OPALTERNATIVES- WHATSONTHEMARKET NOW?
OPALTERNATIVES- WHATSONTHEMARKET NOW?
The decision to temporarily remove organophosphate dips
from the market has increased sheep scab and lice
incidence and left producers confused over alternatives.
Independent vet Chris Lewis takes a look at whats
available and gives his opinions on control options
THE TEMPORARY withdrawal of OP sheep dips has caused major problems for owners and shepherds, particularly those in hill and upland areas.
At the time of withdrawal more than 50% of all scab treatments were by OP dips and their removal caused much concern, which puts into perspective the views of those wanting a permanent ban.
The withdrawal also highlighted the main concern of the licensing authorities: That transferring concentrate from container to dip is the area of greatest contamination risk, and it is now being addressed by manufacturers.
The ban has added cost to the industry and left hill and upland sheep farmers stock exposed to re-infestation from inadequately treated neighbouring stock.
And there are other serious concerns, such as the bans effect on flock welfare. More animals have become infested because there is no long-acting product to treat scab, and some have remained infested due to resistance to synthetic pyreithroids (SPs).
On the positive side, the withdrawal has demonstrated the industrys desire for OPs to be restored as soon as possible.
On the downside, their removal has reduced choice. It may lead to more resistance to SPs, and there are greater environmental risks from using these.
A complicating factor during last winter was the re-emergence of lice. This makes diagnosis more difficult as lice infestation is clinically similar to sheep scab.
Therefore it is essential to obtain an accurate diagnosis from your vet, as injectable endectocides have no action against lice.
There is also evidence that sheep scab mites are developing resistance to SP products and although they are rapidly killed by all three groups of products, persistence is essential to prevent re-infestation.
Only the OP dip diazinon really fulfils this criteria by providing at least 56 days protection. Some SP dips provide 28 days, the same length of protection as one of the injectables.
Ectoparasite
In reality, diazinon sets the gold standard for sheep ectoparasite control. Dilution rates are the same for all parasites and it is the least expensive, costing about 26p/sheep*, irrespective of age or size.
It is also less harmful to the environment, being broken down more quickly than SPs. However, operators must use it carefully and it requires a certificate of competence to purchase.
So what are the alternatives now that OP dips are not available?
They fall into two classes; SPs and injectable endectocides. There are several products available, each with distinctive advantages and disadvantages.
Of the SP dips, there are three products; flumethrin; high cis 80/20 cypermethrin 10%; and micro-emulsion high cis 10% cypermethrin.
All act against sheep scab, mites, lice and ticks and all – except for flumethrin – offer some protection against fly strike.
Flumethrin treats scab, lice, ticks and keds using one litre of concentrate to 900 litres of water and costs 74p/lamb and £1.14/adult. To prevent scab use one litre of concentrate to 1360 litres of water, costing 56p/lamb and 74p/adult sheep.
High cis cypermethrin 10% requires two plungings, 14 days apart to treat scab, but these products offer no protection. Therefore, sheep must be moved to semi-clean pasture – sheep-free for at least 16 days – between each dipping.
For scab and blowfly control the dose must be stronger, at a rate of one litre of concentrate to 400 litres of water, costing £1.10/lamb and £1.42/adult. For just flystrike control, halve the cost by using half this amount of concentrate.
When trying to prevent scab, lice, ticks, keds and flystrike using micro-emulsion high cis 10% cypermethrin dip, dilute one litre with 500 litres of water. This will cost 32p each for lambs and adult sheep.
Producers requiring cost effectiveness, ease of use and reasonable protection against re-infestation from lice and scab should choose micro-emulsion products, as long as the parasites are not resistant. But remember a certificate of competence is required to purchase SP dips.
Of the injectable endectocides, three products are available to control sheep scab. None have action against any other ectoparasites, so vet diagnosis is essential.
The first to be licensed was avermectin. This has little persistence and provides no protection against scab re-infestation.
Two doses must be given under the skin and are required exactly seven days apart at a rate of 1ml/50kg body weight.
After both injections, it is vital that sheep are moved to a pasture that has been sheep-free for 16 days. Treatment with this product costs 88p/lamb and £ 1.80 for every mature sheep.
Another avermectin-based product, doramectin, has better persistence, preventing re-infestation for about 16 days. It should be administered as a single dose into the muscle at 1ml/33kg of body weight.
Treatment
It is sensible to move sheep to semi-clean pasture after treatment and it is a little cheaper; lambs 66p/each and adults £1.30/each.
The third injectable, based on the milbemycins, moxidectin, gives 28 days protection as a single dose under the skin given at 1ml/50kg body weight.
But treating established scab using this product requires two doses, given 10 days apart at the same dose rate. Longer persistence means there is no need to move sheep to clean pasture between doses. It costs 86p/each lamb and £ 1.70 for adult sheep.
When injectables are used, diagnosis and dose rate must be accurate. Doramectin has the advantage of being administered into a muscle, which most operatives find easier, but moxidectin does have longer persistence.
Both have significant advantages over the original avermectin product, and none require a certificate of competence or any fixed equipment. *
*All prices are based on those applicable at April 2000 and assume a flock size of 400-550.
Consider alternatives to OPs carefully, says vet Chris Lewis.
ALTERNATIVES TO OPs
• SP dips.
• Injectable endectocides.
• Follow manufacturers instructions.
SP dips and injectable endectocides are the available OP alternatives.
Chris Lewis is one of a range of experts talking at free seminars at Sheep 2000. The Talking Sheep seminar programme will run throughout the day, and will be held in Severn Hall, covering everything from marketing, costs and subsidies to the internet and ectoparasite control.
10.30am Developing the export market
Gerrard Wakefield and Mike Gooding Farmers Ferry
11.15am Direct marketing – What opportunity? Martin Palmer MLC
Noon Making the most of subsidies and grants Margaret Griffiths ADAS
1.30pm Making the most of todays technology Mark Lindley FWi
2.15pm OPs – With or without? Chris Lewis MRCVS
3pm Keeping a check on unit costs of production Christine Venus ADAS