Animals – Killer worms

Autumn has provided us with some amazing weather, with very little rainfall and higher than normal temperatures. For most sheep and lambs, this has resulted in really good growth rates and condition scores. However, in the last month since the rains have started, our clinic has seen a few cases of lambs and goats dying from parasite burdens.

Worm eggs are continually excreted by livestock in their faeces on to pasture, but while the weather is dry and hot, these eggs lie dormant on the grass and won’t re-infect any other livestock.

When we get warm, damp conditions, such as what we have experienced in the last month, these hibernating eggs hatch out into larvae and make their way to the top of the grass leaf to be ingested by grazing animals. This can lead to a large number of worms being ingested in a very short period of time. The longer the drought lasts, the larger the number of larvae which will hatch out at once, and the larger the burden ingested by grazing animals.

Lambs and goats are particularly susceptible to this mass emergence. If left un-drenched during Autumn and early Winter, it is not uncommon for them to die from these high burdens.

This time of year is also the highest risk period for Haemochus, a type of worm that can affect adult sheep as well as lambs and goats. Haemochus or “Barber’s Pole” is a blood sucking worm, and even very low levels of this worm can cause death in sheep, lambs and goats. For this reason, it is wise to drench all of your stock at the end of autumn as you enter winter.

Due to years of overuse worms are developing resistance to some drenches, so it is worthwhile discussing the best drench to use with your vet. There are four main types of drench actives, also known as drench families. Products which use a single active (such as Ivomec, Cydectin and Dectomax) have high levels of resistance developing, and should only ever be used in adult sheep. When drenching lambs and hoggets a combination drench should be used, ideally one with three of the drench families. It is also important to remember that when drenching goats they require double the dose that sheep need. Alternatively, you can give the normal sheep dose but on two consecutive days.

Drenching is a large topic which is difficult to cover off in one article. It is vital for not only the animals’ welfare, but also maximising their growth rates. For this reason, even if you only have a handful of sheep, it is worthwhile taking some time to get a plan in place with your vet.

Neil Warnock, Wellsford Vet Clinic
www.vetsonline.co.nz/wellsfordvet