Should we be concerned about external parasites?

Dr George Cox

Why should we be concerned about external parasites?

A parasite is an organism that lives in or on another organism (our cow, sheep, goat, pig, horse, chicken and even our selves) and benefits by deriving nutrients (and protection) at the other’s expense. The parasite exploits and gives nothing in return except for disease!

Using the tick as an example:

  • It needs blood from the animal (up to 3ml per tick)
  • With the blood the animal looses protein and other nutrients
  • The animal becomes anaemic and debilitated and more susceptible to disease
  • Due to their long mouthparts penetrating the skin they cause abscesses that can lead to maggot infestations
  • The hide damage reduces the value of the hide
  • The milk production drops, their calves don’t grow as they should
  • They transmit diseases like Heartwater, Anaplasmosis and Redwater

External parasites therefore steal from us and give back nothing in return!

What other important external parasites do we have to manage?

Although ticks inflict the most harm on our animals we dare not underestimate the importance of lice, mites, flies, midges and mosquitoes!

Lice are visible to the naked eye (2-5 mm), chews through the outer layer of the skin and lives from the leaking protein rich serum. Animals itch and stops eating, scratching against trees and poles in an effort to try and rid themselves from the pests. They become more susceptible to disease and the hides again become useless to the leather industry!

Biting flies can transmit anaplasmosis (tick borne gallsickness) and fly worry can force them to stop eating. Midges and mosquitoes transmit diseases like blue tongue and rift valley fever.

How then do I control external parasites on cattle?

We can fortunately see most of the important parasites and that makes them easier to control. We should however never attempt to eradicate ticks but our aim should be to manage them.

Calves are borne with a natural immunity to most of the tick borne diseases. They need infected ticks to bite them to ensure continued immunity and therefore calves should only be dipped when they have excessive tick burdens.

To ensure that they retain their immunity against tick borne disease adults should also have limited exposure to ticks. Dip them when you count 15 – 30 engorged female ticks on one side of 10% of the herd.

Animals affected by fly worry will stand in a circle, heads lowered and pushed in under the bodies of the other cattle with tails swishing continuously. Using products that contain pyrethroids will help you to control flies, midges and mosquitoes.

When should I start to dip?

Parasites survive the winter on our animals. Dipping at least once during the winter will ensure that we start the following summer with fewer parasites. This should be followed by dipping early in spring, 2 – 3 weeks after the first rain (heat and moisture is needed for the eggs to hatch) to ensure that the first generation does not survive to reproduce and this will prevent uncontrollable numbers later in summer

How do I identify parasitised animals?

Cattle suffering from external parasites :

  • Eat less
  • Grow slower
  • Are more diseased – increased outbreaks due to lower immunity
  • Produce fewer calves (calving % down)
  • Produce weaker calves
  • Produce low quality colostrum
  • And Produce less milk
Principles of external parasite control? 

Principle number one:
Start dipping early in the season
Principle number two:
Use the appropriate dip in the recommended way
Principle number three:
Dip to control, not to eradicate

Because every farm differs in climate, vegetation and soil conditions we recommend that you contact your local Veterinarian, animal extention officer or local Zoetis professional representative to tailor a control program for your specific farm.

Disclaimer: Zoetis takes no responsibility for any claims that may arise from information contained in this information sheet. Individual situations may vary from location to location and it is recommended that you consult your veterinarian before any management or treatment decisions are implemented.

Vrywaring: Zoetis neem geen verantwoordelikheid vir enige eise wat mag voortspruit uit inligting vervat in hierdie inligtingsdokument. Individuele situasies varieer van plek tot plek en dit word voorgestel dat u eers u veearts kontak alvorens enige bestuurs- of behandelingsbesluite geïmplementeer word.