Daniel U. Thomson

Plasma concentrations of substance P and cortisol in beef calves after castration or simulated castration

OBJECTIVE To evaluate plasma concentrations of substance P (SP) and cortisol in calves after castration or simulated castration. ANIMALS 10 Angus-crossbred calves. PROCEDURES Calves were acclimated for 5 days, assigned to a block on the basis of scrotal circumference, and randomly assigned to a castrated or simulated-castrated (control) group. Blood samples were collected twice before, at the time of (0 hours), and at several times points after castration or simulated castration. Vocalization and attitude scores were determined at time of castration or simulated castration. Plasma concentrations of SP and cortisol were determined by use of competitive and chemiluminescent enzyme immunoassays, respectively. Data were analyzed by use of repeated-measures analysis with a mixed model. RESULTS Mean +/- SEM cortisol concentration in castrated calves (78.88+/-10.07 nmol/L) was similar to that in uncastrated control calves (73.01+/-10.07 nmol/L). However, mean SP concentration in castrated calves (506.43+/-38.11 pg/mL) was significantly higher than the concentration in control calves (386.42+/-40.09 pg/mL). Mean cortisol concentration in calves with vocalization scores of 0 was not significantly different from the concentration in calves with vocalization scores of 3. However, calves with vocalization scores of 3 had significantly higher SP concentrations, compared with SP concentrations for calves with vocalization scores of 0. CONCLUSIONS AND CLINICAL RELEVANCE Similar cortisol concentrations were measured in castrated and control calves. A significant increase in plasma concentrations of SP after castration suggested a likely association with nociception. These results may affect assessment of animal well-being in livestock production systems.

Use of a Siderophore Receptor and Porin Proteins-Based Vaccine to Control the Burden of Escherichia coli O157:H7 in Feedlot Cattle

OBJECTIVE To quantify the efficacy of a siderophore receptor and porin (SRP) proteins-based vaccine on the burden of Escherichia coli O157:H7 in feedlot cattle. METHODS Two research trials were conducted in field conditions. In each trial, cattle (n = 1252 in trial #1; n = 1284 in trial #2) were systematically divided into 20 pens and were administered either the E. coli O157 SRP vaccine or a placebo (trial #1: days 0 and 21; trial #2: days 0, 21, and 42). Rectal fecal samples were collected on day 0, and pen floor samples were collected on days 21, 35, 70, and 85 for trial #1 and on days 42 and 98 for trial #2. On day 85 of trial #1, rectoanal mucosal swab samples and hide swab samples were collected. Cattle were weighed on days 0, 21, and 85 (trial #1) or 1 week before harvest (trial #2). RESULTS In trial #1, prevalence of E. coli in the feces was lower in vaccinates compared to control animals (p = 0.04). On day 85, the likelihood of an animal being positive at any site was less among vaccinates than controls (p = 0.02). In trail #2, vaccination with SRP was associated with reduced shedding by 85.2% on day 98 (p < 0.01) but not on days 0 or 42. Vaccination with SRP was associated with a 98.2% reduction in concentration of E. coli O157 in fecal samples (2.54 vs. 0.80 log MPN/g of feces; p < 0.01). Cattle performance was not affected by SRP administration. CONCLUSIONS The E. coli O157:H7 SRP-based vaccine might serve as a preharvest intervention to reduce the burden of E. coli O157:H7 on cattle presented for harvest.

Analysis of modern technologies commonly used in beef cattle production: Conventional beef production versus nonconventional production using meta-analysis

Conventional feeding systems use pharmaceutical products not allowed in natural or organic systems for finishing cattle. This review of data compares the performance effects (ADG, G:F, DMI) of technologies used in conventional feeding programs that are prohibited in organic programs, natural programs, or both. The technologies evaluated were steroid implants, monensin, tylosin, endectocides, and metaphylaxis with any antimicrobial. For inclusion in this analysis, studies were conducted in North America, reported randomization to treatment group, used beef cattle, contained an untreated control group, and were sourced from peer-reviewed journals. Forest plots were used to examine the data visually for trends toward a uniform effect of the technology on the outcomes of interest (ADG, DMI, G:F). Technologies that displayed a uniform response on the forest plot compared with negative controls were then analyzed using mixed models. Examination of forest plots for endectocides, steroid implants, monensin, and metaphylaxis technologies appeared to show performance advantages for treated cattle relative to cattle in negative control groups. An insufficient number of studies met the inclusion criteria to conduct meta-analyses comparing endectocides, monensin, or tylosin with negative controls. Average daily gain in feeder cattle given metaphylaxis on arrival was 0.11 kg/d (P < 0.01) greater relative to cattle that did not receive metaphylaxis on arrival. Implanting heifers increased ADG by 0.08 kg/d compared with nonimplanted controls (P = 0.09). Implants had no effect on G:F (P = 0.14) in heifers or on DMI (P = 0.44) relative to nonimplanted control heifers. Implanting steers was associated with greater ADG, by 0.25 kg/d (P < 0.01), and DMI, by 0.53 kg/d (P < 0.01), relative to nonimplanted control steers. Implants also improved G:F in steers relative to nonimplanted steers, by 0.02 (0.17 vs. 0.15; implanted vs. controls, P < 0.01; n = 21 studies). When average estimated differences in ADG and G:F for implanted and nonimplanted steers were incorporated into a breakeven model, implanted steers had a

Efficacy of Escherichia coli O157:H7 Siderophore Receptor/Porin Proteins–Based Vaccine in Feedlot Cattle Naturally Shedding E. coli O157

77/animal lower cost of production than nonimplanted steers and a

Evaluation of two-dimensional accelerometers to monitor behavior of beef calves after castration

349/animal lower cost of production than organically raised steers. These data illustrate the importance of capturing premiums when operating natural and organic production systems to maintain economic viability.

Feedlot health and performance effects associated with the timing of respiratory disease treatment

Escherichia coli O157 is a foodborne pathogen commonly isolated from beef cattle feces and can enter the food chain at harvest. A relatively new vaccine technology uses the iron requirement of pathogenic bacteria by targeting the siderophore receptor and porin proteins (SRP). We evaluated the efficacy of an anti-E. coli O157 SRP-based vaccine in feedlot cattle naturally shedding the organism. Sixty cattle were selected from an original population of 600; 50 of these were fecal positive for E. coli O157 on two occasions and the remaining 10 animals were fecal positive on one occasion. Cattle were stratified based on the results of screening samples and randomly allotted to one of three treatment groups: control, vaccinated with 2 mL per animal of E. coli SRP vaccine, or vaccinated with 3 mL per animal of E. coli SRP vaccine subcutaneously 21 days apart. Control cattle were injected with sterile saline emulsified with an adjuvant. Fecal samples and rectoanal mucosal swab samples were collected two or three times a week for 8 weeks to monitor shedding of E. coli O157. Prevalence of the pathogen was analyzed by repeated measures on animals over weeks. The SRP vaccine at the 3 mL dose reduced prevalence of E. coli O157 compared to the control (17.7% vs. 33.7%; p < 0.01). A similar trend was observed with the 2 mL dose (29.1%), but differences were not statistically significant compared to control (p = 0.40). Additionally, the 3 mL dose of SRP vaccine reduced the number of days cattle tested culture positive for E. coli O157 (p = 0.05) and the number of days cattle were identified as high-shedders (p = 0.02) compared to control.

Feeding Supplemental Dried Distiller’s Grains Increases Faecal Shedding of Escherichia coli O157 in Experimentally Inoculated Calves

OBJECTIVE To determine the accuracy of accelerometers for measuring behavior changes in calves and to determine differences in beef calf behavior from before to after castration. ANIMALS 3 healthy Holstein calves and 12 healthy beef calves. PROCEDURES 2-dimensional accelerometers were placed on 3 calves, and data were logged simultaneous to video recording of animal behavior. Resulting data were used to generate and validate predictive models to classify posture (standing or lying) and type of activity (standing in place, walking, eating, getting up, lying awake, or lying sleeping). The algorithms developed were used to conduct a prospective trial to compare calf behavior in the first 24 hours after castration (n = 6) with behavior of noncastrated control calves (6) and with presurgical readings from the same castrated calves. RESULTS On the basis of the analysis of the 2-dimensional accelerometer signal, posture was classified with a high degree of accuracy (98.3%) and the specific activity was estimated with a reasonably low misclassification rate (23.5%). Use of the system to compare behavior after castration revealed that castrated calves spent a significantly larger amount of time standing (82.2%), compared with presurgical readings (46.2%). CONCLUSIONS AND CLINICAL RELEVANCE 2-dimensional accelerometers provided accurate classification of posture and reasonable classification of activity. Applying the system in a castration trial illustrated the usefulness of accelerometers for measuring behavioral changes in individual calves.

Antimicrobial susceptibility of enteric bacteria recovered from feedlot cattle administered chlortetracycline in feed

Generalized linear mixed models were developed using retrospective feedlot data collected on individually treated cattle (n = 31,131) to determine whether cattle performance and health outcomes in feedlot cattle were associated with timing of treatment for bovine respiratory disease (BRD) during the feeding phase. Cattle that died at any point during the feeding phase were removed from the analysis. Information on individual animal performance (ADG, HCW, quality grade, yield grade) and health outcomes (treatments) were incorporated into an economic model that generated a standardized net return estimate for each animal. Prices were standardized to minimize variation between economic outcomes due to market conditions allowing direct comparisons of health and performance effects between animals. While controlling for sex, risk code, and arrival BW class, potential associations between net returns and the timing of BRD identification were investigated using 2 categorical variables created to measure time: 1) weeks on feed at initial BRD treatment, and 2) weeks from BRD treatment to slaughter. The first model using net return as the outcome identified an interaction between weeks on feed at initial BRD treatment and animal arrival BW. Cattle with arrival BW between 227 and 272 kg (5WT) and 273 and 318 kg (6WT) displayed decreased net returns (P < 0.05) if treated during wk 1 as compared with subsequent weeks in the first month of the feeding phase. The cattle with BW between 319 and 363 kg (7WT) and 364 and 408 kg (8WT) exhibited decreased net returns (P < 0.05) if treated during the later weeks of the feeding phase compared with earlier in the feeding phase. The number of times cattle were treated contributed to variation in net returns for the 5WT and 6WT cattle. For the 7WT and 8WT cattle, HCW was the main factor contributing to decreased net returns when cattle were treated late in the feeding phase. The second model identified an interaction between weeks from BRD treatment to slaughter and arrival BW. The 181 to 226 kg of BW, 5WT, 6WT, 7WT, and 8WT cattle all exhibited decreased net returns (P < 0.05) when cattle were on feed fewer weeks from BRD treatment to slaughter. Cattle with more weeks on feed between BRD treatment and slaughter had greater HCW, decreased ADG, and more total treatments compared with cattle treated closer to slaughter. This research indicates that timing of initial BRD treatment is associated with performance and health outcomes.

Effects of a commercially available vaccine against Salmonella enterica serotype Newport on milk production, somatic cell count, and shedding of Salmonella organisms in female dairy cattle with no clinical signs of salmonellosis

Escherichia coli O157 is an important foodborne pathogen and asymptomatic cattle serve as major reservoirs for human infection. We have shown a positive association between feeding distiller’s grains and E. coli O157 prevalence in feedlot cattle. The objective of this study was to determine the effect of feeding dried distiller’s grain (DDG) on faecal shedding of E. coli O157 in calves experimentally inoculated with E. coli O157. Holstein calves (five per treatment group), fed steam‐flaked corn‐based high‐grain diets supplemented with 0% (control) or 25% DDG, were orally inoculated with a five‐strain mixture (6 × 109 CFU/calf) of nalidixic acid‐resistant (NalR) E. coli O157. Faecal samples were taken three times per week for 6 weeks to determine the prevalence and concentration of NalRE. coli O157. At the end of the study (day 43), calves were euthanized and necropsied. Ruminal, caecum, colon, and rectal contents, and rectoanal mucosal swab (RAMS) samples were collected at necropsy to determine NalRE. coli O157 concentration. There was a trend for an interaction between treatment and faecal sampling day. The concentration of NalRE. coli O157 in the faeces was significantly higher in faecal samples from calves fed DDG compared with control calves on days 35, 37, 39 and 42. At necropsy, the concentration of NalRE. coli O157 was higher in the caecum (P = 0.01), colon (P = 0.03) and rectum (P = 0.01) from calves fed DDG compared with control animals. The number of sites at necropsy positive for NalRE. coli O157 was higher in calves fed DDG compared with calves in the control treatment (P < 0.001). Our results indicate that E. coli O157 gut persistence and faecal prevalence increased in calves fed DDG, which potentially have important implications for food safety.

Prevalence, severity, and relationships of lung lesions, liver abnormalities, and rumen health scores measured at slaughter in beef cattle

OBJECTIVE To evaluate administration of chlortetracycline in feed of cattle as a method to select for tetracycline resistance among enteric bacteria in feedlot settings. ANIMALS 20 steers. PROCEDURES Steers were randomly assigned to an exposed cohort (n = 10) or an unexposed cohort (control cohort; 10). Chlortetracycline (22 mg/kg) in cottonseed meal was administered to the exposed cohort on days 0 through 4, 6 through 10, and 12 through 16. The control cohort was administered only cottonseed meal. Fecal samples were collected from 16 steers on days -7, 0, 2, 6, 8, 12, 14, 19, 22, 26, and 33, and Escherichia coli and Enterococcus spp were isolated. Minimum inhibitory concentration (MIC) of selected antimicrobials was estimated. RESULTS Overall, 56.0% and 31.4% of E coli and Enterococcus isolates, respectively, were resistant to tetracycline. Exposure to chlortetracycline was associated with a significant temporary increase in log(2) MIC for both genera but returned to preexposure values by day 33. Averaged across time, the proportion of tetracycline-resistant E coli and Enterococcus isolates was significantly greater in exposed than in unexposed steers. Although all ceftiofur-resistant E coli isolates were coresistant to tetracycline, exposure to chlortetracycline led to a significant decrease in the proportion of E coli resistant to ceftiofur during exposure. CONCLUSIONS AND CLINICAL RELEVANCE Exposure to chlortetracycline was associated with a temporary increase in the likelihood of recovering resistant bacteria. Exposure to chlortetracycline decreased the likelihood of recovering ceftiofur-resistant E coli isolates, even though isolates were coresistant to tetracycline. These findings warrant further investigation.