By Andrew Dowling, PGG Wrightson
Gastrointestinal parasites (worms) are a significant focus for any farmer as they can impact the animal’s health, reducing weight gains, milk production and, in severe cases, causing death.
Over the last 40 years, we have used highly effective drenches as the cornerstone of worm control, but the worms are not as susceptible to these drenches as they once were.
This is resulting in worm surviving and getting to mate with each other to spread their genes, making the worm population more resistant. This decline in drench efficacy was predicted, but we thought we were different to the rest of the world, and it would not be a major problem here in New Zealand.
We were wrong, but we can still manage these worms on our farms.
The objective is to keep the worm population under control, as it is the total number of worm larva eaten every day that is the problem; eating 5000 larva a day is a lot worse than 1000.
Young stock are both more prone to the effects of worms, and are usually the main polluters on the farm ie. most of the worm eggs on the farm have come from the animals under one year of age.
A highly effective drench removes eggs from the faeces for three weeks after the drench and this is significant.
From about nine months of age the immune system in the lamb or calf is capable of making life tougher for the worms; reducing their lifespan, the viability of their eggs and the ability of the infective larva to become established. Healthy, well-fed animals (especially adults) manage their worm burden better and do not require drenching on a routine basis.
Reducing the total numbers of worms on the farm helps improve the health of all the animals. Adult sheep and cattle are great at reducing the worm population (thanks to their immune systems) and sheep worm do not live in cattle and vice versa. So a good grazing rotation is essential. How this is done on your farm will be different to your neighbour but the concepts are all the same.
Even if the drenches on your farms are still highly effective, there are things that you could change that would help to protect them.
