horse sa horses, bugs and beetles fact sheet 4 "gut parasites and the threat of...

Horses: Bugs & BeetlesSustainable ways to keep your horse www.horsesa.asn.au

Horses, Bugs & BeetlesFact Sheet 4: Gut parasites of horses and the threat of resistance

Istock


Introduction

A looming and important problem is that gut parasites are rapidly developing resistance to the chemicals designed to kill them. If this continues, many current chemicals will become ineffective.

In this Fact Sheet we look at:

• ways to maintain horses’ natural immunity to parasites

• the emerging problem of resistance to chemicals used to control gut parasites

• the role of dung beetles in controlling gut parasites

• the biology of the major gut parasites of horses


Horses and their gut parasites have had millennia of co-evolution

Ongoing presence of low parasite burdens in the gut of the horse is considered essential to ‘prime’ the horse’s immune system

Most healthy horses can respond to a parasite challenge

However, this will depend on the intensity (and effectiveness) of

resistance to worms that and on the

type of gut parasite

Not all horses have such an efficient immune system

J. Raphael


Foals and young horses up to maturity are initially highly susceptible to gut parasites (they have low immunity)

Old and sick horses often have compromised immune systems that fail to control gut parasites

Young, sick and old horses need to be treated with veterinary chemicals

\

Madeline West


Is your horse a ‘shedder’?

Often in a group of horses there is a small number of individuals that have high worm burdens

These horses contribute the majority of the infective stages of the worms to the pastures.

These individual horses are called

‘shedders”

Shedders often remain susceptible throughout their life, so are best treated regularly or removed from the herd

Other horses in the group are best treated less frequently or not at all


Refugia

The gut worms in untreated horses are not exposed to the chemicals

Therefore, these worms do not have an

opportunity to develop resistance

This are a source of susceptible parasites

within a herd which slow or halt the

development of resistance in the parasite population as a whole.

These pockets of susceptible worms are sometimes called ‘refugia’.


Low level worm burdens

There is no need to keep your healthy, adult horses completely free from parasites.

Horses have evolved to cope with gut parasites and there is no evidence that low parasite burdens are harmful.

In fact, a low worm burden may be quite beneficial, promoting natural immunity

Stables & yards are usually mucked out

regularly

-the parasites will be removed from the stable before they reach the infective stage

Benson Park Trail Rides


The problem with gut worms

Heavy infestations of worms will make a horse very sick

Severe small-stronglye infestations will do damage, including where the larvae becomes encysted in the gut wall

The encysted larvae are not completely killed by many of the chemicals used to kill gut worms

This is another way that resistance to chemicals builds up

Very heavy worm burdens treated with chemicals, can cause a high number of worms to simultaneously release from the gut wall, leading to colic


How often should horses be treated for gut worms?

Conventional advice is every 6-8 weeks or at least twice a year

This advice is now out of date

Revised recommendations include

- Individualised treatment programs- Use of faecal egg counts- Good land management practices

Speak to your veterinarian about the latest research


Recognising that horses need treatment

A poor coat, listlessness, failure to thrive and colic are symptoms of a heavy worm burden

Faecal egg counts (FEC) of less that 200 eggs per gram is regarded as a ‘low’ and no further action is required

Encysted worms, tapeworms or worms at the life-cycle stage where eggs are not being laid will not be picked up in FEC’s.

FEC’s will pick up horses with high worm burdens requiring treatment, indicating which ones in a herd need veterinary chemicals

Top right: Ascarid eggRight: Stronglye eggPhotos: Adelaide Plains Equine Clinic


Collecting samples for a faecal egg count

1. Collect a manure ball from the top of a fresh pile.2. Seal in a snap-lock bag or suitable container3. Record horse/owner/date/contact details on the sample4. Put into the fridge until ready to take to the laboratory5. Complete any documentation required to accompany the sample


Madeline West

Slowing the development of resistance

• Read the labels on de-worming products

• Rotate product use

• Identify the ‘shedders’ on your property

• Ensure good nutrition

• Manage pastures to avoid overgrazing


Photo: Katie Wahlheim

Know which chemicals are likely to effect dung beetles


Pasture spelling and cross-grazing to help control gut worms

The infective stages of gut parasites arrive on the pasture as eggs in fresh horse manure

The eggs will hatch into larvae, but will die if no host is available

Larvae are host specific, therefore if a species other than horses graze the paddock, it can break the life cycle

Spelling pastures, so that no host is available, will also break the life cycle


Dung beetles to control gut worms

Dung beetles feed on the juices in dung and then bury it underground

When feeding, they take the infective stages of gut parasites with them

The manure pad is left shredded, dry and hostile to larvae

Therefore, combined with a grazing strategy which spells paddocks, dung beetles can significantly reduce the number of infective stages of gut worms which can be eaten by horses

Dung Beetle Solutions Australia


An integrated solution to promote natural immunity

Is it possible to promote natural immunity among horses and use other, non-chemical worm control measures to eliminate or limit the use of chemicals? As we have seen, parasite control is a tricky issue. We need to reassess the situation, and consider strong natural immunity to gut worms can help control most groups, but the small red worms do not provoke resistance to the same extent as do most other parasites.

• Pasture rotation, strip grazing and cross-grazing are effective ways to reduce parasite survival

• Dung burial by dung beetles can kill the infective stages of gut parasites

• Effective chemicals are available but resistance is developing rapidly

• Frequent use of imidazols has controlled large strongyles, and they are now rare

• Abandoning chemical control may allow large strongyles to re-emerge as a problem

• FECs -useful indicators of worm burdens, (but only strongyles and ascarids & not in all circumstances)

• Some animals (such as foals, and sick and old horses) have low levels of natural immunity and, unless treated chemically, can carry high worm burdens that contribute the majority of the infective stages to the pastures


A strategy for long-term parasite control (part 1)

• Use FECs to identify horses with high worm burdens (mostly foals and the old and sick)

• Target shedders with individual chemical treatment to control their parasites

• Avoid regular treatment of the majority of the horses in a group

• Use chemicals that are known to be effective against a particular target parasite

• Rotate chemicals

• Introduce summer and winter dung beetles

• Use beetle-friendly drenches/pastes

• Spell pastures by rotating horses between paddocks

• Graze sheep and/or cattle in horse paddocks to mop up horse-gut larvae

(cross-grazing)


A strategy for long-term parasite control (part 2)

Recognising shedders using their ‘condition’ and FECs should allow treating only the shedders in a healthy, well-managed group of horses.

This, in combination with pasture rotation and dung beetles, is likely to generate an environment in which gut parasites cease to be a serious problem


The benefits

A program that combines selective worming, rotating chemicals, pasture rotation, cross-grazing and dung beetles provide the following benefits:

• promotion of immunological control of gut parasites

• a major reduction in money spent on veterinary chemicals

• minimal selection for resistance to veterinary chemicals in the parasites

• prolonged availability (many years) of useful veterinary chemicals

• improved pasture due to non-selective grazing (promoted by rotational grazing) and dung beetles


Horses, Bugs & Beetles Fact Sheets 1 – 8 download from www.horsesa.asn.au

horse sa horses, bugs and beetles fact sheet 4 "gut parasites and the threat of...

Education

sick horses

old horses

healthy horses

young horses

group of horses

raphael horses

adult horses

untreated horses