Ostertagia in R2 heifers and cows
Ostertagia is an important parasite in cattle because fewer worms are required to cause significant harm, cattle are slower to develop immunity against it and Ostertagia has a greater ability to cause harm from the suspended state (type II ostertagiosis).
While immunity is robust under normal conditions, adverse factors such as underfeeding, worm-contaminated pasture and periods of stress such as is experienced around calving, reduce the effectiveness of immunity.
The usual lifecycle of Ostertagia once infective stage larvae are ingested is for the parasite to mature and start producing eggs within three to four weeks. A proportion of ingested larvae does not develop to maturity and is arrested in the stomach wall prior to reaching the egg producing adult.
During this suspended state, larvae cause little irritation. When they emerge, they cause the same damage as a mature worm. The animal shows significant clinical disease with symptoms of scouring, loss of appetite and ill-thrift and even death if left untreated.
A more usual outcome is for the suspended larvae to emerge over an extended period and cause chronic type II ostertagiosis. Suspended larvae start to emerge in early spring so a late winter drench effective against type II will remove the burden accumulated during the previous autumn/winter.
Effects of age
R2 heifers are more susceptible than older cows. If their growth rates are low and other effects such as feeding or trace elements are accounted for then parasitism could be the cause.
Drenching at calving makes very good sense every year. A calving drench is advisable for 3 year cows (2nd calvers) as well. Mature cows, because of their greater immunity are at less risk of ostertagiosis.
An assessment of this risk is warranted before making the decision to drench mature cows at calving. Totally Vets is available to discuss these issues and parasite control programmes for all stock classes if you have any concerns or questions.
