Friday, 30 June 2023
Gerrit Bezuidenhout
Increasing hairworm outbreaks in the past two seasons can be attributed to higher rainfall and greater resistance to existing treatments.
Dr Marthie Kleynhans, a partner at the Clocolan Veterinary Clinic, says a significant increase in Haemonchus contortus cases has led to growing resistance to treatments.
“At this stage, only a handful of products can effectively be used against hairworms,” she says. “And because of the pressure, farmers are forced to use them repeatedly. Eventually the hairworms develop resistance, and the only solution then is to use a contact killer.”
Sheep infected with hairworms are typically anaemic and have a protein deficiency. The active ingredient in normal treatments is carried by proteins, so they become less effective.
“Sheep are then treated with a contact killer, and two weeks later they are treated again with a contact killer that acts for longer. However, it is crucial to ensure that these animals are treated at the right time and with the correct dosage, especially lambs,” says Kleynhans.
“Farmers must ensure that the animals are not dehydrated or too thin because we have seen cases where sheep were treated early in the morning before they had drunk. Once these animals start drinking, it leads to side effects.”
Kleynhans says routine vaccinations should also be administered before dosing against hairworms to ensure the sheep’s immune system is strong.
Spread
Farmers should note that the transportation of infected animals can spread hairworms to other areas, she says. “The eggs are shed on pastures, consumed by other animals, and then the cycle repeats. Therefore, it is important that sheep taken to auctions, for example, are first dosed against hairworms to combat the spread of the parasite. The same applies to pasture management, where more sheep are kept on smaller pastures.”
Kleynhans says hairworm dosing is no longer conducted at specific times of the year. “Hairworms can occur at any time of the year. That is why I am a strong advocate for the FAMACHA system, where the flock is examined and sick animals are identified. Only these animals are then treated for hairworms.”
Kleynhans says there may be individuals within a flock that are less susceptible to hairworm infestation, and this genetic trait can be passed on. “A management programme, where ewes are selected based on their hairworm resistance and more susceptible ewes are culled, can provide long-term benefits compared to dosing susceptible animals up to three times a year.”
Nutrition also plays a significant role. “Sheep whose immune systems are stronger because they are free from stress caused by insufficient or incorrect feeding are less susceptible to hairworms. By ensuring the herd’s nutrition is correct, many other issues, including hairworm infestations, can be better managed.”
