30 Jun 2020
Phil Elkins BVM&S, CertAVP(Cattle), MRCVS discusses the practical support vets can provide their clients to help them decide whether to vaccinate their herds.
Phil Elkins
Job Title
Accurate diagnosis of disease is vital, but often missed as part of the decision‑making process. Image: © EUGENI_FOTO / Adobe Stock
Vaccines have been an important part of cattle vets’ armoury in the battle against disease.
In the current climate – with increasing downward pressure on sales of antimicrobials, and tight margins on both beef and dairy production – their role can become even more important, but also potentially come under more scrutiny.
In fact, following turbulence in the milk market due to COVID‑19, some sources have recommended withholding vaccines from cattle as a way of saving money short term – but at what cost?
It is worth considering how vaccines could be classified, as this may influence conversations with farmers on whether the vaccine is useful or beneficial to them.
Vaccines could be categorised as follows:
We have vaccines licensed for the following disease areas: mastitis, respiratory disease, calf scour, clostridial disease, lungworm, ringworm, Leptospira, bovine viral diarrhoea (BVD), Salmonella, bluetongue and Q-fever.
Multivalent vaccines are typically for multi‑agent diseases, including respiratory disease and calf scour.
Monovalent vaccines include those for single‑agent diseases, such as BVD and Q-fever.
For diseases such as infectious bovine rhinotracheitis (IBR), cattle are the only relevant host for control. For multispecies diseases, the role of other species in epidemiology can affect vaccine decisions, as well as potential disease in humans – leptospirosis, Q-fever and salmonellosis can be life-threatening diseases in humans.
Some vaccines are involved in the elimination of a pathogen, such as bluetongue vaccination.
Some vaccines are involved in suppression of onward spread as part of eradication plans, such as BVD vaccines.
Some vaccines purely exist to suppress clinical signs, clinical effects and promote production, such as calf respiratory disease and scour.
Working logically through the journey of decision-making regarding vaccination, the first key point to help farmers and vets understand the role of vaccination is achieving an accurate diagnosis. This may seem straightforward and logical, but is a step often missed.
If a farmer telephones and asks whether a calf vaccination programme would be beneficial for him or her, suggesting a protocol with no diagnosis – or even visiting the farm – is putting the success of any vaccine in jeopardy.
Consider suggesting a multivalent virus vaccine protocol for a primary bacterial issue. It is the author’s experience that this situation would not be uncommon.
Similarly, the role of a vaccine in disease control can only be considered in light of the whole farm situation. For example, selling a multivalent mastitis vaccine to help a severe Escherichia coli mastitis issue (even if this has been confirmed to be E coli) is destined to fail if the overall farm hygiene is beyond poor.
Both of these situations will do little more than erode trust in both vaccines and veterinary advice.
It is outwith the scope of this article to cover the most appropriate diagnostics, and disease‑specific articles are in the press that cover this. However, the importance of accurate diagnosis cannot be stressed enough.
Vaccines should rarely be seen as a silver bullet to cure or eradicate a disease; those options and situations are incredibly rare.
More than 20 years of BVD vaccination with no other advice on disease control did little to advance control of the disease in this country.
Instead, any vaccine use should be considered in light of a holistic, bespoke farm control plan.
Sticking with the example of BVD control, vaccination certainly has one of two roles to play in disease eradication:
However, disease eradication also relies on removal of persistently infected animals, as well as herd biosecurity to prevent importing new disease on to the farm.
Similarly, respiratory disease in calves is a multifactorial disease. Improving the micro‑environment of the calf, nutrition, and colostral protection all play large roles in disease prevention.
Appropriate, farm pathogen-specific vaccine protocols can have large benefits in disease reduction, but the effects will be additive when put in place as part of holistic farm management approach.
When starting conversations with farmers about vaccines, it is important to be honest about the expected duration of use.
For example, with the relatively recent incursion of bluetongue, any vaccination and protection of stock was likely to be short‑lived and allowing the farmer to “ride the storm”. Equally, a calf scour disease vaccination campaign can be started with awareness that control of rotavirus and coronavirus can be achieved through excellent hygiene and colostrum protocols, allowing time for management changes to be put in place. Whereas no IBR vaccine plan should be seen as a quick fix and should be undertaken with awareness that it is part of a long-term plan.
Once the decision has been made to vaccinate, it is key the vaccine is used in the most beneficial way possible.
A recent study showed farm fridges spend, on average, 16 per cent of the time above refrigeration temperatures1. This is particularly prevalent during the summer months, when the requirements for refrigeration are highest. The paper called for urgent improvements in on-farm storage for vaccine efficacy to be maintained. Some veterinary practices offer a vet tech service that includes administration of vaccines, ensuring the cold chain is maintained.
Equally, it is important the peak of immunity correlates with the highest need. This is demonstrated with two examples.
The primary function of BVD vaccination is the prevention of persistently infected animals through protecting the fetus.
Persistently infected animals are the result of maternal infection during the first trimester of pregnancy. Therefore, it is the author’s opinion that the best return from BVD vaccination comes from administering vaccines prior to first service. This will allow most cattle to have peak protection during the first trimester.
This may be difficult to manage in some herds, but certainly is achievable in block calving herds and year-round herds with good management systems.
Calf respiratory disease can afflict animals at different stages within herds. Once causal pathogens have been identified, a suitable vaccine regime must allow for protection prior to challenge and, therefore, disease. This will influence product choice, timing of doses and, in some cases, number of doses.
Where respiratory disease affects animals very early in their life, it is worth discussing with the marketing authorisation holder the possibility of vaccinating preparturient cows with the aim of boosting colostral protection. This would be off-licence use, so must be carefully considered. Obviously, this approach relies on ensuring colostral antibody intakes are sufficient – this should be checked first.
Before considering economic factors involved in vaccinations, it is worth first discussing the alternatives.
For multifactorial disease – such as respiratory disease, calf scour and mastitis – the use of vaccines should be considered in the light of holistic farm management. These discussions will then place the vaccines as either an essential tool to assist where other improvements cannot be made, an adjunct to improving environmental management, a stopgap while changes take place, or kept in reserve should other changes not achieve the full result. As aforementioned, they should not be treated as silver bullets.
As well as alternatives to vaccines, the consequences of not vaccinating need to be considered.
Clearly, continued disease is one consequence. However, the other consequences may be far more serious:
When considering the consequences of not vaccinating, consider both the hazards (what could go wrong) as well as the risk (likelihood of it happening), as well as mitigation factors that can be put in place.
For example, a herd with repeat negative bulk tank wild-type IBR assays could consider not vaccinating. The hazard is high in the naive herd, but the risk is variable. It will be influenced by biosecurity – how many cattle are purchased? Can purchased cattle be screened? Is fencing appropriate? Do farm staff and non‑farm visitors go on other farms, and if so, what precautions are taken to prevent them being fomites? Then if the decision is taken to not vaccinate, the herd can be monitored through regular bulk tank assays.
The final point when considering vaccinations is the financial implications. This has been deliberately left until last as it is, in many ways, the area of most doubt.
The equation for return on investment is, really, quite simple:
The cost is easy to quantify, but it is not just the cost of the vaccines. It is important to also consider the cost to administer the vaccine – farmers may value this time differently to vets.
The benefits is the bigger issue to quantify. Limited accurate disease cost calculators are available for cattle diseases to allow the baseline to be quantified, while limited information is available on the likely impact on vaccination – in particular with regards to multifactorial diseases.
For some diseases, the return on investment from vaccination can be so clearly demonstrated, or the investment so minimal, that vaccination is often clear-cut. For example, blackleg in growing cattle – the vaccines cost less than 50p per dose, so the number of animals that need to be saved to return that investment is minimal.
A successful approach to return on investment exercises is to use farmer input data. This method is used for the Agriculture and Horticulture Development Board dairy mastitis cost calculator – found at https://bit.ly/2NbtjP9 – which allows the user to undertake a “what if” analysis and compare the costs of mastitis in different scenarios.
The author has developed a similar cost calculator for respiratory disease, which allows farmers to enter their input costs, disease rates and expected disease rates, with interventions to demonstrate the expected return on investment.
Whether you use a tool, or just the back of an envelope, a familiarity and comfort with the economics of disease will allow you to have these conversations with clients – get them to suggest the cost of disease in terms of increased days open, lost pregnancies, delayed growth, reduced output and so on. Then use current case rates to quantify the total financial impact.
This will then allow further conversations into the expected response to vaccination and return on investment – or, indeed, any other control mechanism.
Vaccines should not be seen as a silver bullet, but are an important tool in disease control. Placing them appropriately on farm requires a holistic approach and an awareness of other options, and optimised usage.
Familiarity with disease economics is key to disease control discussions.
