Mary Bowron, Wormwise advisor, vet and farmer talks about the opportunities and pitfalls associated with grazing vineyards, orchards and solar farms.
Viticulture, horticulture and now solar farms, all have grass that needs managing between the bits that make the money for their owners. These blocks have long been seen as a grazing opportunity by sheep farmers and traders.
Grazing is generally through the autumn/winter period, and mostly with lambs. These may be sourced from the home farm and head home in the spring as replacements; alternatively, trade lambs may be purchased and finished entirely on the grazing block. Usually there are no other stock on these blocks for the rest of the year.
There are two issues to consider when managing worms in lambs on these blocks:
- Worm challenge - this can build up over time, despite the months of rest when lambs are not grazing.
- Drench resistant worms - the risk of importing resistant worms can be high, and the ability to breed them up till they dominate the block, can also be high.
Worm challenge
A vineyard, orchard or solar array that has never had sheep on it is likely to have low worm challenge - this will be awesome for lamb growth - at least initially!
On the other hand, a block that has been grazed by lambs for many seasons could be high risk for worm challenge, depending on how long lambs graze the block each year and how grass is managed season-to-season in between. Worm larvae love being in a shaded, moist environment, and can survive many months like this. In a farm situation, other stock classes may consume larvae in between lamb seasons. In a vineyard/orchard/solar situation, larvae may sit protected between lamb grazing seasons.
Drench resistance
Getting access to a clean block to graze lambs sounds like an awesome opportunity, right?
But that same “clean” status can make it highly risky for developing a drench resistant worm population, especially if the quarantine and further drenching of introduced lambs is not managed very carefully.
If lambs carrying resistant worms are imported on to worm-free grass, followed by regular drenching with ineffective products, the build-up of resistant worms can be swift and devastating.
Quarantine
How to quarantine lambs onto a grazing block will depend on the source of the lambs and grazing history of the block.
For a highly contaminated block that is already known to have drench-resistant worms on it, a quarantine drench may not achieve much. Possibly trying to import some ‘good’ worms and allowing them to reproduce, to dilute out the resistant population on the grazing block, may be worth considering.
Options to do this include leaving the best and biggest lambs undrenched, importing lambs when they are ‘due’ for a drench (presuming you know that they aren’t carrying a whole bunch of resistant worms themselves), or popping some light, undrenched ewes on the truck with the lambs.
Quarantining onto a known clean block (has never had sheep on it for many years) requires great care, and it’s worth running your plan past someone who know their stuff in this area, to check for any fish hooks you may have missed.
The gold standard quarantine recommendation is a four-way combination of drench actives, including Derquantel or Monepantel (Quarantine drenching). Because most drench actives cannot kill worm eggs, there needs to be a stand-down period after a quarantine treatment, to allow eggs laid by worms prior to drenching, to be passed out, before lambs are allowed to graze clean pastures.
Make sure you follow up with a faecal egg count around 10 days later to check that your quarantine treatment did its job.
Ongoing management
On a really clean block, further drench treatments after quarantine should be unnecessary, but there’s always the possibility of a surprise (guess what, someone had pet goats on it last year, for instance!), so repeat faecal egg counting 28+ days after lambs are introduced is a good way to ensure no nasty surprises.
On a contaminated block, the question is - what further treatment might lambs need, and when? Again, faecal egg counting is a useful way to monitor how quickly lambs are getting wormy. Winter lambs, especially the good-sized ones, could have developed some immunity to worms already. Whole-mob drenching may be unnecessary and leaving the biggest and best lambs untreated (with regular visual monitoring) can be a way to keep some drench susceptible worms cycling on the block.
Vineyard, orchard and solar grazing can be a real win-win - as long as you’re aware of the likely worm contamination and drench resistance on the block and manage accordingly.