Cattle and their Parasites

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Herd of Calves

By Greg Mirams

Tue 13 October 2015


For the past 40 years New Zealand cattle farmers have relied on highly effective anthelmintic treatments to minimise the impact of parasites on their production systems. This investment is approximately $50 million annually. The key point is that after 40+ years of applying these treatments - in a hypothetical situation, if we were to stop drenching our cattle, parasites would quickly destroy the cattle (beef and dairy) industry. Thankfully this scenario is not likely to occur, however it indicates that as an industry, we have never really come to grips with the fact that our drench treatments are little more than a stopgap measure - they certainly play a major role in addressing the problem but they are NOT a cure. When examining this issue, it is not hard to see why this is the case, as 95% of the parasite population are on the ground - a mere 5% are in the animal.

Drench treatments vary in their formulation and efficacy. But generally they will kill most parasites for 3-14 days and prevent egg contamination for approximately 21 - 30 days (assuming they are working). So if you look at a mob of calves on a farm over a year - from a pasture contamination perspective - an effective 4 treatment drench program would prevent eggs being passed on to the farm for a maximum of 120 days, which still leaves 245 days that those calves have the potential to pollute pasture. This highlights the point that farmers will continue to invest millions of dollars every year in a drench reliant approach that is unlikely to ever change the parasite challenge, even though evidence suggests we will continue to lose many of the drench options (through drench resistance) that currently support the industry.

The key components of the issue:

Climate Change (weather patterns)

The dynamics of parasite populations will alter according to changing weather patterns. The result is parasite problems can appear in cattle outside the ‘expected’ risk periods.

Management Systems

Farmers have intensified their cattle operations on relatively small areas of land (from specialised heifer rearing properties in the dairy industry, to intensive bull beef farms). This intensification and mono culturing of animal species, creates the ideal environment for worm populations to thrive.

Drench/ Treatment Failure

Problems with drench failure are developing in the cattle industry similar to the experiences of the sheep industry. The factors that can contribute to drench failure can be wide and varied.

Treatment failure is not a simplistic problem. It can be caused by a number of factors (drench resistance, drench application error and simply drug inefficacy).

Cattle parasites and drench selection

In New Zealand, the predominant parasite in calves under 9 months of age is Cooperia. Many of the most commonly used 3-ML cattle drenches have a poor efficiency against Cooperia, so knowing what parasite species are present, and choosing the appropriate drench is the most effective approach to deal with a parasite problem. Some of the commonly used cattle drenches do not effectively deal with hibernated (inhibited) stages of the parasites, so appropriate drench selection is important when treating older animals.

Consumer/Government Influence

Meat processors ‘best practice’ incentives are now becoming common in some beef supply chains. In 1999 the Danish government outlawed anthelmintic use unless disease is diagnosed; over the years more northern European counties have followed suit.

Brown Bull in a paddock

Traditional inadequate testing systems

In order to manage a problem it is essential to be able to monitor and diagnose it. The industry has used and generally discarded a faecal egg counting (FEC) method developed in the 1950's - this method provides a test sensitivity of either 50 or 100 epg (eggs per gram). Evidence suggests that cattle can be negatively affected by parasites at greater than 100 epg; meanwhile, the traditional method of FEC is simply not suitable to provide accurate and meaningful results in particular when being used to check if a drench treatment has been effective. There are however systems and methods (FECPAK & modified Lab systems) available that provide greater sensitivity (10 epg). These systems have been independently evaluated and are well proven as a valuable tool in the field.

Like many diagnostic tests, FEC testing cattle also has its limitations. Some cattle parasites go through periods of hibernation (Ostertagia) when the egg laying females ‘park up’ in the gut lining and stop laying eggs for a period of time (winter). As a result, they are not detected in a FEC test. Another limitation of FEC in cattle is when testing older cattle. As cattle age, they develop a stronger immunity to parasites. One effect of a stronger immune response is the suppression of the egg production of female parasites, which can impact the accuracy of a FEC (calves are not affected by this issue). When understood, these issues do not mean FEC testing cattle is not valuable, the issues simply need to be understood and FEC results appropriately interpreted. In summary, FEC testing with a sensitive method is a highly effective management tool in animals under 18 months of age (main parasite challenge period).


The definition of ‘management’ is planning, implementation and control; so in order to achieve successful worm management farmers will need to address all these components. Recipe programs based on one drench type need to be replaced with drenches being chosen based on a ‘fitness for purpose’ approach.

For example:
  • Know the worm species present (animal’s age, time of year etc.)
  • Use a drench suited to the task
  • Monitor the results
  • The drench choice must be cost effective and practical
  • Strategic drench timing, based on information (FEC monitoring and animal performance) - not calendar based

In order to control parasites in the future, farmers will need to know the ‘enemy’. This is achieved by isolating each section of the parasite problem, understanding how it interrelates, and formulating an approach that is timely, targeted and future proofed.

© Techion Group Ltd 2015


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