In addition to vaccinating lambs against orf, flock managers who have previously seen the disease on their farm should consider ewe vaccination not less than seven weeks before lambing to help avoid poor lamb growth rates and increased mastitis.
Orf vaccination for ewes and lambs
Survey data collected from 762 English sheep producers in 2012 has helped researchers gain a better understanding of the prevalence of orf across the country, vaccination efficacy and the key disease risk factors. It’s led to the conclusion that, ideally, both ewes and lambs should be vaccinated¹.
Prevalance and risk factors for orf
The study found significant disease prevalence (19.53%) in lambs throughout the country, identifying that weed infestation and an increased number of orphan lambs were associated with increased cases of orf. Alongside vaccination, improved control of the disease should also include the control of thistles, nettles and docks; thistles, in particular, cause skin abrasions that allow the orf virus to enter the body and replicate.
Orf is caused by a virus that can survive for many months in cool, dry conditions and also in lambing sheds (particularly on wooden structures) for many years. However, some flock owners often don’t treat its control as seriously as they should, says independent sheep vet Fiona Lovatt of Flock Health Ltd.
“It’s a debilitating and painful condition for affected sheep – and it can also be caught by people working with infected flocks – but its impact will affect production of both ewes and growing lambs. It can also lead to secondary infections that are usually treated with antibiotics, so as we strive to reduce their use as an industry, disease prevention is the preferred control option.”
Data collected from naturally occurring orf outbreaks on eight farms in the North East of England in 2010, showed that lambs that had had orf between two and five weeks of age were an average of 2.2kg lighter at six to nine weeks old than those lambs that had been disease-free².
The study also suggested that there was an 80% chance that the mother of a lamb with orf also had the disease on her teats. There were also high levels of mastitis in the ewes suckled by infected lambs – so much so that 14% of ewes with clinical orf also suffered from mastitis.
“In fact, when the depressed lamb growth rates, increased lamb mortality and ewe replacement costs, extra lamb feed costs and direct treatment expenses associated with an outbreak were all taken into account the disease costs were frighteningly high,” Dr Lovatt says.
She adds that an orf outbreak will almost always increase levels of ewe mastitis and that the lamb weight discrepancy will remain until weaning. “Arguably these are conservative assumptions and there is no doubt that a growth check in a sucking lamb can have a significant impact on both slaughter dates and carcass quality.”
Vaccinating ewes against orf
Where orf has been confirmed in a flock, vaccination of lambs and ewes offers sheep producers an effective disease management approach when administered correctly. It’s a live ‘scratch’ vaccine and should be checked for ‘take’ seven to 10 days after administration. Ewes should be vaccinated behind the elbow or in the axilla (between the top of the foreleg and chest wall) to minimise the risk of infection transferring to the lips or udder.
Pregnant ewes should not be vaccinated less than seven weeks before housing or lambing. This will allow them to develop sufficient immunity while preventing contamination of the environment from virus-infected scabs that may be shed. Immunity develops within four to eight weeks after vaccination, but the vaccine does not offer long-term protection so ewes need to be boosted annually. Lambs are born naïve to the disease so always need to be vaccinated themselves from one day old.
Orf vaccination tips
- Pregnant ewes should not be vaccinated less than seven weeks before housing for lambing. This will allow them to develop sufficient immunity while preventing contamination of the environment from virus-infected scabs that may be shed.
- Immunity develops within four to eight weeks after vaccination, but the vaccine does not offer long-term protection, so ewes need to be boosted annually.
- Lambs are born naïve to the disease so can be vaccinated from one day old.
- J.Onyango, F.Mata, W.McCormick, S.Chapman. Prevalence, risk factors and vaccination efficacy of contagious ovine ecthyma (orf) in England. Vet Rec (2014)
- Lovatt et al 2012. Vet Rec.