During the summer months, we are always aware of the problems posed by gut roundworms and lungworms and we correctly dose our calves and weanlings at pasture appropriately throughout the grazing season. Sometimes what we neglect to take into account is that roundworms, in this case the larval stage of Ostertagia, can become inhibited or hibernate within the stomach wall during late autumn only to emerge the following spring with severe consequences.

In the winter, Ostertagia, as part of its survival mechanism, enters a period of delayed development during the larval stage. It sits quietly, hibernating if you will, during periods of cold within the gut, waiting for more suitable warmer and wetter conditions to resume its lifecycle. This ensures the survival of the parasite from year to year. Type II Ostertagiasis is a result of high stocking densities the previous autumn, and/or inadequate dosing at the end of the grazing season and during the housed period.

The hibernating larvae all emerge at the same time. These larvae together will cause huge damage to the lining of the bowel, leading to a profuse scour, weight loss and dehydration.

It can be so severe that the weanling will go down. It often occurs in younger animals. You will first see a scour with a bottle jaw in one or two animals and then suddenly some of the weaker, younger stock will get a debilitating scour that can result in high mortality rates in affected animals.

Vets always recommend faecal analysis to look for roundworms, liver fluke, rumen fluke and coccidia, but care must be taken when interpreting roundworm results at this time of year, as the worms may be in a period of hibernation. Adult roundworms may be scarce and faecal analysis will only find eggs produced by adults. Therefore, dosing with an anthelmintic recommended by your vet is essential.

Not all dosing products are effective against Type II Ostertagia. Some of the older levamisole-based products will not kill the inhibited or hibernating larvae. Therefore, your vet will choose a more modern product (that might also include a flukicide) that will suit your farm and your previous dose regime.

I think it is worthwhile to separate the younger and weaker 20% of weanlings in a slatted unit for individual care and attention including correct dosing.

*Sean Coffey works at Mulcair Vet Clinic, Newport, Co Tipperary. Mulcair Vet Clinic is part of XLVets. XLVets is a group of progressive practices working to achieve a better future.