New EU veterinary medicine regulations
A paper by More et al (2022) (Irish Veterinary Journal https://doi.org/10.1186/s13620-022-00209-6) focuses on the new EU Veterinary Medicines Regulation (2019/6), which has not been implemented in the UK (including NI), but which is applicable across all member states of the EU from 28 January 2022. Prophylactic use of antimicrobials (AMs) in groups of animals is now banned, metaphylactic use in groups of animals is restricted, and certain AMs are reserved for human use only. The authors then focus on mastitis, although the implications of the legislative change are clearly far wider reaching than this. They state that in the Irish dairy industry, as elsewhere, successful implementation of the Regulation will require a high level of mastitis control across all herds, and measures to support high standards in antibiotic stewardship. For private veterinary practitioners, the Regulation will lead to specific prescribing changes, including the requirement to shift from blanket to selective dry cow therapy. Further, prescribing choices will need to be guided by the categorisation for AMs developed by the European Medicines Agency. A herd health approach will be critical, and on those farms with sub-optimal mastitis control, mastitis issues need to be sustainably resolved.
It is not yet clear what changes may be implemented in the UK as a result of this EU change, but the general direction of travel and best practice is clear. We all need to look carefully once again at our prescribing decisions. The reduction in AM use in UK food animal production has slowed in recent years and it is time we looked very critically at prophylactic use. The following two papers are relevant to this, in forcing us to question common practice once again.
Antibiotic use in calf diarrhoea
Gastrointestinal disease is the most common cause of mortality in dairy calves. Septicaemia is an important sequela of diarrhoea, and the possibility of bacteraemia is the primary justification for AM therapy. Garcia et al (2022) (Journal of Dairy Science https://doi.org/10.3168/jds.2020-19819) hypothesised that the prevalence of bacteraemia in calves with diarrhoea and systemic signs of illness is less than prior estimates (~31%), and that clinical signs or haematological values would be associated with the presence or absence of bacteraemia. Female calves less than 21days of age with and without diarrhoea were enrolled from two commercial dairy farms over a 10-week period. Diarrhoeic calves were enrolled if they were newly diagnosed, had loose to watery stool, had either dehydration (assessed by skin tent and eye position) or depression (assessed by suckle reflex and standing ability), and had no prior AM treatments. Complete health assessments were conducted at 0, 7, and 14 days following enrolment. An aseptic jugular venous sample was collected and cultured using aerobic and anaerobic methods, and bacterial species were identified using mass spectrometry. The prevalence of bacteraemia in diarrhoeic and healthy calves was 9.26% (95% confidence interval: 4.5–16%) and 14.8% (95% confidence interval: 1.4–28.2%), respectively. Among calves with diarrhoea, those with a fever (>39.7°C) or depression were 4.8 and 6.5 times more likely, respectively, to have bacteraemia. Only 1 of 47 calves (2%) without signs of depression had bacteraemia. The prevalence of bacteraemia in diar-rhoeic calves with signs of systemic illness (depression or dehydration) was significantly lower than previous estimates, and bacteraemia was rare among calves without observed depression. The authors conclude that AM therapy targeting bacteraemia is not currently justified in routine cases of diarrhoea in preweaning calves without signs of depression.
Antibiotic spray and disbudding
Oxytetracycline is commonly applied as a topical agent to burn lesions post cautery disbudding of calves. Judicial use of antibiotics dictates that they should only be used where necessary to reduce the risk of development of AM resistance. The objective of this study by Ridgway et al (2020) (Frontiers in Veterinary Science https://doi.org/10.3389/fvets.2022.745632) was to evaluate the efficacy of topical oxytetracycline spray on wound healing post cautery disbudding of dairy calves over a 6-week period. Dairy calves were disbudded by using a standard cautery disbudding protocol. Oxytetracycline spray was randomly applied to the right or left horn bud of each animal, while the other horn bud received no antibiotic spray (NA). The outcomes measured were wound diameter and lesion score, either normal healing or abnormal healing. These assessments were conducted every 14 days following disbudding, until 42 days. A total of 360 animals completed the study. There was a difference in wound diameter and lesion score on day 14 post disbudding between the two groups. Cautery lesions sprayed with oxytetracycline were 0.5 ± 0.15 mm smaller than NA lesions, and there were fewer abnormal healing lesions for oxytetracycline compared with the NA. There were no differences at day 28 and day 42 post disbudding, and on day 42, 34% of wounds had healed in both groups. In summary, the authors were unable to demonstrate a difference in healing between the groups using the described methods, making the routine use of prophylactic oxytetracycline spray when disbudding calves unjustified.