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Worm burdens and treatment thresholds for goats


Source: Roundworm life cycle (wormboss.com.au)
Source: Roundworm life cycle (wormboss.com.au)

Why are worm burdens my burden?

Worms are a major health problem of goats in Australia. They constrain efficient goat production via production losses, clinical disease, cost of treatment, and death.

The most important internal parasites of goats in Australia are:

  • Haemonchus contortus (barber’s pole worm)
  • Trichostrongylus species (black scour worm)
  • Teladorsagia species (small brown stomach worm)
  • Fasciola hepatica (liver fluke)

Sheep and goats tend to share the same worms, Goats and cattle also share some worms.

How do worm eggs develop into infective larvae?

Most roundworms share a basic lifecycle moving between a Dung stage, Pasture stage and Host stage (Figure 1).

Generally, the eggs of roundworms are not tough and require a favourable set of conditions within a week (barber’s pole worms) or 3-4 weeks (black scour worms or brown stomach worms) of being deposited on pasture to successfully hatch into infective larvae.

Development of eggs into infective larvae requires moisture (approximately 10-15 mm of rain, or waterlogged areas combined with high humidity) and adequately warm temperatures between 10°C  to 30°C depending on the type of worms and region.

Progressive and consistent cold weather slows and stops the development of worm eggs to infective larvae on pasture.

Wormy winters

Unlike eggs, larvae can survive for many months, and generally speaking the colder the better. This means that frosts will not simply kill all worm larvae.

Worm burdens can become a risk to your stock during winter if proper management and treatment are not applied to prevent eggs from developing to infective larvae in autumn.

Understanding the lifecycle and preferred conditions for worms gives you the upper hand to undertake management strategies when heading into autumn to minimise wormy winters in your goats. Before choosing your strategy, it is important to understand the level of burden you are dealing with.

Determining burden

Good news! There are several practical tools that producers can use that can identify an emerging worm problem before visual signs appear. Once worm burden is understood, appropriate management strategies and treatments can be applied.

 

Test

Purpose

Frequency

Barber’s pole worm areas

Scour worm areas

Worm egg count (WEC)

Estimate the burden of adult worms in monitored animals or check overall status of a mob

Twice monthly in times of high worm pressure, 6-8 weekly over winter

Monthly to 8 weekly

FAMACHA score (requires training and an accredited chart)

Assesses an animal’s level of anaemia. Five colour scores are compared to the colour of mucus membranes inside the lower eyelid

Check score weekly during high worm-risk periods, and monthly during low worm-risk periods

Check score weekly to fortnightly in summer and autumn as warmer and wetter weather may result in barber’s pole worm burden

Body condition score (BCS)

Assesses the level of body fat as an indicator of general condition

Check BCS monthly

Check BCS monthly

Faecal consistency score

Assesses the wateriness of faeces as an indication of scour worms. Barber’s pole worms, however, cause constipation.

At the same time as checking FAMACHA score, check for watery scours (Faecal consistency score of 5)

Check scour score monthly

Treatment thresholds

The need to treat existing worm burdens in goats is best determined by WEC and larval egg cultures.

Worm egg count (epg*)

Treatment decision

0 – 100

Treatment with drench unlikely. Consider another worm test 4-6 weeks after significant rain, or before a ‘management event’ such as a summer drench, pre-kidding, or signs consistent with parasitism.

100 – 200

Consider another worm test 4-8 weeks after significant rain, or before a ‘management event’ (see above).

200 – 500 

Depending on prevailing weather conditions. Iffavourable, consider drenching. Otherwise repeat worm test in 4 weeks.

500 – 1000

Treatment with an effective drench will be required.

1000 – 2000

Production losses could be quite significant and clinical signs may be obvious.

2000+

Treating with a highly effective drench and moving stock to low-risk paddocks.

*strongyle eggs per gram of faeces (epg)


Treatment options

Treatment thresholds help provide you with an indication of what treatments are appropriate for the worm burden at a particular point in time. While we would like them to be binary, that is often not the case, and several other factors need to be considered. These include:

  • age of stock
  • metabolic condition of stock (i.e. pregnant, lactating, dry)
  • body score condition
  • nutrition
  • tactical value of drench

There are several drenches currently registered for use in goats in Australia. The legal use of products not registered for goats requires an off-label recommendation from your veterinarian. All worm treatments currently registered for goats in Australia will only remove the susceptible worms that are present in goats at the time of treatment.

Other management strategies that reduce the exposure of stock to worms and reduce the reliance for drenches include:

  • Grazing management strategies
  • Nutrition
  • Genetics

Remember to only drench when necessary!

 

For more information on worm control in goats, including the Drench Decision Guide, see WormBoss for goats.