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When ewes started showing signs of worms within weeks of their pre-lambing drench in September 2017, Murray Nielsen knew that the triple combination drench he had relied on for some years wasn’t doing the job anymore.  Murray came to a WormBoss presentation seeking solutions to this drench problem, but ultimately became a participant in the MLA-funded New England WormBoss Producer Demonstration Site, during which he has learned what’s involved in implementing a program to keep his ewes safe during lambing.

Murray runs superfine Merino ewes on his property, “Winterville”, 35 km north west of Guyra, with  wethers on a block a few kilometres away.

When Murray joined the WormBoss program, he was faced with two priority activities. The first was to find out how all drench groups were performing on his property and the second was to get the paddock contamination under control before next lambing.

In early 2018, Murray carried out a Drench Resistance Test to assess the efficacy of all drench groups. Following the WormBoss protocol, he tested levamisole, fenbendazole (BZ or white drenches), abamectin and moxidectin (macrocyclic lactones), closantel, naphthalophos, derquantel (only available in combination with abamectin) and monepantel.

Murray said, “The results were disappointing, though not surprising, considering the problems I had already experienced. But I now know that it’s a waste of money choosing the drenches I was previously using.”

By testing individual actives, the efficacy of various combinations could be predicted, which would be needed due to the severe levels of drench resistance.

Murray said, “Because the drenches that work for me can’t be mixed together, I sometimes need to do concurrent drenching—up the race with one drench, then up the race with the other drench to get a combination effect.”

Murray also tested the effectiveness of a long acting moxidectin injection. He used a primer drench of monepantel, derquantel and abamectin when the test group of weaners were injected, to be sure that all adult worms were killed.

“I worm tested again at 14, 28 and 40 days, and then weekly, I couldn’t believe there were barber's pole worm eggs in some of the samples from 40 days instead of after 3 months,” Murray said.

With Murray’s drench choices virtually limited to Monepantel, Derquantel plus abamectin and Naphthalophos, it was decided that Barbervax®—the barber’s pole worm vaccine—was also going to be needed so these drenches could be used as little as possible.

The next job was to prepare for the coming lambing—the time of year when he’d previously had the most problems.

If he could prepare a low worm-risk lambing paddock it would get the ewes through lambing and help to limit further worm problems. As the worms on Winterville were almost only barber’s pole (Haemonchus contortus) a grazing management strategy would be very effective, but there were going to be some challenges.

Firstly, most of the lambing paddocks had to be used during the preparation period, as there was a drought and he didn’t have cattle to cross graze in these paddocks. This meant the sheep needed to be free from worms, but how could that be done cost-effectively with the limited number of effective drenches?

“I started the Barbervax vaccinations in March, giving the first 3 primer injections about 2 weeks or so apart to build the immunity as quickly as possible and also to have them ready before lambing started. I also used the moxidectin long acting in the sheep that were grazing the lambing paddocks in autumn. Even though it only gave a short protection period, it covered an important time to prevent new contamination of the paddock before the cold weather set in, just to get things started,” Murray said.

For Murray and other producers in the coldest areas of New England, who typically lamb from September, the 6-month preparation period for the lambing paddock includes 4 very cold months: May–August, during which the daily maximum temperatures are almost always below 18°C—if they are not, it is typically too dry.

At these temperatures (or if it is dry) almost no barber’s pole worm eggs will hatch to larvae, which means Murray can allow wormy sheep onto the paddocks in those cold months without them re-contaminating the paddock.

This means the earlier two months—March and April—were his focus for paddock preparation, and the long acting moxidectin was useful for part of this period.

At the pre-lambing drench he used napthalophos and monepantel and successfully got through to lamb marking. Derquantel/abamectin were given a little later in conjunction with a Barbervax, but counts rose swiftly afterwards and it was found that the derquantel had not been as effective as hoped. 

For producers in a situation such as Murray’s, where drench resistance is very severe, frequent—at least monthly—worm testing is critical; Murray has been doing his own egg counts for years now. Sole reliance on drenches to combat worms is just not possible and a combination of strategies is essential to chip away at the worms from a number of angles.

Aside from paddock preparation and using the Barbervax vaccine, Murray is also breeding more worm resistant sheep, buying Merino rams with WEC ASBVs around -25 to -40.