Antibiotic resistance in human- and animal-associated pathogens is a well-known and emerging problem (Singer et al., 2003; Dong et al., 2021). Although the contribution of the dairy sector to the antibiotic resistance problem in humans is quite low, we should act more responsibly when it comes to using antibiotics (Tel et al., 2012; Nobrega et al., 2018).
Antibiotics on dairy herds are typically used related to udder health and a reduction in the use is possible by maximizing prevention and by applying selective dry cow therapy. Implementing selective treatment of non-severe clinical mastitis is a valuable third option.
Recently, M-teamUGent at Ghent University, Belgium started a field trial as part of a larger Flanders Innovation and Entrepreneurship-funded project (HBC.2020.3192) together with Animal Health Service Flanders, Hooibeekhoeve and the Flanders Research Institute for Agriculture, Fisheries and Food. The project aims at transferring relevant scientific findings towards dairy practice through communication and training.
Selective treatment of non-severe clinical mastitis is based on the knowledge that in mild and moderate cases of clinical mastitis, antibiotic treatment is redundant when the causative pathogen is gram-negative, a yeast or a fungus (Burvenich et al., 2003; Roberson et al., 2004). In cases of clinical mastitis due to Mycoplasma spp., the recommendation is to cull the cow (Nicholas et al., 2016). By using rapid tests, it is possible to differentiate to some extent what microorganism is causing a clinical case within 18 – 24 hours (Viora et al., 2014; Griffioen et al., 2018; Lago and Godden, 2018). In cases of growth of a gram-positive bacteria or when the milk sample was defined as contaminated, antibiotic treatment is recommended. In cases of no growth or growth of gram-negative bacteria, one should not treat with antibiotics. This approach can lead to a reduction in antibiotic use up to 50% (Lago et al., 2011a).
Preceding field studies on selective treatment of clinical mastitis were using on-farm rapid testing (Lago et al., 2011a; Vasquez et al., 2017; Bates et al., 2020; Griffioen et al., 2021). The dairy producers and the employees were trained in taking milk samples, inoculating the rapid tests in a small milk laboratory on farm and in interpreting the results.
Recently, M-teamUGent at Ghent University, Belgium started a field trial as part of a larger Flanders Innovation and Entrepreneurship-funded project (HBC.2020.3192) together with Animal Health Service Flanders, Hooibeekhoeve and the Flanders Research Institute for Agriculture, Fisheries and Food. The project aims at transferring relevant scientific findings towards dairy practice through communication and training. Twelve veterinary practices and fifty dairy farms in the Flemish region were recruited to participate in a two-year clinical trial through which the impact of selective treatment of non-severe clinical mastitis on udder health, milk yield and antibiotic use will be estimated by comparing the results of a selective treatment group with the results of a control group per herd. Unlike previous studies where rapid tests were conducted on-farm, on-practice testing will be implemented: milk samples of cases of mild (abnormal milk) and moderate (abnormal udder and/or milk) clinical mastitis will be collected by the producer and immediately transferred to the veterinary practice where a trained veterinarian or veterinary nurse will initiate a rapid test in the practice’s milk laboratory. When the result is available (after 18-24h incubation), the veterinary practice will communicate the result, including a treatment advice (gram-positive bacteria or contaminated samples will be treated, all other cases will remain untreated), to the farmer. This on-practice approach is new and specifically implemented because of the relatively small size of Flemish dairy herds an the relatively small distances from the veterinary practices to the (mostly family-run) farms. A small number of dairy cows within a herd implies – under good udder management – a relatively low incidence of mild and moderate clinical mastitis cases making it hard for the farmer to obtain enough routine, confidence and expertise to conduct and interpret the rapid test results. One may also question the profitability of investing in a milk laboratory on farms with very few cases of non-severe clinical mastitis every month. This new service is, however, an opportunity for bovine veterinarians to create or extend a new/existing business model, strengthening the relationship with the dairy producers and enabling the vets to get more involved in topics such as udder health and milk quality with the clients.
The veterinarians and their employees received a training to get familiar with rapid testing of milk samples and the use of lab-software to help analyze and report the results. The dairy producers were trained in taking milk samples secundum artem during on-farm workshops.
Per herd, cows developing a mild or moderate clinical mastitis case will be randomly assigned to two groups with a different treatment protocol: a protocol of direct antibiotic treatment (as before, control group) or a protocol of postponed rapid test-based antibiotic treatment. All included cows are checked daily by the farmer and information such as clinical symptoms and body temperature is recorded until the cow is free of symptoms for at least two days in a row.
Control cows receive antibiotic treatment at day 0 (day when the clinical case is detected) whereas cows in the selective treatment group receive antibiotic treatment only when gram-positive bacteria are detected using the rapid test performed at the veterinary practice or when the sample is deemed contaminated. Supportive treatment with NSAID’s is allowed but should be given to all cows on this herd when a producer decides to do so for cows in the treatment group. Additional milk samples of the inflamed quarter are taken at day 0 and 21 for analysis at a regional laboratory as the gold standard, allowing comparison with the results generated by the veterinary lab (day 0 sample) and checking for bacteriological cure of the quarter (day 21 sample).
Halve of the veterinary practices use Vétorapid (Vétoquinol) and the other six practices use Micromast (Prasek) as rapid test. Vétorapid consists of selective agars for the detection of gram-negative bacteria, Staphylococcus spp. and Streptococcus spp., respectively, whereas Micromast consists of selective agars for gram-negative bacteria, gram-positive bacteria, and of a non-selective agar. At the end of the field trial, the test characteristics of both tests will be determined using the results of the regional lab as gold standard.
Data will be collected through the on-farm checklists filled in by the farmers, DHI-records and culture results. MEX@LAB and KenoTM-M software will be used (MEXTM). Antibiotic use data will be extracted from the mandatory government-handled recording systems of the herds (Sanitel-Med).
With this project, including the two-year field trial, we are aiming at demonstrating that on-practice culturing is a valuable and sustainable (new) service for veterinary practices allowing selective treatment of non-severe clinical mastitis without compromising udder health nor milk production, yet combined with a substantial reduction in antibiotic use, similar as the results reported before (Lago et al., 2011b; Vries et al., 2016; Vasquez et al., 2017; Bates et al., 2020; Griffioen et al., 2021). In addition, the experiences and results will be shared with the Flemish dairy community through webinars, workshops and trainings driving change in the treatment of non-severe clinical mastitis in the Flemish dairy sector. In addition, the culture results will be combined with udder health management information per farm in order to also maximize mastitis management as a basis for better prevention.
Bates, A., R. Laven, O. Bork, M. Hay, J. McDowell, and B. Saldias. 2020. Selective and deferred treatment of clinical mastitis in seven New Zealand dairy herds. Prev Vet Med 176:104915. doi:10.1016/J.PREVETMED.2020.104915.
Burvenich, C., V. Van Merris, J. Mehrzad, A. Diez-Fraile, and L. Duchateau. 2003. Severity of E. coli mastitis is mainly determined by cow factors. Vet. Res 34:521–564. doi:10.1051/vetres:2003023.
Dong, L., L. Meng, H. Liu, H. Wu, H. Hu, N. Zheng, J. Wang, and M. Schroyen. 2021. Effect of therapeutic administration of β-lactam antibiotics on the bacterial community and antibiotic resistance patterns in milk. Journal of Dairy Science 104:7018–7025. doi:10.3168/JDS.2020-20025.
Griffioen, K., A.G.J. Velthuis, G. Koop, and T.J.G.M. Lam. 2021. Effects of a mastitis treatment strategy with or without on-farm testing. Journal of Dairy Science 104:4665–4681. doi:10.3168/JDS.2019-17871.
Griffioen, K., A.G.J. Velthuis, L.A. Lagerwerf, A.E. Heuvelink, and T.J.G.M. Lam. 2018. Agreement between four commercial diagnostic tests and routine bacteriological culture of milk to determine the udder infection status of dairy cows. Preventive Veterinary Medicine 157:162–173. doi:10.1016/J.PREVETMED.2018.07.003.
Lago, A., and S.M. Godden. 2018. Use of Rapid Culture Systems to Guide Clinical Mastitis Treatment Decisions. Veterinary Clinics of North America: Food Animal Practice 34:389–412. doi:10.1016/J.CVFA.2018.06.001.
Lago, A., S.M. Godden, R. Bey, P.L. Ruegg, and K. Leslie. 2011a. The selective treatment of clinical mastitis based on on-farm culture results: II. Effects on lactation performance, including clinical mastitis recurrence, somatic cell count, milk production, and cow survival. J Dairy Sci 94:4457–4467. doi:10.3168/JDS.2010-4047.
Lago, A., S.M. Godden, R. Bey, P.L. Ruegg, and K. Leslie. 2011b. The selective treatment of clinical mastitis based on on-farm culture results: I. Effects on antibiotic use, milk withholding time, and short-term clinical and bacteriological outcomes. Journal of Dairy Science 94:4441–4456. doi:10.3168/JDS.2010-4046.
Nicholas, R.A.J., L.K. Fox, and I. Lysnyansky. 2016. Mycoplasma mastitis in cattle: To cull or not to cull. The Veterinary Journal 216:142–147. doi:10.1016/J.TVJL.2016.08.001.
Nobrega, D.B., J. De Buck, and H.W. Barkema. 2018. Antimicrobial resistance in non-aureus staphylococci isolated from milk is associated with systemic but not intramammary administration of antimicrobials in dairy cattle. Journal of Dairy Science 101:7425–7436. doi:10.3168/JDS.2018-14540.
Roberson, J.R., L.D. Warnick, and G. Moore. 2004. Mild to Moderate Clinical Mastitis: Efficacy of Intramammary Amoxicillin, Frequent Milk-Out, a Combined Intramammary Amoxicillin, and Frequent Milk-Out Treatment Versus No Treatment. Journal of Dairy Science 87:583–592. doi:10.3168/JDS.S0022-0302(04)73200-2.
Singer, M.E., I. Harding, M.R. Jacobs, and D.H. Jaffe. 2003. Impact of antimicrobial resistance on health outcomes in the out-patient treatment of adult community-acquired pneumonia: a probability model. The Journal of antimicrobial chemotherapy 51:1269–1282. doi:10.1093/JAC/DKG220.
Tel, O.Y., M. Bayraktar, and O. Keskin. 2012. Investigation of antibiotic resistance among Staphylococcus aureus strains of human and bovine origin. Ankara Universitesi Veteriner Fakultesi Dergisi 59:191–196. doi:10.1501/VETFAK_0000002524.
Vasquez, A.K., Nydam, D.V., Capel, M.B., Eicker, S., and Virkler, P.D. 2017. Clinical outcome comparison of immediate blanket treatment versus a delayed pathogen-based treatment protocol for clinical mastitis in a New York dairy herd. Journal of dairy science 100:2992–3003. doi:10.3168/JDS.2016-11614.
Viora, L., E.M. Graham, D.J. Mellor, K. Reynolds, P.B.A. Simoes, and T.E. Geraghty. 2014. Evaluation of a culture-based pathogen identification kit for bacterial causes of bovine mastitis. Veterinary Record 175:89–89. doi:10.1136/VR.102499.
Vries, E.M.M., J. Lücking, N. Wente, C. Zinke, M. Hoedemaker, and V. Krömker. 2016. Comparison of an evidence-based and a conventional mastitis therapy concept with regard to cure rates and antibiotic usage. Milk Science International – Milchwissenschaft 69:27–32.