Internal Parasites Such as Worms and Coccidiosis

Overview

Internal parasites such as worms and coccidiosis can cause significant production losses in North Coast regions, particularly in cattle under two years old.  Signs can include poor body condition or failure to gain weight, scouring, anaemia and a dull, harsh hair coat.  Severe cases can progress to bottle jaw (swelling under the jaw), weakness, recumbency and eventually death.

The main species of concern in the North Coast reason are small brown stomach worm (ostertagia), barbers pole worm (haemonchus), and small intestinal worm (cooperia).  Younger cattle, particularly weaners in confined conditions, are at the highest risk, with animals over two years old usually developing a good immunity to worms.  Bulls can be the exception for worm resistance, and can carry high worm burdens throughout their life.

Reducing parasite burdens within cattle and on pasture results in increased weight gain in grower operations, and improved reproductive performance in breeding enterprises.

Life cycle

Intestinal roundworms have a simple direct life cycle, meaning they spend the reproductive period of their lives within a host animal, and the “growth” phase of their life free living in dung and on pasture.

The combination of a mild climate with minimal temperature extremes and high rainfall on the North Coast create perfect conditions for worm larvae to survive for extended periods on pastures.

Control

Control has traditionally focussed on chemical “drenches” to kill worms, but utilisation of pasture management, rotational strategies, and breed selection in combination with chemical control is the key to long-term sustainable worm control.

Drenching

It is important when utilising chemical control for worms in cattle to observe the ACTIVE INGREDIENT instead of just the trade name.  The active ingredient is always listed on the label, usually under the trade name.

Drenches for cattle can be divided into three classes:

  • Macrocyclic Lactones (ML; names of active ingredients end with “-ectin”)
    • These are the most frequently used class of chemical due to ease of application (injectable or pour-on), wide range of effectiveness (they often cover ectoparasites such as flies and ticks as well as internal parasites), and extended efficacy.
    • However they are expensive, and there is potentially emerging resistance to this class of chemical across northern NSW.
  • Benzimidizole (BZ or “white” drenches; names of active ingredients end with “-zole”)
    • The BZ drenches are significantly cheaper than ML drenches, and often more effective against the economically significant worm species in our region.  However they are only available as oral drenches, requiring increased labour inputs for treatment.  There is some reported resistance within this class of drench.
  • Levamisole (Lev or “clear” drench)
    • Highly effective against cooperia, and some (off-label) effectiveness against stomach fluke.  Predominantly oral formulation, there is one pour-on combination version available.

Drenching programs should focus on young cattle up to around 18 months old, with treatment of adult cattle only on an as-needed basis when symptomatic.  Breakdowns in adult immunity tend to occur secondary to stressful events such as drought, nutritional deficiencies, calving, and occasionally in breeding bulls.  There is little evidence to support routine drenching of adult cattle, and it is only of economic benefit in symptomatic animals.

Ineffective drenching is a common occurrence, and it is important to differentiate this from true drench resistance in worm populations.  Ineffective drenching can occur when animals are treated with short-acting products and then immediately returned to heavily infested paddocks, or when they are dosed at sub-lethal levels

  • when weight is misjudged and animals are under-dosed
  • rain occurs soon after a pour-on product is applied
  • animals have dirty/dusty coat when pour-on products are applied

True resistance is when the worm population develops genetic resistance to the chemical active ingredient in the drench product, and will survive treatment despite appropriate dosing and application of product.  It is important to differentiate true resistance from rapid reinfestation. Risk factors which select for resistant survivors within a worm population include

  • Frequent drenching (especially without rotating drench type)
  • Long-acting formulations
  • Sub-lethal doses (under-dosing or the tail end of long-acting formulations)
  • Unnecessary drenching (treating animals who have a low worm burden, or drenching during periods unfavourable for worm survival)

Times when a drench is strongly recommended are at (and often again soon after) weaning, and a quarantine drench when new animals are brought onto the property.  It is important to ensure a quarantine drench is highly effective, and a drench with multiple actives from different classes is recommended for this.

It is also important to consider a drench’s effect on the dung beetle population of a property, as dung beetles are an important part of an integrated pest management strategy.

Worm Testing and strategic drenching

Strategic drenching is where worm testing is utilised to ensure animals are only treated when worm burdens are likely to be pathogenic (reducing production).  Strategic drenching targets high risk (usually young) cattle over lower risk animals.

Worm testing is a method to “measure” the likely worm burden in animals.  A number of faecal samples are taken from individuals or randomly from the mob, and the number of worm eggs per gram (epg ) are calculated.  This can assist in not only selecting when is an appropriate time to drench animals (“strategic drenching”), but can also be utilised for a “drench test” to ensure a drench has been effective (a drench is classed as having been effective if it kills >95% of worms).

Integrated Pest Management

Integrated Pest Management focuses on increasing animals’ resistance to worms, reducing larval challenge within the environment (creating “safe” pastures), combined with strategic drenching as-needed.

Animal Resistance Factors

  • Genetic selection
    • Worm resistance is heritable, so if possible select animals who consistently have lower WEC  for breeding
  • Nutrition
    • Well-nourished animals are able to develop better immunity to worms
  • Stress
    • Stressed animals are less able to resist worm infestation, and more likely to succumb to disease at lower worm levels.  Stress can be caused by poor nutrition, increased metabolic demands (growth, pregnancy, calving) as well as management (high stocking density) and environmental factors (cold weather, prolonged wet weather, drought)

  • “Safe” pastures can increase interval between chemical treatments by reducing exposure to infective larvae
    • Long rests (although in this area larvae can survive up to nine months on pasture, which is often an impractically long time to have pastures out of grazing rotation)
    • Hay or silage making removes large numbers of eggs and larvae, as well as making conditions unfavourable for survival of remaining parasites
    • Cropping rotation or newly established pastures reduce parasite burdens due to soil disturbance as well as the long period ungrazed while the crop or pasture establishes.
    • Graze “long” pastures – most worm larvae are low down near the ground, so overgrazing increases risk of larval ingestion.
    • Rotation with other species such as sheep or horses as these animals do not share worm species with cattle.
    • Rotation of high risk young animals with adult low risk cattle for six months can also be effective
    • Avoid returning drenched animals to “dirty” paddocks
    • Avoid constantly running young animals on the same paddocks year after year (Calf nurseries)

Coccidiosis

Coccidia are an opportunistic protozoal parasite that can cause bloody scouring, which can occasionally be severe and life-threatening but is more often mild to moderate yet limits growth of young stock.  The syndrome is very common in young cattle, especially weaners when yarded and stressed.  Prevention can be achieved by ensuring good quality nutrition and reducing overcrowding where possible.  Treatment can be in the form of coccidiostats in commercial feeds such as weaner pellets, or an oral product containing toltrazuril.  Worm egg counts usually include a count of coccidia.

For more information on identifying and controlling Internal parasites in your animals, please contact your North Coast Local Land Services District Veterinarian on 1300 795 299 or your local vet.