Seasonal Outlook for Livestock Parasites in Summer-Autumn 2022

‘The Girl’ has caused a big turnaround in the weather!

La Nina weather patterns over the Pacific Ocean have brought a wet summer to eastern Australia, with rainfall over the spring and summer causing flooding and havoc for cereal harvests. This contrasts strongly with the drier conditions in previous years (see Figures 1-3 below).

Figures 1, 2 & 3: Maps showing annual rainfall compared to historical average. 2019 (left) had some of the lowest rainfall on record, 2020 (centre) was a transitional year, while 2021 (right) had average to above average rainfall across most of the country (source Bureau of Meteorology).

The upshot of the moist conditions is that we are going through summer and into autumn in these regions with high levels of vegetation cover on paddocks, high levels of moisture in the soil and high humidity at ground level. These conditions could have been requested by both internal and external parasites for maximum survival and multiplication.

1. Worms: the larvae of common livestock worms such as Barber’s Pole worm and Cooperia are usually killed off quickly over summer due to heat and dryness. However this year, soil moisture levels are high and good sward height means the larvae, which live on the bottom 1-3 cm of the grass, aren’t exposed to the lethal UV rays and will survive in record numbers. Once past autumn, cool conditions over winter mean that worm larvae in pastures will last right through to next spring.
2. Liver fluke: the snails that are necessary for the liver fluke life cycle love moisture and temperatures between 10-30⁰C. A single snail can produce 3,000 offspring per month in these conditions. The infective cysts on herbage also love humid conditions and although they die off at higher temperatures, any cysts (metacercariae) present in late autumn will survive right through winter (at temperatures below 12-14⁰C).
3. Ticks: cattle ticks on pasture in northern Australia have higher hatching and survival rates in warm, humid conditions and high grass, while bush ticks and paralysis ticks also have better survival when there is plenty of ground cover and humidity.
4. Lice: sheep lice can be killed by extended wet weather, but that doesn’t mean they will go away. Cattle lice prefer the long coats and cooler weather of autumn and winter to build up numbers.
5. Flies: buffalo flies, sheep blowflies and nuisance flies all have higher survival rates in humid conditions. This will mean higher survival of the pupae that hatch and release the adult flies that will feed on our livestock wet weather also means higher susceptibility of sheep to flystrike due to wet fleece and bacterial growth.

Forecast

Rainfall is predicted to stay above average for much of north-eastern Australia and average for the rest of the country over the next three months (see Figure 4 below).

Figure 4: Predicted rainfall for Australia over the period Feb-April 2022 (source Bureau of Metorology).

Monitoring is key to effective management

Ideal conditions for survival and multiplication of internal and external parasites means that livestock producers will need to be on the alert for a range of parasite problems over the next year. Test, check and monitor to ensure you do not suffer productivity losses.