Drench Resistance in Merinos

August 2008
A predicted annual wool loss of $1.2million in the Merino and $1million in the Mid Micron sectors through drench resistance alone has been highlighted by the S cubed Project - an exploration into sustainable parasite management.

It is a significant loss to industry and does not take into account the additional loss in animal performance and labour costs, and is simply due to farmers using an ineffective drench.

The S cubed Project was initiated by a small number of industry individuals and a group of elite merino and mid-micron breeders. The strength of the project is that it is farmer driven research, for farmers.

All farms are unique and should be treated as such said Dr Jon Hickford of Lincoln University, Each property operates under different management with different stock types, pastures and climate differences not to mention drench status and parasite species mix. All of these combine to create a completely unique situation, he said.

The project established some very clear recommendations for industry and provided some take home tools for farmers to utilise in their parasite management.

Key points made at the field day

o Each property is unique understand what is happening on your own farming operation.

o Seek quality advice

o Use effective drenches know what works

o Quarantine your property manage your risk and dont import someone elses problems

o Farmers need to use all tools available - such as FEC, condition score and weight to assist in timing drench treatments to limit contamination and assist production

o Utilise genetics select rams that are highly productive and more resistant to parasites

o Do not assume that dag score is representative of the level of FEC (faecal egg count)

Of the 37 merino and mid-micron breeder farmers who participated in the project, 45% were found to be using drench that was later proven to be ineffective and none had an effective quarantine protocol in place at the commencement of the project. It is felt that the project highlighted that an effective quarantine protocol is a fundamental component in protecting the drench resistance status of a property.

The data collected through the project also revealed that within a mob of animals approximately 13% of the animals contribute 50% of the egg output contamination. This information provides breeders and commercial farmers with an additional means to managing parasites by identifying and removing those animals causing the bulk of the contamination.

The project hopes to highlight the fact that there is a toolbox of parasite management tools available to farmers, and that its just a matter of farmers learning to use the right tools at the right times dependent on the individual property situation.


S3 is a project that brings together two sectors of the sheep breeding industry that views the sustainable management of parasites critical to their and their commercial clients futures.

The project does not focus on a single element of parasite management but instead addresses the synergy between sustainable parasite management, breeding for resistance and property bio-security, to enhance farming operations.

The S3 Project is quite unique in its approach, by bringing together a consortium of participants, a variety of expertise and an inclusive approach to working on solutions for industry.

The project has been designed for the farmer participants to get a better understanding of the unique parasite status of their property. This includes identifying the propertys drench resistance status, identifying the parasite species present on a property at particular times of year, and examining the relationship between parasite levels, sire line, weaning weight, weight at 7-8 months, dag score, and DNA footrot status.

The project will then report the overall results to industry, record the parasite resistant sire lines on SIL and Lambplan and look to benchmark drenching practices across all project participants. Robust quarantine protocols have been established to safe guard the commercial clients of these elite breeders against the transfer of resistance parasites

between properties.

The development of these best practice protocols will then be transferred through the industry for wider adoption among all farmers.

Farm Analysis Reports have been produced to provide each farmer participant with an overview of their property and identify areas to assist in the management of the parasite component of their breeding operations.

Project Parameters what we did?

The S3 Project reviewed various approaches to parasite management; the areas that were reviewed are detailed below:

FECRT Faecal Egg Count Reduction Test

The test we used to determine the drench resistance status for sheep drenches on the project properties is called a Faecal Egg Count Reduction Test (FECRT). This test is based around the fact that when parasites are first ingested by grazing animals, it will take 18 - 21 days before it is able to produce eggs and betray its presence.

Put another way, if a fully effective drench treatment has been administered, the earliest we would expect to see eggs in faecal samples is 18 - 21 days later. If we drench accurately and then see eggs in samples 10 days post-treatment, then this is normally accepted as evidence that some worms have survived the treatment, i.e. the drench is not working properly.

FECRT tests are normally expressed as the percentage reduction in eggs counted between the pre and post-drench (10 days) periods. A treatment that is 100% successful would result in all worms being killed and egg counts at day 10 would be 0. In this case, the reduction would be 100%. In other words the higher the percentage (%) figure the better the drug is performing.

Quarantine Protocols

Irrespective of which drenches you select and how you use them, if you fail to adequately quarantine drench all stock as they leave or enter the property you run the risk of exporting or importing drench resistance. If adequate quarantine procedures are put in place on your property, you can protect your propertys present drench resistance status and provide other farmers confidence, when they transfer stock from your property, that they are not importing any drench resistance problems.

Growth Rate per Day

Growth Rate per Day is a measurement of an animals live weight growth over a period of time and can provide information to determine if animals are growing at desired levels.

To obtain a growth rate per day figure for a mob, first calculate the average weight at one point in time and average weight at another point in time. The difference in grams between the two weights is then divided by the number of days between the two periods. This then calculates the Growth Rate per Day.

Within the project, the average weights at Round One were calculated with the average weights at Round Two. Remember: Gut fill can significantly affect the live weight of an animal. Ensure that weighing at each point is undertaken with similar gut fills.

Dag Score

Along with individual FECs, dag scores were recorded to determine if there was any relationship between the dag score and the FEC level. Many farmers base treatment decisions around dag scores or the visual appearance of dags, however high parasite levels may not always be the cause of daggy animals.

A variety of reasons can cause animals to be daggy such as a change in feed or access to water. In this report the average FEC count within a Dag score Rating Group has been presented, ie for all animals with a dag score of 4 the average FEC count was calculated and presented in the table. No significant relationship between dag score rating and FEC level was identified through reviewing all participants data.

It is important to note that when selecting animals for breeding, the inference that a daggy animal has a high infestation of parasites can not be made. Dag score is not a reliable indicator of parasite challenge in animals.

FEC/Weight Relationship

Farmers ideally require animals that can demonstrate high liveweight gain performance, yet shed few eggs onto pasture (are resistant). For example the heaviest animal in the mob may carry a high parasite burden (i.e. a high FEC contaminator).

Although these animals growth may not be affected by the parasite challenge, their high FEC output will have a detrimental affect on subsequent animals grazing these paddocks.

From a mob perspective, the most advantageous animals to breed from are those that have high growth weights and carry low FEC levels.

By utilising the individual data collected for both weight and FEC levels, animals within a mob that are above average weight and have low FEC counts have been identified. It is recommended to make selection decisions when animals are six months of age or older, as the animals natural immunity will be expressed at this time.

Results from round two have been used to identify the top 20 animals within the mob using these two selection criteria.

Cost of Production

Cost of Production information can be used in a variety of ways within a farming operation such as:

To compare Drench Spend from one year to the next, assisting in measuring financial performance within an operation or to identify areas where costs could be minimised within an operation

To identify any financial loss or gain through changing a treatment within an operation (i.e. the loss incurred by using an ineffective drench)

To provide a basic understanding of what the drenching programme is costing per animal

Cost of Production data has been generated through the processing of drench usage data (Farm Survey) and the application of set average prices to the cost of each drench treatment. This enables the cross-comparison of all project participants to demonstrate what the project farmers spend in relation to others in the project.

Information regarding the cost of other drench selections is also supplied to enable clear comparison of other treatment options available, so as not to ignore the cost of treating when making selection decisions.

While all drench options are presented in the table it is important to refer to the FECRT Results to identify which drench types are effective options on a property, as an inexpensive drench is not inexpensive if it does not work.

Other things to consider that affect drench spend, may be frequency of treatments, type of treatment applied, the resistance status of the property and strategic drenching policies.

This section only takes into account the cost of the drench treatment and does not account for costs relating to time, labour, or loss of production caused by the use of an ineffective drench.

Best Practice Drench Usage Strategies

The key here is simple: use an effective drench, administer it correctly and monitor parasite levels to know when the timing is right.

The following are some guidelines for effective drench use:

Drench Selection

Select a drench active that is proven to be effective on the property (FECRT Report)

Select a drench product that is suited to the relevant situation ie short withhold period for works lambs, quarantine drenching

Drench Product

Ensure the product you are purchasing is within its expiry date

Shake thoroughly and follow all instructions on the label

Store product safely and out of direct sunlight

Check if the product is more or less effective on a full or empty gut

Drenching Equipment

Check the drench gun is clean and operating correctly

Undertake a gun dose check by setting the dose correctly and squeezing 5 doses into an accurate measuring cylinder. The 5 doses should equal the combined total of 5 individual doses

Repeat this procedure prior to any drenching activity or each hour of a drenching activity

Drenching Technique

Weigh some of the heaviest animals in the mob and set the gun dosage to the heaviest weight

If there is a wide weight variation in the mob, it is possible to draft (over scales) off a heavier and lighter line, and treat each line at a different dose rate

Place the gun nozzle over the back of the tongue and squeeze gently. Do not squirt the drench with

force as this action can trigger an oesophageal grove reflex causing the drench to bypass the rumen

which can reduce efficacy

Using a drench identification marker (Spotchek) can also help to eliminate repeat or missed dosing

Timing your Drench Treatments

Parasite challenge is heavily influenced by seasonal factors, so as a result we can expect the timing of a worm challenge to vary within and between seasons. Other factors also impact the parasite challenge an animal may face, such as the age of the animals, nutrition, or a management event (shearing).

The production impacts of parasites in an animal are often sub-clinical with no visual signs of challenge being exhibited. Along with body condition scoring, regular FEC monitoring of animals can indicate rising parasite levels before they start to impact an animals performance.

By getting the timing of your treatments right you can:

Stop any production losses due to parasites

Limit pasture contamination

Only use drench when a parasite problem exists