When we talk about drenching and being ‘wormwise’, we are talking about roundworms of the intestine affecting productivity – liver fluke, lungworm and tapeworm are kept as another topic.
Michael Catley
Most species of worms are specific to the species of animal – sheep worms affect sheep (and goats), cattle worms affect cattle. The main problem is the affects they have on the true stomach (abomasum) and the small intestines.
The exception is some Trichostrongylus species that can be found in both cattle and sheep and significantly affect productivity.
The lifecycle of roundworms is not particularly complex. Adult worms live in the animal; worm eggs are deposited on pasture in poo; eggs develop into larvae in poo and migrate to pasture, where they develop to an L3 infective stage.
L3 infective larvae are ingested by livestock and develop into adults inside the animal. The female adult worm then mates inside the animal and produces eggs in about 21 days.
Development from an egg to infective L3 larvae can take from one to 10 weeks depending on environmental conditions; 20-25 degrees Celsius with moisture is required. Variability from these conditions will slow development or cause destruction of eggs/L1/L2 larvae.
L3 infective larvae are the exception and can survive for long periods on pasture. In cool environments, this can be up to a year or longer. In dry environments, this can be as little as 2-3 months (surviving on their own reserves).
A blackbird eats a worm. Photo: Phil Mitchell
Therefore, we sometimes steer away from the 28-day drenching intervals, with delayed development and life cycle in the larvae (but followed up with FEC monitoring). Different grazing patterns also affect the infection cycle, with lax grazing reducing the intake of infective larvae from pasture. Typically, it takes 21 days from when a sheep ingests a worm larvae to when worm eggs appear in dung samples (the prepatent period).
Seasonal patterns of worm burdens generally follow a consistent pattern, with an early peak in spring and a later larger peak in autumn.
Wintering numbers, stocking rates and feed levels at calving/lambing can affect the trends in this curve, with higher counts when nutrition is suboptimal (associated with a pre-partum rise in egg counts) and reaching peak lactation.
Most contamination contribution comes from young stock, particularly those less than 12 months (that season’s lambs or dairy beef mainly).
Understandably, the peak occurs in autumn due to the number of young stock under the age of 12 months, the seasonal conditions, preventative drenching programmes and cross-grazing policies.
See: Wormwise with livestock, part one
Worms. Photo: Sippakorn Yamkasikorn, pexels.com
