Flock and Herd logo

CASE NOTES

The use of Ovilis Footvax® as part of a virulent footrot control and eradication program

Felicity Wills, Ruminant Technical Advisor, Coopers Animal Health

Posted Flock and Herd November 2024

Introduction

Footrot needs to be controlled during spread periods so that the prevalence of infection in the flock is reduced to a level where eradication is feasible and possible. The aim of control is twofold. Firstly, to have as few infected sheep as possible at the start of the eradication stage. Secondly, control is necessary to prevent production losses and for the welfare of the sheep. There are many elements that go into the planning and execution of a good control and eradication program (Figure 1) once a diagnosis of virulent footrot is made.

Chart of virulent footrol control
Figure 1. Dealing with virulent footrot disease

Good control of footrot is essential to eradicate the disease. When good control is achieved, very few sheep with severe lesions are found at the summer inspections. Because of these low numbers, it's an easy decision to cull the remaining infected sheep. Footrot spreads during warm (average daily temperature above 10°C), wet periods (averaging 50mm or more for several consecutive months), typically in spring (August, September and October), but the exact timing of spread periods varies from season to season and between districts1. Spread periods occur less commonly in late summer to autumn. A sign that spread is occurring is when some sheep have red, active looking Score 1 and 2 feet. The severity of lesions in these feet will rapidly worsen. Control during a spread phase is achieved by either vaccination or regular foot bathing or a combination of both. The choice between control methods is very complex and should be carefully considered.

A good footrot control program has the following goals:

Aspects of a footrot control program to consider include selective culling, foot paring, foot bathing, vaccination and antibiotics.

Selective culling

Susceptibility to footrot is hereditary and consistent culling is likely to reduce the prevalence of footrot over a period of years in closed flocks. In control programs culling the worst affected sheep or sheep that do not respond to treatment is a good policy for animal welfare, productivity and reducing the number of infected sheep going into the eradication period2.

Foot paring

Paring is used to remove under-run sections of hoof. This hoof care allows footrot bacteria to be exposed to oxygen and foot bathing chemicals. Paring alone can help to cure footrot lesions but is best used in combination with other methods. Paring should not be overzealous, and the drawing of blood should be avoided where possible because it obscures visibility of any lesions and reduces the efficacy of topical treatment. Foot paring is recommended before the start of foot bathing in spread periods and diagnostic paring during summer inspection in the eradication phase1,2,3.

Foot bathing

Foot bathing is the most commonly used option for the control of footrot. Used alone, foot bathing can reduce the severity of infection and number of sheep infected during the spread period but will not eradicate footrot1,3. It also assists healing in feet that are already affected. Foot bathing can be effective in controlling the transmission of footrot in the spread period. Foot paring is often an important part of a foot bathing program as foot bathing chemicals only kill on contact and therefore paring of underrun lesions is essential for effective contact1,2,3.

There are two options for foot bathing for footrot control:

Walkthrough foot bathing is effective against Score 1 and 2 lesions and must be done at least weekly.

Stand-in foot bathing with solutions such zinc sulphate with lauryl sulphate or Radicate® can provide up two weeks of protection1.

If done properly, foot bathing alone can be very effective. However, most farms, especially those with large numbers of sheep, find foot bathing very time consuming. In addition, it is not practical for ewes with lambs, especially during the spring spread period. These scenarios are where foot bathing can be used in conjunction with other control methods such as vaccination or where vaccination may be used in place of foot bathing1.

VACCINATION

There are two vaccine types used in the control of virulent footrot, strain-specific vaccines, or a multi-serotype vaccine. The strain-specific vaccine is an autogenous vaccine made that targets the serogroups of footrot present on a given property. While these vaccines can be produced to target multiple serogroups, the efficacy of the vaccine is reduced if more than two groups are included2,3. This reduction in efficacy is due to antigenic competition and is also seen in the multi-serotype vaccine. It is common for there to be multiple serotypes of virulent footrot present in any one flock1 making the use of a multi-serotype vaccine a reasonable choice. Footvax® is an inactivated multi-serotype (10 strain) vaccine registered to aid in the control of footrot in sheep. Footvax® contains strains from serogroups A, B, C, D, E, F, G, H and I. Footvax® does not contain a strain from the M serogroup. Currently only the multi-serotype vaccine is available in Australia.

Effective use of the Footvax® vaccination in a control program can provide a protection rate of up to 80%4 of the flock and cure around 60%5 of infected sheep. To initiate a Footvax® program two 1ml subcutaneous vaccinations at least six weeks apart and no longer than 12 months apart are required. Effective immunity develops after the second dose. Following the second dose sheep are protected against footrot for up to 10-12 weeks in merinos and up to 16 weeks in British breeds3. After the initial vaccinations, booster vaccinations can be given anywhere from 10 weeks to 12 months later, if required due to seasonal conditions and will again provide a similar protection period as the initial vaccination course3. Figure 2 below outlines a scenario for Footvax® use through a typical and extended spread period.

Chart of virulent footrol vaccination timing
Figure 2. Footvax vaccination timing

Given that the protection provided by the vaccine is short term, timing of a vaccination program is critical.The booster vaccination needs to be timed just before the expected start of the spread period, so sheep have high levels of immunity when they are most susceptible to getting footrot. For a lot of areas in Australia the booster dose will need to be given in late August. The inability of the vaccine to give total protection or cure all affected sheep means vaccination is only part of a well-planned footrot program.

Vaccine use is extremely valuable in situations where sheep cannot be foot bathed regularly, such as with lambing ewes, extensive properties where mustering is difficult or any property where labour shortages or facilities preclude effective foot bathing. The effective use of a vaccine program can reduce the use of foot bathing and can therefore be very cost effective. The best control can be achieved with a combination of vaccination with foot bathing. Depending on the area, a booster vaccination may be required 10-12 weeks after the initial vaccination course, if conditions are still suitable for footrot spread. On some occasions the vaccination of lambs may need to be considered. Lambs have safely been vaccinated down to marking age. If conditions are drying out, foot bathing weekly until conditions are dry will be sufficient. If pastures are likely to be green for more than 4-6 weeks a further vaccination may be justified3.

The recommended vaccination site is under the skin behind the ear to minimise carcase damage. Vaccinated sheep may develop a reaction in response to vaccination with swelling appearing at the vaccination site and in some cases abscesses may develop. Footvax® is an oil adjuvanted vaccine that should be administered subcutaneously and not into the skin or into the muscle. Injection should occur under the skin, on the side of the neck behind the base of the ear. It is recommended to use an 18-gauge 1/4-inch needle in all sheep. Lambs and ewes with short or no wool should be injected at a 45° angle and mature sheep with long wool at a 90°angle. Due care should be taken to avoid self-vaccination and medical attention sought as soon as reasonably possible if self-vaccination occurs. Please contact Coopers Animal Health on 1800 226 511 if a case of self-vaccination occurs.

ANTIBIOTICS

Based on the Australian Antimicrobial Prescribing guidelines for Sheep, antimicrobial treatment should be confined to four scenarios:

Best results are seen when sheep are pared, foot bathed, treated and kept on slatted floors for 12-24 hours after treatment. Following treatment and holding, move sheep to a dry paddock and then inspect 3-4 weeks later. Cull any non-responders. Antibiotics recommended for use when treating virulent footrot include, Oxytetracycline LA, Erythromycin, and Procaine penicillin. Erythromycin is particularly useful if a short withholding period is needed6.

Conclusion

Virulent footrot can have a profound effect on animal welfare, the productivity of sheep flocks and the mental health of producers. The implementation and execution of effective control and eradication programs are essential in achieving improved welfare, healthier and more productive sheep, easier market access for producers, lower treatment and labour costs and an increased confidence in state-based control programs. Vaccination can play an important part of a control and eradication program, particularly in challenging management situations with lambing ewes, extensive properties where mustering is difficult or any property where labour shortages or facilities preclude effective foot bathing.

References

  1. Abbott K (2019) The Practice of Sheep Veterinary Medicine. Downloadable free at www.adelaide.edu.au University of Adelaide Press
  2. Australian Wool Innovation Ltd. (2016) Sheep Connect Tasmania. Footrot A guide to identification and control in the field
  3. Abbott K (2005) Current approaches to the management of ovine footrot The Veterinary Journal
  4. Purdue, Footrot in Sheep and Goats
  5. Liardet et al. (1989) Reduction of the prevalence of footrot in New Zealand farms with vaccination
  6. Animal Medicines Australia (2022) Antimicrobial Prescribing Guidelines for Sheep

 

Site contents Copyright 2006-2024©