Sheep producers should take every possible step to reduce abortion levels this season after last year’s shortage of anti-abortion vaccine could herald higher lamb losses.
According to John McFarlen, Alnorthumbria Vets, XL Vets, many sheep farmers were unable to vaccinate replacements against enzootic abortion, with even fewer able to protect their stock against toxoplasmosis.
“The success of the vaccination system relies on protecting replacements, and as a result, there has got to be a higher level of abortion this season,” he says.
However, it is not too late to reduce the level of losses in your flock, particularly in terms of enzootic abortion.
“The antibiotic, oxytetracycline (oxytet), can work well to reduce abortion levels when administered at 115 days of pregnancy or 115 days after the tup has gone out,” Mr McFarlen explains.
It may also be appropriate to give the antibiotic every two weeks from about week 13 of pregnancy, but this decision should be made after consulting your vet, says Steve Borsberry, 608 Vet Group.
Typically, when an abortion outbreak is seen, it will be a result of infection in ewes that were exposed last year, but did not abort. Although injecting with oxytet will not stop abortion completely, it can dramatically reduce the level of losses, with one farmer reporting an 85% reduction, according to Mr McFarlen.
However, deciding to use an antibiotic will depend on the level of risk to a particular flock. “When a farm is breeding their own replacements and have vaccinated for a number of years, the level of challenge is likely to be low, so it may not be worth going down this route.”
But, when a producer is buying in stock from a flock of unknown enzootic abortion status, using oxytet may be worth doing. “Ask yourself a serious question over the disease status of the source farm. If you don’t, infection could become established in the flock, not only causing abortion this year, but also next.”
However, antibiotics will only help control the situation for one year. Consequently, all stock should be vaccinated later in the year when vaccine becomes available. This will provide long-term protection against abortion.
In terms of toxoplasma, an antibiotic can be used in the face of an outbreak, but there is no real evidence to suggest its worth. Instead, management should prevent cats (the toxoplasma host) from accessing feed bins. Ewe feed can also be medicated with decoquinate for the last 14 weeks of pregnancy.
Any non-vaccinated flock should investigate all abortion cases this season, stresses Mr McFarlen. “Make sure a clean diagnostic sample is provided in a clean bag to ensure accurate interpretation.”
In these flocks, oxytet could be administered after early-season diagnosis to protect later lambers. In an undifferentiated outbreak of abortion, blanket treating with oxytet has been reported to offer improvements in abortion rates. However, according to Mr McFarlen, abortion levels are likely to improve the further you progress into lambing anyway.
In a vaccinated flock, abortions should be treated in the same manner as any other year, with samples being sent for analysis when more than 2% of the flock has aborted or a lot of abortions are seen at once.
It could be more advisable to lamb replacement stock separate from the main herd, says Mr Borsberry.
“Enzootic abortion is spread from ewe to ewe at lambing time, so when you haven’t been able to vaccinate and you have ‘clean’ replacements, it is well worth housing them separately. If you don’t, you could see abortion problems for several years.” Equally, bought-in stock are a risk to the current flock.
Reducing abortion risk
• Try to lamb replacements as a separate group to the main flock – this will prevent long-term abortion problems
• View any aborting ewes as potentially infectious and isolate them from other sheep until any discharges have cleared up (about four weeks in some cases)
• Injecting with oxytetracycline can reduce the level of abortion, but not eliminate it