Breed and parasite challenge influence rate of lamb growth
Take Home Message: Texel lambs are less affected by parasite burden at grass than Suffolks, although Suffolks grow faster when parasite challenge is low.
Suffolk lambs grow faster than Texel lambs when parasite infection is minimised. And the interaction between breed and level of parasite challenge shows that the breed differences in lamb growth depend on level of parasite challenge.
Just two of the findings of research, carried out by scientists at Teagasc in Ireland, to evaluate differences in breed performance when grazed under contrasting level of parasite challenge.
“We also found that the impact of parasite infection on Suffolk lambs increases as the grazing season progresses,” Seamus Hanrahan told delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.
Suffolk sheep have substantially lower faecal egg counts for gastrointestinal nematode parasites than co-grazed Texel sheep and these breeds also have different nematode burdens in the abomasum and small intestine.
The impact of these differences in resistance to parasite infection on animal performance needs to be established in order to determine whether there are breed differences in resilience to gastrointestinal parasite infection,” said Dr Hanrahan, explaining the rationale behind his work.
The study was repeated over two grazing seasons using 143 Suffolk and 151 Texel lambs from the Teagasc flock. The ewes in these flocks are housed between December and lambing (early to mid March) and are turned out, with their lambs, to pasture within two to three days after lambing.
Lambs were weighed at 18 weeks of age and the level of nematode infection was monitored by faecal egg counts at regular intervals up to 18 weeks of age and the number of infective larvae on pastures was evaluated weekly in year one.
Two pastures with different grazing histories were used. The ‘clean’ pasture’s sward was established in the autumn prior to year one of this study and not grazed by sheep prior to turnout in spring of year one. And the ‘dirty’ permanent old pasture that had been grazed by sheep only for at least 10 years prior to year one.
The management of the ‘clean’ sward during the late summer and autumn of year one was designed to minimise any accumulation of infective larvae so that herbage larval challenge in year two was maintained at a low level.
“We found that the ‘clean’ group had essentially zero counts at 14 weeks whereas the dirty group averaged 300 eggs/g,” said Dr Hanrahan.
There was a highly significant breed and pasture type interaction for weights at 14 and 18 weeks of age and growth rate from five weeks to weaning. “These interactions reflected the much greater impact of ‘dirty’ grazing on Suffolk lambs,” explained Dr Hanrahan. “At 18 weeks of age Suffolk lambs on ‘dirty’ pasture were 4.6kg lighter than Suffolk lambs on ‘clean’ pasture whereas the corresponding difference for Texel lambs was only 1kg.”
There was no evidence for an effect of grazing treatment on lamb growth rate between birth and five weeks and it was evident that the negative impact of dirty grazing on Suffolk lambs increased as the season progressed.
“There was also evidence for a breed x grazing treatment interaction for some aspects of ewe performance,” added Dr Hanrahan. “The live weight of Texel ewes at weaning was unaffected by grazing system whereas Suffolk ewes on the ‘dirty’ pasture were 4.7kg lighter than those on ‘clean’ pasture.”
Presented to the British Society of Animal Science Annual Conference, 12-14 April , 2010, Queen’s University, Belfast.
Full details: Hanrahan JP and Good B: “Performance of Suffolk and Texel sheep grazing pastures that presented contrasting levels of parasite challenge.”
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