Best practices for control of winter scour worms in prime lambs in Western Australia
Danny Roberts, DPIRD, Albany, WA
Corresponding author: danny.roberts@dpird.wa.gov.au
Introduction
Prime lamb production forms an important part of sheep production systems in Western Australia. Profitability in prime lamb production relies on high growth rates, which can be impacted by worm burden. A high worm burden can limit lamb growth rates and therefore reduce the profitability of a prime lamb enterprise.
There are no published reports regarding the impact of worms on prime lamb enterprises in Western Australia. Jacobson et al. (2006) found surprisingly high worm egg counts in lambs sampled in lairage prior to slaughter with a mean worm egg count for scour worms of 1150 eggs per gram (epg), and above 2000 epg in 22% of cases.
This suggests that uncontrolled parasitism is common in Western Australian prime lamb flocks with the potential for lost productivity.
We perceived a need for worm control programs specific to prime lamb enterprises to maximise the rapid growth rate during the growing season essential for profitability. We attempted to quantify the potential loss of growth and value in prime lambs due to non-Haemonchus sp worms.
Materials and Methods
Information was collected from 42 flocks from 2013 to 2015 located in medium and high rainfall zones of Western Australia. The design was a case-control i.e. lambs not drenched (producer-program group) were compared to lambs given drenches to suppress worms (worm suppressed group).
Both groups of lambs grazed the same pastures and were part of a larger group of prime lambs. Drenches (long acting moxidectin and oral moxidectin) were administered to the control group of lambs in each flock on a schedule based on time after the start of lambing (SOL).
Measurements on the lambs were collected at similar times (events) after the start of lambing in the 42 flocks. The average interval from lamb marking or Event 1 to Event 5 (average of 156 days after the SOL) was 105 days.
By standardising the schedule of property visits according to the time since the start of lambing, it allowed combining of information from different flocks each year and between years. It also reduced any confounding effects on growth rates and worm egg counts by having excessively variable dates when visiting each property.
Results and discussion
At each visit, there was a gradual increase in adjusted liveweight of lambs in the worm-suppressed group compared to the producer-program group (no drench). A 1.1kg difference between treatment groups is evident by Event 5 (average of 156 days after SOL). This is because 86% of flocks recorded a higher growth rate in the worm suppressed prime lamb compared with the producer-program group.
On individual flocks over 3 years, 28% of prime lamb flocks had a ‘worm effect’. These flocks had significantly higher difference in average worm egg count (WEC) of 474 epg compared with 261 epg in the unaffected flocks (p=0.005).
Lambs from the worm suppressed group in ’worm effect’ flocks gained an 8% advantage in growth rates. These ‘worm effect’ flocks were located in the medium and high rainfall zones of Western Australia.
No risk factor was associated with ‘worm effect’ flocks. However, growth rate of the prime lambs from lamb marking to 14 weeks after SOL was one potential protective factor that appears to help mitigate some of the effects of higher worm burdens.
At slaughter, the average difference between the two treatment groups was $5.73 per head in ‘worm effect’ flocks. The increase in carcase weight gain at slaughter composed 70% of this value and 30% was due to an increase in the average cents per kilogram per carcase weight price paid for the worm-suppressed group.
General thresholds beyond which worm-related production loss is expected is the basis for control recommendations. The results suggest that best-practice worm control over the critical period for prime lamb growth should include: avoiding grazing green pastures during the winter growing season (April to October) and accumulating high scour worm burdens, as these will reduce the liveweight and carcase weight at slaughter and the dollar value received for the carcase.
How to maximise profitability of prime lambs at slaughter
Prepare low scour worm burden paddocks in autumn by:
- Drenching ewes with an effective drench around the first week of April, well before the “break of season”. An effective drench kills more than 98% of Brown Stomach worms.
- Employing refugia if ewes are given a summer drench. Leave 10-20% of sheep with a condition score greater than 3 un-drenched.
- Monitoring pregnant ewes four weeks before lambing. Collect 20 faecal samples and drench if the average worm egg count is more than 100 eggs per gram.
- Only pre-grazing with sheep with low worm egg counts (less than 100 epg) during autumn and early winter. This ensures any faeces deposited on pastures in the planned lambing paddocks does not contribute to higher worm contamination during winter.
Monitor prime lambs about 10 weeks after the start of lambing by collecting 20 fresh faecal samples from lambs in each mob and treat based on the results:
- If greater than 250 epg (average), give an effective drench to the lambs. Re-sample four weeks later, and if greater than 250 epg – then give another drench.
- If less than 250 epg at 10 weeks, wean and drench as per normal practice.
If worm egg counts are not checked, a drench should always be given by 16 weeks after the start of lambing at the latest, regardless of how well lambs appear to be growing. It is important to:
- Ensure average growth rates in lambs are 240 grams per head per day or greater, 10 to 14 weeks after the start of lambing to mitigate some of the effects of scour worms.
- Maintain good growth rates in lambs after 14 weeks from the start of lambing – do not let Feed-On-Offer (FOO) go below 1500kg/ha.
- Select lower worm burden paddocks to wean prime lambs onto, as otherwise worm burdens are likely to be high within four weeks.
Plan options to provide weaned lambs lower worm burden paddocks from August to November including:
- Paddocks with FOO more than 1500kg/ha and pasture height greater than 3cm.
- Paddocks grazed by adult non-pregnant sheep with low worm egg counts.
- Pasture paddocks that have not been grazed in preparation for hay production.
- Paddocks sown for hay production.
- Standing fodder or cereal crops.
- Spray-topped or hay-freeze pasture paddocks.
- Renovated pasture paddocks.
- Paddocks grazed by cattle.
Give a single fully effective summer drench about four weeks after the pastures have dried off, or as sheep move onto a crop stubble.
Resources
Report:
Capacity building and validation of integrated parasite management in prime lambs in Western Australia, B.AHE.0072, Meat and Livestock Australia
Research article:
Jacobson C, Bell K and Besier B (2009) Nematode parasites and faecal soiling of sheep in lairage: evidence of widespread potential production losses for the sheep industry. Animal Production Science 49: 326–332.