Herd management practices associated with bovine leukemia virus incidence rate in Michigan dairy farms.

The objective of this study was to identify associations between herd management practices and the incidence rate of bovine leukemia virus (BLV) infections in Michigan dairy herds. Previous management risk factor studies were of antibody prevalence rather than the rate of recent infections. Milk samples were collected from cohorts of cows on 112 Michigan dairy herds and tested for BLV using an antibody capture ELISA (n = 3849 cows). Cows were subsequently followed for an average of 21 months. Cows negative for anti-BLV antibodies and still present in their respective herds were retested by the same antibody capture ELISA to estimate within-herd incidence rates. The overall crude incidence rate was 1.46 infections per 100 cow-months at risk for the 1314 retested cows in 107 herds. The average within-herd incidence rate was 2.28 infections per 100 cow-months (range: 0 to 9.76 infections per 100 cow-months). A negative binomial regression model was used to identify herd management practices associated with the within-herd incidence rate. Results of the final multivariable model identified higher herd prevalence, milking frequency, needle reuse, as well as housing post-parturient cows separately, to be associated with increased incidence rate. Utilization of sand bedding for the lactating herd was found to be associated with decreased incidence rates. Results of this study suggest potential routes of BLV transmission which should be further investigated as disease control targets in ongoing control programs.

Short communication: Herd-level variables associated with overmilking in Michigan dairy herds.

The objective of this study was to determine the herd-level variables that are associated with overmilking in 64 Michigan dairy herds with a mean herd size of 451 cows (range: 59-2,771 cows). Participating producers completed surveys to indicate their mastitis management practices and attitudes. Additionally, milking protocols were observed and milk flow dynamics for 3,824 cows were estimated using digital vacuum recorders. The median duration of overmilking was 47 s (95% confidence interval, CI: 38.6 to 55.9 s), with a mean of 55% (95% CI: 49.5 to 61.1%) of cows within each herd overmilked by at least 30 s. Median milking time for all herds was 324 s (95% CI: 302 to 346 s) and was found to be positively correlated with median duration of overmilking (r = 0.670). Backward multivariate analysis was used to determine which of 45 herd-level milking and management variables were associated with median duration of overmilking. Median duration of overmilking was negatively associated with the duration of time needed to complete 1 milking for the entire herd (adjusted R2 = 0.13). Herds that operate milking facilities below maximum daily capacity may be prone to overmilking. Given the low coefficient of determination, variables unaccounted for in this study, such as equipment function or manual detachment by milking operators, are likely the most important risk factors for overmilking.

Decreased milk yield is associated with delayed milk ejection.

To determine whether individual cow milking vacuum (within the short milk tube and the liner mouthpiece) could be substituted for milk flow technology to identify delayed (bimodal) milk ejection, and the possible relationship between bimodal milk flow and milk yield, we recorded milking data from 663 Holstein cows on a 3,600-cow Michigan dairy that milked 3 times per day. Overall, delayed milk ejection occurred in 45.6% of the milkings, and 98% of the cows with delayed milk ejection also had bimodal flow. Multivariable analysis revealed that milk yield during each individual cow milking was positively associated with increasing lactation number but negatively associated with increasing days in milk and delayed milk ejection. As the time between unit attachment and the estimated milk letdown (the lag period) increased, milk yield decreased; relative to a lag of <30 s, milk yield decreased by 1.8 and 3.1 kg for lags of 30-59 and ≥60 s, respectively. The final multivariate model had an adjusted coefficient of determination of 0.27. The negative association between delayed milk ejection and decreased milk yield in this study suggested that milking vacuum parameters from individual cows could serve as a useful tool to qualitatively estimate milk flow within a herd and that this information may be used to enhance herd productivity.

Herd-level variables associated with premilking stimulation time in Michigan dairy herds.

The objective of this study was to determine the herd-level variables that were associated with total stimulation time during the premilking routine in 64 Michigan dairy herds. The mean herd size was 452 cows (range = 59 to 2,771 cows). For each herd, surveys were administered to producers to gather mastitis management practices and attitudes. Additionally, milking protocols were observed and milk flow dynamics were measured by use of digital vacuum recorders. Backward multivariate regression analysis was used to determine which of 47 herd-level milking and management variables were associated with mean total stimulation time. Mean total stimulation time was 14.2 s (range = 2.4-40.8 s) and was positively associated with increasing latency period (time interval between first stimulation and cluster attachment). Total stimulation time was negatively associated with greater herd size and number of visits to each cow in the premilking routine. In summary, increased stimulation time is more likely in herds that foster a lower sense of urgency of cow throughput during milking, as evidenced by a positive association with longer latency periods and fewer preparation visits per cow. Tactile stimulation is critical for efficient milk ejection; if inadequate, cows are at greater risk of delayed milk ejection and bimodal milk flow, which in turn has been associated with teat congestion and reduced milk flow. This study offers insight as to some of the herd factors that may be limiting adequate tactile stimulation.

Herd-level variables associated with delayed milk ejection in Michigan dairy herds.

The objective of this study was to determine which herd-level variables were associated with delayed milk ejection (bimodal milk let-down) in 64 Michigan dairy herds. Median herd size was 294 cows (range 59 to 2,771 cows). For each herd, milking protocols were observed and milk flow dynamics were estimated by use of digital vacuum recorders. Surveys were also administered to the producers to measure mastitis management practices and attitudes. Milk flow dynamics were recorded for a total of 3,824 cow milkings, with a mean of 60 milkings per herd (range of 11 to 154). Backward multivariable analysis was used to determine which of the 47 herd-level milking and management variables were associated with delayed milk ejection (cows with milk let-down periods between milking cluster attachment and the incline phase of milk flow of >30 s). Delayed milk ejection occurred in an average of 25% of the cows in each herd (range 0 to 75%). A multivariable model found that the proportion of cows in a herd with delayed milk ejection was negatively associated with mean total time of tactile stimulation during premilking routines and positively associated with herd size.

Antimicrobial treatment of clinical mastitis in the eastern United States: The influence of dairy farmers' mastitis management and treatment behavior and attitudes.

To assess both the behaviors and social variables related to antimicrobial therapy for clinical mastitis, we sent a survey to 1,700 dairy farms in Michigan, Pennsylvania, and Florida in January and February 2013. The survey included questions related to 7 major areas: sociodemographic and farm characteristics, milking proficiency, milking systems, cow environment, infected cow monitoring and treatment, farm labor, and attitudes toward mastitis and related antimicrobial use. The overall response rate was 41% (21% in Florida, 39% in Michigan, and 45% in Pennsylvania). Herd size ranged from 9 to 5,800 cows. Only a small proportion of herds frequently or always cultured milk samples for bacteriology from cows with a high somatic cell count (17%), cows with clinical mastitis (18%), or bulk tank milk (13%). Likewise, only 56% of herds frequently or always maintained records of all treated cows and 49% reviewed records before administering mastitis treatments. Multivariate analysis determined that use of treatment records was associated with increased likelihood of frequent use for both intramammary (IMA) and systemic (SYA) administration of antimicrobial drugs for therapy of clinical mastitis. As would be expected, use of natural (organic) therapies was associated with decreased use of IMA, as was the respondent being a member of an Amish community. Lower levels of education and the use of bacterins to control Staphylococcus aureus mastitis were also associated with decreased IMA, whereas increased use of IMA at dry off and the belief that "bad luck" plays a role in mastitis problems were associated with increased IMA. Use of an internal teat sealant, the respondent being the sole proprietor, being from Michigan, use of conductivity to measure subclinical mastitis, the respondent placing increasing importance on decreasing antibiotic residues in cull cows, and having financial incentives for employees linked to somatic cell count were associated with increased use of SYA for the treatment of clinical mastitis. Use of sand or mattresses for bedding were associated with decreased SYA. These findings highlight the need to improve the acceptance of practices that are consistent with prudent antimicrobial use for the treatment of clinical mastitis on dairy farms. Additionally, the willingness of dairy farmers to administer antimicrobial drugs for the treatment of clinical mastitis is associated with other mastitis-related practices and attitudes.

Effect of infection with bovine leukemia virus on milk production in Michigan dairy cows.

The objective of this study was to determine the association between individual cow-level milk production and bovine leukemia virus (BLV) infection as measured by milk BLV-ELISA. Dairy Herd Improvement technicians collected milk samples from 10 cows from each of first, second, third, and 4+ parity cows in 105 Holstein herds with ≥ 120 milking cows. Milk samples were tested for the presence of anti-BLV antibodies by ELISA. Additional data regarding the cows and the herds were collected by farm survey and Dairy Herd Improvement records. A set of mixed-effect models using all cows and only 2+ parity cows were used to investigate the association between BLV ELISA-corrected optical density and 305-d mature equivalents of individual cows. The BLV milk positivity was associated with decreased 305-d mature-equivalent yields, especially among the older cows. Additionally, increasing milk ELISA-corrected optical density was associated with increasing loss of milk production at the cow level. In summary, our results provide evidence that BLV infection is associated with decreased milk production in Michigan dairy cows.

Cultural lag: A new challenge for mastitis control on dairy farms in the United States.

Recent changes in the US dairy industry include increases in herd size and the proportion of milk that is produced by large herds. These changes have been accompanied by an increased reliance on hired employees and an increasing role of immigrant labor to perform critical tasks such as milking cows. Thus, there is a growing need for training and education programs for dairy employees because many employees lack previous dairy experience and employee turnover rates are problematic on many farms. Although extension programs have played an important role in the education and support of dairy producers and allied professionals in attaining improved milk quality, dairy employees have limited access to educational programs. Additionally, metrics to assess employee learning are not validated and the ability to sustain work-related behavioral change has not been well described. In this article, we propose a model that may further our understanding of communication and cultural barriers between dairy managers and employees, based on a demonstration project in 12 Michigan dairy herds. As part of this demonstration, a pilot survey was tested to assess the management culture on dairy farms. Results from this survey found that only 23% of employees across all herds were able to meet with farm management on a regular basis, 36% of employees did not know somatic cell count goals for the farm for which they worked, and 71% of employees stated they primarily received training on milking protocols by other employees or that they learned on their own. Latino employees were more likely to not know farm goals or receive primary training on milking protocols from other employees or on their own compared with their English-speaking counterparts. The survey information, along with input from focus group discussions with participating dairy producers, veterinarians, and employees, suggests that extension needs to build capacity for on-farm training and education for employees to support their engagement within dairy operations.

Herd management and social variables associated with bulk tank somatic cell count in dairy herds in the eastern United States.

The ability to reduce somatic cell counts (SCC) and improve milk quality depends on the effective and consistent application of established mastitis control practices. The US dairy industry continues to rely more on nonfamily labor to perform critical tasks to maintain milk quality. Thus, it is important to understand dairy producer attitudes and beliefs relative to management practices, as well as employee performance, to advance milk quality within the changing structure of the dairy industry. To assess the adoption rate of mastitis control practices in United States dairy herds, as well as assess social variables, including attitudes toward employees relative to mastitis control, a survey was sent to 1,700 dairy farms in Michigan, Pennsylvania, and Florida in January and February of 2013. The survey included questions related to 7 major areas: sociodemographics and farm characteristics, milking proficiency, milking systems, cow environment, infected cow monitoring and treatment, farm labor, and attitudes toward mastitis and related antimicrobial use. The overall response rate was 41% (21% in Florida, 39% in Michigan, and 45% in Pennsylvania). Herd size ranged from 9 to 5,800 cows. Self-reported 3-mo geometric mean bulk tank SCC (BTSCC) for all states was 194,000 cells/mL. Multivariate analysis determined that proven mastitis control practices such as the use of internal teat sealants and blanket dry cow therapy, and not using water during udder preparation before milking, were associated with lower BTSCC. Additionally, farmer and manager beliefs and attitudes, including the perception of mastitis problems and the threshold of concern if BTSCC is above 300,000 cells/mL, were associated with BTSCC. Ensuring strict compliance with milking protocols, giving employees a financial or other penalty if BTSCC increased, and a perceived importance of reducing labor costs were negatively associated with BTSCC in farms with nonfamily employees. These findings highlight the need for a comprehensive approach to managing mastitis, one that includes the human dimensions of management to maintain the practice of scientifically validated mastitis control practices.

Short communication: use of the BetaStar Plus assay for detection of ceftiofur antimicrobial residues in milk from individual cows following intramammary treatment for mastitis.

Development and use of on-farm assays to detect antimicrobial residues in milk is important to reduce the risk of violative residues in marketed milk. The objective of this study was to evaluate the effectiveness of a lateral-flow immunodiagnostic assay (BetaStar Plus, Neogen Corp., Lansing, MI) in detecting ceftiofur residues in milk from individual cows treated for mastitis. This assay is currently approved by the US Federal Drug Administration (FDA) for detecting ß-lactam residues in commingled milk. Forty-five dairy cows with clinical mastitis from 4 dairy farms were enrolled and treated intramammary with 125 mg of ceftiofur hydrochloride (Spectramast LC, Zoetis, Madison, NJ) according to the manufacturer's label recommendation. Composite milk samples were collected (A) before first intramammary antimicrobial treatment, (B) before the last intramammary antimicrobial treatment, (C) the last milking of the product-labeled milk withhold, (D) the first milking after the product-labeled milk withhold had been met, and (E) 72 h after the product-labeled milk withhold had been met. Samples were tested using the BetaStar Plus assay within 48 h of collection. Parallel samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and for somatic cell count and milk components. The BetaStar Plus assay identified 6.7, 60.0, 46.7, 22.2, and 6.7% positive samples at each of the respective time points. The assay had sensitivity and specificity of 100 and 84.7%, respectively, compared with liquid chromatography-tandem mass spectrometry analysis using FDA published residue tolerance levels for ceftiofur (or ceftiofur metabolites) as a threshold. The BetaStar Plus assay could be useful for detecting ceftiofur residues in milk from individual cows following intramammary treatment for mastitis before the milk is shipped for processing.

Cows and herds constitute distinct hierarchical levels of heterogeneity in the variability of and association between milk yield and pregnancy outcome in dairy cows.

The objectives of this study were to investigate heterogeneity in the variance of and the association between milk yield (MY) and pregnancy outcome (PO) in dairy cows, formally separating the within-herd (i.e., cow-level residual effects) from the between-herd (i.e., herd-level random effects) components. Based on a recently developed extension to bivariate generalized hierarchical linear mixed models, we specified functions of residual and random effect variances and covariances as linear combinations of fixed and random effects to infer upon heterogeneity in the variation of and the association between MY and PO at first postpartum insemination. As potential sources of heterogeneity, we evaluated various management practices and herd attributes of interest by assessing model fit using the deviance information criterion. Our data consisted of 89,105 Dairy Herd Improvement Association cow records from 379 dairy herds in Michigan. Within herds, no evidence of a cow-level (residual) association between MY and PO was observed, as the corresponding association parameter did not significantly depart from zero. However, the herd-level (random effects) relationship between MY and PO was antagonistic and depended on management practices that determine the baseline level of fertility for a herd. In other words, herds with greater average MY at the time of first postpartum insemination had lower pregnancy rates, but within such herds, cows with higher daily yields did not seem to be any more or less likely to become pregnant than lower-yielding herdmates. Nevertheless, Michigan counties differed in the magnitude of the herd-level association between MY and PO, thus indicating that regional environmental conditions or management practices may partially alleviate the herd-level antagonism between MY and PO. The heterogeneity in variability of MY was substantial and primarily explained at the cow level by management conditions and other herd-specific attributes. In summary, the nature of the variability of and the association between MY and PO in dairy cows is complex due to the heterogeneous contributions of both cow- and herd-level components. Further research should be pursued to investigate additional management scenarios that ameliorate or even enhance the association between MY and PO in commercial dairy cows during first postpartum insemination.

Bovine leukemia virus and cow longevity in Michigan dairy herds.

To determine the association between infection with bovine leukemia virus (BLV) and cow longevity, a stratified random sample of 3,849 Holsteins in 112 Michigan dairy herds was followed for an average of 597 d following testing for BLV antibodies with an ELISA milk test. The hazard ratio of 1.23 indicates that BLV-positive cows were 23% more likely than their BLV-negative herd mates to die or be culled during the monitoring period. This result is adjusted for lactation number, which is also positively associated with an increased risk of leaving the herd. Because herd was included in models, the effect of BLV ELISA on cow longevity was a within-herd comparison in which BLV-infected cattle were compared with their uninfected herd mates. The analysis of 4 ELISA optical density (OD) groups demonstrated a dose response such that cows with higher OD values had decreased survival compared with cows with lower OD values. Cows with OD values above 0.5 were at 40% greater risk of dying or being culled than were their uninfected herd mates. These results support the contention that the association of BLV with cow longevity, when added to other economic impacts, may warrant the control of BLV in our US dairy cow population.

Vaccination strategies for mastitis.

Presently, the most successful use of vaccination strategies as part of a dairy herd mastitis control program involves GNCABs, of which the J-5 bacterins are best understood. Immunization protocols employing this technology should be adapted to individual herd needs. Ironically, the success of these bacterins may rely, in part, on the systemic pathogensis of severe coliform mastitis. Because immune function is impaired in the mammary gland of a lactating dairy cow, and the difficulty in maintaining effective concentrations of antibodies in milk following vaccination, vaccines developed against pathogens that cause more chronic IMI, while promising, have significant obstacles to overcome.

Association between bovine leukemia virus, production, and population age in Michigan dairy herds.

The objective of this study was to determine the herd-level effect of bovine leukemia virus (BLV) infection on dairy production, culling, and cow longevity. During routine herd testing, Dairy Herd Improvement Association technicians collected milk samples from about 40 cows from each of 104 randomly selected Michigan dairy herds averaging ≥120 milking cows and 11,686 kg of milk/yr. Milk samples were analyzed for the presence of anti-BLV antibodies by ELISA, and herd- and lactation-specific estimates of BLV prevalence were computed to determine which were the most predictive of herd milk production, culling rate, and cow longevity (proportion of cows in their third or greater lactation). On this basis, the herd BLV index (an unweighted mean BLV prevalence rate for lactation number 1, 2, 3, and ≥4) was selected as the measure of BLV prevalence that was the most highly associated with BLV economic impact. Step-down multivariate analysis was used to determine the extent to which any of 19 herd-level management variables may have confounded the association of BLV index and measures of herd economic impact (milk production and cow longevity). The BLV index was not associated with the 12-mo culling rate, but was negatively associated in the final multivariable model with the proportion of cows that were ≥third lactation, and was negatively associated with herd milk production. In summary, increased prevalence of BLV within Michigan dairy herds was found to be associated with decreased herd milk production and decreased cow longevity. Our results provide evidence that BLV infection is associated with herd-level economic impacts in high-performing dairy herds.

Veterinarian injuries associated with bovine TB testing livestock in Michigan, 2001.

Testing all the cattle in an entire state with a uniform procedure for each animal affords an opportunity to relate human injury data to a known number of animals handled while carrying out a standardized procedure. Our objective was to describe the type and incidence density of injuries associated with TB-testing a large number of cattle herds, and to delineate the various factors associated with the risk of injury. A survey was mailed to all veterinarians (N = 259) who had completed at least five official bovine TB (bTB) herd tests in Michigan in 2001. We collected data regarding basic demographics and health status, work experience, veterinary specialty, and practice information. Each veterinarian was also requested to complete a separate injury questionnaire for each injury received while TB testing livestock in 2001. Accurate addresses were found for 247 eligible veterinarians, 175 (71%) of whom returned the survey. Thirty-six veterinarians reported a total of 53 injuries (10 major, 12 minor and 31 self-treated). Hands (29%) and legs (21%) were the anatomic locations most frequently injured, with sprains/strains (30%) and abrasion/contusion (30%) the most common types of injuries sustained. The overall incidence density of injuries was 1.9 per 10,000 animals tested. Female gender (RR = 3.3), being employed by the government (RR = 4.5), and smoking (RR = 6.0) were significantly associated with a higher rate of injury. Significant colliniearities were found between some risk factors associated with an increased rate of injury and participants thought 81% of their injuries could have been prevented. These results are explained by the administrative structure of the bTB testing program in Michigan, and the changing demographics of the veterinary workforce.

Assessment of a new disposable introducer for spinal needles.

The compatibility between spinal needles and their introducers varies between manufacturers and can significantly influence the usable length of the spinal needle available resulting in failure to locate CSF in larger patients. The usable length of 90-mm pencil point spinal needles from four manufacturers ranged from 68 to 79 mm when the needle was used in combination with its introducer. A new purpose-built introducer needle is described which, when used with a 25 g or finer spinal needle, maximises the usable length of the needle. Using this new introducer the usable needle length of a 90-mm Whitacre needle was increased by a further 7 to 86 mm resulting in only a 4 mm loss of total needle length. The new introducer was well received by users.

Hyperimmunization of steers with J5 Escherichia coli bacterin: effects on isotype-specific serum antibody responses and cross reactivity with heterogeneous gram-negative bacteria.

Isotype-specific antibody responses and cross reactivity were profiled following hyperimmunization of steers with J5 Escherichia coli bacterin. The vaccine was administered at time 0, 30 d later, and every 2 wk for 10 subsequent immunizations. Blood was collected preimmunization and multiple times following each immunization. Isotype-specific anti-J5 Escherichia coli antibody response profiles in diluted sera harvested from each sample were assayed by ELISA and recorded as optical density. Selected sera were assayed for anti-J5 Escherichia coli antibody titers and used to determine cross reactivity against a variety of gram-negative bacteria. Immunization number and day postimmunization influenced response profiles for anti-J5 E. coli IgM, IgG(1)and IgG(2) antibodies. Two immunizations increased mean serum IgM and the IgG(1)antibody profiles above preimmunization levels, but 5 immunizations were required to detect significant IgG(2) antibody responses that were above preimmunization levels. Isotype-specific cross reactivity of the serum antibodies with a variety of heterologous gram-negative bacteria was also increased by hyperimmunization. However, no cross reactivity was observed for Staphylococcus aureus, purified lipopolysaccharide, or lipid A. Our results indicate that multiple booster doses of J5 E. coli bacterin may be required to elicit high levels of cross-reactive serum IgG(2) antibodies.

Comparison of antimicrobial susceptibility of Staphylococcus aureus isolated from bulk tank milk in organic and conventional dairy herds in the midwestern United States and Denmark.

An observational study was conducted to compare the antimicrobial susceptibility patterns of Staphylococcus aureus isolated from bulk tank milk in organic and conventional dairy farms in Wisconsin, United States, and southern Jutland, Denmark. Bulk tank milk samples and data regarding management and production were collected from 30 organic and 30 conventional dairy farms in Wisconsin and 20 organic and 20 conventional dairy farms in Denmark. S. aureus isolates were tested for resistance against 15 antimicrobial agents by semiautomatic microbroth dilution methods in each country. Of the 118 bulk tank milk samples in Wisconsin, 71 samples (60%) yielded at least one S. aureus isolate, and a total of 331 isolates were collected. Of the 40 bulk tank milk samples from Denmark, 27 samples (55%) yielded at least one S. aureus isolate, and a total of 152 isolates were collected. Significant differences between organic and conventional dairies were detected only to ciprofloxacin in Wisconsin and avilamycin in Denmark. Significant differences (P < 0.05) between the two countries were detected in nine antimicrobials. Denmark had a higher probability of having reduced susceptibility to ciprofloxacin and streptomycin (P = 0.015 and 0.003, respectively). Wisconsin isolates had a higher probability of having reduced susceptibility to seven other antimicrobial agents (bacitracin, gentamicin, kanamycin, penicillin, sulphamethoxazole, tetracycline, and trimethoprim). We found small differences between organic and conventional farm types in each country and larger differences between the two national agricultural systems.

Efficacy of systemic ceftiofur as a therapy for severe clinical mastitis in dairy cattle.

The objectives of this study were to determine the efficacy of intramuscular administration of ceftiofur to reduce the incidence of case-related death and culling following severe clinical mastitis in lactating dairy cattle. A total of 104 cows with severe clinical mastitis (systemic signs) were enrolled in the study and randomly assigned to one of two treatment groups. Immediately after detection of the case, one group was administered 2.2 mg/kg of ceftiofur intramuscularly, and the dose repeated at 24-h intervals for a total of five doses. The second group of cows did not receive systemic antibacterial therapy. Additionally, all cows in both treatment groups received intramammary pirlimycin (Pirsue) in the affected quarter every 24 h for a total of up to three doses. Also at the onset of the case, all cows on the trial were administered a supportive therapeutic regimen of fluids and anti-inflammatory agents that varied from farm to farm, but was standard within each herd at the discretion of the herd manager and veterinarian. Of all cases 14/104 (13.5%) resulted in a lost cow (died or culled). The proportion of cases that resulted in a lost cow and were treated with ceftiofur (4/51; 7.8%) did not statistically differ from cows that were not treated with ceftiofur (10/53; 18.9%). However, the proportion of cases that resulted in lost cows was higher for those cases that yielded a coliform organism on culture (14/56; 25.0%) than cases that did not yield coliforms (0/48; 0.0%; P < 0.001). Thus, among coliform cases, cows that were not treated with ceftiofur were more likely to be culled or die (10/27, 37.0%; P < 0.05) than cows treated with ceftiofur (4/29, 13.8%). We conclude that intramuscular administration of ceftiofur did not affect the outcome of severe clinical mastitis when all etiologic agents are included in the analysis. However, for severe clinical mastitis cases caused by coliform organisms, ceftiofur therapy reduced the proportion of cases that resulted in cow death or culling. This benefit may be realized because of the amelioration of bacteremic-related pathogenesis.

Clinical responses to intramammary endotoxin infusion in dairy cows subjected to feed restriction.

Nonpregnant, midlactation primiparous Holstein cows were fed ad libitum (n = 12) or at 80% of maintenance energy requirements (n = 12) to determine whether feed restriction influences clinical response to endotoxin-induced mastitis. After 2 wk of ad libitum or restricted feeding, one mammary quarter per cow was infused with 100 microg of endotoxin. Within 3 to 6 h of intramammary infusion, endotoxin increased mean rectal temperature, heart rate, and milk somatic cell count and immunoglobulin (IgG) concentration; and decreased blood leukocyte count and rumen motility in both restricted and ad libitum-fed cows. Mean serum and milk tumor necrosis factor-alpha (TNF-alpha) concentrations showed only modest increases following endotoxin infusion. Restricted fed cows had slightly different acute fever responses and significantly increased heart and respiration rates than ad libitum fed cows. However, feed restriction did not influence mean total leukocyte count, rumen motility, serum TNF-a concentrations or milk IgG and TNF-alpha concentrations. Thus, results of this study suggest that energy balance does not significantly alter clinical symptoms following acute endotoxin-induced mastitis, at least in midlactation cows. As such, negative energy balance may not underlie the increases in severe coliform mastitis commonly observed in periparturient dairy cows.