The dry sunny weather of the beginning of the year has been followed by some significant rain and continuing warm weather. What does this mean for the worm population on farms and their likely effect on sheep?
During hot dry conditions, worm egg hatching and larval development on pasture are slow. Worm larvae that do develop tend to remain associated with their nearest source of moisture - the dung pat.
When the rains come, the environment within the pasture becomes much more favourable for larval development; the rate at which worm eggs hatch and grow into infective larvae greatly speeds up, and the larvae themselves are able to migrate out into the pasture sward, to be ingested by feeding stock.
As long as conditions remain warm and moist, these infective larvae will survive very well over the summer and into autumn, creating an ongoing worm challenge for stock.
We know that the challenge to the animal's immune system created by a big daily intake of worm larvae is huge, and in many cases is actually more harmful than the adult worms themselves. This challenge creates a big cost in growth performance, so what can we do to minimise its effects?
- We know that crops and new grasses have low larval contamination, so use these for priority classes of young stock.
- We also know that in the face of larval challenge, stock will do better on easily digestible feed with high protein and ME levels - ie pastures with a high clover content in a short vegetative state. Tetraploids and low endophyte ryegrasses are a great choice, if available.
- We know that worm larval survival is enhanced on mat-forming, browntop dominant pastures; keep young stock off these where possible.
- The greatest percentage of worm larvae (plus most other nasties such as facial eczema spores and other fungal toxins) are found in the lowest part of the pasture sward - don't force young animals to graze to this level.
- Also be aware that the immune system of mixed-age ewes won't always cope with pressure of this sort, and they too may develop a significant worm burden coming into tupping.
You could use a long-acting worm control product - but there are some fish hooks to this - see below.
While the use of long acting drenches or boluses in lambs may seem tempting given the current excellent conditions for worms, be very careful! These climatic conditions favour the development and survival of larger numbers of larvae than at other times of the year - this could be a major problem if you have oncoming drench resistance on your property. The reason being that the only larvae which survive that long-acting product are the resistant ones; they will develop to adults that will seed the pastures with resistant eggs, which will develop rapidly into infective larvae, which when ingested will survive the treatment and spit out more eggs.... This effect can continue for many months depending on the product and the way it is used.
That said, if you are using a long-acting drench product or bolus in your lambs, it is easy to monitor the faecal egg counts of lambs while under treatment. This can give you an early warning of the situation described above, and may lead to us looking in more detail at the overall drench resistance status of your farm.
Totally Vets offers an efficient and cost-effective egg count monitoring service, plus we have vets with a special interest in parasite management, who can help with both drenching and overall management advice to help maximise the performance of your lambs.
