15 ways to protect your stock from worms

Worm burdens are a huge factor in the health and welfare of livestock on a block. You may not realise the biggest contributors of parasites are the young, or that drenching all your stock is one of the worst things you can do.

The objective of good worm management is to minimise the impact of worms on animal performance while minimising the selection for drench resistance.

Young stock are the major contributors to internal parasite populations in pasture. Systems that are dominated by animals less than nine months of age are very susceptible to high worm challenges.

1. Reduce the worm challenge HOW: manage the worm challenge

Young stock are the major contributors to internal parasite populations. If your block is dominated by animals less than nine months of age, it will be very susceptible to high worm challenges.

The number of lambs carried into autumn and where they graze sets the risk of future worm burdens. You want to avoid grazing lambs during the summer and autumn in pasture where ewes will be lambing the following spring.

3 ways to prevent the build-up of large worm populations:

• put in new pasture • feed crops, hay or silage to slow down your pasture rotation • cross-graze with other types of stock, eg cattle, horses

2. Improve the gene pool HOW: breed for parasite-resistance

Rams that have been selected for resistance or resilience against worms and have high performance offer a real genetic advantage.

Important progress has been made by some sheep breeders who have been selecting for either low faecal egg count levels (resistance), or time to first drench (resilience), along with high animal performance.

It appears that resistance or resilience don’t necessarily have to come at the cost of animal production. One good tool is the CARLA saliva test which helps you to select sheep for these traits. It provides an accurate and simple way to work out which animals suffer less from the effects of parasitic worms, and which pass fewer worm eggs onto pasture. www.carlasalivatest.co.nz

3. Practice good drenching

HOW: use faecal egg count testing, and drench strategically Do a faecal egg count (FEC) test 10 days after drenching to check that a drench is working. The first drench after weaning and the first autumn drench are good times to make the check. A full drench test should follow if the FEC test is not zero.

It’s desirable to leave the healthiest ewes or lambs in a mob undrenched. This helps to maintain a reservoir of susceptible worms in the population to dilute down any resistant worms.

4 good drenching practices

• Use a derquantel/abamectin or monepantel drench for quarantine drenching sheep and a triple combination for cattle. • Hold stock for 24 hours after quarantine drenching and then let them out onto a ‘wormy’ paddock so that any resistant survivors are quickly diluted down amongst the population in the pasture. • Where possible, extend the drench interval to help preserve drench effectiveness. This must be done with care after consideration of the level of worm challenge, FEC tests and/or liveweight gain measure*. • Do not drench at less than 28 day intervals.