MSD: Vital to establish the causes of sheep aborting
“Last year, I dealt with a 500-ewe flock which had an outbreak of enzootic abortion. Sixty ewes aborted, leading to the loss of 100 lambs. All the ewes that aborted were culled and a strict vaccination programme for both enzootic abortion and toxoplasmosis is now in place,” he said.
Problems with toxoplasmosis five years ago led Ronan to introduce vaccination of his own flock at Carrowcarden, Enniscrone.
A well-known pedigree Texel breeder, his Enniscrone Texels consists of 60 pedigree Texel ewes and 100 commercial ewes, which are used to carry embryos. His plan is to produce 90% of his pedigree stock through embryo transfer within the next few years. Currently, the split between “natural” and embryo transfer is 50/50.
“I vaccinated the entire flock for toxoplasmosis and enzootic abortion the first year. After that, just the replacements are vaccinated at least a month before they are mated. The one shot of both vaccines generally gives lifetime protection,” he said.
He has noticed that abortion problems are becoming more common in recent years. “It is not spoken about very much but it is definitely becoming a bigger issue.”
“My advice to farmers is to always investigate the reasons for abortions. Contact your veterinary practitioner who will arrange for swabs to be sent to FarmLab Diagnostics in Elphin and for foetuses and placentae to be sent to the regional veterinary laboratory,” he said.
Ronan is a member of the recently established expert working group on sheep abortion. It consists of Teagasc specialists, veterinary practitioners and representatives from industry including MSD Animal Health.
As well as running his pedigree sheep business, he is a veterinary practitioner with Kilbride Veterinary Clinic in Swinford. Through his company ProStar Genetics, he also provides a nationwide sheep AI, embryo transfer and ram testing service.
The one-shot vaccines for toxoplasmosis and enzootic abortion (EAE) can be given to breeding ewes and lambs (from five months of age) during the non-pregnancy season. Vaccination must be completed at least four weeks before sheep go to the ram.
The two vaccines can be administered at the same time, but not mixed, and must be given in separate injection sites. Generally, just one shot of each vaccine is required during the lifetime of the ewe. It is important to get veterinary advice on the most appropriate vaccination strategy for your farm.
“As well as weak and sickly lambs that die soon after birth, many farmers also accept barren ewes, leading to cumulative abortion rates of up to 10%. However, anything above two percent is likely to be due to an infectious cause and should be investigated,” said Sharon Magnier (pictured), veterinary adviser with MSD Animal Health.
“Lambing time offers an ideal opportunity to establish the cause of losses.” She said analysis by regional veterinary laboratories shows toxoplasmosis and enzootic abortion (EAE) to be the leading causes of abortion in sheep.
“Toxoplasmosis, caused by a microscopic parasite Toxoplasma gondii (T. gondii), is most commonly caused by contaminated cat faeces in feed, bedding or manure or directly on to pasture.
“A single cat dropping can contain enough eggs to infect more than 100 ewes. It takes only one brief visit from a cat to contaminate the farmyard or pasture and almost 75% of ewes are believed to come in contact with T. gondii during their lifetime,” she added.
Symptoms of toxoplasmosis can include barren sheep, abortions, stillbirths, weakly lambs and mummified foetuses. While heavy infections, typically in smaller groups of sheep, can cause infertility in half or more of the flock, the impact is normally less dramatic, with the number of lambs lost at around six percent. The disease is not passed from sheep to sheep.
Sharon Magnier said that vaccination is the only way to effectively build uniform immunity to toxoplasmosis in the flock. As older ewes are more likely than younger ewes to have already been in contact with T. gondii, it may be an option to vaccinate the younger sheep and then vaccinate all replacements as they enter the flock.
“Where the risk of infection is high on a heavily contaminated farm populated with previously unexposed sheep, initial whole-flock vaccination is cost effective. As each situation is different, farmers should consult their vet about the most effective vaccination strategy for their flock,” said Sharon.
An outbreak of enzootic abortion (EAE), caused by a bacteria-type organism called Chlamydophila abortus, can result in 30% of sheep aborting. The disease is usually caused by infected bought-in replacements but it can also be spread by wildlife carrying infected placentae from farm to farm.
Unlike toxoplasmosis, it is highly infectious and organisms are passed from ewe to ewe in infected afterbirth, on new lambs and in vaginal discharges for up to three weeks after lambing. Lambs can also be born already infected from mothers carrying the disease.
Sharon Magnier explained that when a ewe aborts she sheds large numbers of organisms, which can infect any in-contact ewe or lamb. These newly infected sheep will not show any signs of infection.
“The organisms remain dormant in the body until the ewe lambs again. In infected lambs, they can remain dormant for up to two years. About three weeks before lambing, the placenta becomes inflamed and abortion occurs,” she said.
“While ewes that aborted often continue to have a normal lambing in subsequent years, they are carriers of the disease and may still shed organisms resulting in infection of other sheep and lambs,” she added.
Where enzootic abortion is diagnosed, she stressed the importance of keeping aborted ewes separate from the rest of the flock and not fostering lambs on to aborted ewes. She advised farmers to discuss the use of an antibiotic injection with their vet. It may not stop the outbreak but may reduce the number of abortions in the current season.
“Vaccination will effectively reduce the risk of enzootic abortion as part of a flock health plan. Because there is no test to identify latently infected sheep, it is important to vaccinate all breeding sheep in the first year. After that, only replacements need to be vaccinated,” she advised.
For further information, please contact your veterinary prescriber, the product SPC or MSD Animal Health, Red Oak North, South County Business Park, Leopardstown, Dublin 18.
Tel: +353 1 2970220. Email: firstname.lastname@example.org;