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Sunday 4 December 2016

Watch out for parasites affecting lamb thrive

John Shirley

Published 31/05/2011 | 05:00

In spite of our efforts to avoid it, we ended up with a couple of pet lambs again this season. Both were twins from yearling hoggets which were rejected by their mothers. I concluded it wasn't worth the struggle to force the young mothers to accept them.

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The tiny pair of Charollais-cross pets were lively and going great for three to four weeks. Then a black scour appeared and the flesh seemed to melt off their backs. They continued to drink but thrive had gone into reverse.

Surely these lambs were too young to get hit with Nematodirus scour? Most likely, the problem was coccidiosis. I treated them with Vecoxan and the lambs seem to have recovered. Assuming that other lambs in the flock were exposed to the same coccidian challenge, I treated everything but the big singles. When the group was gathered, weaker ones were dosed for worms as well.

Enquiring around, I discovered that coccidiosis is quite prevalent this spring. It is found in calves and lambs.

Coccidia and close relative Cryptosporidia are cropping up more and more on rearing farms. These parasites are neither bacterial nor viral. They are protozoa, which are not killed by antibiotics or wormers. But they can cause scouring, ill thrift and death in young lambs.

Coccidia is the more common of the two parasites. Coccidia of various types are a normal inhabitant of the sheep's gut. Stress and dirty conditions can trigger an outbreak, making lambs ill and scoury, sometimes with blood in the scour. Cold and wet weather can also lead to a lamb's resistance breaking down in the face of a coccidia challenge. Hence my pets succumbed to the challenge while the others in the flock sailed on. A diagnosis of coccidial scour is often only confirmed when the lambs are shown to respond to treatment.

In the first month of life, lambs can have maternally transferred resistance to coccidian and so are immune when challenged at this stage. In this respect, a little dirt may stimulate the lamb's resistance. Lambs that have survived a bad infection of Coccidia can have their intestine damaged for life, leading to scouring even as an adult sheep.

The most susceptible period is thought to be 4-10 weeks.

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In a Scottish trial looking at Coccidia and the worm Nematodirus, one group of lambs was deliberately infected with Coccidia only. A second group was infected with Nematodirus only. The third group was infected with Nematodirus and Coccidia.

Lambs in the first two groups showed minor infections but little loss of thrive. Here, the lambs' immune system stood up to the challenge. This is why lambs that are growing and thriving, getting lots of milk from the mother plus access to creep feeding, do not respond to worm dosing.

But the third group of lambs got ill with some deaths. The modern treatments for coccidia include in-feed medication with Deccox or dosing with Vecoxan. The rules on in-feed medication now have feed compounders less anxious to incorporate Deccox in a ration. This results in more flockowners using Vecoxan as the treatment of choice.

Cryptosporidia scour differs from Coccidia in that it hits lambs from about two days until two weeks. Given that Cryptosporidia is such a widespread problem in calves, and even humans, it is surprising that it is not a bigger issue in lambs. However, some flocks have had major crypto problems.

Under vet advice, and cascade rules, flockowners have good response from using Halocur to control crypto in lambs and calves. This is a difficult product to administer as the animals have to be dosed daily for several days. Consult your vet on the issue.

John Shirley farms at Gortnahoe, Co Carlow

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