Worms in Cattle

25 Sep, 2018

What to Drench? When to Drench? Which Drench?

By Dr Murray Grant

“A few simple rules can help the Cattle producer design an efficient and effective worm prevention strategy in your herd”

What to Drench?

There is no simple answer to the question of what cattle on the place require treatment for worms. My advice will vary from operation to operation depending on a number of factors:

  1. climate,
  2. type of pastures/production system,
  3. type / breed of cattle
  4. age profile of the herd
  5. desired level of risk management
  6. stocking rate

A basic rule accepted by most animal health advisers is that young cattle, cattle under nutritional stress, old cattle and working bulls are prone to developing production limiting (life threatening in some cases) worm burdens.

One thing that I’m certain of is that weaner cattle, in all but the most arid cattle producing areas, will benefit from treatment for worms.

Therefore fairly standard advice is to treat all weaner cattle that are to be retained on the property at least a couple of times through their first year.

Even in the extensively grazed properties in the semi arid zones, I believe the benefits of relieving young cattle of sub-clinical worm burdens (where the calves have worms but are showing no obvious outward signs) are very underrated. Anecdotally, treated calves haven’t been nearly as badly affected by nutritional stress or 3 day sickness compared with untreated weaner calves in these situations. I would like to see some good scientific investigation in this area.

Another fairy standard piece of advice for pasture based producers is to treat their first calving heifers generally prior to calving or marking time – which ever fits in with other management and health procedures the best.

It is also now generally understood that some sort of infestation of cattle worms is required for the animal to adequately develop a natural immunity to infestation. A balance therefore does have to be achieved between keeping the animal healthy and productive and overdoing it with the worm drench.

It is fairly settled amongst advisers that from their second calf on, pasture-fed cows do not require drenching for the benefit of their own health as they have built up a sufficient worm infestation resistance. This is true as long as they are not under nutritional/trace element stress where the old adage “unhappy host, happy parasite\” comes into play. In some instances, in pasture based systems with high stocking rates, there is a case (especially if the producer is risk adverse) for treating this class of stock purely for the purpose of preventing pasture contamination with worm eggs. Remember, that in these systems, stocking rate is still the key to a high gross margin for the enterprise.

There are two classes of stock often overlooked by producers:

Firstly, the old girls in the herd. Many times as a practising veterinarian I have seen 9-10 year old cows (yes, there are some in every herd) in real trouble due to worm infestation. These old cows lose their worm resistance and are just as susceptible as young cattle.

Secondly, the working bulls whose immune system will run down over the joining period. (a handy lesson for all those young bucks and buckeroos out there) It is therefore good practice to treat all the bulls prior to the joining period.

When to Drench?

Once we have decided which animals in the herd require drenching for worms the next thing to decide is when to drench.

Two general rules help us here:

  1. Production loss due to cattle worms must be prevented rather than treated after it has been allowed to occur!! Preventing disease rather than treating it is the key to any health program.
  2. Drenching should, whenever possible, fit in with other herd management / health procedures.

Following these two rules means that drenching of stock should follow a planned approach (strategic)

In my veterinary practice I had a number of clients who could only work their cattle in the weekends. By combining management and preventative health (including drenching) procedures generally we could show them how they could do all their cattle work in 4-6 weekends.

For example a common program in southern pasture based cow/calf systems is as follows

  • Drench weaners – endectocide e.g. Vetmec
  • 2nd 5/1 or 7/1 vacc weaners
  • Drench  + 5/1 the 1st calving heifers
  • Preg Test + 5/1 Cows
  • Trace element cows if necessary
  • Consider drenching cows if very high stocking rate, producer is risk adverse or fluke present (Vetmec F)
  • Consider lice treatment/prevention cows+  bulls if not drenched
  • Marking 5/1 or 7/1 calves
  • Consider drenching 1st calf heifers especially if not treated pre-calving
Joining (combined with above often)
  • Drench bulls
  • Check serving ability/reproductive soundness
Yearling Heifer/Steer management
  • Drench at least once more during winter / spring depending on calving time (spring or autumn)

Programs such as these, and there can be many variants for other production systems such as those up North, prevent worms in the herd ever becoming a problem. They are not based on waiting for the signs of a worm burden to show and then drenching, as by this stage, you will have already suffered significant production and economic loss.

The use of worm egg tests (faecal egg counts, FEC) are used by some producers to gauge the time and need for drenching. This is sometimes beneficial in young cattle; however the very low egg output of ostertagia, the main cattle worm, is on many occasions very low. Therefore in most cases, the FEC test is a very poor predictor of whether the cattle require drenching or not.

Remember, on the prevention line of things, strategies other than strategic worm drenching should also be employed. Such as:

      1. The most susceptible stock must, if possible, be placed on the least worm contaminated areas. After drenching the weaners or first calvers for instance if they can be placed on an area/paddock that has been grazed by sheep (or adult dry cattle) or cropped then reinfection can be prevented and the time until the next drench lengthened dramatically.
      2. Rotational grazing  of susceptible stock especially controlled so that the pasture is not grazed too low to the ground will help prevent worm burdens as the majority of the infective stage worm larvae are in the first 2-3 cm of the sward.
      3. Supplementary feeding of 1st calvers early on until the autumn or spring growth really gets going combined with really monitoring ‘after-calving body weight gain/loss’ over this period will not only ensure you get them back in calf quickly  (along with stocking rate the other “must\” in a profitable herd) but will help prevent worm burdens being a problem

Which Drench?

The rule to follow here when choosing a cattle worm drench is simple:

‘Use the most effective option at the lowest cost’

Chemvet Australia’s ‘direct to the farmer’ Vetmec range of products are high quality, very effective and low cost.

White Drenches

Whilst the white drench options (eg albendazole, fenbendazole etc) are still available and in many cases are still effective – having to give them orally often rules them out of the equation. The effectiveness of these drenches against ‘arrested’ ostertagia can also be problematic. These drenches (especially concentrated low volume options) are coming back into vogue as worm resistance fighters when used in combination with a more potent ML drench but that is another story.

’Mectin Drenches

Currently the most effective drenches are the macrocyclic lactones (ML’s) more commonly known as the ’mectin type of drench products. A well as treating worms (internal parasites) they are also effective against external parasites such as lice or ticks. Common products in this class include Ivermectin (eg Ivomec) Moxidectin (eg Cydectin), Doramectin (eg Dectomax) and Abamectin (eg Vetmec)

These products are mostly available in either the injectable or pour-on form.

As a general rule:

  1. If worms are the major issue I favor the injectable products.
  2. If lice are the major target then I tend to favor pour-on products

Whilst the various different “mectin” products have features that validly differentiate them from the others it is my opinion that at a producer level one could consider them all mostly equal in terms of effectiveness. As long as there is the accompanying customer service, professional backup and advice and prompt delivery the most cost effective in most cases could be considered the best option.

Liver Fluke

A complication to choice of drench is whether liver fluke is present in the herd to a sufficient level to be causing a problem.

My advice regarding liver fluke is to find out for sure and not just rely on “it looks like ‘flukey’ country I better treat for fluke” as this could be a costly assumption. If you feel fluke may be a problem take some faecal samples from cattle that were grazing the ‘flukey’ area over the early summer to autumn. Have this tested for fluke eggs. Alternatively seek feedback from the abattoirs or check the livers of sheep run over these areas when you kill them for the house or send them to the abattoirs.

If fluke is a problem use a product that includes a flukicide e.g. clorsulon.

A ’mectin product in combination with clorsulon such as Vetmec F is an ideal product to keep fluke in check on your property. If used at the times suggested in the above programs in the ‘when to drench section’ very effective fluke control will be achieved. There is an old adage: ‘that for effective fluke control drench during the 2 A’s’ ie April and August. Without writing reams on the scientific argument this advice mostly remains true.


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Blood Levels Vetmec