by Elanco Animal Health

November 2017

 

Summer drenching is the cornerstone of effective worm control in southern Australia¹.

For a summer drench program to work it must be done at the right time with the right drench.

The right drench is a drench that kills greater than 98%¹ of worms. Using a less effective drench will not only reduce worm control, it will also increase the development of resistance.

Zolvix Plus (a new combination drench containing monepantel and abamectin) was launched by Elanco Animal Health in March of this year, so is now available to be used as a summer drench for the very first time.  Zolvix Plus can deliver high-level broad-spectrum efficacy^2,3 regardless of existing resistance status to other drench classes^3,4, making this product well suited for this purpose.

In the winter dominant rainfall areas of southern Australia, the main production limiting worms are the black scour worm (Trichostrongylus spp) and the brown stomach worm (Teladorsagia spp). These two worms mainly cause problems from a few weeks after the autumn break to the middle of October when worms again become less available on the pasture.

The worm larvae on pasture during autumn and winter predominantly come from the eggs deposited in faeces in the previous spring and summer⁵.  The key to controlling the rise in winter worm counts is therefore to control egg deposition through summer.

When to summer drench?

Historically, two summer drenches were commonly recommended regardless of seasonal variation. Over the last 10–15 years, however, advisors have modified the program to increase its effectiveness and minimise the development of drench resistance.

The exact timing of the first summer drench will vary depending on the local conditions. Usually the ideal time to give the first summer drench is when the pasture is ‘haying off’, which may coincide with weaning in a spring lambing flock.

A second summer drench should only be given if required.  This may be due, for example, to pick up of worms after summer rain or if the first summer drench has been less than fully effective.

Worm egg count monitoring should be undertaken from about six weeks after the first summer drench. If egg counts exceed 80–100 epg, then a second summer drench would be recommended¹.  

Table 1: National summary of drench resistance tests conducted in 2009–2012 indicating the percentage of properties with evidence of resistance (i.e. differentiated faecal egg count reduction <95% reduction) to white, clear and macrocyclic lactone drenches and their combinations in Australian sheep flocks.⁶

Active Ingredient	Brown stomach worm % Properties	Black scour worm % Properties	Barbers pole worm % Properties	Any worm* % Properties
BZ	88	87	75	96
LEV	82	86	30	96
IVM	76	31	74	87
ABA	49	25	83	77
MOX	38	14	52	54
BZ/LEV	79	48	19	81
BZ/LEV/IVM	27	20	11	35
BZ/LEV/ABA	22	6	14	28

Which drench?

A summer drench needs to be highly effective (>98% effective), as even a low level worm egg count across summer may result in a winter worm disaster.

Even slight decreases in efficacy may amount to very large differences in pasture contamination.

Increasing levels of drench resistance may adversely affect the success of a summer drench program in adequately preventing autumn and winter worm problems.

If you haven't carried out a resistance test in the last 2–3 years¹ and you don’t know your own drench resistance status, it is worth considering the data from a recent national drench resistance survey. This survey found widespread resistance to white, clear and macrocyclic lactone (‘mectin’ or ML) drenches and their combinations in Australian sheep flocks⁶ (Table 1), and emphasises the need to check which drenches work on your property.  

Why integrate Zolvix Plus into a summer drench program?

New drenches should be incorporated into drench programs in a way that helps to preserve the efficacy of existing active ingredients while maintaining productivity⁶.

Zolvix Plus is ideal as a first summer drench as it is able to deliver high-level broad-spectrum efficacy^2,3 regardless of existing resistance status to other drench classes^3,4, minimising egg deposition through summer and providing a solid foundation for effective worm control in the following autumn and winter.

Image: Zolvix Plus, from Elanco Animal Health.
Always read and follow label directions before use. 

References:

1. http://www.wormboss.com.au/programs/sheep.php 

2. Hosking, B.C. et al. (2010). A pooled analysis of the efficacy of monepantel, an aminoacetonitrile derivative against gastrointestinal nematodes of sheep. Parasitol Res 106:529-532.  

3. Refer to registered label. 

4. Baker, K.E. et al. (2012). Efficacy of monepantel and anthelmintic combinations against multiple-resistant Haemonchus contortus in sheep, including characterisation of the nematode isolate. Vet Parasitol 186(3-4): 513-7.  

5. Anderson, N. (1983). The availability of Trichostrongylid larvae to grazing sheep after seasonal contamination of pastures. Aust J Agric Res 34:583–592.  

6. Playford, M.C. et al. 2014. Prevalence and severity of anthelmintic resistance in ovine gastrointestinal nematodes in Australia (2009-2012). Aust Vet J 92: 464-471.