Online Learning: South Australia—Grazing Management

Worm eggs that have passed from the goats in dung hatch and develop through first (L1) and second (L2) larval stages to become infective larvae (L3). The success and speed of this development depends on weather conditions, specifically warmth and moisture, and require a minimum of 4 days and rarely more than 10 days.

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Temperature requirements vary for each worm type, but most require about 15 mm of rain over a few days (but also depends on evaporation rates) to provide sufficient moisture for development. The L3 leave the dung moving onto pasture and soil, rarely more than 25 cm from where they were deposited in the dung.

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Infective larvae are relatively tough and can withstand dry, cold and moderately hot conditions. All populations of living things vary in their life expectancy and worms are no different; some larvae will die within days, but some will live to around a year or more.

Generally, over 90% of larvae will be dead within 6 months under cooler conditions and as little as 3 months when temperatures are ideal.

Under extremely hot, dry conditions larvae will be desiccated and can die in a few days to weeks of these conditions, explaining why worms are rarely a problem in the arid zone.

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.

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).

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Paddocks are considered low worm-risk when over 90% of the worm larvae have died. The graph (right) shows the decline in barber’s pole worm larvae on pasture over time and under different temperature conditions when the relative humidity is 60%.

Paddocks prepared for spring use need 5 or 6 months of preparation, whereas paddocks prepared for summer or autumn use need about 3 months of preparation time.

Source: Modeled from death rate of the L3 population in ‘Simulation of pasture larval populations of Haemonchus contortus’ by IA Barger, PR Benyon & WH Southcott. Proceedings of the Australian Society of Animal Production (1972) 9: 38

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Barber’s pole worms are quite long (20 to 30 mm) and clearly visible. Only adult females have the characteristic ‘barber’s pole’ appearance due to the pink (blood-filled) intestinal tract of the worm twisted around the paler reproductive tract; whereas the males are smaller (around 15 mm) and pale pink. Females are prolific egg layers, laying up to 10,000 eggs per day, as such, higher worm egg counts are usually seen with these worms.

Adult female black scour worms lay 100–200 eggs per day. Black scour worms live in the first three metres of the small intestine of the goat and cause damage to the lining of the gut. The adult female in the small intestine lays eggs, which are passed out in the dung.

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The following practices or a combination of these can create paddocks with less worm contamination and lower worm-risk.

• Intensive Grazing.

This system typically involves creating a higher stocking rate with larger mobs (at least twice the set-stocking density) and introducing them to the paddocks when the pasture is about 7 cm high and grazing down to 3 cm high. Aim to have a non-grazing rest period of at least 2 months in winter and 3 weeks during the active pasture growth phase. (see life cycle page and Factors contributing to paddock contamination with worms)

• Grazing with cattle

While grazing with cattle is used frequently for preparing safe paddocks for sheep as cattle do not share the same worms, goats are different as they have some worms in common. Notable exceptions are the ability of barber’s pole worm and stomach hairworm (Trichostrongylus axei) to successfully reproduce within goats and young cattle (i.e. pre-weaning). Goats can also be severely infected by brown stomach worms (Ostertagia ostertagi) from cattle, unlike the situation with sheep and lambs. Using dry adult cattle for alternate grazing is preferable, but large benefits still arise from using cows and calves and this should not prevent their use for this purpose.

• Grazing with adult goats or sheep that have a tested low worm egg count (less than 50 epg)
• Grazing with goats only in the 18 days or sheep only in the 20-30 days after they have received an effective drench.
• A non-livestock use in at least the 6–8 weeks prior to use with weaners
  • Cropping
  • Haymaking
  • New pasture establishment

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Sheep and alpacas can carry goat worms. While young cattle/calves also carry some goat worms, adult cattle tend to have very low burdens of goat worms and contribute very little to contamination of pastures with worms affecting goats.

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