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Home Worm Control Program – South Australian winter rainfall Appendices: Further Information on Sheep Worm Control for SA Winter Rainfall

Appendices: Further Information on Sheep Worm Control for SA Winter Rainfall

The life cycle of sheep roundworms

Image: The roundworm life cycle (Source: Sheep CRC)


The availability of infective larvae of the winter scour worms on pasture, showing a peak around June–August (depending upon the timing of the autumn break).

Source: The epidemiology and control of gastrointestinal parasites of sheep in Australia. Edited by A.D. Donald, W.H Southcott and J.K. Dineen, Division of Animal Health, CSIRO 1978.

Factors contributing to paddock contamination with worms

The following table applies to:

Factor Time or conditions Effect
Minimum time before worm eggs can become infective larvae. 4–10 days Short graze periods (less than 4 days) prevent ‘auto-infection’ (animals becoming infected by larvae arising from worm eggs the same mob have recently deposited onto the pasture).
Conditions required for significant numbers of worm eggs to hatch and become infective larvae. 4–10 days of:
Brown stomach worm
Temperature: daily maximum >8°C1
Moisture in this time: >10–15 mm rainfall2
Black scour worm
Temperature: daily maximum >15°C for
T. colubriformis or >12°C for T. vitrinus
Moisture in this time: >10–15 mm rainfall3
Barber’s pole worm
Temperature: daily maximum >18°C1
Unsuitable conditions prevent eggs hatching and developing into infective larvae.
Note: The eggs of the brown stomach worm are much more tolerant of cold and dry conditions, and in general, grazing management has less effect on its control.
Moisture in this time: >10–15 mm rainfall3
1Some hatching of worm eggs of all worm species can occur below these daily maximum levels, but this is usually at a small and insignificant rate.
2Brown stomach worm eggs can develop at low rates without rainfall even in a relatively dry faecal pellet.
3Development to infective larvae may occur without rainfall if soil moisture profile is high.
Maximum time worm eggs can live awaiting suitable hatching conditions. Brown stomach worm: 21 days
(Note that some brown stomach worm eggs may survive for longer periods)
Black scour worm: 16 days
Barber’s pole worm: 5 days
Prolonged periods without the right conditions (temperature/moisture) for egg development will result in the eggs dying. This lowers the worm-risk of paddocks.
However, once hatched, infective larvae of both black scour and brown stomach worm can remain in the faecal pellet until conditions are more suitable.
The time for about 90% of the barber’s pole worm infective larvae (L3s) to die (making paddocks low worm-risk).
Note: larvae of brown stomach worm and black scour worm can survive longer because they can remain in the faecal pellet for extended periods.
Cold – Maximum temperature: < 15℃
Time for 90% larvae to die: 4 months
Warm – Maximum temperature: about 22℃
Time for 90% larvae to die: 3 months
Hot – Maximum temperature: about 35℃
Time for 90% larvae to die: 1.5 months
Very Hot – Maximum temperature: > 40℃
Time for 90% larvae to die: 1–2 weeks
L3 larvae do not feed. While waiting to be eaten by animals, they wriggle randomly in drops of moisture, more so in warmer conditions. Increased activity in warm weather depletes their energy reserves faster, hastening death.
In extremely hot, dry and windy conditions the larvae dry out and die.
Minimum time for infective larvae eaten by animals to mature and lay eggs (the ‘pre-patent period’). Sheep: minimum of 18 days for most sheep roundworms.
Goats: minimum of 14 (typically 21) days for barber’s pole worm and 21 days for scour worms.
Worm larvae eaten by animals soon after an effective drench will take at least 18 days (in sheep) or 14–21 days (in goats) before they can lay eggs. During this period after administering an effective drench, animals are not re-infecting the pasture.

Drench groups and actives

Drench groups and actives Worms Examples* of brand names/comments
BZ or benzimidazole group (‘white’)B albendazole
barber’s pole worm, ‘scour worms’, adult liver fluke, nodule worm, aids control of intestinal tapeworm (Moniezia) Valbazen (albendazole)
WSD Fenbendazole (fenbendazole)
Oxfen (oxfendazole)
LV or levamisole group (‘clear’)B levamisole barber’s pole worm, ‘scour worms’, nodule worm Nilverm, Levamisole Gold (levamisole)
ML or macrocyclic lactone groupB (sometimes called ‘mectins’)
barber’s pole worm, ‘scour worms’, nodule worm Ivomec, Noromectin (ivermectin) Absolute, Vetmec, Paramectin (abamectin) Cydectin (moxidectin)
AD or amino-acetonitrile derivative groupB
barber’s pole worm, ‘scour worms’ Zolvix
SI or spiroindole groupM
barber’s pole worm, ‘scour worms’, nodule worm Derquantel is only found in a combination: Startect (abamectin + derquantel)B
OP or organophosphate groupM naphthalophos (NAP)
(OPs have lower or variable efficacy against ‘scour worms’ in the upper GIT and immature barber’s pole worm)
barber’s pole worm, ‘scour worms’ Rametin (naphthalophos is commonly used in combinations)
TZ or benzimidazole group (flukicide)N triclabendazole Liver fluke (all stages); not effective against round worms Tremacide
SA or salicylanilides/phenols groupN
Liver fluke (> 9 weeks and adult) and barber’s pole worm
Liver fluke (adults) and tapeworm
Closicare (closantel)
Oxyclozanide is only found in a combination: Nilzan (levamisole + oxyclozanide)B
IQ or isoquinolone groupN
Intestinal tapeworm (Moniezia) PraziquantelN is only available in combination with broad-spectrum drenches. First DrenchB, Genesis TapeB
*ParaBoss does not endorse specific brands, these are presented here as examples only.

Breadth of activity across different worm species: BBroad-spectrum; MMid-spectrum; NNarrow-spectrum

Actives: An ‘active’ is the chemical in a drench responsible for killing worms. Some drenches have more than one active and are called ‘multi-active’ or ‘combination’ drenches.

Combination or multi-active treatments: Proprietary treatments containing more than one active. Formulated to be compatible as a mixture. Note: Do not mix your own drenches unless the labels state that you can.

Product formulation: All single actives are available as oral drenches. Moxidectin is also available in injectable products. Intra-ruminal/controlled release capsules are available with BZ and/or ML actives. Abamectin is also in a pour-on formulation for both lice and worm control.

Length of protection: Varies from short-acting (‘knock-down’ that kills susceptible worms within the animal) to mid-length (1–3 weeks) and long-acting (approx. 3 months), which not only kill susceptible worms already in the animals, but also susceptible infective larvae that the sheep eat during the protection period.

‘Scour worms’: Mainly black scour worm and (small) brown stomach worm, but also others.

Label: Check product labels for full details. Follow the label.

Other parasites: The Drench Decision Guides show effectiveness of groups against other parasites of minor importance.

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