (40.7 degrees C) occurred 6 h postinfusion, and peak somatic cell count (6.5 log10/mL) occurred at 12 h postinfusion. Neither measure was influenced by Se treatment.

Effects of adjuvants on safety and efficacy of an Escherichia coli J5 bacterin

The effects of using a water-soluble adjuvant or an emulsified oil-based adjuvant on the safety, antibody titer, and clinical responses of an Escherichia coli J5 bacterin were tested in an experimental infection trial. Fifty-one cows were assigned to 17 blocks of 3. Two cows within each block of 3 were vaccinated with a commercially prepared E. coli J5 bacterin containing either a water-soluble adjuvant or the same bacterin preparation emulsified in oil. One cow in each block was an unvaccinated control. Cows were immunized at drying off and 42 d later. The right or left front mammary quarter of each experimental cow was challenged by intramammary infusion of E. coli 727 between 14 and 35 DIM. Areas of inflammation at the primary injection site were greater 1, 2, and 3 d following primary vaccination for bacterin containing oil-in-water adjuvant compared with bacterin containing water-soluble adjuvant. Whey anti-E. coli J5 IgG titers were higher at calving for cows vaccinated with bacterin containing oil-in-water adjuvant than for cows either vaccinated with bacterin containing water-soluble adjuvant or unvaccinated controls. Serum x-E. coli J5 IgG titers were higher at calving for vaccinated cows than for unvaccinated controls. Peak bacterial counts in milk from challenged quarters were greater for unvaccinated controls than for cows vaccinated with bacterin containing water-in-oil adjuvant. Bacterial counts in milk from challenged quarters and clinical score both were greater in unvaccinated controls than cows vaccinated with bacterin containing water-in-oil adjuvant between 12 and 24 h postchallenge. Clinical responses were similar between unvaccinated controls and cows vaccinated with bacterin containing water-soluble adjuvant.

Short Communication: Association Between Milk Yield at Dry-Off and Probability of Intramammary Infections at Calving

The association between milk yield at dry-off and intramammary infections at calving was evaluated from 116 lactations in one herd. Duplicate quarter samples were collected within 3 d after calving to estimate prevalence of intramammary infection at calving; information on cows' parity, daily milk yields, weekly somatic cell counts, and dry-off and calving dates were available for the data analyses. Generalized linear models with logit link were used to model the probability of a cow or a quarter being infected at calving, accounting for the clustered data. Increasing milk production at dry-off was a significant risk factor for both a cow and a quarter being infected with environmental pathogens at calving, but infections caused by coagulase-negative staphylococci at calving were not associated with milk yield at dry-off. For every 5-kg increase in milk yield at dry-off above 12.5 kg, the odds of a cow having an environmental intramammary infection at calving increased at least by 77%.

Iron uptake by Escherichia coli cultured with antibodies from cows immunized with high-affinity ferric receptors

The synergistic effects of immunoglobulin G (IgG) from cows vaccinated with ferric citrate receptor (FecA) and IgG from cows vaccinated with ferric enterobactin receptor (FepA) were measured in an in vitro iron uptake assay. Serum was isolated and pooled within treatment from five cows each vaccinated with FepA or FecA or not vaccinated. Immunoglobulin G was isolated by ammonium sulfate precipitation and protein G affinity chromatography. Six Escherichia coli isolates from bovine intramammary infections were cultured in an iron-depleted medium to induce high-affinity iron acquisition systems and, in iron-depleted conditions, to specifically induce the expression of FecA. The bacterial cells were mixed with either 3 or 6 mg/mL of purified IgG and 55Fe. The radioactivity of 55Fe taken up by the bacterial cells was measured by a liquid scintillation counter after 5-, 10-, and 15-min incubations at 37 degrees C. The combination of anti-FecA IgG and anti-FepA IgG reduced 55Fe uptake compared with either anti-FecA or anti-FepA alone. Iron uptake was reduced more by anti-FecA IgG than by anti-FepA IgG when the ferric citrate system was induced. Reduction of iron uptake did not differ between anti-FepA alone and anti-FecA alone when citrate was absent from the medium.

Antimicrobial susceptibility of mastitis pathogens from first lactation and older cows

Increasing antimicrobial resistance has become a serious concern worldwide and antimicrobial use in animal agriculture is currently under scrutiny. Mastitis is the most common reason for antibiotic use in dairy herds and thus, antimicrobial resistance of mastitis pathogens has received recent attention. The purpose of this study was to describe and compare antimicrobial susceptibility of mastitis pathogens isolated at calving from first lactation and older cows. A total of 202 bacteria were isolated from intramammary infections (IMIs) within 3 days after calving over a 16-month study period in the Krauss Dairy Research Herd at the Ohio Agricultural Research and Development Center (OARDC) in Wooster, OH. Of these IMIs, 78% were caused by coagulase-negative staphylococci (CNS). Forty-four percent of them were resistant to at least one antibiotic. Most resistance was observed against penicillin, 39% of the isolates from older cows and 26% from first lactation cows being resistant to penicillin (P > 0.05). Also MIC90 for penicillin was higher among isolates from older cows. On the other hand, resistance to tetracycline was more common and MIC90 higher among isolates from first lactation cows than from older cows. Differences in the proportions of resistant isolates between first lactation and older cows were not statistically significant, though. The resistance patterns of the CNS isolated during the study are concordant with antimicrobial usage in the study herd. This is in agreement with the generally accepted notion that selection pressure from the use of antibiotics is a main factor in development of antibiotic resistance.

Growth responses of Escherichia coli to immunoglobulin G from cows immunized with ferric citrate receptor, FecA

Effects of purified immunoglobulin (Ig) G from cows immunized with ferric citrate receptor, FecA, on the in vitro growth of Escherichia coli were investigated. Twenty-one cows were assigned to one of 3 treatments: 1) FecA immunization, 2) E. coli J5 bacterin immunization, and 3) unimmunized control. FecA was derived from E. coli UT5600/pSV66. Immunoglobulin G was purified from pooled colostral whey for each treatment group. The IgG from FecA immunized cows had higher titers against FecA compared with other treatment groups. Bacterial isolates tested were 14 E. coli from intramammary infections and E. coli UT5600/pSV66. Iron depletion decreased the growth of E. coli compared with growth in Fe-replete medium. The presence of IgG further decreased the growth compared with the growth under iron restriction alone. Bacterial growth did not differ among IgG sources nor between IgG concentrations. Replenishing media with exogenous iron overrode the inhibitory effects of the Fe-depletion and IgG. Vaccinating cows with FecA had little effect on the growth inhibitory properties of IgG toward E. coli mastitis isolates cultured in Fe-deplete media.

Changes in Vitamin C Concentrations in Plasma and Milk from Dairy Cows After an Intramammary Infusion of Escherichia coli

Plasma and milk concentrations of ascorbic acid and dehydro-L-ascorbic acid (DHAA) were measured before and after 21 Holstein cows (approximately 26 DIM) were given an intramammary infusion of Escherichia coli. Blood, milk from the unchallenged quarters, and milk from the challenged gland were sampled immediately before challenge (d 0) and 24 h and 7 d postchallenge. Plasma vitamin C (ascorbic acid + DHAA) concentrations decreased 39%, and concentrations of vitamin C and ascorbic acid in milk from the challenged quarter decreased 52 and 62%, respectively, in samples taken 24 h postchallenge. No change was observed in vitamin C concentrations in milk from unchallenged quarters. The concentration of DHAA in milk from challenged quarters increased 67% 24 h postchallenge. The duration of clinical mastitis, peak body temperature, number of colony-forming units of E. coli isolated from the infected gland, and loss in milk yield were associated with a change in concentration of vitamin C in milk from the challenged quarter. Increased severity of clinical signs was associated with large decreases in concentration of vitamin C in milk from the challenged quarter. Similar, but statistically weaker, relationships were observed for changes in plasma vitamin C concentrations.

Opsonic activity of serum and whey from cows immunized with the ferric citrate receptor

The effects of immunizing dairy cows with the ferric citrate receptor, FecA, on the opsonic activity of serum and whey were measured in a phagocytosis assay. Fifteen cows were assigned to five blocks of three cows based on date of expected parturition. Cows within a block were randomly assigned to one of three treatments: 1) FecA immunization, 2) immunization with a commercially available Escherichia coli J5 bacterin, and 3) unimmunized controls. Cows were challenged at approximately 21 DIM by intramammary infusion of E. coli 727 into one mammary quarter. Escherichia coli 727 were opsonized for the phagocytosis assay with either 10% heat-inactivated serum or 50% heat-inactivated whey collected from each cow at calving, immediately before challenge and 7 d after challenge. Cows immunized with FecA or the E. coli J5 bacterin had increased IgG titers against FecA and E. coli 727 compared with unimmunized control cows. However, sera and whey collected from cows immunized with FecA did not enhance opsonization of E. coli 727 compared with sera and whey from control cows. Immunization with the E. coli J5 bacterin increased opsonization of sera greater than immunization with FecA. Immunoglobulin M antibody titer against E. coli 727 in whey and phagocytic indexes were positively correlated. The phagocytic index of whey immediately before challenge and 7 d after challenge were negatively associated with peak bacterial counts in mammary quarters challenged with E. coli 727. Results of the current trial suggest that the immune response resulting from immunization with FecA did not enhance opsonization and in vitro phagocytosis of E. coli 727.

Effect of immunoglobulin G from cows immunized with ferric citrate receptor (FecA) on iron uptake by Escherichia coli

The effects of immunoglobulin (Ig) G from cows immunized with the ferric citrate receptor (FecA) on iron uptake by Escherichia coli were investigated. Receptor FecA was purified from E. coli UT5600/pSV66. Cows were immunized with 400 microg purified FecA three times at 21 d intervals during late lactation and the nonlactating period. Immunoglobulin G was purified by protein G affinity chromatography from colostral whey from cows immunized with FecA and from unimmunized control cows. The purified IgG from FecA immunized cows had higher IgG titers against FecA compared with control IgG. Fifteen E. coli isolated from intramammary infections and E. coli UT5600/pSV66 were grown in an iron-depleted medium containing 1 mM citrate to induce FecA. The bacterial cells were mixed with 0, 2, and 4 mg/ml purified IgG, and 55Fe was added to the assay. After 5, 10, and 15 min incubations at 37 degrees C, samples were passed through 0.45-pm pore size filters. Filters were washed with saline three times, and the radioactivity of 55Fe taken up by the bacterial cells on the filters was measured by a liquid scintillation counter. The measurements were expressed as numbers of 55Fe atoms per colony-forming unit and transformed to log10. The assay was repeated three times for each isolate in a partially balanced incomplete block design. The presence of IgG decreased 55Fe uptake by E. coli mastitis isolates and E. coli UT5600/pSV66. Anti-FecA IgG reduced 55Fe uptake by E. coli greater than IgG from unimmunized cows.

Phagocytosis and serum susceptibility of Escherichia coil cultured in iron-deplete and iron-replete media

The susceptibility of Escherichia coli cultured in either iron-deplete or iron-replete media to phagocytosis by bovine neutrophils and the bactericidal activity of bovine serum was tested in vitro. Fourteen E. coli isolates from naturally occurring intramammary infections (IMI) were cultured overnight at 37 degrees C in iron-replete media and iron-deplete media. The iron-replete media were trypticase soy broth or a chemically defined medium. The iron-deplete media were either trypticase soy broth plus 0.2 mM alpha, alpha' dipyridyl and 1mM citrate, or the chemically defined medium plus 0.2 mM alpha, alpha' dipyridyl, and 1 mM citrate. Iron-replenished medium was the chemically defined iron-deplete medium plus 40 mM ferric citrate. Bacteria grown in iron-deplete media were less susceptible to phagocytosis compared with bacteria grown in iron-replete media. Replenishing the chemically defined iron-deplete medium with ferric citrate obliterated the decreased susceptibility to phagocytosis observed in iron-deplete media. The iron availability in media used to culture E. coli before assay did not affect the bactericidal action of either the classical pathway of complement or the antibody independent alternative pathway of complement in serum. The growth of bacteria in iron-deplete medium did not alter the expression of capsule compared with growth in iron-replete medium. Iron availability during culture of E. coli altered the susceptibility of isolates to phagocytosis by neutrophils, but had no effect on the susceptibility of isolates to the bactericidal activity of serum.

Efficacy of immunization with ferric citrate receptor FecA from Escherichia coli on induced coliform mastitis

The effects of immunization with the ferric citrate receptor FecA on antibody responses and on experimentally induced mastitis following intramammary challenge were investigated. Twenty-one cows were assigned to seven blocks of three cows based on expected parturition. Cows within block were randomly assigned to one of three treatments: 1) FecA immunization, 2) Escherichia coli J5 immunization, and 3) unimmunized controls. Challenge was by infusion of approximately 60 cfu of E. coli 727 into one uninfected mammary gland between 13 and 31 d after parturition. Cows within block were challenged on the same day. Cows immunized with FecA had higher immunoglobulin (Ig)G titers against FecA in serum and in mammary secretions at calving, immediately before challenge, and 7 d after challenge than did cows immunized with E. coli J5 or control cows. Immunization with FecA also increased IgG titers against whole-cell E. coli 727 in serum and in mammary secretions at calving. Serum IgM titers against FecA were higher in FecA immunized cows than in other treatment groups immediately before challenge. Bacterial counts in milk, duration of bacterial isolation in milk, rectal temperature, and milk somatic cell counts following intramammary challenge were similar among treatments. Milk production and dry matter intake did not differ among treatments. The ferric citrate receptor FecA was immunogenic in cows, but immunization had minimal effect on the clinical severity of experimentally induced E. coli mastitis.

Efficacy of intramammary immunization with an Escherichia coli J5 bacterin

Intramammary immunization was investigated as a procedure to reduce the clinical signs of coliform mastitis. Twenty-four cows were equally distributed to the following Escherichia coli J5 immunization schedules: 1) Subcutaneous injection 14 d prior to the end of lactation, intramammary immunization 7 d after drying off, and subcutaneous injection 30 d into the dry period; 2) subcutaneous injections at drying off, at 30 d into the dry period, and within 12 h after calving; and 3) unimmunized controls. Intramammary immunizations were the infusion of vaccine via the teat canal into each of the four mammary glands. Cows were challenged by infusion of E. coli 727 into one uninfected mammary quarter at approximately 30 d after calving. Intramammary immunization enhanced antibody titers against E. coli J5 and E. coli 727 compared with subcutaneous immunization. Immunoglobulin G titers against E. coli J5 and E. coli 727 in whey were greater at the time of challenge and 7 d after challenge for cows that received the intramammary immunization than for cows immunized by only subcutaneous injections. Serum IgG titers against E. coli 727 were enhanced at 7 d after challenge for cows receiving intramammary immunizations compared with conventionally immunized cows. Serum IgM titers against E. coli 727 were higher at calving for cows receiving intramammary immunization compared with conventionally immunized cows. Immunization schedule had minimal effect on systemic and local signs of clinical mastitis following challenge.

Antigenic homology of the inducible ferric citrate receptor (FecA) of coliform bacteria isolated from herds with naturally occurring bovine intramammary infections

Expression of ferric citrate receptor FecA by Escherichia coli and Klebsiella pneumoniae isolated from bovine mastitis was investigated. Transformant E. coli UT5600/pSV66, which produces large quantities of FecA in the presence of citrate, was constructed. The FecA of E. coli UT5600/pSV66 was purified by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and used to prepare polyclonal antiserum in rabbits. All coliform isolates of E. coli (n = 18) and K. pneumoniae (n = 17) from naturally occurring bovine intramammary infections in five herds induced iron-regulated outer membrane proteins when grown in Trypticase soy broth containing 200 microM alpha-alpha'-dipyridyl and 1 mM citrate. Polyclonal antiserum against FecA was used in conjunction with an immunoblot technique to determine the degree of antigenic homology of FecA among isolates. In the presence of citrate, each isolate expressed FecA that reacted with the anti-FecA polyclonal antiserum. The molecular mass of FecA ( approximately 80.5 kDa) was also highly conserved among isolates. Therefore, the ferric citrate iron transport may be induced in coliform bacteria and utilized to acquire iron in milk for survival and growth. The FecA is an attractive vaccine component for controlling coliform mastitis during the lactation period.

Bacterial counts associated with sawdust and recycled manure bedding treated with commercial conditioners

Bacteria counts associated with untreated organic bedding materials were compared with those of bedding treated with either an alkaline commercial bedding conditioner, acidic commercial bedding conditioner, or hydrated lime. Bedding materials were recycled manure and kiln-dried sawdust. The effects of bedding treatments on bacteria counts differed between bedding types. Each of the bedding treatments significantly reduced bacteria in recycled manure prior to use. The alkaline conditioner and hydrated lime effectively inhibited bacteria in recycled manure for 1 d. Bedding counts and teat swabs of cows housed on recycled manure treated with the alkaline conditioner were reduced on d 2. The use of the acid conditioner in recycled manure had little effect on bacteria in bedding. Sawdust differed from recycled manure in that bacteria in untreated sawdust prior to use were minimal, and populations increased rapidly during the first 2 d after use as bedding. The acid conditioner had a bacteriostatic effect in sawdust, evident by the reduction of bacteria on d 2. The alkaline conditioner and hydrated lime did not alter bacteria counts in sawdust compared with untreated sawdust. Antibacterial activity of each conditioner deteriorated between d 2 and d 6 in both beddings. The antibacterial activities of conditioners were related to the pH of bedding materials. The use of commercial bedding conditioners initially reduced bacterial counts; however, the antibacterial effects had diminished between d 2 and 6 after use in bedding.

Efficacy of an Escherichia coli J5 bacterin administered to primigravid heifers

The efficacy of an Escherichia coli J5 bacterin for reducing the incidence of intramammary infections and clinical signs of mastitis was tested in first lactation heifers. Ten primigravid heifers were immunized with an E. coli J5 bacterin. Four heifers received a placebo. The bacterin and placebo were injected subcutaneously approximately 60 d prior to calving, 28 d later, and within 48 h after calving. Vaccinated and placebo-injected heifers were challenged by intramammary infusion of E. coli 727 in one mammary gland between 23 and 37 d after calving. All challenged quarters were diagnosed with an intramammary infection within 6 h after bacteria were infused. The severity and duration of local signs of clinical mastitis were reduced in vaccinated heifers compared with placebo-injected heifers. Systemic signs of clinical mastitis were limited and did not differ between treatment groups. Bacteria counts in milk from challenged quarters were lower in vaccinated heifers than in control heifers at 12, 15, and 48 h after challenge. Serum immunoglobulin G titers against whole-cell E. coli J5 antigen at calving were higher in vaccinated heifers than they were in controls. Vaccinated heifers had higher immunoglobulin G titers than did controls in mammary secretions at calving and immediately prior to challenge. Immunization of primigravid heifers with an E. coli J5 bacterin during the last trimester of gestation and at calving reduced the severity and duration of clinical signs following intramammary challenge with a heterologous strain of E. coli.

Growth responses of coliform bacteria to purified immunoglobulin G from cows immunized with ferric enterobactin receptor FepA

The ability of purified bovine immunoglobulin (Ig) G from cows immunized with ferric enterobactin receptor FepA to inhibit the growth of coliform bacteria derived from bovine intramammary infection was investigated in iron-restricted media. All isolates of Escherichia coli (n = 21) and Klebsiella pneumoniae (n = 21) were tested for growth in a chemically defined medium containing 0.5 mg/ml of apolactoferrin and in a pooled source of dry cow secretion. The addition of 4 mg/ml of purified bovine IgG directed against FepA in the synthetic medium resulted in significant growth inhibition for both E. coli and K. pneumoniae isolates. Growth reduction of E. coli was greater than that of K. pneumoniae. In dry cow secretions, the growth of each E. coli isolate but of less than half of K. pneumoniae isolates (43%) was inhibited by IgG from cows immunized with FepA. Purified bovine IgG from cows immunized with E. coli J5 had a minimal inhibitory effect on the growth of both E. coli and K. pneumoniae isolates in the synthetic medium. In dry cow secretions, IgG from cows immunized with E. coli and K. pneumoniae isolates. Supplementation with 50 microM of ferric chloride to the medium completely reversed the inhibitory effects of the antibodies and lactoferrin. Bovine IgG directed against FepA apparently inhibited the growth of coliform bacteria by interfering with the binding of the ferric enterobactin complex to the cell surface receptor FepA.

Evaluation of an acriflavine disk assay for differentiating Staphylococcus aureus from other staphylococci isolated from bovine milk

OBJECTIVE

To develop an acriflavine disk assay for identification of Staphylococcus aureus and to test whether the acriflavine disk assay could be used to differentiate S aureus from other staphylococci isolated from bovine milk samples.

DESIGN

Prospective study.

SAMPLE POPULATION

882 staphylococcal isolates from bovine milk samples and 3 S intermedius isolates from dogs.

PROCEDURE

Paper disks saturated with various amounts of acriflavine were used in a growth inhibition assay to determine the amount of acriflavine that would most reliably differentiate S aureus from other staphylococci. For all isolates, hemolytic pattern, results of tube coagulase tests after 4 and 24 hours of incubation, growth on acriflavine-supplemented media, results of an acriflavine disk assay, and results of an automated identification system were determined.

RESULTS

10 micrograms of acriflavine/disk was determined to be the most appropriate concentration for use in the assay. All 112 isolates identified as S aureus by the automated identification system were resistant to this concentration of acriflavine, and only 1 of 236 isolates identified as non-S aureus staphylococci was resistant. There was substantial agreement between results of using the acriflavine disk assay as a diagnostic criterion for differntiating S aureus isolates from non-S aureus staphylococci and results of the automated identification system. Agreement between results of determining hemolytic pattern and results of other diagnostic tests was only moderate.

CLINICAL IMPLICATIONS

The acriflavine disk assay, using 10 micrograms of acriflavine/disk, was a practical, accurate method for differentiating S aureus isolates from non-S aureus staphylococci.

Immunization of cows with ferric enterobactin receptor from coliform bacteria

The serum and milk immunoglobulin (Ig) G responses of lactating dairy cows were determined following immunization with ferric enterobactin receptor FepA. Escherichia coli 471 was cultured in iron-depleted medium, and outer membrane proteins were extracted by 2% N-lauroylsarcosine sodium salt and 2% Triton X-100. The FepA was isolated from the outer membrane proteins by ion-exchange chromatography. Twenty cows were assigned to four treatment groups of 5 cows blocked by breed and days in milk. Treatment groups were vaccinated with 100 micrograms of FepA, 500 micrograms of FepA, Escherichia coli J5 bacterin, or sterile phosphate-buffered saline. Primary immunization was at approximately 200 d in milk, and booster immunizations were given 14 and 28 d later. Serum and whey IgG titers to FepA in cows vaccinated with FepA were significantly higher than those from cows vaccinated with either E. coli J5 bacterin or phosphate-buffered saline. Serum and whey IgG titers to FepA were elevated by 14 d in cows vaccinated with FepA. Significant differences were not observed between doses of FepA. The degree of cross-reactivity of purified IgG from cows vaccinated with FepA to E. coli and Klebsiella pneumoniae isolates was significantly higher than that to a control isolate that lacked FepA production. Immunization with FepA elicited an immunological response in serum and milk.

Inhibition of in vitro growth of coliform bacteria by a monoclonal antibody directed against ferric enterobactin receptor FepA

The ability of a murine monoclonal antibody that blocks the enterobactin ligand-binding site of the ferric enterobactin receptor FepA to inhibit the growth of coliform bacteria derived from a bovine intramammary infection (IMI) was determined in an iron-restricted medium. Bacterial isolates from bovine IMI in five herds were tested by the chrome azurol sulfonate assay to detect siderophore production. Each of the isolates of Escherichia coli (n = 25) and Klebsiella pneumoniae (n = 25) were positive for siderophore production. Each isolate expressed iron-regulated outer membrane proteins when grown in trypticase soy broth plus the iron chelator alpha-alpha'-dipyridyl. Immunoblots revealed that the monoclonal antibody recognized FepA that was expressed by each of the E. coli isolates (n = 25). Only 4 of 25 K. pneumoniae isolates produced FepA that reacted with the monoclonal antibody. This result coincided with the results of an in vitro growth assay. Growth of all E. coli isolates was significantly inhibited by the addition of monoclonal antibody to synthetic medium containing apolactoferrin. Antigenic variation in the enterobactin-binding site resulted in a low percentage of K. pneumoniae isolates that were inhibited by the monoclonal antibody. Inhibition of bacterial growth by the monoclonal antibody was dose-dependent. As little as 50 micrograms/ml of purified antibody had an inhibitory effect on bacterial growth in the synthetic iron-restricted medium. Monoclonal antibody specific for the enterobactin ligand-binding site of FepA inhibited the growth of E. coli that was isolated from bovine IMI.

Concentrations of alpha-Tocopherol after intramammary infusion of Escherichia coli or lipopolysaccharide

Fifteen Holstein cows were used in a trial involving intramammary challenge to determine the effects of acute clinical mastitis on the concentrations of alpha-tocopherol in milk and plasma and the concentrations of neutrophils in milk and blood. Cows were assigned to one of three experimental groups challenged by intramammary infusion of lipopolysaccharide, Escherichia coli, or sterile phosphate-buffered saline. All quarters infused with lipopolysaccharide or E. coli were diagnosed with clinical mastitis on d 1 and 2 after challenge. Acute inflammation caused by intramammary infusion of lipopolysaccharide or E. coli resulted in increased concentrations of alpha-tocopherol in milk in challenged quarters but had no effect on concentrations of alpha-tocopherol in plasma. Concentrations of alpha-tocopherol in milk and blood neutrophils did not differ among treatment groups. Concentrations of alpha-tocopherol did not differ between milk and blood neutrophils. Approximately 25% of the alpha-tocopherol in milk from glands with clinical mastitis was associated with neutrophils, and < 10% of the alpha-tocopherol in milk from nonmastitic glands was associated with neutrophils. A shift toward sources of alpha-tocopherol other than synthesized milk fat occurred during acute inflammation in the mammary gland.

Responses of antibody titers to intramammary immunization with Escherichia coli J5 bacterin

The effect of an immunization schedule on responses of antibody titers was tested following vaccination with an Escherichia coli J5 bacterin. Eighteen cows were equally distributed among three immunization schedules: 1) subcutaneous injection at 14 d prior to the end of lactation, intramammary immunization at 7 d after drying off, and subcutaneous injection at 30 d into the dry period; 2) subcutaneous injections at drying off, at 30 d into the dry period, and within 12 h after calving; and 3) unimmunized controls. The E. coli J5 bacterin consisted of 5 ml of 10(9) boiled cells/ml of 0.9% NaCl plus 0.005% phenol emulsified with 5 ml of Freund's incomplete adjuvant. Subcutaneous injections were administered on the upper part of the rib cage, posterior to the scapula. Intramammary immunizations of 2.5 ml of bacterin were infused via the teat canal into each of the four mammary glands. Intramammary immunization increased rectal temperatures at 12 h after infusion, but subcutaneous injections did not induce febrile responses. Intramammary immunization enhanced immunoglobulin G titers in serum and whey on d 0 of lactation compared with subcutaneous immunizations. Immunoglobulin G titers in serum also were greater at d 30 of the dry period and at d 14 and 21 of lactation for cows that received intramammary immunization than for cows that were vaccinated by subcutaneous injections only. Immunoglobulin M titers in whey and serum on d 21 of lactation were greater for cows that received intramammary immunizations than for cows that were immunized by subcutaneous injections only.

Bacteria counts in sawdust bedding

Bacteria counts in untreated sawdust bedding were compared with those in sawdust bedding after the addition of lime and after daily replacement of bedding in the back one-third of the stalls. Addition of 1 kg of lime to 10 kg of sawdust reduced Gram-negative bacteria, coliforms, Klebsiella spp., and streptococci prior to use as bedding. Sawdust treated with lime also showed decreased bacteria counts compared with bacteria counts for sawdust that was replaced daily and compared with bacteria counts for control bedding after 1 d in the stall. The decrease in bacterial populations was related to an increase in bedding pH. Mean pH in the sawdust treated with lime was greater prior to use and after 1 d in the stall than the pH of other treatments. After 2 and 6 d in stalls, however, bacteria counts and pH were similar among treatments. Dry matter content of bedding did not differ among bedding treatments. Bacteria counts in bedding were positively correlated with teat skin swabs. Gram-negative bacteria and Klebsiella spp. counts on teat swabs were lower for cows housed on bedding treated with lime on d 2 compared with those for cows housed on control bedding and bedding that was replaced daily. Addition of lime to sawdust in the back one-third of tie stalls caused a decrease in exposure of teats to environmental mastitis pathogens in bedding for 1 d. Daily replacement of bedding had a minimal effect on bacteria counts in bedding and on teat skin.

Effect of vitamin E supplementation in diets with a low concentration of selenium on mammary gland health of dairy cows

Sixty-six cows and heifers (Holsteins and Jerseys) were assigned to one of three treatments at 60 d before anticipated calving. Treatment 1 consisted of 100 IU/d of supplemental vitamin E during the dry period and 100 IU/d during the first 30 d of lactation. Treatment 2 was 1000 IU/d of vitamin E during the dry period and 500 IU/d during lactation. Treatment 3 was 1000 IU/d of vitamin E during the first 46 d of the dry period, 4000 IU/d during the last 14 d of the dry period, and 2000 IU/d during lactation. Plasma concentrations of alpha-tocopherol decreased at calving for cows fed dietary treatments with low or intermediate concentrations of vitamin E, but not for cows fed the high vitamin E treatment. High dietary vitamin E increased concentrations of alpha-tocopherol in blood neutrophils at parturition, but no difference was found for the other two treatments. The percentage of quarters with new infections at calving was not different (32.0%) between cows receiving treatments that contained low and intermediate concentrations of vitamin E but was reduced (11.8%) in cows receiving the high vitamin E treatment. Clinical mastitis affected 25.0, 16.7, and 2.6% of quarters during the first 7 d of lactation for cows receiving the low, intermediate, and high vitamin E treatments, respectively. Cows with plasma concentrations of alpha-tocopherol < 3.0 micrograms/ml at calving were 9.4 times more likely to have clinical mastitis during the first 7 d of lactation than were cows with plasma concentrations of alpha-tocopherol > 3.0 micrograms/ml.

Dietary vitamin E and selenium affect mastitis and milk quality

Vitamin E and selenium (SE) are essential nutrients that are integral components of the antioxidant defense of tissues and cells. Soils in many of the important dairy regions of the world are Se-deficient, and feedstuffs grown on these soils will not provide adequate dietary Se. Cattle consuming stored forages are likely to be low in vitamin E unless supplemented, and vitamin E deficiencies are frequently observed in peripartum dairy cows. Many new intramammary infections (IMI) occur in the 2 wk before and after calving. Deficiencies of either vitamin E or Se have been associated with increased incidence and severity of IMI, increased clinical mastitis cases, and higher somatic cell counts (SCC) in individual cows and bulk tank milk. Somatic cell counts are a primary indicator of mastitis and milk quality in dairy herds. The polymorphonuclear neutrophil (PMN) is a major defensive mechanism against infection in the bovine mammary gland. A know consequence of vitamin E and Se deficiency is impaired PMN activity and postpartum vitamin E deficiencies are frequently observed in dairy cows. Dietary supplementation of cows with Se and vitamin E results in a more rapid PMN influx into milk following intramammary bacterial challenge and increased intracellular kill of ingested bacteria by PMN. Subcutaneous injections of vitamin E approximately 10 and 5 d before calving successfully elevated PMN alpha-tocopherol concentrations during the periparturient period and negated the suppressed intracellular kill of bacteria by PMN that commonly is observed around calving.

alpha-Tocopherol concentrations in milk and plasma during clinical Escherichia coli mastitis

Eighteen cows were challenged by intramammary infusion with Escherichia coli 727 to determine the effects of acute clinical mastitis on alpha-tocopherol concentrations in plasma and milk. Cows were fed diets supplemented with 1000 IU of vitamin E/d from calving through the experimental period. At challenge, geometric mean DIM was 33 d. Each mammary quarter was diagnosed with an IMI and clinical mastitis at 24 and 48 h after challenge. The alpha-tocopherol concentrations in milk from challenged quarters were approximately 60% greater by 24 and 48 h after challenge than concentrations at prechallenge and 168 h postchallenge. Plasma alpha-tocopherol concentrations did not change after intramammary challenge. The alpha-tocopherol in plasma and milk was correlated at 48 and 168 h postchallenge but not at prechallenge or 24 h postchallenge. Milk alpha-tocopherol and SCC were correlated positively across all sample periods. Milk fat and milk alpha-tocopherol concentrations were correlated at each sample period except 24 h postchallenge. Increases in milk alpha-tocopherol during clinical mastitis were not correlated to milk production, DMI, or BSA concentration in milk. Changes in milk alpha-tocopherol concentration during clinical mastitis were similar to the dynamics of milk SCC.

Antigenic crossreactivity and lipopolysaccharide neutralization properties of bovine immunoglobulin G

We investigated a possible mechanism by which immunization against core and lipid A determinants of lipopolysaccharide reduced clinical cases of mastitis and symptoms commonly associated with heterologous Gram-negative IMI. The IgG fraction of sera from cows immunized with either Escherichia coli J5 bacterin, E. coli J5 lipopolysaccharide conjugate vaccine, or unimmunized controls was purified by precipitation with caprylic acid and ammonium sulfate. The degree of IgG crossreactivity with Gram-negative bacteria that were isolated from clinical quarters was greater than that with Gram-positive isolates of Staphylococcus aureus. The highest magnitude of crossreactivity was against smooth strain E. coli isolates, followed by heterologous species of Enterobacter, Serratia, and Klebsiella isolates. Serum IgG from cows immunized with conjugate was highly crossreactive to E. coli J5, E. coli O111:B4, Serratia marcescens, Klebsiella pneumoniae, and Salmonella typhimurium lipopolysaccharides. The magnitude of antibody crossreactivity with lipopolysaccharides coincided with the ability of IgG to suppress the mitogenic effect of lipopolysaccharides on bovine lymphocytes.

Environmental streptococcal intramammary infections of the bovine mammary gland

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

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

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

Immunization of dairy cows with an Escherichia coli J5 lipopolysaccharide vaccine

Development of a lipopolysaccharide-protein conjugate vaccine and the immunological response to the vaccine were investigated. Lipopolysaccharide derived from Escherichia coli J5 was detoxified by mild alkaline hydrolysis. Detoxification reduced endotoxin activity 2500-fold compared with that of native J5 lipopolysaccharide. The conjugate vaccine was synthesized by covalently coupling detoxified lipopolysaccharide to chicken serum albumin by reductive amination. Dairy cows were immunized with 8.35 mg of conjugate (n = 3) or 5 x 10(9) heat-killed J5 bacterin (n = 5) at 215 DIM and received a secondary immunization 14 d later. Control cows were not immunized. Immunization enhanced serum antibody titer to J5 lipopolysaccharide antigens. Whey IgG and IgM titers to J5 lipopolysaccharide were not different among treatment groups. Serum and whey IgG titers to J5 whole-cell antigens were elevated in immunized cows within treatment groups. Immunization did not enhance whey IgM to J5 whole-cell antigens. Conjugate immunization elicited an immune response comparable with or greater than that of immunized cows with J5 bacterin.

Effect of forage to concentrate ratio on disappearance of vitamins A and E during in vitro ruminal fermentation

The effects of forage to concentrate ratio and the commercial form of vitamins A and E on in vitro ruminal disappearance of retinol and alpha-tocopherol were studied. Ruminally fistulated cows were fed diets with either 80 or 50% forage. In vitro substrates that were similar to those fed to the donor cows were incubated with buffered ruminal fluid for 24 h. Different commercial forms of vitamin E (spray-dried, silicic acid adsorbate, and lipid-encased forms) and vitamin A (gelatin beadlet and lipid-encased forms) were added to the flasks. The vitamin E was all-rac-alpha-tocopheryl acetate, and the vitamin A was all-trans-retinyl acetate. The amount of alpha-tocopherol in the flasks was not affected by diet or form of vitamin E and did not change over the 24-h incubation. Retinol disappearance was not affected by form of vitamin A but was substantially higher for the 50% forage diet than for the 80% forage diet (72 vs. 20% at 24 h). These data suggest that ruminal metabolism of vitamin E is minimal and not affected by forage to concentrate ratio. Additionally, vitamin A destruction in the rumen was much higher when cows were fed a typical lactation diet than when fed a typical dry cow diet.

Efficacy of recombinant bovine interleukin-2 as an adjunct to dry cow therapy

Recombinant bovine interleukin-2 was tested as adjunct therapy to intramammary infusion of antibiotics at drying off. Cows were assigned randomly within three commercial herds to either recombinant bovine interleukin-2 or PBS treatment groups at drying off. Ninety-five cows received intramammary infusions of 1 mg of recombinant bovine interleukin-2 in each quarter immediately preceding intramammary infusion of a product for antibiotic therapy of dry cows. Ninety-four cows received intramammary infusion of 10 ml of endotoxin-free PBS in each quarter immediately preceding the antibiotic therapy. Cure rates for IMI present at drying off did not differ between cows treated with recombinant bovine interleukin-2 and those treated with PBS. Intramammary infusion of recombinant bovine interleukin-2 did not affect the rate of new IMI during the dry period. Milk production and SCC during the first 3 mo of lactation subsequent to therapy did not differ between treatment groups. Intramammary infusion of recombinant bovine interleukin-2 was not effective as an adjunct to antibiotic therapy for dry cows.