A decision to start vaccinating gimmers against Toxoplasmosis this summer has been taken by Kintyre Monitor farmer, Duncan Macalister.
Mr Macalister took the decision, which he describes as a “no-brainer”, following the results of blood tests to investigate the failure of some ewes which had definitely scanned in lamb to produce any offspring this year.
The sheep enterprise at Glenbarr Farms, a 1,730 acre unit on the west coast north of Campbeltown, totals 550 ewes with all progeny finished, other than retained replacements.
The ewes are split into two distinct flocks.
The “home farm” flock of 300 indoor lambing, mainly Lleyn crosses are crossed with Cheviot and Suffolk tups for prime lamb production.
The “Barr Mains” flock has 250 outdoor lambers, half of which are Scottish Blackfaces with the other half Lleyn crosses.
Tups in this flock are exclusively Lleyns with female replacements for both flocks chosen from this group.
“Eight ewes in the home flock scanned in lamb but were empty at lambing,” Mr Macalister told the community group at a recent monitor farm meeting.
“There were more in the Barr Mains flock where 17 young sheep turned out to be empty.”
The farm’s vet, Catriona Wilson of Westwards Veterinary Practice in Campbeltown, took blood samples from the eight, empty “home” flock ewes, to test for trace element deficiency (vitamin B12, copper and selenium), Enzootic Abortion and Toxoplasmosis.
“Trace element levels were fine,” explained Miss Wilson.
“And the Enzootic Abortion tests were negative but three of the eight ewes showed positive for recent exposure to Toxoplasma, with the remaining five also showing signs of less recent exposure.
So it seems that Toxoplasmosis was the most likely cause of the problem.”
Toxoplasmosis in sheep is caused by the ingestion of eggs of the Toxoplasma parasite.
If the sheep are in-lamb the parasite, which has hatched inside the sheep, breaks down the placenta.
Toxoplasma requires an intermediate host. It lives in tissue cysts in the brain and muscles of infected animals with rodents and small birds frequent reservoirs.
Cats which eat their Toxoplasma infected prey become intermediate hosts.
The Toxoplasma multiplies in the cat’s gut, producing large quantities of eggs, which are shed in faeces and urine.
Depending on moisture and climate, these eggs can survive for lengthy periods in the environment.
Feed stores, water supplies and pasture can become contaminated and susceptible sheep become infected when they consume the eggs.
The involvement of feral and domesticated cats makes the risk of infection difficult to control, observed Miss Wilson.
The effects vary, depending on the stage of pregnancy. In early pregnancy the fetuses are likely to die and be resorbed.
Mid-pregnancy the lambs are likely to die and be aborted and in late pregnancy the lambs are likely to either die and be aborted or be born dead.
Alternatively they can be born alive but very weak and in the case of twins one is often born dead or small and mummified.
If sheep are infected when they are not in-lamb, they suffer a transient fever, which often goes un-noticed. In all instances, the infected sheep develop a life-long immunity.
Veterinary Investigation Diagnosis Analysis figures between 1995 and 2003 show that over a quarter of diagnosed cases of sheep abortion were due to Toxoplasma.
Toxoplasmosis affects most warm-blooded animals, including humans, so pregnant women should stay far away from lambing ewes and avoid handling clothing which has been worn by people working with lambing ewes or new-born lambs.
However, there is an effective vaccine which protects sheep from Toxoplasmosis.
“This is a live vaccine,” explained Miss Wilson, “and so pregnant women shouldn’t get involved with the administration of this either.
“The gold star approach would be to vaccinate the entire flock but, at between £5 and £6 per head, the cost may daunt some sheep farmers.
“A worthwhile approach is to routinely vaccinate all in-coming, replacement females at any time between five months of age and three weeks before tupping. Do not vaccinate in-lamb females.
“The vaccine manufacturers state that the vaccine provides protection for two years.
It’s a live vaccine, so if there is some left over after all replacements have been vaccinated, rather than waste it, use up the remaining vaccine on the oldest ewes, to help boost their protection.”
Miss Wilson also recommended that if the group decided to vaccinate against Toxoplasmosis, they should order the vaccine as promptly as possible, as it is often difficult to obtain as tupping time draws near.
Monitor farmer Duncan Macalister needed no encouragement to vaccinate the 120, home-bred replacement gimmers coming into the flock this autumn.
As the vaccine is “live” he promptly administered it within the expiry date.
“I’ve learnt the lesson of BVD (Bovine Viral Diarrhoea),” said Mr Macalister. In 1997 and 98, a total of 60 calves were lost due to BVD and while the herd is now clear the cattle are still routinely BVD vaccinated with a herd check test also carried out annually.
“The Toxoplasmosis has crept up on us and, like the BVD, we hadn’t considered it until we discovered that our stock were infected.
So if we can provide the gimmers with lengthy protection against Toxoplasmosis and help break the cycle of infection, for around £6 a head, especially with the price of lambs as they are, it’s a no-brainer as far as I’m concerned!”
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Source: Argentine Beef Packers S.A.
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