Wormwise vet and farmer Mary Bowron draws on her experience to outline the critical steps required to effectively manage worms on forage crops used for finishing lambs.
Non-grass forage crops for finishing lambs can be a powerful tool for providing nutritious and quality feed with a lower parasite challenge. However, you can’t just shut the gate and go on holiday.
For our farm in Northern Marlborough, we finish our own lambs and if the season allows, we buy in trade lambs to finish. Both short and long-term forages are sown, as part of a pasture renewal programme and to give us options if it goes dry.
As a vet, and part of the Wormwise team, parasite management is an important consideration when planning what crops we choose, and where and how we graze them. They are not a cheap investment so it’s important to get the processes right but still keep things practical.
Our crops aren’t perfect; for example, we have grass edges as we can’t spray right to the fencelines, and these can still harbour worm larvae. Bug damage hammered the crop seedlings last spring so in some paddocks, plants are sparse and weeds are abundant! It’s all part of farming but we make allowances for that.
Monitoring to stay ahead of the game is important. We measure faecal egg counts (FECs) and lamb growth rates to keep tabs on worm challenge and performance. It’s not always about the number we get; it’s more about the trend, especially with FECs. We also note behaviour, which is easy to see when moving lambs frequently. If they are skipping and jumping, we figure they are feeling pretty good and being well fed.
After a weaning drench, lambs either stay on a plantain/clover mix they’ve been on since birth or transitioned onto a brassica. A drench check 10 days post weaning is part of the plan to check the drench used is effective. We collect 10 fresh poo samples in the paddock and do our own FECs in the woolshed.
About 28 days after drenching, we check FECs again. It tells us whether the lambs need another drench and how wormy the paddock has become. Some of our areas have quite a bit of grass around the edges which is mostly browntop, so it can be a worm haven. Our plantain/clover blocks could become quite contaminated after the first season so FECs are used to monitor that.
We weigh some lambs periodically to get an idea of growth rates. This helps to recalibrate the ‘eyeometer’ that lambs are ‘doing ok’. Or it can be a reality check that stock aren’t performing as we thought. Doing this sooner rather than later, gives us time to take action before lambs start going backwards.
Good growth rates help lambs reach market weight sooner, reducing farm larval contamination and ensuring ewe lamb replacements are ready for hogget mating.
Where does refugia fit in our system? Adult ewes are not drenched, so they are a key part in providing drench-susceptible worms on our lamb blocks.
Remember for the first 21 days after drenching, the only eggs coming out in the lambs’ faeces will be from worms that have survived the drench. Over time, if drenched lambs are the only stock grazing a block, the predominant worm larvae in that block become those drench survivors.
At our place, mixed age ewes graze the new plantain/clover areas after lambs have been through, providing some ‘good’ parasite larvae to dilute out any resistant larvae left by the lambs.
Another trick is to run light ewes in with the crop lambs. The ewes gain weight prior to tupping and provide refugia, if required. They also help to show lambs brassica is ok to eat, funnily enough it is not their first choice!
For short-term crops such as the rape or leafy turnip, refugia is less of a concern. Fewer larvae survive on these crops to begin with because they tend to be grazed to open ground (larvae don’t stand UV light for long), and more will perish in the re-grassing process.
For trade lambs, depending on their origin, we may or may not quarantine drench them. We know we have some combination drench resistance, so sourcing susceptible parasite larvae can help reset the worm population.
If we quarantine treat, we use a novel drench. Then we do a drench check at 10 days to check that treatment has worked.
Crops have enabled us to decrease our use of drench. Many lambs are killed without having been drenched at all, and most others only get 1 or 2 drenches after weaning, saving us time and money. It has been a worthwhile investment for us, lifting our lamb growth rates and finishing more lambs.
Crops are a great tool, put some steps in place to monitor and manage parasites, to ensure you reap the rewards on your farm.