Use of antibiotics at dry off is coming under increasing scrutiny and this could change how we dry cows off in future.
- Responsible or prudent use of antibiotics means using as little as possible, and as much as needed, to not compromise animal health.
- Since mastitis control accounts for over 85% of the antibiotics used on NZ dairy farms, the use of antibiotics at dry off is a logical place to reduce antibiotic usage.
- There has been some uncertainty about how well non-antibiotic alternatives perform for cows wintered in systems perceived to have a high risk of mastitis due to environmental bacteria.
- A study on two farms in Southland, one wintering cows in a barn and the other on fodder beet, indicated that internal teat sealant can be as effective as dry cow antibiotics for preventing mastitis.
- Planning is underway for a multi-herd study in 2017 to investigate herd-level measures of the risk of mastitis, and support the development of prudent use guidelines for dry cow products.
- Good mastitis health records will be vital for deciding dry cow treatment plans that involve prudent use of antibiotics, appropriate for individual herds. Vets are likely to advocate more bacterial culture work to support antibiotic treatment.
Concerns about antimicrobial resistance
Governments and public health organisations around the world are increasingly voicing concerns about the emergence of antibiotic or antimicrobial resistance (AMR) among human and animal pathogens1,2.
Organisations such as the US Centre for Disease Control and Prevention report that AMR “is one of our most serious health threats”1 and estimates that over two million people are sickened each year through antibiotic-resistant infections.
Such powerful language is beginning to affect how antimicrobials and, more specifically, antibiotics are used in both human health and agriculture.
The “One Health Initiative”3 has been championing global collaboration across many health sectors. Established in the United States in 2008, and supported by a growing number of medical and veterinary organisations around the world, this forum recognises that “human health and animal health are linked, and that a holistic approach is needed to understand, protect and promote health of all species”.
One of the main priorities is to address the link between agricultural use and emergence of AMR in human healthcare. Although the connections and causal relations can be debated4, many reports agree that use of antibiotics in any sector ultimately drives development of AMR.
Each time a new antibiotic is released, new bacterial isolates that are resistant to it emerge within years, months, or sometimes weeks2. Extending the life of existing antibiotics, therefore, becomes an important part of prudent stewardship of antimicrobials.
For some countries, the risk of AMR has become real. In the Netherlands in the late 2000’s, significant pockets of methicillinresistant Staphylococcus aureus (MRSA) bacterial strains were detected in pigs and, at the same time, cases of MRSA-infections among farmers and vets involved with the pork industry were reported at hospitals5.
Over a period of 4 years, the Dutch parliament legislated that antibiotic use across all livestock industries should be drastically reduced, initially by 20%, then 50%, and then 70% in 2015, compared with amounts used in 20095.
Similarly, the Department for Environment, Food and Rural Affairs (DEFRA) in the UK has recently committed to an almost 20% reduction in antibiotic use in livestock and fish farmed for food6.
Responsible stewardship of antibiotics
The UK-based organisation RUMA (Responsible Use of Medicines in Agriculture) suggests that prudent or judicious stewardship means to “use medicines as little as possible and as much as necessary”7. But what does this mean in practice? Generally, responsible stewardship of antimicrobials involves four core actions:
- Prevent new infections and prevent the spread of resistance
- Surveillance and tracking of resistant bacteria
- Improve the prescribing and stewardship of today’s antibiotics, and
- Promote development of new antibiotics and diagnostics for resistant bacteria.
The challenge for all parties will be to ensure that prudent use can be achieved, without compromising animal health, welfare and productivity.
Prudent use in dairy
About 85% of the antibiotics used on NZ dairy farms is used for mastitis control, with about half used as dry cow antibiotics at drying off8.
Recent guidelines for dairy vets9 recommend that antimicrobial treatments are increasingly reserved for situations where; a) there is evidence of a bacterial infection (or sufficient cause to suspect one) and b) that the infection would be unlikely to resolve without antimicrobial therapy.
So, treatment of clinical masitis cases will continue to remain acceptable, but antibiotic use at dry off will require justification.
In SmartSAMM Technote 1410, it is recommended that all cows be protected at dry off with either DCT, internal teat sealants (ITS), an effective alternative to antibiotics, or a combination of the two, depending on infection status of the herd.
Internal teat sealants, of which there are now a number available commercially, involves infusion of an inert, dense, non-antibiotic material, called bismuth subnitrate, into the teat at drying off. This material remains in the teat sinus until calving, providing a physical barrier to bacteria, and preventing them establishing an infection in the udder tissues.
Survey data indicates that at least 85% of dairy cows in NZ receive some form of treatment at dry off. The majority (50-60%) of farmers use DCT to treat all cows in the herd, with another 20% treating all cows with a combination of DCT and ITS. These approaches are often referred to as “blanket” therapy.
Only a small proportion, probably less than 10% of farmers, protect low SCC cows with ITS alone. This figure is considerably lower than the 30 to 40% of farmers that use ITS to protect heifers prior to their first calving.
The reasons why ITS alone might not be selected for low SCC cows at dry off are varied, but lack of confidence in the outcomes for older cows and concerns about consequences of poor infusion techniques will be part of the reason.
Also, in systems perceived to have a higher risk of mastitis, antibiotic treatments tend to be preferred, but defining factors that make a system “high risk” are largely based on intuition and past experience. Previous studies of the protective effect of ITS alone used farms that wintered cows on pasture11, 12, and there are no equivalent NZ data for farms that winter cows on forage crop or in wintering barns.
During winter 2015, a study was conducted in Southland. Three interventions at dry off were compared with no protection for low SCC cows. The study was conducted across two farms. One managed cows in a free-stall wintering barn, bedded on water-cushioned rubber mats, and fed predominantly grass silage and straw. Another herd was wintered on fodder beet, supplemented with baled grass silage and hay.
Only cows with a relatively low SCC; i.e. below 250,000 cells/ ml at the first three herd tests of the preceeding season, and with no clinical mastitis in lactation, were assigned to this study. The interventions at dry off are described in (Table 1).
Effect on clinical mastitis
After calving, the proportion of unprotected cows that developed clinical mastitis was almost three fold higher than for protected cows (Figure 1). Of the cows protected with an internal teat sealent, 4.4% developed clinical mastitis. This was statistically similar to cows protected with DCT only (3.6%) or DCT + ITS (3.4%). Despite small numbers of cows developing cinical mastitis in the dry period, the trend was consistent with post-calving results (Figure 1).
Types of bacteria isolated from clinical cases varied between the herds. For the herd wintered in the barn, Streptococcus uberis and E. coli were predominant, with both pathogens isolated from 36% of cases. For cows wintered on crop, Strep. uberis and Staphylococcus aureus were predominant, isolated from 33% and 20% of cases, respectively.
Effect on cow SCC
The consequences of no protection at dry off was sufficient to increase group average cow SCC for the herd wintered in the barn only (Figure 2). No differences were observed between the different protective interventions.
The results from this study were reassuring, with few differences observed between the three forms of protection, in terms of clinical mastitis or SCC. Teat sealant alone was sufficient to achieve almost a 70% reduction in dry cow mastitis, across two quite different wintering systems, and appeared to provide a realistic alternative to DCT, for cows that previously had a relatively low SCC.
A larger study, using up to 40 herds, is planned for 2017 to test the protective effect of ITS alone across many different herds. This study will also shed light on herd-specific risk factors that contribute to the higher incidence of mastitis observed on different farms.
Prudent use of antibiotics will mean using as little as possible, but as much as required. Current recommendations in SmartSAMM Technote 14 provide an important starting point for identifying what this might look like for individual herds, supported by good animal health treatment records. Discuss with your herd veterinarian how you can develop a prudent approach to antibiotics for your herd.
- Anon. 2013. Antibiotic resistance threats in the United States. US Centers for Disease Control and Prevention, Atlanta, US. Accessed March 2015 at: http://www.cdc.gov/ drugresistance/threat-report-2013/
- O’Neill, J. 2014. Review on Antimicrobial Resistance. Antimicrobial Resistance: Tackling a Crisis for the Health and Wealth of Nations. Chaired by Jim O’Neill. Accessed Feb 2015 at: https://amr-review.org/
- Kahn-Kaplan-Monath-Woodall-Conti One Health Initiative. 2008. One Health Initiative. Accessed Dec 2016 at: http://onehealthinitiative.com/contact.php
- Chang, Q., W. Wang, G. Regev-Yochay, M. Lipsitch, and W. P. Hanage. 2015. Antibiotics in agriculture and the risk to human health: how worried should we be? Evolutionary applications 8(3): 240-7.
- Speksnijder, D. C., D. J. Mevius, C. J. M. Bruschke, and J. A. Wagenaar. 2015. Reduction of veterinary antibiotic use in the Netherlands. The Dutch success model. Zoonoses and public health 62: 79–87.
- Anon. 2016. Government response to the Review on Antimicrobial Resistance. Published by Department of Health, HM Government. Accessed Sept 2016 at: https://www. gov.uk/government/publications/government-response-the-review-on-antimicrobial-resistance
- RUMA. 2009. RUMA promotes ‘as little as possible, but as much as necessary’ Antibiotic use, for the good of Animal Health and Welfare. Press release 30th March 2009. Accessed Sept 2016 at http://www.ruma.org.uk/ruma-promotes-little-possible-much-necessary-antibiotic-use-good-animal-health-welfare/
- Compton. C., and S. McDougall. 2014. Patterns of antibiotic sales to dairy farms in the Waikato region of New Zealand. Proceedings of The Society of Dairy Cattle Veterinarians of the NZVA Annual Conference. Pp. 3.6.1 - 3.6.8.
- Anon. 2016. Antibiotic judicious use guidelines for the New Zealand veterinary profession – Dairy. Published by New Zealand Veterinary Association, Wellington. Accessed Aug 2016 at: http://amr.nzva.org.nz/home
- DairyNZ. 2012. SmartSAMM Technote 14 Decide dry cow management strategy. Published by DairyNZ. Accessed Jan 2017 at http://www.dairynz.co.nz/animal/mastitis/toolsand-resources/guidelines-and-technotes/technote-14/
- Woolford, M., J. Williamson, A. Day, and P. Copeman. 1998. The prophylactic effect of a teat sealer on bovine mastitis during the dry period and the following lactation. New Zealand Veterinary Journal 46: 12-9.
- Compton, C.W., F. R. Emslie, and S. McDougall. 2014. Randomised controlled trials demonstrate efficacy of a novel internal teat sealant to prevent new intramammary infections in dairy cows and heifers. New Zealand Veterinary Journal 62: 258-66.
This article was originally published in Technical Series March 2017