Ostertagia – or brown stomach worm – is a significant problem for all ruminant livestock grazing New Zealand pastures. Infestations of this parasite are harmful to productivity and can ultimately lead to death.

It is noticeable from autumn well into the spring. Drenching allows us to enhance production as well as protect the welfare of our stock. The disease, known as Ostertagiasis, occurs in two forms, Type I and Type II.

The Type I form occurs in young stock during their first grazing season as a result of maturation of ingested larvae in the abomasum. The Type II disease occurs in animals aged nine to 12 months as a result of resumed development of larvae, which have undergone arrested development – or hibernation – from early-autumn to late-winter-spring.

Winter monitoring

Monitoring during the winter period is not easy because faecal egg counts may not be a reliable indicator due to the ability of the worm to hibernate and not yield large numbers of eggs. Where eggs appear in the faeces third-stage larvae can be cultured and identified as Ostertagia. Elevated blood pepsinogen levels may also be diagnostic of Type II Ostertagiasis.

Ultimately a routine drench of all young stock is a sound approach. Even though rising two-year-olds should be immune to worms some individuals may still be susceptible, so targeting those under-performing lighter animals is a good idea.

A drench treatment known to be effective against the inhibited fourth larvae stage is a key part of control for stock. Also overstocking should be avoided by using pasture management to avoid the accumulation of infective larvae on herbage.

Quarantine drench

There is also a lot of stock movement at this time of year so travelling stock should be quarantine drenched with a triple-active drench, either on their return from grazing, or on their arrival at their new grazing property. This should be followed by holding them in a quarantine area for 24 hours, and subsequent grazing on pasture that is not necessarily “clean”.

Preventing the introduction of potentially drench-resistant Ostertagia to your property is not to be underestimated. Effective treatment would provide a short-term benefit to the introduced stock as well as provide some assurance of control in the longer term for future stock.

In summary Ostertagia sp are still the main parasites that compromise production. Selection of a drench with active ingredients that target the parasite at this time of year in young stock is very important. For more information on how best to control this harmful parasite, contact your local vet clinic.