16 July 2008
War on Blowflies
Posted by Richard under: Sheep; Smallholding .
I officially hate blowflies. Four out of the ewe lambs have got flystrike. It’s not the end of the world - just frustrating as we have done things pretty much right.
The official advice from the man from the ministry (DEFRA) on flystrike prevention is to:
- Dag to reduce soiling and/or remove dirty wool around the breech (yep - no dagging needed, nice clean behinds)
- Reduce the incidence of soiling by avoiding nutritional upsets causing scouring and
having a sound worm control strategy (check - no scoury lambs, nice pea-sized firm black droppings) - Tail sheep (we tailed all our lambs in the first few days)
- Avoid breeding from sheep that are habitually struck and/or tend to soil themselves
due to their conformation (hmmm - tricky to say as all our ewes were new to us, but no obvious soiling issues) - Dispose of carcases quickly (I didn’t notice any carcases in the locality)
- Reduce the incidence of footrot (Footrot free this year, so far!)
We used Crovect on the entire flock five weeks ago, and knew that they needed a fresh treatment this week - but the flies got there first. Since finding the outbreak on Monday we have clipped back with handshears and treated the infected areas with Crovect, but it wasn’t stopping new infestations appearing
Andy came over this evening and sheared them back with his electric shears and Kate treated them again - this time there is no hiding place for a single maggot.
On Andy’s advice we are going to change our prevention strategy to Dysect on the breeding ewes and rams (including lambs we are keeping) and Vetrazin on any lambs going to slaughter. He has been using this method for 15 years and has minimised flystrike. The problem he has with Crovect is that it is only effective where the spray hits…Vetrazine moves through the wool, while Dysect enters the blood/skin - both giving wider protection. One note - Vetrazine can’t be used as a treatment once infestation occurs.
In the end, we followed a ‘best practice’ course of prevention and treatment - but the lifecycle of a blowfly is such that one adult can lay 250 eggs which will be maggots in 24 hours. The ewe lambs are on the mend - and a dose of Dysect tomorrow should keep them free from strike for a couple of months - even if they do look a little odd with sheared backsides.
5 Comments so far...
susi Says:
17 July 2008 at 6:38 pm.
It seems to be a bad year for fly strike in some areas, a lot of people were talking about it round the sheep pens at the North Yorkshire Show - I wrote a bit about it on my site on June 18th after the show.
The DEFRA advice is not wrong, it’s just inadequate (like most things that come out of DEFRA). Flies will lay eggs on clean sheep as well as dirty sheep so your shearer is right - you have to use a preventive. I’ve no idea what they mean by the bit about not breeding from some sheep - all sheep can get fly strike because all sheep smell like sheep to a fly.
A lot of people seem to think that Crovect is an all-over preventive - it is not, it is an insecticide based on cypermethrin and will kill insects (at any stage in their life cycle) that come into contact with it.
Vetrazin, which spreads through the grease in the fleece, contains cyromazine which is an insect growth regulator - that is, it stops the eggs hatching into maggots.
We have used Vetrazin (for ewes and lambs - saves buying more than one product) for sixteen years and have only ever had one case of maggots - and that was between a sheep’s toes of all places. We shear in the second week of May if the weather’s okay, spray with Vetrazin the day after shearing and then spray every eight weeks through to September.
Novartis, the Swiss company who make Vetrazin, also make Clik, a similar product which lasts longer but costs quite a bit more. They also make Magik which lasts even longer (twenty-four weeks per spraying) exclusively for the Australian market so I think their products must be pretty good - after all, 120 million Aussie sheep can’t be wrong.
By the way, if you are unlucky enough to still get maggots even when you’ve used a preventive, you do not have to use expensive Crovect to kill them. You can buy an aerosol of maggot killer from your agricultural merchant or, probably, from your vet.
Richard Says:
17 July 2008 at 8:16 pm.
Susi - those are really helpful comments, much appreciated. It sort of confirms they way we are heading. Andy has been using Vetrazin for 15 years and you for 16, and both of you seem to have flystrike under control.
susi Says:
17 July 2008 at 8:46 pm.
Just another thought on this - when you buy any of these products always check the “use by” date. When you only have a few sheep the Vetrazin, or whatever, will last you more than one year. There used to be an animal health shop near here that always tried to shift the stuff that was nearly out of date and we got caught by this once.
I don’t know how vital the “use by” dates are but I prefer not to risk it.
katie Says:
31 July 2008 at 10:10 am.
We’ve been using the Redtop fly traps - they are apparently more attractive to the flies than the sheep. They seem to be working well so far…..
Jo Knight Says:
17 August 2008 at 2:27 pm.
I know someone who did have a problem when they used out-of-date Crovect; their ram was very badly affected by flystrike which considering they’d only treated the sheep a fortnight before, was a shock to them. On the vet’s advice they checked the ‘use by’ date on the bottle; & sure enough, it was over the expiry.
We’ve had one case of flystrike this year; our first ever. It was utterly revolting & must have been dreadful for the wether concerned. We treated it with Cooper’s ‘Spot On’ & were extremely impressed with the speed & efficacy with which the product worked.
Here’s hoping none of us have any more cases….