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Controlling sheep internal parasites
This material addresses aspects of the following syllabus outcomes:
H2.2 describes the inputs, processes and interactions of animal production systems.
The work presented in the following section contributes towards understanding the following syllabus content areas:
Students learn about:
Animal pests and diseases
- animal disease
- integrated pest management (IPM)
Extract from Stage 6 Agriculture Syllabus NSW Board of Studies Amended 2009
How to control internal parasites
There are several steps involved in controlling internal parasites in sheep. Control involves the following measures.
- Identification of the number and type of worms being carried by the sheep. It is important that the extent of the problem is known so the appropriate
treatment can be selected. This information is provided by carrying out a Wormtest on a sample of sheep.
- Development of an efficient grazing management program. This involves growing a balanced, highly nutritious pasture and preparing low worm pastures
for feeding weaners.
Sheep that are in good condition can tolerate heavier burdens of worms than sheep in poor condition. Also sheep in good condition develop immunity to worms at an earlier age than sheep in poor condtion therefore requiring less drenching.
Weaners are highly susceptible to parasites and should only have limited exposure. After drenching, weaners should be moved to low worm pasture with good feed. A low worm pasture is one that has only been grazed by adult dry sheep or cattle for the last 6 to 12 months, or has been cropped, cut for hay or is a new pasture.
Paddocks that have been grazed by ewes with lambs will be the most heavily contaminated pasture and should be avoided for grazing by weaners.
- It is important that farmers use drenches that are effective against the particular worms that are affecting their animals.
Resistance occurs in the following way:
Imagine a sheep had an infestation of 100 worms. After the first drenching, 95 worms were killed leaving 5 resistant worms to breed . These resistant worms then increase in number, so with subsequent drenchings greater and greater numbers of worms survive, all being resistant to the particular drench. For this reason, drenching needs to be strategic. This means the drench type must be changed to decrease the chance of resistance and must be timed to maximise effectiveness.
Increasing the frequency of drenching doesn't solve problems in the long run. Drenches are expensive chemicals that need to be used strategically to achieve the best result. NSW Agriculture
, Rural Lands Protection Boards and CSIRO have developed drenching
programs designed for various areas in NSW. Drenchplan, Wormkill and WestWorm are strategic worm control programs which aim
to control worms and save money, reduce chemical usage and delay the development of drench resistance. The CSIRO have a site providing information
about breeding for sustainable worm control .
There are a large number of drenches on the market which can be used to control internal parasites. Drenchplan, Wormkill and Westworm programs are based on using both broad and narrow-spectrum drenches.
Broad-spectrum drenches are able to control a variety of parasites while narrow-spectrum drenches are specifically for one type of parasite.
Drenchplan has been designed for use on the south-west slopes and climatically similar areas where black scour worm and brown stomach worm are the major parasites and barber's pole worm may be a problem in some years.
Wormkill has been designed for use on the northern tablelands of NSW and climatically similar areas where barber's pole worm and black scour worm are problems.
WestWorm and FarWestWorm have been designed to control sheep worms in non-irrigated areas of western NSW.
Lets take a more detailed look at Wormkill.
WORMKILL PROGRAM
| Month | Management | Lambs | Hoggets | Adults |
|---|---|---|---|---|
| Sept | Lambing: create first weaner paddock with cattle or dry sheep older than 24 months. | |||
| Oct | Marking | SEP | SEP | |
| Nov | Spell weaner paddock and move cattle or dry sheep to second weaner paddock. | |||
| Dec | Weaning: drench and move weaners OFF LAMBING PADDOCK to 1st weaner paddock. | BS and SEP | BS and SEP | BS and SEP |
| Jan | ||||
| Feb | Drench and move to second weaner paddock. | BS and SEP | SEP | SEP |
| March | ||||
| April | Drench and move again if possible. | BS | MON | |
| May | ||||
| June | MON | |||
| July | ||||
| Aug | BS |
BS = Broad-spectrum drench
SEP = Seponver, a narrow spectrum drench effective against barber's pole worm as well as late immature and mature liver fluke.
MON = Monitor sheep with a faecal egg count test and drench only on veterinary advice.
If fluke is also a problem them sheep should be drenched with Fasinex at Seponver drenching.
Wormkill is designed not just to de-worm sheep at the time of drenching, but to produce 'cleaner' pastures with respect to worms.
Two different types of drenches are used in Wormkill.
- Seponver - a narrow spectrum drench for barbers pole.
- A broad-spectrum drench - to control other important worms.
Four groups of broad-spectrum drenches are available:
- Benzimidazoles (BZ or white)
- Levamisole/Morantel (clear)
- Ivermectins (Ivomec)
- Combination (BZ and clear)
Worms in sheep develop resistance to ALL drenches.
Rotating to an effective broad-spectrum drench group on a yearly basis will delay the development of drench resistance.
To ensure that the drench is effective have a Faecal Egg Count Reduction Test (FECRT) carried out.
Do not put lambs or weaners onto the lambing paddock.
Grazing management is paramount to sustainable worm control. Move lambs and weaners to prepared 'low worm' pastures after drenching.
'Low worm' pastures can be prepared by grazing with cattle or ADULT DRY SHEEP OVER TWO YEARS OF AGE, by cropping, hay making or not
grazing at all.
Tips for making every drench count.
- Select a highly effective drench.
- Test the drench gun's accuracy.
- Use the recommended dose rate.
- Dose to the heaviest in the mob.
- Weigh the sheep so that the dose can be calculated accurately.
- Reduce feed before drenching to increase the drench effectiveness.
- Monitor sheep prior to drenching with an egg count.
- When drenching, place the drench gun over the tongue to increase effectiveness.
- Use grazing management.
The Wormkill program can be easily adjusted to accomodate a different lambing program, as the one above is designed to best suit a spring (September) lambing.
Activity
Integrated Pest Management (IPM) involves using a variety of control methods to control a problem organism. The control methods take into account the nature of the host organism, the problem organism and the environmental conditons that influence the incidence of the disease.
After reading through this work on controlling internal parasites in sheep, make a summary of the methods available for controlling the incidence of worms in sheep that could be used in an IPM program.
Now try Resistance in sheep internal parasites.
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