Wise words on worms
Autumn is a key time of the year to monitor and identify the potential risks for worm burden. The risk of worm burden increases with warm, wet summer conditions and where there are green pastures over summer, as seen in many places this season.
In Australia there are three main roundworm species that infect sheep and goats, these include:
1. Barbers pole worm (Haemonchus contortus)
o Blood sucking parasite
o Infections worse in wet summers (this year)
o Worm egg counts (WEC) typically much higher than scour worms
o Clinical Signs: anaemia, lethargy, collapse, weight plateau, bottle jaw, death
2. Black scour worm (Trichostrongylus sp.)
o Occur across Australia
o Multiple species of black scour worm
o Some species occur in warm summer rainfall areas while others occur in winter rainfall areas
o Clinical Signs: Lethargy, collapse, weight loss, scouring, death
3. Brown stomach worm (Teladorsagio [Ostertagia] circumcincta)
o Major parasite in winter rainfall areas
o Don’t feed on blood but damage and inflame lining of stomach
o Clinical Signs: rapid condition loss, lethargic, collapse, scouring, death
Life Cycle of Most Roundworms:
Worm eggs are passed from the sheep onto pasture through their dung. The L1 and L2 stages develop inside the dung to become the infective L3 stage. With optimal conditions (warm and moist) this can occur in four to ten days.
The L3 larvae move off the dung onto the pasture/soil where they can be ingested by the next grazing animal.
L4 larvae stage occurs in the gut before becoming adults and completing their life cycle. It will take at least 18 days before the worms reproduce and lay eggs that are passed through the dung to start the life cycle again.
How to break this life cycle:
L3 larvae concentration is highest at the base of pastures, as they generally don’t climb higher than 10cm. Therefore, avoid grazing pastures below 10cm in length or right to the ground. Allow spelled paddocks to be grazed by the most susceptible stock first, weaners and lactating ewes, followed by less susceptible animals such as your older sheep. Cattle can be utilised to reduce L3 larvae as sheep and goat worms are specific to these species and will not survive in cattle (and horses).
Consider how long it can take for a contaminated paddock to become a low-worm risk. Studies suggest that 90% of larvae will die on a spelled paddock, after six months in cold conditions or after three months of hot weather (above 25-30°C). L3 survive on energy reserves and die when these are used. They also dry out and die in temperatures exceeding 40°C.
Implement a ‘Smart Grazing Program’, which speeds up the grazing rotation. Mobs can be moved to clean pasture before they are infected with larvae recently deposited by the same mob. Four to ten days is the duration of worms developing from L1 into the infective L3 larvae. Thereby, essentially slowing down the rate of infection.
Regular worm tests every 4-6 weeks can also assist in early detection of a potential worm burden and should always be conducted if there are visible signs.
The ParaBoss website also provides resources such as a drench decision guide tool to strategise drench rotations. It also offers other recommendations for important times of the year to test for worms in the link below.
https://tools.wormboss.com.au/sheep-goats/tests-tools/drench-decision-guide.php
Worm-Control-Program-NSW-non-seasonal-rainfall.pdf (wormboss.com.au)
Dr Brown Besier from ParaBoss gave a seasonal worm update on the 13th of February 2024, follow this link to watch the full webinar recording: https://paraboss.com.au/webinars-videos-podcasts/seasonal-worm-update/