Use of vaccination to control disease in breeding herds

The use of vaccines has increased in Irish cow herds in an effort to control endemic diseases such as leptospirosis, BVD, IBR, salmonellosis and neonatal calf diarrhoea. Vaccination is considered synonymous with herd health planning. However, this is a one-dimensional view of herd health and is over-simplistic.

Vaccines are frequently used on cows without knowing the disease status of the herd or having a risk assessment completed on the farm. In this case, the vaccination protocol is likely to be ineffective and a poor investment. Furthermore, the use of vaccines in isolation is unlikely to prevent disease outbreaks – for example, the frequent finding of BVD PIs in vaccinated herds.

For maximum efficacy, vaccination programmes must be designed and tailored to the needs of the individual herd.

Vaccines should be handled and administered correctly, with exact protocols adhered to.

Do I need to vaccinate?

Vaccination increases the immunity of that herd against a particular disease. If an infection is introduced, the amplified level of immunity will reduce the level of spread within the herd and minimise disease. In essence, the use of vaccination is a bio-containment measure. In contrast, biosecurity measures prevent disease from being introduced to the herd. Methods include maintaining a closed herd, having 3m-wide boundaries, providing protective clothing and foothbaths for visitors, etc. Vaccination alone will not prevent a disease from getting on to your farm. It will, however, reduce the effect of an outbreak should it occur. Realistically, very few Irish farms have adequate bio-security measures in place.

Evaluating herd status

This is an important first step in herd health management. With this knowledge in hand, and with veterinary support, you can decide on a disease-by-disease basis whether or not a vaccination programme is worthwhile on your farm. Over-reliance on bulk tank samples to evaluate herd status is of little value in evaluating true herd status.

On-farm risk assessment

Your vet is the most qualified person available to perform a biosecurity and epidemiological risk assessment on your farm, especially in herds that are undergoing expansion. They know your farm and can assess the main risks for each disease. They will put measures in place to minimise the risks identified which will reduce costs, improve productivity and promote animal welfare.

Leptospirosis

Leptospirosis has an estimated herd prevalence of between 79% and 82% in Ireland. It causes abortions, weak calves, infertility and milk-drop. It is also a zoonotic disease with dairy farmers at higher risk due to urine aerosols in milking parlours. Its introduction is mainly through the purchase of infected cattle/bulls. Assessing herd status is difficult as neither antibody testing nor bulk tank sampling provides an accurate picture. Your vet will calculate the required minimum number of blood samples required to assess individual herd status accurately.

Investigation of abortions is valuable as leptospirosis is a common cause. Submission of foetal kidney tissue for PCR testing is an exciting new option for diagnosis. Maintaining a disease-free status is practically impossible in Ireland. Isolation and testing of bought-in animals is important, but given the prevalence and the significant zoonotic risk to farmers, herd vaccination is advised as the most effective control measure.

BVD

This year, all negative herds will be assigned negative herd status (NHS). It is advised to work with your vet to attain NHS by testing animals with unknown status, removing PI animals or by investigating outbreaks of BVD using the recently launched investigation service. If BVD enters a herd that has low herd immunity the consequences can be considerable; large numbers of PI calves, infertility, abortions and calf health issues are all synonymous with BVD infection. The decision to vaccinate or not depends on knowing the status of your herd, the status of contiguous herds and the prevalence of other risk factors such as buying in stock. There is a new live BVD vaccine on the market in Ireland this year. Your vet is best placed to advise you on which vaccine is most suitable for your farm, and more importantly, the right way to use it.

Infectious bovine rhinotraceitis (IBR)

IBR has an estimated herd prevalence in Ireland of between 75% and 80% and causes approximately 3% of abortions. Disease is characterised by fever, milk drop, respiratory disease and ocular signs. Once infected, animals become latent carriers and reactivation and shedding is precipitated by stress, transport, calving, onset of lactation, bad weather and overcrowding.

In unvaccinated herds, a negative bulk tank indicates the herd is free from infection. To diagnose its presence in your herd, the optimum number of blood samples can be calculated and taken by your vet. A ready reckoner is available in literature from Animal Health Ireland. Given the prevalence in Ireland, vaccination is the only practical control measure in infected herds, and advice on specific vaccination protocols is best optained from your vet.

Salmonellosis

Salmonellosis has a high prevalence in dairy herds in the south of Ireland and is a significant cause of losses through peracute disease and abortions. Research suggests that at a milk price of 24c/litre, salmonellosis costs dairy herds €79/cow and that vaccinated herds enjoy increased profits of €68/cow. Risk factors include buying in infected cattle, hygiene, stress, liver fluke infestation and fomites. The recommendation is that infected herds should minimise the risk factors and vaccinate where losses are occurring or likely to be.

Neonatal calf diarrhoea

Neonatal calf diarrhoea can be caused by E. coli, rotovirus, coronavirus, cryptosporidium and salmonella. The intake of adequate colostrum is the number one control measure for neonatal calf diarrhoea followed by proper hygiene management in calf pens. The use of vaccines to increase the antibody levels in cows’ colostrum is regularly used on Irish farms and has improved the clinical picture on many problem farms. Testing of calf scour samples to establish the cause of outbreaks is vital especially as cryptosporidium infection is fast becoming the number one cause. While no vaccine is available against cryptosporidium, vaccination against other causes of NCD is an option that can be discussed with your vet.

Well-designed vaccination programmes are used successfully on many farms. A common feature is that a veterinary-led, risk-based approach is used to maximize efficiency and profitability.