Summer Forage Crops Prove Inhospitable For Internal Worm Larval Development

Drench resistance is a major, and growing, issue for the sheep and cattle industry. New data, from a collaborative study between PGG Wrightson (PGW) and PGG Wrightson Seeds (PGW Seeds), proves summer forage crops reduces worm challenges and the reliance on chemical interventions.

“New Zealand’s sheep and cattle farms rely heavily on pasture. However, our temperate climate and moisture levels means our pasture, grass and clover mixes, are a favourable environment for infective worm larvae. For significant periods during the year, our pastures have a high larval challenge,” says Jason Leslie, PGG Wrightson Technical Expert for Animal Production.

Most infective larvae live in the first two to three centimetres of the pasture sward and top one centimetre of the soil. This danger zone is also where much of our stock feed year-round.

“This is where the best quality pasture is, but unfortunately it is also where the worms are. This is particularly problematic for young animals, in their first 12-months, whose immune systems are too immature to tolerate worms in high numbers,” Jason explains.

Summer forage crops, also highly nutritious, grow taller, more upright, and are more open in growth habit than pasture. These crops allow sunlight to kill off larvae during the establishment phase and create a less hospitable environment for parasites overall.

“Until this trial, the concept of using forage crops was more theoretical as we had limited supporting data for modern forage options. However, this multi-year trial conducted in collaboration between PGG Wrightson and PGG Wrightson Seeds, gives us the data to prove replacing pasture with summer forage crops is an effective mode of action in the fight against worm challenge and drench resistance,” says Jason.

The trial was conducted at multiple locations throughout the country: PGG Wrightson Seeds’ facility in Lincoln, Kimihia Research Centre, several PGW Seeds satellite sites, and on commercial farms in the North and South Islands.

“Kimihia has the resources to allow us to manage the lambs and forage crops under reasonably tightly controlled conditions,” says Charlotte Westwood, PGG Wrightson Seeds Veterinary Nutritionist.

“We were pleased to see the benefits of using forage crops for worm management showing up on commercial farms, beyond the controlled conditions at Kimihia,” she says.

The trial focused on the traditional 28-day drenching cycle and used Faecal Egg Counts (FEC) to track potential worm burden breakthrough for 70-days.

“500 eggs per gram is when most farmers consider re-drenching stock. We took several mobs of weaned lambs and selected a few to check their faecal samples weekly out to 70-days. The stock that had grazed pasture reached 500 eggs per gram between 28 and 35 days. However, the mobs on summer forage crops had extended intervals. Some never broke through the 500 eggs per gram zone by the end of 70-days,” explains Jason.

“Your next drench, for stock grazing on the different forage crops, should be based on a FEC, with regular monitoring after 28-days from introduction to the crop to determine when, and if, they need another drenching,” he says.

Preventing crop-fed stock from ingesting pasture is critical to achieving the best results.

“Any blade of grass gives worms a hiding place,” says Charlotte.

“You must employ top-shelf agronomic planning and monitoring to keep unwanted weeds and grasses out of the base of the forage crop.”

To keep grasses and weeds out of the crop, Jason and Charlotte recommend a thorough clean-out of the paddock before planting summer forage crops, and ongoing monitoring to prevent reestablishment of grasses and weeds as the crops grow.

“You need to achieve an effective spray out of the existing pasture before direct drilling, or better yet, cultivating your paddock to disrupt the larvae’s environment. Then, the forage crops need to establish without any stock entering the paddock to prevent the introduction of new larvae. This takes somewhere between six weeks to three months, depending on the type of forage crops,” explains Charlotte.

For PGG Wrightson and PGG Wrightson Seeds, the data is a positive result for farmers and stock.

“The conversation around drench resistance can be very doom and gloom, but this is proof we can do something positive on farm to reduce worm challenge without contributing to chemical resistance while also improving our farm systems,” says Jason.

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