Sophie Mahendran stresses the importance of protecting cattle from disease entry and spread, and outlines methods of prevention.
Over the past few decades, a dairy practitioner’s skill set has had to evolve from pure individual animal medic to cattle health advisor, focusing on prevention and elimination of disease in the entire herd.
This evolution is now widely embraced, with much-improved teaching at university level and excellent resources available via CPD courses and accreditation schemes. However, practical application and provision of advice to farmers is often not simple due to the complicated nature of many dairy enterprises.
Developing a successful herd health plan hinges on understanding the on-farm disease status and a risk analysis to highlight potential infection sources. A key component is biosecurity – measures and activities designed to protect a farm from the entry and spread of pests and diseases. Farm biosecurity is the owner’s responsibility, and that of each person visiting or working on the farm, including vets.
Though difficult to make a farm totally biosecure, risks can be managed and reduced by addressing other disease control points.Many European countries have adopted the practice of a farm providing its own protective clothing for visiting vets, therefore reducing the chance of introducing infectious diseases from improperly disinfected clothing and equipment. However, this has yet to happen in the UK, so vets must be vigilant about their hygiene and appropriate disinfectant use between farms.
Farmer action-based biosecurity
As well as focusing on the animals, farmers must consider measures around the rest of the farm. Field boundaries can be an important place for close contact between animals from different farms, which can spread infectious disease (Figure 1). Ideally, farmers should avoid simultaneous grazing of neighbouring paddocks, but this is not always possible. Instead, double fencing with a three metre gap can be used, along with avoidance of shared water sources, including streams and rivers.
If possible, neighbouring farmers should be encouraged to share their herd health status details with each other.
Farmers working together to develop a local disease prevention strategy gives more chance of maintaining sustainably low disease levels in geographical areas. Farm visitors are another potential source of infection spread.
Farmers should:
- keep a record of visitors
- try to make them park away from livestock (this is especially important for deadstock collectors or livestock hauliers)
- ask them to wear clean protective clothing and the farmer should provide suitable disinfection points, such as a boot dip
Farmers should also avoid sharing machinery or spreading livestock manure from other farms on to pastures as this can be a source of infectious material.
Disinfection is a way of reducing the number of viable microbes on surfaces. Many disinfectants can be used, with available products generally containing one or more microbiocides and chemicals.
One commonly used product is an iodophor disinfectant containing iodine that is bactericidal, fungicidal and virucidal. This includes Defra approval for use against foot-and-mouth disease, swine vesicular disease and TB.
Whatever the disinfectant, include the concentration used, contact time required for action and the effect of organic matter contamination on the product effectiveness.
Disease spread by poor biosecurity
A vast number of infectious diseases can spread to farms due to poor biosecurity. The main ones include Johne’s disease, infectious bovine rhinotracheitis (IBR), leptospirosis, bovine viral diarrhoea, bTB, digital dermatitis, Salmonella, ringworm, endoparasites and ectoparasites. Some key points that can affect disease spread are mentioned in Panel 1.
Panel 1. Factors that can affect disease spread
Infectious bovine rhinotracheitis
- Caused by bovine herpesvirus 1.
- Once a cow is infected, the virus is harboured in the trigeminal nerve and the animal remains a carrier for life. Shedding can re-occur following periods of stress.
Leptospirosis
- Bacteria can remain in the kidneys for an extended period post-infection, leading to a long period of shedding in the urine.
- Can be spread by co-grazing with sheep.
Bovine viral diarrhoea virus
- Persistently infected (PI) animals continually shed the virus for the duration of their lives.
- Vaccination does not work on PI animals and their presence reduces vaccination effectiveness in the rest of the herd due to continued high exposure levels to the virus.
bTB
- Caused by Mycobacterium bovis.
- Bacteria shed in bodily secretions – especially respiratory secretions of cattle.
- The main wildlife reservoir is badgers – it is important to deter badgers from coming into contact with cattle or their feed:
- close off access to feed stores
- put cattle feed in raised troughs in fields
- fence off badger latrine areas
Keeping a closed herd is the most secure way of maintaining biosecurity and herd health status. However, if farmers buy in animals or borrow bulls, they should buy from a closed herd of known health and accreditation status.
If possible, they should avoid purchase from livestock markets. Bought-in animals must be quarantined for three weeks, which allows for incubating disease monitoring. Quarantined animals should be at least three metres away from other livestock (to avoid nose-to-nose contact), with separate feed and water.
Biocontainment via vaccination
Biocontainment is disease-spread management in a herd. The most commonly used method of biocontainment is vaccination.
Many diseases are endemic in the UK, with vaccination offering a suitable method for disease control once a disease is identified in a herd, and to protect a naive herd if biosecurity risks are high. However, vaccination does not prevent disease – it just reduces clinical signs and shedding.
Commonly used vaccines in the UK are for IBR, BVD, leptospirosis, Salmonella and respiratory pathogens. Deciding vaccination is needed is often an easy decision, but deciding which vaccine, and how best to complete initial and booster doses, can be a logistical challenge.
Vaccination regimes for breeding heifers must be done prior to the start of their first breeding period, with yearly boosters for the whole herd then generally used. Combining herd vaccination timing with other handling events, such as the second day of TB testing, can reduce the extra time and resources needed to vaccinate large groups, as well as the stress of an additional handling event on cattle.
Other factors that can affect vaccine efficacy are to check the vaccine is administered via the correct route and dose. Storage before use is important, as most vaccines require cold chain compliance, which can be difficult in the summer without cool bags and ice blocks.
Other things to check are that vaccine equipment is clean and calibrated, and farmers don’t over-order vaccine amounts, as storage and use after expiry dates can reduce efficacy.
Accreditation schemes
Accreditation schemes – such as Cattle Health Certification Standards, BVDFree England and Scottish EVD Eradication – can offer guidelines for farmers to help ensure herds become free from disease and be a financial incentive due to accredited stock having increased value.
Farmers subscribing to a scheme provides more “motivation” for applying biosecurity on farm – especially to maintain practices long term.
Reasons for poor biosecurity
Most of the aforementioned control points have been standard veterinary recommendations for years, but uptake and compliance is still patchy across the industry. In a survey across practising cattle vets, 52% of respondents indicated the reason they thought clients did not practise good biosecurity was due to a lack of knowledge and understanding. It can be challenging to find time to have these discussions with clients, with many only spending time talking to their vet during routine fertility visits – often while multitasking.
As the vet role evolves, it is imperative to try spending constructive time discussing important topics with farmers in a more formal setting, such as around the kitchen table. This can help focus discussions and ensure farmers are properly informed about topics such as biosecurity. Running practice farmer talks can also help, but the key to success will be ensuring farmers understand why biosecurity is important, and following up with farm-specific recommendations you can monitor.
Source: Vet Times
