Exploring potential risk factors of antimicrobial use in beef cattle

Livestock species are major contributors to the increase of antimicrobial (AM) resistance which is a worldwide concern for both human and animal health. The over-use of AM is widely acknowledged, however, unlike pigs, poultry and dairy cattle, knowledge on potential risk factors affecting AM usage (AMU) in beef industry is limited. Hence, this study aimed to investigate the impact of farm, breed, sex and season of arrival of purchased beef cattle on AMU in Italian beef cattle. Data on 1063 batches were collected from January 2016 to April 2019 from specialised beef fattening farms located in the north of Italy. Information on breed, sex, date of arrival, performance traits and AM agents used on farm was collected, and the treatment incidence 100 (TI100) indexes per batch were calculated using the defined daily dose animal estimated according to Italian summaries of product characteristics. Factors affecting TI100 indexes were investigated using a cross-classified multilevel model. Farms largely differed in terms of AMU. Males had greater AMU than females (P < 0.001), likely due to their higher susceptibility to disease. Statistically significant differences were observed between seasons of arrival with summer and spring having lower TI100 indexes than winter and autumn (P < 0.001). Indeed, winter is commonly linked to an increase in respiratory diseases in beef cattle. Finally, the TI100it indexes tended to be different among breeds with Blonde d'Aquitaine and Limousine having greater AMU compared to the other breeds. Results of this study provided valuable information on potential risk factors of AMU in beef production which may be useful to address its reduction. For instance, the development of tailored management strategies for specific breeds, targeted approaches to improve the health of males as well as greater care towards batches purchased in winter are possible advice to implement on-farm for a more responsible AM stewardship.

Characterization of Brachyspira hyodysenteriae isolates from Italy by multilocus sequence typing and multiple locus variable number tandem repeat analysis

AIMS

To evaluate and compare the capabilities of multilocus sequence typing (MLST) and multiple locus variable number tandem repeat analysis (MLVA) techniques to characterize Brachyspira hyodysenteriae isolates and to investigate the relationship between pleuromutilin resistance and genetic variability.

METHODS AND RESULTS

MLST genotyping was performed on 180 B. hyodysenteriae isolates, and the results were evaluated considering profiles from 108 other strains previously reported in the database. In total, 37 sequence types were obtained. The MLVA approach completely characterized 172 strains and grouped the isolates into 22 different profiles. The combination of MLST and MLVA showed a slight increase in the discriminatory power, identifying 33 joint profiles. An antibiotic resistance analysis showed a reduction in the susceptibility to pleuromutilins over time, and a weak association between susceptibility to valnemulin and inclusion in clonal complex 4.

CONCLUSION

MLST and MLVA are reliable methods for characterizing B. hyodysenteriae strains and they have comparable discriminatory power.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genotyping of B. hyodysenteriae isolates and a database of all the genetic profiles collected during the diagnostic activities could support traditional epidemiological investigations in identifying infection sources and routes of transmission among herds, and in developing more effective control measures.