Autumn Worm challenge

The down side of the dry summer many of us have experienced this year is that when we do get rain, it’s very likely there will be a surge of infective worm larvae. This can really catch sheep farmers out, resulting in significant losses due to outbreaks of PGE (parasitic gastro enteritis), particularly from Trichostrongylus (Black Scour worm).The reason for this is not simply that the larvae will spring into action with wetter conditions. Many lambs, particularly in the hotter, driest areas, will also not have had a challenging enough worm burden this summer to allow them to acquire a good level of immunity, leaving them more susceptible.


The three main risk factors are:

1.      Weather conditions – a dry summer/early autumn followed by mild, wet conditions will normally result in a flurry of autumn worm activity. When it is dry, the larvae tend not develop and to migrate on to the pasture; only when moisture returns do they venture form the safety of their dung pats!


2.      Pasture History – how contaminated is the grazing likely to be? This is affected by which sheep and for how long they have grazed, stocking densities etc. For example, permanent grass field grazed by ewes and lambs to weaning will be high risk; one that has had a couple of crops of silage off it will be lower risk. Forage crops will normally have very low levels of contamination compared with a grass, but they can also become a risk later in the year and should not be assumed to be ‘clean’.


3.      Previous exposure of the lambs to worms is also important. Low levels of exposure since the spring means they are less likely to have developed their immunity. Ewe lambs from hill farms with low worm burdens that are brought on to highly contaminated lowland pastures in the autumn are a classic example.

Please contact us for details of treatment strategies

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