Bruce R. Hoar

An examination of risk factors associated with beef cattle shedding pathogens of potential zoonotic concern

The prevalence of three waterborne zoonotic pathogens (Campylobacter sp., Giardia sp. and Cryptosporidium parvum) in rectal faecal samples from a random sample of adult beef cattle was determined. Management factors that may be associated with shedding of these organisms were examined. For Campylobacter sp. prevalence was 5.0%, and the number of females on the farm was positively associated with the proportion that tested positive. For Giardia sp. prevalence was 6.5%, and none of the management factors examined was significantly associated with the proportion in a herd testing positive. C. parvum was identified in 1.1% of samples. The length of calving season and whether any procedures were performed on the calves in the first 2 days of life were positively associated with the proportion that tested positive. We conclude that this sample of adult beef cattle represent a relatively limited threat to water supplies and subsequent disease transmission to humans from these pathogens.

Improved Quantitative Estimates of Low Environmental Loading and Sporadic Periparturient Shedding of Cryptosporidium parvum in Adult Beef Cattle

ABSTRACT Our primary goal was to generate an accurate estimate of the daily environmental loading rate of Cryptosporidium parvum oocysts for adult beef cattle, using immunomagnetic separation coupled with direct immunofluorescence microscopy for a highly sensitive diagnostic assay. An additional goal was to measure the prevalence and intensity of fecal shedding of C. parvum oocysts in pre- and postparturient cows as an indicator of their potential to infect young calves. This diagnostic method could detect with a ≥90% probability oocyst concentrations as low as 3.2 oocysts g of feces−1, with a 54% probability of detecting just one oocyst g of feces−1. Using this diagnostic method, the overall apparent prevalence of adult beef cattle testing positive for C. parvum was 7.1% (17 of 240), with 8.3 and 5.8% of cattle shedding oocysts during the pre- and postcalving periods, respectively. The mean intensity of oocyst shedding for test-positive cattle was 3.38 oocysts g of feces−1. The estimated environmental loading rate of C. parvum ranged from 3,900 to 9,200 oocysts cow−1 day−1, which is substantially less than a previous estimate of 1.7 × 105 oocysts cow−1 day−1 (range of 7.7 × 104 to 2.3 × 105 oocysts cow−1 day−1) (B. Hoar, E. R. Atwill, and T. B. Farver, Quant. Microbiol. 2:21-36, 2000). Use of this highly sensitive assay functioned to detect a greater proportion of low-intensity shedders in our population of cattle, which reduced the estimated mean intensity of shedding and thereby reduced the associated environmental loading rate compared to those of previous studies.

Evaluation of twice-daily, low-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorticism

OBJECTIVE To evaluate the effects of twice-daily oral administration of a low-dose of trilostane treatment and assess the duration of effects after once-daily trilostane administration in dogs with naturally occurring hyperadrenocorticism (NOH). DESIGN Prospective study. ANIMALS 28 dogs with NOH. PROCEDURES 22 dogs received 0.5 to 2.5 mg of trilostane/kg (0.23 to 1.14 mg/lb) orally every 12 hours initially. At intervals, dogs were reevaluated; owner assessment of treatment response was recorded. To assess drug effect duration, 16 of the 22 dogs and 6 additional dogs underwent 2 ACTH stimulation tests 3 to 4 hours and 8 to 9 hours after once-daily trilostane administration. RESULTS After 1 to 2 weeks, mean trilostane dosage was 1.4 mg/kg (0.64 mg/lb) every 12 hours (n = 22 dogs; good response [resolution of signs], 8; poor response, 14). Four to 8 weeks later, mean dosage was 1.8 mg/kg (0.82 mg/lb) every 12 or 8 hours (n = 21 and 1 dogs, respectively; good response, 15; poor response, 5; 2 dogs were ill). Eight to 16 weeks after the second reevaluation, remaining dogs had good responses (mean dosages, 1.9 mg/kg [0.86 mg/lb], q 12 h [n = 13 dogs] and 1.3 mg/kg [0.59 mg/lb], q 8 h [3]). At 3 to 4 hours and 8 to 9 hours after once-daily dosing, mean post-ACTH stimulation serum cortisol concentrations were 2.60 and 8.09 Pg/dL, respectively. CONCLUSIONS AND CLINICAL RELEVANCE In dogs with NOH, administration of trilostane at low doses every 12 hours was effective, although 2 dogs became ill during treatment. Drug effects diminished within 8 to 9 hours. Because of potential adverse effects, lower doses should be evaluated.

Spatial analysis of Yersinia pestis and Bartonella vinsonii subsp. berkhoffii seroprevalence in California coyotes (Canis latrans).

Zoonotic transmission of sylvatic plague caused by Yersinia pestis occurs in California, USA. Human infections with various Bartonella species have been reported recently. Coyotes (Canis latrans) are ubiquitous throughout California and can become infected with both bacterial agents, making the species useful for surveillance purposes. This study examined the geographic distribution of 863 coyotes tested for Y. pestis and Bartonella vinsonii subsp. berkhoffii serologic status to gain insight into the natural history of B. vinsonii subsp. berkhoffii and to characterize the spatial distribution of the two agents. We found 11.7% of specimens positive to Y. pestis and 35.5% positive to B. vinsonii subsp. berkhoffii. The two pathogens had distinct spatial clusters: Y. pestis was more prevalent in eastern portions of the state and B. vinsonii subsp. berkhoffii in coastal regions. Prevalence of Y. pestis increased with increasing elevation, whereas prevalence of B. vinsonii subsp. berkhoffii decreased with increasing elevation. There were differences in the proportions of positive animals on a yearly basis to both pathogens.

Healing of surgical castration wounds: a description and an evaluation of flunixin.

Previous studies have shown that surgical castration wounds take between 10 and 61 d to heal. The objectives of this work were to describe healing, inflammation, lying behavior, and serum concentration of substance P after surgical castration in beef calves and to evaluate the effect of a possible intervention, a single injection of flunixin meglumine (1.1 mg/kg IV, a NSAID), on the healing process. Calves (mean±SE: 25±2.0 d of age; 54±1.4 kg BW) were surgically castrated with or without an injection of flunixin immediately before the procedure (n=24/treatment). Healing was measured with a 5-point scale (1=fresh wound, 5=no visible incision or inflammation) as well as weight gain, scrotal size, and scrotal surface temperature, on d 1, 2, 3, 7, 14, 21, 28, 35, 49, and 63 after castration. Serum concentration of substance P was recorded on all d, including d 0, but not d 63. Lying behavior was recorded with loggers from 2 d before to 29 d after castration. Inflammation, as measured by scrotal size, peaked on d 2 and 3 after the procedure (e.g., 51±1.0 mm on d 2 versus 28±1.3 mm before castration) and then declined with time (P<0.001). The first wound to score as fully healed (i.e., 5/5) was seen on d 28; by d 63, 98% of wounds were fully healed. The greatest changes in healing score occurred between d 21 and 35; this was also the peak of wound surface temperature and may correspond with revascularization. Serum concentration of substance P was highest before castration (41±1.2 pg/mL), possibly because the sample was collected after the lidocaine ring block was administered, which was likely painful, and because of separation from the dam and restraint. Values began to drop by d 3 (34±1.2 pg/mL) and leveled out by d 21 (30±1.2 pg/mL; P<0.001). Calves given flunixin had more lying bouts than those that received saline (flunixin by time interaction; P=0.052), but this pattern emerged on and after d 8, well after the 3 to 8 h half-life of this NSAID. In conclusion, castration caused inflammation in the days that followed, and the wounds required a minimum of 4 wk to heal. Provision of an NSAID had no effect on these outcomes.

Longitudinal prevalence and molecular typing of Escherichia coli O157:H7 by use of multiple-locus variable-number tandem-repeat analysis and pulsed-field gel electrophoresis in fecal samples collected from a range-based herd of beef cattle in California.

OBJECTIVE To evaluate seasonal patterns and risk factors for Escherichia coli O157:H7 in feces in a beef cattle herd and determine strain diversity and transition in E coli over time by use of multiple-locus variable-number tandem-repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE). SAMPLE POPULATION 456 samples of freshly passed feces collected over a 1-year period from cattle in a range-based cow-calf operation located in the foothills of the Sierra Nevada Mountains in California. PROCEDURES E coli O157:H7 was recovered from feces by use of immunomagnetic separation and 2 selective media. Virulence factors were detected via reverse transcriptase-PCR assay. Escherichia coli O157:H7 isolates were subtyped with MLVA and PFGE. Prevalence estimates were calculated and significant risk factors determined. A dendrogram was constructed on the basis of results of MLVA typing. RESULTS Overall prevalence estimate for E coli O157:H7 was 10.5%, with the prevalence lowest during the winter. Mean temperature during the 30 days before collection of samples was significantly associated with prevalence of E coli O157:H7 in feces. Nineteen MLVA and 12 PFGE types were identified. CONCLUSIONS AND CLINICAL RELEVANCE A seasonal pattern was detected for prevalence of E coli O157:H7 in feces collected from beef cattle in California. Subtyping via MLVA and PFGE revealed a diversity of E coli O157:H7 strains in a cow-calf operation and noteworthy turnover of predominant types. Given the importance of accurately determining sources of contamination in investigations of disease outbreaks in humans, MLVA combined with PFGE should be powerful tools for epidemiologists.

Giardia duodenalis in feedlot cattle from the central and western United States

BackgroundGiardia duodenalis is a ubiquitous protozoan parasite that has emerged as a significant opportunistic human pathogen. G. duodenalis may have a deleterious effect on animal growth and performance, therefore its potential as a production limiting organism should not be discounted. We therefore undertook this study to determine management and environmental factors in feedlots that influence the prevalence and environmental load of G. duodenalis cysts in fecal material deposited by feedlot cattle in the central and western United States.ResultsTwenty two feedlots from 7 states were included in the study, and up to 240 fecal samples were collected from pen floors of up to 6 pens per feedlot. Giardia duodenalis cysts were identified and counted using direct immunofluorescent microscopy. The estimated overall point prevalence of G. duodenalis was 19.1%, representing feedlots from a wide range of climates and management systems. Pen-level prevalence varied from 0 to 63.3%, with pen-level shedding estimates ranging from 0 to 261,000 cysts/g feces. Higher environmental temperatures, increased animal density, and increased time in the feedlot were associated with a lower prevalence of G. duodenalis. Removing manure before placing a new group of cattle in a pen was associated with a decreased prevalence of G. duodenalis in fecal pats. Using coccidiostats as a feed additive was associated with a higher prevalence of Giardia.ConclusionManagement practices could be employed that would limit the probability that feedlot cattle shed G. duodenalis in their feces and therefore potentially limit contamination of their environment.

Prevalence and Molecular Characterization of Escherichia coli O157:H7 by Multiple-Locus Variable-Number Tandem Repeat Analysis and Pulsed-Field Gel Electrophoresis in Three Sheep Farming Operations in California

A year-long study was conducted to determine the fecal prevalence of Escherichia coli O157:H7 in three sheep ranches. Strain diversity and persistence were compared with multiple-locus variable-number tandem repeat analysis and pulsed-field gel electrophoresis. Ranch C, a feedlot, consisted of young sheep raised predominantly on a high-grain diet. The other two sites consisted of sheep raised on native pasture and a combination of native and irrigated pasture. Forty fecal samples were collected every month from each ranch. Samples were examined for E. coli O157:H7 by immunomagnetic separation and culture of the magnetic beads onto selective media. Detection of virulence markers in positive isolates was determined by PCR. E. coli O157:H7 was isolated from 100 (22.7%) of 440 fecal samples collected from ranch C. On ranch B, 9 (1.9%) of the 480 fecal samples were positive for the pathogen, while none of the samples from ranch A were positive. On ranch C, the odds of detecting E. coli O157:H7 was 3.2 times greater during the warmer months compared with the cooler months of the year. There was no association between days spent in the feedlot and fecal prevalence of the pathogen (P = 0.62). Most multiple-locus variable-number tandem repeat analysis types were isolated only once from ranch C (14 of 23), but several strains were isolated over 4 to 6 months, often in many intervening negative months. This study revealed that the prevalence of E. coli O157:H7 can be high in some sheep ranches in California, especially in feedlots where young sheep are fed predominantly high-grain rations.

Pain sensitivity and healing of hot-iron cattle brands

Hot-iron branding is painful for cattle, but little is known about the duration of or effective methods to control this pain. This work quantified pain sensitivity and healing in branded and unbranded animals. In addition, the effects of a single injection of nonsteroidal anti-inflammatory drug (NSAID) were also considered; this has been suggested as practical method of mitigating pain in the hours after the procedure. Calves (mean±SE, 126±2.2 d and 112±2.8 kg) were hot-iron branded and allocated to 1 of 4 treatments: branded with or without flunixin meglumine (intravenous; 1.1 mg/kg) and unbranded with or without this NSAID (n=12/treatment). Pain sensitivity was assessed by applying a known and increasing force with a von Frey anesthesiometer in the center of the brand (or equivalent area in nonbranded treatments) until animals showed a behavioral response. Healing was measured with a 6-point scale (1=fresh brand and 6=no scabbing and fully repigmented). These measures, along with weight gain and surface temperature, were recorded 1, 2, 7, 14, 21, 28, 35, 42, 56, and 71 d after branding. Lying behavior was recorded with loggers from the day before to d 27 after branding. Brand wounds were more painful than nonbranded tissue (P<0.001). These differences were most pronounced in the days immediately after branding (e.g., d 7; 113±36 g of force for Brand vs. 449±23 g force for No brand, mean±SE) but persisted until d 71 (380±37 g force for Brand vs. 453±23 g of force for No brand, mean±SE); only 67% of brands were fully regimented or healed by this time. The first fully healed brand was identified 8 wk after the procedure. Giving a single injection of flunixin had no brand-specific effects on sensitivity, surface temperature, or healing but improved weight gain in the days after branding in all treated groups (flunixin×brand×day, P<0.001). Flunixin-treated animals also spent 0.7 h less time lying down on the day of branding but tended to spend more time lying on d 15 and 26 after the procedure. The magnitude of these differences is small, less than the day-to-day variation, and not brand specific. In summary, brand wounds take at least 8 wk to heal. These wounds remain painful for a least this long, and a single injection of NSAID has no measurable effect in mitigating pain associated with branding, even in days immediately after the procedure.

Effect of a cooling gel on pain sensitivity and healing of hot-iron cattle brands

Hot-iron branding is painful for cattle, but little is known about how long this pain lasts or effective alleviation methods. Previous work with pigs indicated that cooling burns with a gel (active ingredient: tea tree oil) improved healing compared to untreated wounds. Steers (210±21 kg) were hot-iron branded and allocated to 1 of 3 treatments: control (n=24), 1 gel application immediately after branding (1X; n=12), or 2 gel applications, 1 immediately after branding and one 1 d later (2X; n=12). Pain sensitivity was assessed by applying a known and increasing force with a von Frey anesthesiometer in 5 locations (in the center, at the top of, and 5 and 10 cm above the brand and on the equivalent location on the nonbranded side of the body) until animals showed a behavioral response. Healing was measured with a 6-point scale (1=fresh brand and 6=no scabbing and fully repigmented). Both measures, along with weight gain and surface temperature of the wound, were recorded before and 1, 2, 3, 7, 14, 21, 28, 35, 56, and 70 d after branding. The gel cooled the brand, with the most obvious differences on the day it was applied (3.7 to 4.2°C cooler than control; day×gel interaction, P=0.004). All wounds were at least partially repigmented by 70 d, but only 46% of brands were fully healed at this time. The healing process was slowed when a gel was applied twice (e.g., at 21 d, healing score of 2.5±0.1 and 2.7±0.1 vs. 2.0±0.2 for control and 1X vs. 2X, respectively; P=0.001). Brands tended to remain painful throughout the 70 d (in the center of the brand; before vs. d 1-35, P≤0.001; d 56, P=0.058; and d 70, P=0.092). Overall, gel had little effect on pain sensitivity. Weight gain was reduced on d 1 after branding compared to all other time points (P<0.001) but was not affected by gel application (P=0.277). In conclusion, applying gel did not improve outcomes after branding. In addition, by 70 d after the procedure, hot-iron brands still tended to be more painful than nonbranded tissue and 54% were not fully healed. These results raise additional animal welfare concerns about hot-iron branding.