Investigation of a Reduction in Tylosin on the Prevalence of Liver Abscesses and Antimicrobial Resistance in Enterococci in Feedlot Cattle.

Recent concerns over linkages between antimicrobial resistance in human pathogens and antimicrobial use in livestock have prompted researchers to investigate management strategies that reduce the current reliance on in-feed tylosin to control liver abscesses in feedlot cattle. A total of 7,576 crossbred yearlings were allocated to the study (~253 animals/pen, 10 replicate pens per treatment) and individually randomized to one of three treatments. Tylosin phosphate (11 ppm) was included in-feed (1) for the first 125 days on feed (DOF) (FIRST-78%), (2) for DOF 41 to 161 (LAST-75%), or (3) for the entire feeding period (CON; day 0-161). Fecal composites were collected from the pen floor on days 0, 81, and 160 of the finishing period. Serial dilutions were spread plated for enumeration of enterococci on Bile Esculin Azide (BEA) agar and BEA amended with 8 µg/ml erythromycin. Results indicated that although the proportion of EryR enterococci increased with DOF (P < 0.01), neither treatment (P = 0.34) or treatment × DOF (P = 0.37) affected antimicrobial resistance. Of the 538 isolates, 97% were enterococci, with mixed species isolated early in the feeding period and only Enterococcus hirae isolated at the end. Isolates were most frequently resistant to tylosin (86%), erythromycin (84%), and doxycycline (31%). Macrolide and tetracycline resistant isolates harbored erm(B), msrC, and tet(L), tet(M), tet(O) genes, respectively. Overall, the proportion of EryR enterococci increased (P < 0.05) in all three treatments over the feeding period. Compared to the control cattle, FIRST-78% cattle had more severe (P < 0.05) liver abscesses, while there was a trend (P < 0.08) for this response in LAST-75% cattle. There was no difference (P > 0.05) in total liver abscesses, growth performance, carcass traits, morbidity, or mortality among treatments. These results support the potential to reduce the duration and therefore quantity of tylosin administered to feedlot cattle during the feeding period without impacting animal productivity.

Complete Genome Sequences of 16 Mycoplasma bovis Isolates from Canadian Bison and Cattle.

Here, we report the complete genome sequences of 12 Mycoplasma bovis isolates cultured from Canadian bison and 4 cultured from Canadian cattle. The sequences are of value for understanding the phylogenetic relationship between cattle and bison isolates and will aid in elucidating the genetic basis for virulence and host specificity.

A serologic survey of Mycoplasma spp. in farmed bison ( Bison bison) herds in western Canada.

Mycoplasma bovis is emerging as an important pathogen of farmed bison in North America and is associated with high morbidity and mortality in affected herds. We developed an in-house ELISA to detect antibodies against Mycoplasma spp. in bison sera. The aims of the study were to estimate the seroprevalence against Mycoplasma spp. in bison herds with or without past history of M. bovis-associated disease, and to determine potential risk factors for seropositivity to Mycoplasma spp. in farmed bison in western Canada. A total of 858 serum samples were collected from bison >1 y of age from 19 bison herds. The individual and herd-level seroprevalence of Mycoplasma spp. was 12% and 79%, respectively. The proportion of seropositive animals was 0-41% and 0-9% for herds with or without a history of M. bovis-associated disease, respectively. Mycoplasma spp. appear to be widespread in bison in Manitoba, Saskatchewan, and Alberta. Eight of 11 herds with no history of M. bovis-associated disease were seropositive for Mycoplasma spp., which suggests that bison can be subclinically infected with Mycoplasma spp., or that infection may be underdiagnosed. Although not specific to M. bovis, the in-house ELISA developed to detect antibodies against Mycoplasma spp. may prove to be a valuable herd-level screening tool, providing insight needed for the development of appropriate prevention and control measures for Mycoplasma-related disease in bison herds.

Risk factors for Mycoplasma bovis-associated disease in farmed bison (Bison bison) herds in western Canada: A case-control study.

North American bison producers have been attempting to control and prevent Mycoplasma bovis-associated disease without the benefit of bison-specific knowledge. The objective of this study was to determine the clinical presentation of disease associated with M. bovis infection in western Canadian farmed bison, and to identify herd-level risk factors for M. bovis-associated disease. Bison producers (n=49) from western Canada (Manitoba, Saskatchewan, Alberta, and British Columbia) were selected for a 1:2 case-control study. Data were collected by an in-person interview using a questionnaire regarding clinical presentations of outbreaks and herd-level management factors. Risk factors associated with M. bovis outbreaks were identified using multivariable logistic regression analysis. All 17 case herds had a laboratory-confirmed diagnosis of M. bovis infection within the last 5 years. In 11 (65%) of the 17 case herds, disease associated with M. bovis infection recurred in subsequent years. Overall, 88% of case herds had recently introduced bison that later developed clinical signs associated with M. bovis infection. Within a bison operation, a median of 8% (Inter Quartile Range [IQR]: 3-11%) developed clinical signs: lameness, reluctance to move, swollen joints, difficulty breathing, coughing, sluggishness, and loss of body condition. Also, calving percentage the year after the first M. bovis outbreak was lower than calving percentage the year before the outbreak. Herd-level mortality risk during the first M. bovis outbreak in case herds ranged from 0.5 to 50% (median 5%, IQR: 3-10%) and the median case fatality risk was 100%. Case herds were more likely than control herds to have a feedlot unit (OR=7), to receive regular visits from rental trailers or trailers from other farms (OR=15), to annually vaccinate bison (OR=7), and to lose at least one bison due to fatal respiratory disease in the previous year (OR=9). These findings will aid development of evidence-based recommendations for management to prevent and control Mycoplasma bovis in farmed bison in Western Canada.