The impact of worms on production begins as soon as larvae are ingested from pasture.
Michael Catley
The affect this has is a continuum, from no exposure (and no impact) to the presence of heavy burdens leading to disease and death.
There is a cut-off point where the worm burden causes clinical parasitism, such as scouring, dehydration and weight loss, but before this point is reached there is a production limiting affect called sub-clinical parasitism.
Minimising these effects optimises growth rates in your stock and increases efficiency and profitability.
Animals pick up infective L3 larvae from the paddock when grazing pasture (L1 & L2 larvae can be picked up but are not infective).
These larvae are foreign to the animal in a similar way to bacteria and viruses.
The level of contamination will determine the level of impact.
Any level of worm burden, even when drenches are used every 21 days, will cause a growth rate depression in livestock.
These affects are due to stock spending less time grazing and more time lying down due to parasitism, as well as the immune response the animals mount to the worm larvae picked up. Therefore, the more worms picked up, the bigger the depression in growth rates.
Young animals have no specific immunity to worms and as a result the worms establish and become ‘resident’ in the animal, multiplying worm populations which become a major source of contamination.
Young animals also use a large amount of energy and protein to grow, so are highly susceptible to the effect of parasites.
Cattle and sheep generally develop full immunity by 18-20 months of age.
Exposure to worms is important to develop immunity – and there is no shortage of exposure to them with pasture grazing – so a successful worm management plan minimises exposure of worms to young stock to allow an immune building response, while minimising growth and nutritional impacts.
Next time, we will focus on worm biology and how understanding this can improve management of pastures and animals.
A blackbird eating worms. Photo: Phil Mitchell, pexels.com
Worms. Photo: Sippakorn Yamkasikorn, pexels.com
