S. R. Rust

Factors Associated with Shiga Toxin-Producing Escherichia coli Shedding by Dairy and Beef Cattle

ABSTRACT Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogen that can cause hemorrhagic colitis and hemolytic-uremic syndrome. Cattle are the primary reservoir for STEC, and food or water contaminated with cattle feces is the most common source of infections in humans. Consequently, we conducted a cross-sectional study of 1,096 cattle in six dairy herds (n = 718 animals) and five beef herds (n = 378 animals) in the summers of 2011 and 2012 to identify epidemiological factors associated with shedding. Fecal samples were obtained from each animal and cultured for STEC. Multivariate analyses were performed to identify risk factors associated with STEC positivity. The prevalence of STEC was higher in beef cattle (21%) than dairy cattle (13%) (odds ratio [OR], 1.76; 95% confidence interval [CI], 1.25, 2.47), with considerable variation occurring across herds (range, 6% to 54%). Dairy cattle were significantly more likely to shed STEC when the average temperature was >28.9°C 1 to 5 days prior to sampling (OR, 2.5; 95% CI, 1.25, 4.91), during their first lactation (OR, 1.8; 95% CI, 1.1, 2.8), and when they were <30 days in milk (OR, 3.9; 95% CI, 2.1, 7.2). These data suggest that the stress or the negative energy balance associated with lactation may result in increased STEC shedding frequencies in Michigan during the warm summer months. Future prevention strategies aimed at reducing stress during lactation or isolating high-risk animals could be implemented to reduce herd-level shedding levels and avoid transmission of STEC to susceptible animals and people. IMPORTANCE STEC shedding frequencies vary considerably across cattle herds in Michigan, and the shedding frequency of strains belonging to non-O157 serotypes far exceeds the shedding frequency of O157 strains, which is congruent with human infections in the state. Dairy cattle sampled at higher temperatures, in their first lactation, and early in the milk production stage were significantly more likely to shed STEC, which could be due to stress or a negative energy balance. Future studies should focus on the isolation of high-risk animals to decrease herd shedding levels and the potential for contamination of the food supply.

Comparing the Genetic Diversity and Antimicrobial Resistance Profiles of Campylobacter jejuni Recovered from Cattle and Humans

Campylobacter jejuni, a leading cause of gastroenteritis in humans, is a foodborne pathogen that can reside in chickens, pigs, and cattle. Because resistance to fluoroquinolones and macrolides, which are commonly used to treat human infections, has emerged in C. jejuni, it is imperative to continously monitor resistance patterns and examine the genetic variation in strains from human infections and animal reservoirs. Our previous study of C. jejuni from human campylobacteriosis cases showed a significantly higher rate of tetracycline resistance compared to national trends, and identified multilocus sequence type (ST)-982 and a history of cattle contact to be associated with tetracycline resistance. To further investigate these associations, we conducted a cross-sectional study to determine the frequency of antimicrobial resistance and examine the genetic diversity of C. jejuni recovered from 214 cattle at three Michigan herds. Overall, the prevalence of C. jejuni was 69.2% (range: 58.6–83.8%) for the three farms, and 83.7% (n = 113) of isolates were resistant to one or more antimicrobials. Resistance to only tetracycline predominated among the cattle isolates (n = 89; 65.9%) with most resistant strains belonging to ST-459 (96.5%) or ST-982 (86.4%). Among the 22 STs identified, STs 459 and 982 were more prevalent in one feedlot, which reported the use of chlortetracycline in feed upon arrival of a new herd. PCR-based fingerprinting demonstrated that the ST-982 isolates from cattle and humans had identical banding patterns, suggesting the possibility of interspecies transmission. Resistance to macrolides (1.5%) and ciprofloxacin (16.3%) was also observed; 14 of the 22 ciprofloxacin resistant isolates represented ST-1244. Together, these findings demonstrate a high prevalence of antimicrobial resistant C. jejuni in cattle and identify associations with specific genotypes. Continuous monitoring and identification of risk factors for resistance emergence are imperative to develop novel methods aimed at decreasing pathogen persistence in food animal reservoirs and the frequency of resistant infections in humans.

Effects of butyrate precursors on electron relocation when methanogenesis is inhibited in ruminal mixed cultures

Aims:  Inhibition of ruminal methanogenesis often causes accumulation of H2, formate and ethanol, which are not energy substrates for ruminants. It was hypothesized that the addition of butyrate precursors would avoid the formation of these products and relocate electrons into butyrate.

The Effects of Thiamine Inhibition on Ruminal Fermentation: a Preliminary Study

Inhibition of methanogenesis in ruminal cultures was attempted by hindering thiamine availability through its degradation by ‘polyphenols’ and competition for active sites on enzymes and transporters using thiamine structural analogs. Effects on fermentation were small and not consistently reversed by adding thiamine. Lack of major effects of the compounds evaluated could be due to intracellular synthesis of thiamine covering most requirements.

Effects of tail docking on health and performance of beef cattle in confined, slatted-floor feedlots.

Tail docking of feedlot cattle is a management practice used in some confined, slatted-floor feedlots of the midwestern United States. Justification for tail docking in these management systems is to reduce tail injuries and their sequelae and improve performance, but limited evidence exists to support these claims. The primary objective of this study was to determine the effect of tail docking on performance, carcass traits, and health parameters after tail docking in feedlot cattle raised in slatted-floor feedlots. Three separate trials were performed. Trial 1 consisted of 140 Angus-cross (370-kg) yearling steers that spent 144 to 160 days on feed (DOF). Trial 2 consisted of 137 Angus-cross (255-kg) weaned steers that spent 232 DOF. Trial 3 consisted of 102 Holstein steers (370 kg) that spent 185 to 232 DOF. Cattle were randomly assigned to 1 of 2 treatment groups: docked (DK) or control (CN). All steers received an epidural following surgical preparation of the sacrococcygeal area and postoperative intravenous flunixin meglumine. Approximately two-thirds of the tail of DK calves was removed and an elastrator band was placed near the tail tip for hemostasis. Performance parameters collected included daily gain, final weight, feed intake, and feed efficiency. Carcass data included HCW, subcutaneous fat thickness, LM area, KPH percent, marbling, USDA yield grade, and USDA quality grade. Morbidity, mortality, incidence of lameness, and incidence of tail lesions were recorded. Across all 3 trials, there was no significant effect (P < 0.05) of treatment on performance parameters, carcass traits, or health parameters. In all 3 trials, tail tip injuries occurred in 60 to 76% of undocked (CN) calves, developed while living in the slatted-floor environment, compared to 100% of DK calves, whose injuries were a result of the tail docking procedure. We were unable to identify a performance or significant health advantage to tail docking. However, tail tip injuries still occur in cattle raised in slatted-floor facilities. Because of the animal welfare issues associated with tail docking and tail injuries, we recommend pursuing alternative solutions to reducing the incidence of tail tip injury in feedlot cattle housed in confined slatted-floor facilities.