Written by Dr Hanré Ferreira, Afrivet
In some parts of the country summer is present all year round. Producers in these areas know that they need to look out for worms throughout ithe year, especially wireworm. This is of even greater importance in areas where it is warm, where its rains or where irrigation is used. In colder parts of the country worms are not a problem in winter.
Wireworm larvae can withstand extreme cold. Because the larvae cannot feed, they die once their stored energy reserves are depleted. However, they use much less energy in winter than in summer when they are more active. This means the larvae stay alive longer during winter.
The larvae usually die after six months on grazing, although some can survive for longer than a year, even in snow. Dry, warm conditions with temperatures above 35°C will cause most larvae to die within two months.
Beware of spring infestations
There is no safe level of larvae infestation on grazing in winter and early spring. Even in winter and spring sheep can become infested with larvae from the previous wireworm season.
As such, sheep can already be infested in winter and early spring with larvae that survived on the grazing. If temperatures rise and it rains, the surviving eggs will again release infected larvae.
This has been seen in egg counts done throughout South Africa. Certain animals continuously excrete worm eggs, even in winter, while the counts of others increase rapidly after winter.
The dormancy phase of wireworm larvae in a sheep’s tissue also plays a role in early spring. It is speculated that when larvae undergoing hypobiosis are ingested in winter, they are reactivated as soon as conditions as well as the sheep’s nutritional levels improve.
For effective control, producers should get their plans and actions in place prior to the typical wireworm season.
Administration of Wirevax G4200, a vaccine that establishes immunity against wireworm in the sheep and reduces grazing infestation by 80 to 90%, must start before the season commences.
Management aspects for wireworm control in spring and the approaching wireworm season include:
- A wireworm programme that is adjusted regularly to keep up with seasonal differences. A herd immunised against wireworm with Wirevax will require significantly less dosages, while sheep that have not been immunised will need to be dosed more often. Monitor your flock and adjust your programme accordingly.
- A grazing management programme that will ensure a lower risk of infestation in camps. Rest the camps long enough and bear in mind that it relates to temperature and moisture. Rotate the grazing with cattle or horses. Sheep immunised with Wirevax excrete 80 to 90% less eggs.
- Place newly purchased sheep or goats in quarantine. This will reduce the risk of buying in resistant worms. Dose the animals with a new generation dewormer that contains derquantel or monepantel. Perform egg counts on the animals before they are allowed into the flock. If your flock was immunised with Wirevax, it is advisable to also immunise these animals to build their immunity and reduce the chance of resistant worms spreading.
- Dose for the right parasite at the right time. A liver fluke infestation can be confused with a wireworm infestation if you focus only on bottle jaw and the mucous membrane of the eye. Perform worm egg counts and post mortems if mortalities occur.
- Use effective anthelmintics. Perform faecal egg count reduction tests to determine whether the drug you are using is still effective.
- Only dose animals that really need dosing. Use the Famacha system to this effect. Cull animals that need dosages constantly or early in the season. Select for hardy animals in this way.
- Stimulate animals’ immune system to reduce wireworm infestation by using the wireworm vaccine. The importance of trace elements and minerals must also be considered for a healthy immune system. Zinc and selenium are especially important for any immune reaction. Oral supplements such as Ovimin (V24722) are easy to administer in sheep.
The wireworm vaccine has been used in Australia since 2014 and in South Africa since 2016. It is important that the vaccine is administered correctly. Stick to the prescribed immunisation schedule.
For more information, contact the nearest veterinarian or Afrivet agent, or download the Wirevax app. Phone Afrivet on 012 817 9060 or visit www.afrivet.co.za.