Organic Farming: Internal Parasites of Sheep

Note Number: AG1268
Published: December 2006

Introduction

Internal parasites are one of the most problematic animal health issues in sheep in southeastern Australia. Controlling internal parasites is particularly challenging in the high winter rainfall areas of southeastern Australia because of the moist conditions, increasing the survival period of free-living larvae on pasture. Conventional control practices for internal parasites rely heavily on chemical treatment that is prohibited in an organic farming system. Therefore organic farming systems must focus on preventative management. This may include the use of strategies such as grazing management, sheep management, breeding and monitoring.

For a general overview of the certification process and/or general information on the organic sheep industry in Australia, this agnote should be read in conjunction with ‘Organic Farming: The certification process’ and ‘Organic Farming: Prime Lamb Production’.

Organic Standards Requirements

The National Standard for Organic and Biodynamic Produce (2005) states that animal welfare is paramount and Commonwealth, State and Territory legislation requirements must be observed. Management practices should be developed to encourage the natural immunological defences of livestock. This can be achieved through the provision of adequate and high quality feed produced in accordance with the National Standard and the development of management practices that encourage the animal’s resistance to disease and the prevention of infections. The reliance on substances rather than management practices for control of pests and diseases is not in accordance with organic farming practices.

The use of treatments not in accordance with the standards, due to veterinary advice, results in extended withholding periods or loss of certification status (Table 1). Livestock treated with prohibited substances have to be quarantined from other stock for at least three times the withholding period or three weeks, which ever is longest. All treatments given to individual animals must be recorded so that full trace back can be achieved.

Table 1. Withholding periods and conditions for re certification of products after treatments.

(National Standard for Organic and Biodynamic Produce; 2005)

Internal Parasites

Figure 1. A typical life cycle of a round worm (Source: Larsen 1991).

The major gut parasites (roundworms) of sheep in Victoria include, Brown Stomach Worm (Ostertagia spp), Black Scour Worm (Trichostrongylus spp), Thin Necked Intestinal Worm (Nematodirus spp) and Barber’s Pole Worm (Haemonchus contortus). Although each major roundworm species affects sheep differently, they all have a similar lifecycle (Figure 1) that consists of a parasitic stage and a free-living larval stage.

The impact of internal parasites on sheep can range from being virtually undetectable, through to obvious clinical signs or even death. Heavy worm burdens can lead to scouring, anaemia, reduced or slower growth, poor production of milk and wool and poor carcass quality. Symptoms are often aggravated by periods of stress such as lambing (ewes), weaning (ewes and lambs) and poor nutrition (ewes and lambs).

Management Strategies

Infective third-stage worm larvae as found on blade of grass.

i.  Paddock Management

• Grazing susceptible sheep (eg. weaners and lambing ewes especially maiden ewes) on clean or low risk paddocks. These include:
• • crop stubbles
  • fodder crops
  • hay aftermath
  • new pastures
  • paddocks that have not been grazed
  • paddocks only grazed by cattle
  • paddocks grazed by dry sheep over two years old
  • paddocks that have been un-grazed since the autumn break and/or a minimum of 10 weeks.
• High-risk paddocks are those that have had lambing ewes, weaners, or maiden ewes on them since the previous summer.

• Infective third-stage worm larvae in paddock.

• Most larvae are found within two centimetres of the soil so erect pasture species may reduce larval intake and increase larval desiccation through drying out. Figure 2 shows parasite larvae on pasture.
• There is also some evidence that suggests that plants that contain condensed tannins can reduce worm egg counts. (eg. Chicory (Cichorium intybus), Plantain (Plantago lanceolata), Lotus (Lotus spp.) and Sulla (Hedysarum coronarium)).
• Dung beetles can have an important influence on parasite chances of survival. The dung beetles not only remove surface faecal matter, which is important for larvae survival in summer and winter, but they also consume parasite eggs and larvae.

ii.  Sheep Management

• Reduced stocking rates can reduce the density of eggs dropped on the pasture.
• Sheep that are well nourished (fat score 3) are less susceptible to worm infections and will cope with a higher worm burden.
• Providing adequate protein through forages, grain and/or protein meals to help boost the animals’ natural immunological defences.
• Selecting breeders with low faecal worm egg counts allows the farmer to increase the flock’s resistance to parasites. Breeder selection must be based on a number of faecal worm egg counts from the weaning stage and the adult stage including during lambing and lactation

iii.  Grazing Management

• Rotational or cell grazing will help reduce worm numbers on the pasture if the paddock is left ungrazed for a minimum of 10 weeks in autumn/winter.
• Cross grazing is where grazing is alternate between cattle and sheep. This strategy can be used because most worm species are host specific, although there are exceptions to this rule eg. Barbers Pole Worm. In this case adult cattle are preferable.
• Cross grazing applies to all species of livestock but not goats.

iv.  Monitoring

• Faecal worm egg counts are a useful guide to check the level of parasitism in sheep flocks or individuals. A faecal worm egg count is simply a count of the number of worm eggs present in one gram of sheep dung. The actual number at which worms become a problem varies with individual species. For example a faecal worm egg count of 300 eggs per gram is not significant for Barbers Pole Worm but would be significant for Black Scour Worm (AWI 2006). A larval culture may be needed to clarify the results.

There are two ways you can collect the faecal sample:

1. Freshly deposited dung off the ground (method commonly used for a mob sample). Sheep can be held in a corner of a paddock for 10 mins and then allowed to walk away. Then collect about ten random manure samples off the ground for analysis.

2. Directly from the rectum of the sheep using a gloved hand. This is the preferred method of sampling when wanting to identify individual samples eg. when worm resistance testing.

• Farmers can also do their own faecal worm egg counts, with commercially available worm egg counting kits. A laboratory microscope (hobby ones are not suitable), an egg-counting chamber, some beakers and mixing implements and a supply of saturated salt solution are required. For more information on this method, please see www.wormboss.com.au.
• Dag scores is a method that can be used easily to score a mob’s or an individual’s potential to have internal parasites. Dags can be scored on a 0 (no dags) to 5 (heavy dags) basis. This method is only recommended when used in conjunction with faecal egg count monitoring as production losses can occur before dags appear.

References

• Australian Wool Innovation (2006) 'Wormboss' http://www.wormboss.com.au/
• Laffan, J. (2000) Organic Farming: Livestock NSW Agriculture. CB Alexander Agriculture College, Tocal
• Larsen, J. (1991) ‘Wormplan – Managing drench resistance in your flock.’(Agmedia: Melbourne)
• Organic Produce Export Committee (2005). National Standard for Organic and Biodynamic Produce. Australia, AQIS. Organic Federation of Australia http://www.ofa.org.au/ 

Key Industry Contacts

Victorian parasite diagnostic service providers

Further Information

Organic Federation of Australia http://www.ofa.org.au/
PO Box Q455, QVB Post Office, Sydney NSW 1230
Ph: +61 2 9299 8016
Fax: +61 2 9299 0189
email: info@ofa.org.au

Wormboss http://www.wormboss.com.au/

Coleby, P. (2000) Healthy Sheep Naturally Landlinks Press, Australia.

Laffan, J. (2000) Organic Farming: Livestock NSW Agriculture. CB Alexander Agriculture College, Tocal.

Veale, T. 'Para-site Diagnostic Service' http://www.parasite.com.au/

Department of Primary Industries

Michelle Smith – Project Scientist
RMB 1145, Rutherglen VIC 3685
Ph: (02) 6030 4500
Fax: (02) 6030 4600
email: michelle.smith@dpi.vic.gov.au

Viv Burnett – Research Scientist, Organic Farming Systems
RMB 1145, Rutherglen VIC 3685
Ph: (02) 6030 4500
Fax: (02) 6030 4600
email: viv.burnett@dpi.vic.gov.au

Acknowledgments

We acknowledge the funding provided by the Naturally Victorian Initiative for the Organic Prime Lamb Project.

ISSN 1329-8062