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How to reduce pasture larval challenge

How to reduce pasture larval challenge

How to reduce pasture larval challenge

Reducing the number of worm larvae your stock unwittingly eat every day improves their performance, resulting in higher growth rates, milk production and less scouring.

Another significant benefit is the potential to reduce the number of drenches administered to each animal, saving time and money and reducing the opportunity for resistant worms to breed with each other.

The worm eggs and larvae are in faecal pats, and infective larvae live in topsoil and on pastures, together making up 90 to 95 percent of the worm population on-farm. Faecal pats provide a stable environment for egg and larvae development, protecting them from damaging ultraviolet light (UV). With sufficient moisture, the larvae migrate from the faecal pats to continue developing to the infective stages.

Strategies to reduce the number of worm larvae ingested by stock include:

  • Start with a low-worm challenge. Sheep worms do not or have poor development in cattle and vice versa, so prepare lamb-weaning country with cattle rather than weaning back onto lambing country.
  • Use of specialist forage crops. These provide lower worm challenge areas, and the high quality feed enables animals to better withstand the damaging effects of parasites. Also, the spraying and desiccating of pasture exposes worm larvae to damaging UV light radiation. The grazing height of forage crops is an unfavourable environment for infective larvae.
  • Grazing adults in a rotation with younger stock classes. The adult stock can be net removers of parasite larvae, add refugia and help with pasture quality control.
  • Having cattle and sheep in the same grazing rotation.
  • Effective drenches give a three-week period of no or very low egg output in faeces. Do a drench check faecal egg count (FEC) one to two weeks after drenching to ensure the drenching is highly effective.
  • Grazing paddocks where hay and silage have been harvested. Reducing the number of worm larvae on pasture also decreases refugia, so drenching frequency must also be reduced. Use FEC to indicate the number of adult worms breeding in your stock, so regular FEC from four weeks after the drench is an indicator of the need to drench.

An unintended consequence of this strategy could be the creation of a high worm challenge in the paddocks grazed four weeks and longer since the last drench, so targeting these paddocks for later grazing with cattle or older stock classes could be beneficial.

Animals fed a balanced diet where their protein, energy and mineral requirements are met, are better able to manage the impacts of a worm burden. Specialist summer and autumn forages offer both the opportunity to have a high-quality diet combined with a lower worm challenge; factors identified as critical to high growth rates in young stock.

Talk to your local PGG Wrightson Technical Field Representative about whether summer and autumn forages could be used as an important part of your worm control strategy.