Authorisation of Dry Cow Therapy
To assist veterinarians to comply with the requirements for authorising Dry Cow Antibiotic Treatment (DCAT).
Treatment of existing intramammary infections (IMI) at the end of lactation (dry-off) and prevention of new IMIs over the non-lactating (dry) period and at calving are cornerstones of udder health management in dairy cattle.
Effective management of udder health around the time of drying off and over the dry period is typically achieved through careful attention to cow nutrition, udder hygiene, milking management, minimisation of environmental risks, and stock handling. However, most farms will also seek to minimise negative animal welfare outcomes and optimise the effectiveness of their dry-off management through use of restricted veterinary medicines (RVMs) including teat sealants and antimicrobial products.
While antimicrobials are an effective element within an udder health management programme, their use must be justified in the context of antimicrobial resistance and food residues. This applies both during lactation, and at dry-off.
Veterinarians authorising antimicrobial RVMs for use at dry-off must have clear justification for this use. This includes having a sound understanding of the current prevalence and incidence of clinical and subclinical mastitis in the herd, the bacteria involved and the effectiveness of antimicrobial therapies against them, and mastitis management controls in use on the farm.
- A veterinary authorisation for DCAT is a key component in managing risks and preventing antimicrobial resistance in animals.
- Veterinary authorisations are discretionary and require veterinarians to make a professional judgement.
- DCAT must only be authorised following a consultation and as part of an ongoing udder health programme in which the authorising veterinarian is involved.
- If more than one veterinarian (e.g. general practitioner and a veterinary consultant) is involved in managing the udder health programme on a farm, each must seek owner’s consent and should communicate with the other(s) to share appropriate information in order to optimise treatment and welfare outcomes.
Validated diagnostic culture, screening culture, and PCR herd testing systems can provide accurate information at an individual cow level and may be used as a routine screening tool for identification of mastitis-associated pathogens pre dry off.
The SmartSAMM system provides criteria for the management of cows prior to, during and after drying off and the administration of products, particularly Internal Teat Sealants (ITS), are fundamental to a successful drying off process.
For herds with a low bulk milk somatic cell count, low incidence rate of clinical mastitis and low culling percentage for mastitis-related problems, it is likely that few cows are truly infected at drying off. For these herds, routine use of antimicrobials in every quarter of every cow at the end of lactation is not justified.
Internal teat sealants should be used in preference to antibiotic dry cow therapy to prevent new infections over the non-lactating period, in those cows unlikely to be infected at drying off.
As a general principle, antibiotic dry cow therapy isn’t justified unless there is indication that the herd has a high mastitis risk – see table 1 and SmartSAMM Technote 14 criteria.
Measure of infection
Criteria indicative of hers with a high risk of mastitis*
Bulk milk SCC
Seasonal average is equal to or above 250,000 cells/mL
Clinical mastitis in dry period
2 or more cases/100 cows over the dry period
Clinical mastitis in early lactation
10 or more cases per 100 cows in the first month of lactation
Individual cow SCC in early lactation
More than 25% of herd with cos SCC over 150,000 cells/mL at herd tests in first six months of lactation
Dry period new infection rate
15% or more cows have an increase in SCC from below 150,000 cells/mL, to above 150,000 cells/mL, over dry period
*For herds to be considered eligible for whole herd DCAT, it is recommended that all five criteria are met, or three criteria if no individual cow SCC data is available.
Current recommended best-practice is to ensure that all cows are protected by some form of treatment during the dry period – either internal teat sealant (ITS) and/or DCAT.
Internal teat sealants (ITS) are used to:
- Protect uninfected quarters from becoming infected during the dry period and at calving
- Extend the period of protection when used in combination with DCAT.
DCAT is used to treat existing intramammary infections
Cows which are at low risk of having an intramammary infection at the time of dry-off do not require DCAT. Therefore, herds with indicators of a low prevalence of infection should not use DCAT in every quarter of every cow.
The threshold for authorising at a herd level is similar to that required for an individual animal; you must have sufficient contact with the herd/animal to be able to justify that authorisation. The authorising veterinarian must have visited the herd at least once in the previous 6 months.
When authorising DCAT, veterinarians are expected to identify cows with evidence of infection and only authorise DCAT for use in those cows that are likely to be infected (i.e. selective DCAT treatment).
Veterinarians must be able to justify each individual animal’s treatment plan by ensuring there is sufficient clinical evidence to support a need for DCAT use for each animal for which the product is authorised i.e. full herd test results, or validated diagnostic culture, screening culture, or PCR herd testing systems.
Where herds do not undertake herd testing, alternatives such as a hand-held rapid mastitis test (RMT), or automated conductivity or somatic cell measures via the milking management system, may be used to define intramammary infection status.
Veterinarians should only authorise whole herd DCAT to manage animal welfare in herds with indicators of a particularly high prevalence and/or a justifiable risk of infection as per the criteria in table 1.
Where a veterinarian authorises whole herd DCAT, they must also ensure a comprehensive udder health improvement plan is implemented. This should include mastitis diagnostics e.g. culture and sensitivities, and milking time visits to identify mastitis risk factors. The aim should be to reduce yearly mastitis rates to transition the herd to selective treatment i.e., whole herd, or blanket, DCAT must not be used as a substitute for other mastitis control measures.
The authorising veterinarian must ensure all persons administering RVMs are competent (see this technical advice for more information), this includes providing advice on adequate teat disinfection, administration technique (NZVA’s Dry-off resources are a best practice approach and should inform veterinarians decisions) and milk and meat withholding periods.
Where ITS are used alone the application requires appropriate hygienic insertion to avoid potential intramammary infection and animal welfare issues and veterinarians are expected to ensure all persons administering RVMs are competent to do so.
Veterinarians must include in dry-off authorisation documents/clinical records the following information as a minimum:
- a clinical history
- consultation and examination details
- animal or herd identification
- the decision-making process and supporting evidence and the results of any diagnostic tests that led to the decision for treatment, and their reasons for deciding to use the antibiotic in individual cows including the diagnosis (confirmed or suspected)
- the name of the product and details about administration
- the communications and instructions given to the owner or person in charge
Information on current best practice for udder health management is available via the DairyNZ SmartSAMM programme.
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