Trial – Eradication of lice in Merinos
Result:
All trial work done now results in no lice found after using a combination IGR OP chemical blend when using side nozzles for Merinos. Observations commonly involve a 12 month period of inspection after one application.
Object:
To establish the outcomes of using Electrodip on Merinos, against the sheep biting louse, Bovicola ovis.
Trial Location:
Property of Mr. Tony Matthews
Raetahi
Wanganui District NZ.
Trial Period:
20/8/1998 - 30/1/2000
Farm Details:
Area: 4,000 ha hill country
Average Annual Rainfall: 1200mm
Stock:
3000 Merino wethers (18.0 - 19.0 micron)
12,000 Romney ewes
1300 Fattening cattle
Background:
Merino wether hoggets are bought in from North Otago high country during September and farmed for wool on the trial property. The Merinos run separately from the Romney flock on the back country, above the winter snow line. Shearing is carried out in August using a cover comb due to severe climatic conditions. Heavy infestations of the sheep biting louse, Bovicola ovis, show up at this time.
Recent louse control has been Eureka Gold immediately off-shears. Due to the cost and labour involved with the pour-on back line treatment, it was decided to investigate the feasibility of using Electrodip for the purpose. Des Carey of Electroquip Ltd provided a standard Electrodip machine for the purpose. Electrodip had not been used on this property before. This machine has been achieving total lice control in medium to coarse wool sheep in as little as one run per annum. However evidence of difficulty with the clearance of lice in Merinos had shown up at this time.
A mob of 30 badly louse infected cully wethers were drafted from the main mob and run separately, while the main mob were shorn and treated with Eureka Gold and put back on the high county. A third mob were shorn and showered in a run-through shower race, with a very strong mixture of Diazinon. These were subsequently run with the other 30 trial sheep.
20th August 98 First Application
The sheep selected for Electrodip treatment were irregular in wool lengths and shearing times. Seven cull sheep were identified by numbered tags and simple lice counts done. A further sixteen were tagged but not numbered - no lice count as all inspected had lice. Many lice were found, from 1 to ten partings, to 6 lice per partings, mostly in lower rib areas. Woolly sheep were well covered with lice all over, all generally, more in lower rib area. After shearing, all sheep with lice were still well covered, some of which could be brushed of like dust. Short wool made very small partings and counts seemed pointless. Longer wool left around the shoulder and neck area affording good protection still for the lice.
Immediately after shearing the sheep were jetted via the Electrodip using Asuntol oil. Dilution used was 260mls Asuntol oil to 220 litre drum of water plus methyl blue dye. Approx 2 litres of wash per sheep was used. Nozzle patterns made by methyl blue dye were recorded on video and irregular patterns were noted against the tag numbers.
8th Sept 98 Inspection
Lice were cleared from higher regions of the body. There was a major reduction in lice numbers. No pattern could be seen on sheep which had shown lopsided jetting on 20th August. Two sheep were jetted again with chemical left over from previous jetting.
5th Oct 98 Inspection
Many dead lice. One small patch of long wool on the lower belly harboured a close formation of lice in all sizes. The sheep jetted again on the 8th September still had lice.
Interim Summary
No real patterns emerged on sheep with lopsided jetting or different lice numbers. Treatment on sheep badly affected had, on occasion, reduced populations to levels lower than on those lightly effected sheep. Clearance of lice was the same on both sides of sheep with lopsided jetting.
The evidence suggested that Electrodip standard nozzle configuration does not give sufficient belly coverage to clear lice from Merinos. It was decided to do no further jetting with the Electrodip with this nozzle configuration. Given the information on hand, a side nozzle arrangement was then devised.
9th October 98 First Application with Side Nozzles
Dipped 52 Merino Wethers including 20 dipped previously. These had been shorn the day before using cover comb. There were no patches of long wool. Lice was not so easily found but still present in good number. Lots of biting and scratching among the mob.
The mob was divided into 3 groups which were dipped with Diazinon. After consulting with Stuart Edwards , NZ Woolpro, Diazinon was decided on due to the short lived nature of the chemical. The reasoning being that at wool scouring stage there is low residue counts. Three differing dilution rates (1 to 400), (3 to 400), (5 to 400) were decided on. The differing rates were an attempt to see what relevance there might be in chemical strength.
27 October 98 Inspection
No lice could be found on any of the sheep that were jetted on 9th October.
One sheep not jetted in these trials but having joined the group, recently shorn appeared to have no lice where shorn close to the skin but in difficult to shear areas of longer wool there were probably 20 lice to each parting.
Final Summary
Jetting with standard nozzle configuration suitable for fly strike did not give sufficient body coverage to clear more than 90% of lice from the adult Merino wethers with recommended chemical strength. Many patches of lice survived on the lower sides of the body.
The successful jetting involved a reduced application to the backs of the sheep, with a fairly even coverage of the lower bodies from the side and lower nozzles. Volume used was 1.7 litres.
In the first jetting 2 litres of chemical was applied mostly to the backs of the sheep. This obviously flowed down the sides and gave effective coverage much further than the dye indicated. The sheep were wet to touch all over but the lice coverage was patchy where the wool fibre was directing the chemical (or wash) away from the body. The presence of chemical in that area is obvious otherwise the insect coverage would have been more even.
The results demonstrated at Matthew’s site indicate that a simple wash volume application is not the answer with Merinos. The chemical application needs to be strategic. The final result gave no indication of the chemical dilution rates required.
Lice Recovery.
In the original groups of animals, jetted, showered or wanded, on or around 20th August 98 to 9th October 98 only one louse was found to survive beyond 6 weeks of treatment. This was in the group treated by Eureka Gold found on 8th Sept.
In spite of this, re-infestation occurred by the following autumn. This was wide spread throughout all groups at about the same level and gave cause to suspect a survival of eggs. On the 16th Sept 99 a further trial was undertaken on the Matthews’ property.
This involved the use of Diazinon and Diflubenzuron (Fleece Care) mixed together. This had also been used by Brian Jephson in March 99 Via the Electrodip and results to date were encouraging.
Observation up to 30th January 2000 of those dipped 16th Sept 99, showed no recovery of lice. This was the period of time were previously, re-infestation was wide spread. Brian Jephson of Cape Palliser Station, Masterton, after shearing in March, reported only 1 in 200 of the 1400 ewes jetted 12 months previously (and well infested at the time), to have a low lice count. This was a better result than he had been able to achieve previously using pour-ons or other methods.
The effective use of Electrodip using the Organo Phosphate - Diflubenzuron combination, is further confirmed by the C.H. McKay reported 15/5/99 trial.