LIVESTOCK
Intestinal worms
Lambs grazing at a Lincoln University farm. ‘Resilient lambs have greater growth potential.’
Resistant and resilient lambs similar gains BY: LYNDA GRAY
W
hich lamb produces more meat: one that is resistant or one that is resilient to gastro-intestinal worms? It turns out that there’s very little difference, according to the latest Lincoln University research. “The results indicate that selection for
resistance or resilience will eventually result in a similar level of performance although resilient animals did have a growth advantage until six months of age,” lead researcher and animal production scientist Andy Greer says. Results from previous parasite challenge growth trials have confirmed the superior liveweight gain (LWG) of ‘resilient’ lambs – those that can tolerate high worm burdens -
compared with ‘resistant’ lambs – those that have high immunity to internal parasites. However, in most of these trials the resilient and resistant animals were run together so that the increase in pasture larval species and internal parasite infection, and the effect this had on lamb LWG of each group was hard to isolate. “It was hard to tease out the epidemiological benefits of resilient versus resistant lambs, but we’ve been able to do this by running them separately over a long time.” In the five-year study which will wrap up in 2022, the lambs from resistant and resilient Romney lines were compared on three farmlets. On each block they were weaned at 10 weeks and set-stocked in their respective birth paddocks for 210 days. Every month the lambs were weighed, and saliva, fecal egg and pasture pluck samples taken. Lambs were removed from the paddock early April each year and the paddocks rested until required in August for the next lambing. On both Farmlet 1 & 2 the lambs got no anthelmintic treatment. On farmlet 3 resilient and resistant lambs were co-grazed under a ‘suppressive’ anthelmintic drench system. This involved the Bionic capsuling of ewes prior to lambing, a short-acting oral drench of lambs at weaning followed by a Cydectin injection. Analysis of results showed resilient lambs had a far greater growth response following drench than did resistant lambs up to 210 days. Also, the cumulative LWG of drenched resilient lambs was about one-third greater than un-drenched resilient lambs over the same period. This result highlighted the greater impact and opportunity cost that
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Country-Wide
October 2021
