William Powell Country

Grouse and Medicated Grit


Article written by 27 December 2012

There was an interesting talk on medicated grit at the recent North of England Grouse Conference atHarrogate, organised by The Game and Wildlife Conservation Trust.  This is a           bi-annual event and draws owners, keepers and managers of grouse moors to hear the latest update from the GWCT’s research.

There was acceptance this year by the GWCT that it was likely that the Strongyle worm will at some time become resistant in some form or another with the current wormer used on medicated grit.  To try and prevent or delay this disastrous event occurring, the GWCT stressed the need for medicated grit not to be used throughout the whole year, but for there to be a long withdrawal period.  By law all medicated grit has to not be available to grouse at least 28 days before they are shot and go in the food chain.  However, the GWCT also suggested that the use of medicated grit should not begin until March, each year. If there isn’t any real build up of worm by then, it seems unlikely to us that other than as a “preventative”, you would need to use a wormer in March, and if there is already a significant worm problem by say the preceding October, then using medicated grit in March (some 5 months later) is likely to be far too late, as most cock grouse with high worm numbers die in February and with hens, they often/mostly die in April, but will already be very weakened by March and as a result not very capable of breeding properly.

The GWCT also admitted at the recent meeting (for the first time that I had heard), that theCambridgeVet, Doug Wise may have been right with his initial research (done after the crash in grouse numbers in 2004/5).  This was at the time completely at odds with what the GWCT thought about wormers back then.  Doug Wise said that he thought it would only be a matter of time before the wormer that we are currently using on grouse grit would go the way of all other wormers used in farm animals throughout the world.  This is that the worms would ultimately become resistant to it.  Secondly, he could not see on the basis of his trials using actual grouse, how single or even double-strength grit would contain enough wormer to cleanse any significant quantity of worms from an already heavily worm “infected” grouse.  In his view, in order to absorb enough wormer, the grouse would have to eat so much single or double coated (with wormer) grit that they could not possibly take off, let alone fly!

The GWCT now believe after having had recent meetings with Doug Wise and Richard Byas an eminent avian Vet from Thirsk, North Yorkshirethat they now think that Doug Wise may have been right in that single or even double-strength medicated grit may not be strong enough to kill adult worms.  This is in stark contrast to what was previously thought.  We are struggling to understand the worm age profile, but if Doug/Richard are indeed right, then whilst we do know that single strength, strength-and-a-half or even double-strength wormers are apparently working on many moors to keep worm burdens low, with the GWCT reporting that in recent consecutive years on 5 out of their 6 monitored estates, this has indeed happened, but on the 6th moor, they believe the reason this one bucked the trend and did experience a large worm build up was due to under-shooting and hence that moor leaving too big a stock of over-wintering grouse.   We know from personal experience that on some moors and for some reason(s), the worm burden has risen this year despite these moors using medicated grit.  On two of “our” moors, this has happened.  This perhaps could be because of too much old heather (certainly on one) or perhaps by leaving too big a stock (maybe on both) or even a combination of these and/or even other factors, such as weather.  There are still some imponderables we do not know about, but whilst using medicated grit seems overall to be working well on most moors, it does not seem to be foolproof everywhere.  There seems to be good evidence that “normal” medicated grit prevents a worm build up (which is why many moors have recently been so successful), but it will not clean out an already-established high worm burden, because there simply isn’t enough wormer on the grit to do this, but in contrast the very high strength medicated grit developed by Doug Wise and now Richard Byas will effectively flush out the worms as will direct dosing – although the GWCT never mentioned this at their briefing.  From the experience of others, we know that direct dosing does indeed flush out almost immediately even a high worm burden in a grouse, but we still do not really know what else may be happening by using this method of worm control.  Will it in time exacerbate the resistance by the worms to the wormer?

What was also very interesting at that talk was a paper given by Dr. Alisdair Wood on “Bulgy Eye”.  Dr. Wood is in charge of Avian pathology at The Moredun Institute.  Because of their work analysing dead grouse with this very visual phenomena, we now know exactly what disease “Bulgy Eye” is.  It is Cryptosporidiosis of which Coccidioris (commonly found in pheasants and partridges) is one example.  Hexamita and Trichomonas are other types also found in game birds.  We do not know why the signs of that disease have only very recently (first seen in 2010) shown up.  Has it been present for years but at a lower level than now, which is why the grouse appearance did not change, or if it is has only recently occurred at all, what has suddenly made this happen?  Bulgy eye has been found in grouse in bothEnglandandScotlandand often on moors nowhere near where there are any number of pheasants or partridges, so cross contagion seems unlikely.  What has caused the first recognisable grouse disease?

Dr. Wood did say that;

i)          the disease was untreatable

ii)         we will probably never know why it has suddenly occurred

iii)        the best way of avoiding any build up of disease is to avoid consistently having high numbers of any animals in close proximity i.e. lots of grouse on a moor, all year round and for several years running – perhaps not what we wanted to hear, but fully understandable all the same!

The worrying thing is that in these circumstances, will we experience other and possibly worse diseases than “Bulgy Eye” where there are large numbers of grouse year on year?

Lots to think about.


Mark Osborne - FRICS, FAAV, MBAE

Mark Osborne is founder and Managing Director of JM Osborne & Co. and has been a qualified Chartered Surveyor and Land Agent for over 30 years. He trained on two large traditional landed estates (Chatsworth and Castle Ashby), before s.. Read more.

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