Outdoor veal system
The aim of a study undertaken by Becker et al (2020) (Preventive Veterinary Medicine doi. org/10.1016/j.prevetmed.2020.104907) was to evaluate a novel concept for calf fattening aimed at reducing antimicrobial use without compromising animal health. The ‘outdoor veal calf’ concept, implemented in 19 intervention farms (IF), is based on three main measures: purchased calves are transported directly from neighbouring birth farms to the fattening facility without mixing in transit; each calf is vaccinated against pneumonia after arrival and completes a 3-week quarantine in an individual hutch; and the calves spend the rest of the fattening period in outdoor hutches in groups not exceeding 10 calves. A covered and bedded paddock and group hutches provide shelter from cold weather and direct sunshine while allowing constant access to fresh air. Nineteen conventional calf fattening operations of similar size served as controls (CF). Every farm was visited once a month for a 1-year period, and data regarding animal health, treatments, and production parameters were collected. Treatment intensity was assessed by use of the defined daily dose method (TIDDD in days per animal year), and calf mortality and daily weight gain were recorded in both farm groups. Mean TIDDD was 5.3-fold lower in IF compared with CF, mortality was 2.1-fold lower in IF than in CF and mean daily gain did not differ between groups. A drastic reduction in antimicrobial use and mortality was achieved in the novel ‘outdoor veal calf’ system without compromising animal health.
Quarter-based selective dry cow therapy
The objective of a randomised controlled trial undertaken by Kabera et al (2020) (Journal of Dairy Science doi.org/10.3168/jds.2019-17438) was to assess the efficacy of an on-farm culture system using Petrifilm for targeted treatment decisions at the quarter level at dry-off and its effects on dry period intramammary infections (IMI) and udder health and milk production in the subsequent lactation. A total of 568 cows (2,247 quarters) from nine dairy herds with bulk tank somatic cell count <250 000 cells/ml were systematically enrolled and randomly allocated to four groups: two quarter-based selective (QSDCT) groups, using results of quarter-milk culture on Petrifilm, and two blanket dry cow therapy (BDCT) groups. The two QSDCT groups consisted of antimicrobial to infected quarters and internal teat sealant (ITS) to healthy quarters (QSDCT/ITS); and antimicrobial and ITS to infected quarters and ITS to healthy quarters (QSDCT+ITS/ITS). The two BDCT groups were antimicrobial alone to all quarters (BDCT); and antimicrobial and ITS to all quarters (BDCT+ITS). Quarter milk samples were collected at dry-off and after calving for routine bacteriological culture at the laboratory to monitor IMI; data on milk production, somatic cell count, and clinical mastitis recorded up to 120d in milk were retrieved from health and production records. The probability of avoiding antimicrobial treatment in QSDCT groups was estimated at 48.3%. There was no significant difference between the four treatment groups regarding acquisition of new IMI or persistence of existing IMI over the dry period. In the subsequent lactation, there was no difference between groups regarding incidence of clinical mastitis, mean milk somatic cell count, or mean daily milk production during the first 120d in milk. The authors conclude that QSDCT using the Petrifilm on-farm culture system to detect infected quarters at dryoff, is an interesting option to decrease antibiotic use without any negative effects on udder health or milk production in the first 120d of the subsequent lactation.
AMU in different milking systems
Mastitis is one of the major causes for antimicrobial use on dairy farms. On farms with an automatic milking system (AMS), diagnostics differ from those with a conventional milking system (CMS), with potentially a different attitude toward mastitis treatment. This may result in differences in AMU between these two types of farms. The aims of a study by Deng et al (2020) (Journal of Dairy Science doi. org/10.3168/jds.2019-17960) were to compare AMU between AMS and CMS farms, to identify variables associated with AMU in both types of herd, and to describe the distribution of mastitis-causing pathogens and their anti-microbial resistance patterns. Data on AMU were collected for 42 AMS and 254 CMS farms and were expressed as animal-defined daily dose (ADDD). The ADDD variables were total usage (ADDDTOTAL), intramammary usage during lactation (ADDDIMM), usage for dry cow therapy (ADDDDCT), and usage by injection (ADDDINJ). Eighteen AMS farms and 24 CMS farms participated in a survey on factors potentially related to AMU. These farmers collected quarter milk samples from quarters with clinical mastitis or high somatic cell count, which were subjected to bacteriological culture and antimicrobial susceptibility testing. In addition, routinely collected udder health data were used in the analysis. Differences in treatment strategy were unrelated to total antimicrobial usage or overall udder health. The distribution of mastitis-causing pathogens and their antimicrobial resistance were comparable between AMS and CMS farms. In conclusion, the study shows that AMU on AMS farms was similar to that of CMS farms, but AMS farmers tend to apply more injectable and fewer intramammary treatments than CMS farmers. Across both farm types, farmers' attitudes toward udder health in general and toward mastitis treatment are associated with AMU.