As usual we’ll start by taking a look back at what the weather has been doing over the last few months. At the time of writing, the first half of August has been largely cool and damp, with considerable local variation across the country in rainfall levels, but temperatures generally below average across the board. July was warmer than normal for the whole country, but much drier in the normally wetter western side of the country. This all followed on from a warmer than normal and much drier than normal (except for the south east corner) June.
Weather Charts from Summer 2021 - courtesy of the Met office
So what does this mean for the parasites now, and what can we expect in the coming weeks?
Blowfly The NADIS risk alert remains at high for the majority of the country, with only the north and west of Scotland still on medium risk. The blowfly lifecycle thrives in warm humid conditions, and although July was dry for many, those areas that had some rainfall will have seen fly numbers increasing rapidly. The current cooler conditions will not significantly impede blowfly activity, so sheep farms should remain vigilant until average temperatures drop to single figures.
Ticks also thrive in warm humid conditions. The dry conditions may have limited tick activity in some areas, but if temperatures rise again into September, there will be enough moisture in the environment for another spike of tick activity.
Roundworm development in the environment speeds up in warm conditions, so the time taken to go from an egg landing on the pasture to an infective 3rd stage larva, waiting to be eaten, can be as little as two weeks. Although, some moisture is necessary for the eggs to hatch and larvae to develop, and in hot dry conditions larvae are at risk of desiccation, so are unlikely to survive for long on pasture. Therefore, many areas have had low pasture larval levels up to the end of July (i.e. low worm challenge), but this could change rapidly as cooler damp conditions are ideal for the larvae to survive.
Lungworm will also be a risk for grazing cattle. Youngstock that have not been vaccinated should be monitored closely and treated as required before housing time.
Liver fluke disease with weather conditions generally warm and dry in June and July, the
challenge overall is predicted to be low and to arrive later this season. However, there is
likely to be huge variation between farms. Those farms where wet areas have remained (e.g.
pond margins, ditches and boggy areas) will have seen mud snails thrive in the warm
conditions; where there are mud snails there will be a fluke risk. This risk will not turn into a
fluke challenge for grazing animals until the fluke have been through the life cycle stages
in the snail. So, where are the fluke at the moment? Test Don’t Guess when it comes to fluke,
and use the right active for the right stage of fluke in the right animals at the right time.
Resources: For more information on the health of your livestock visit the following pages on farmanimalhealth: