Parasite Control In Sheep Requires A Holistic Approach

Internal parasites in sheep are an ever-present problem, and the only way farmers can minimise their impact on the flock is through proper management.

- Izak Hofmeyr

There is no such thing as worm-free status in sheep, says Prof Gareth Bath, emeritus professor at Onderstepoort and convener of the Small Stock Health Advisory Body (SSHAB). “The aim is to follow a balanced strategy that can be implemented to manage the worm population on your farm as efficiently as possible.”

Five aspects of management

This strategy is based on the so-called ‘Big Five’ aspects of management, namely:

• Selecting your sheep based on genetic resistance or tolerance.
• Managing your grazing so it creates as hostile an environment as possible for worms.
• Knowing the life cycle of the worms concerned.
• Implementing an effective monitoring strategy so you can identify and selectively treat (and then cull) animals that show signs of worm stress.
• Implementing a dosing strategy that will delay the build-up of resistance to a specific agent for as long as possible.

He says it is important to note that using chemical agents against worms entails the last facet of the management programme. “Chemical agents must never become the only practice farmers rely on to combat worms. The danger of building up resistance to the agents is too great, and there just aren’t enough active agents available to justify the indiscriminate use of these agents. It is therefore imperative to have all the other management facets firmly in place.”

Undesirable management practices

Using the analogy of a traffic light with red, yellow and green options, Prof Bath divides management practices into ‘undesirable’ (red light), ‘use caution’ (orange light) and ‘desirable’ (green light).

He lists the following under ‘undesirable’: