This episode featured in partnership with PGG Wrightson. Make sure to contact PGG Wrightson to plan your crop and pasture requirements.
Two summers of forage crop trials have tested whether farmers can cut how often lambs need drenching for internal parasites.
Jason Leslie, Technical Expert in Animal Health at PGG Wrightson, and Charlotte Westwood, Veterinary Nutritionist at PGG Wrightson Seeds, say some paddocks pushed that interval well beyond the usual cycle on pasture.
Westwood says the crops are likely breaking the life cycle of internal parasites.
“It’s also growing young sheep and cattle at a faster rate so that they reach a heavier weight at a younger age, and that’s somewhat protective against the effects of internal parasites,” she says.
The trials looked at chicory clover mixes, plantain, clover mixes, summer brassicas and lucerne. Leslie says the approach sits within the WormWise toolbox, though modern forages needed more research.
“We needed to know what good or gold looked like, so we had very strict trial sites where that was purely just their sole forage,” he says.
Westwood says the issue often comes down to the animal’s size as a percentage of its mature weight. Trial lambs averaged 23kg, with some as light as 15 to 16kg, chosen deliberately to carry a heavy worm burden without forage crops.
The trials measured reinfection rates on pasture against novel forages, testing whether crops carry fewer infective larvae. Paddocks ranged from new plantings to crops one to two years old, with one site regrazed to reinfest it with larvae.
Westwood says brassica crops with as much grass excluded as possible produced the strongest results over the two years of trials, reaching 70 days after the effective drench.
“The summer just gone, we got out as far as 159 days without needing a drench,” she says.
Westwood says grass like poa, twitch and couch under a crop gives L3 larvae plenty of places to survive.
“If we have a straight crop that’s quite clean underneath, we tend not to have as nice a place for infective L3 larvae to live.”
She says direct drilling can leave thatch behind, letting grass regrowth undo the benefit if the paddock has only had a single spray-out.
Leslie says the starting point is an agronomist, to confirm what will grow in the paddock, with clear goals on stock class and how long it stays in crop versus pasture.
“You need to be growing more feed than you should get from pasture and of a better quality.”
He says drenching stock into the crop takes advantage of the lower larval challenge, with monitoring until reinfection occurs.
This episode featured in partnership with PGG Wrightson. Make sure to contact PGG Wrightson to plan your crop and pasture requirements. You can find your local Technical Field Representative or store team at https://store.pggwrightson.co.nz/find-your-store
CountryWide CONNECT with Andy Thompson & Sarah Perriam-Lampp is our daily rural show livestreamed from 11am-1pm. Visit country-wide.co.nz on how to watch/listen or download the CountryWide CONNECT mobile app, available on Apple iOS and Android.
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