Worms in cattle: high-risk periods at pasture

Assessing and reducing pasture risk is a key element of a successful worm management plan. It can help to reduce our reliance on anthelmintics and provide quality grazing for our livestock.

The risk of infection and disease varies according to the type of parasite. Generally, a disease caused by stomach and lungworms is seen in the summer and autumn.

Creating a map of your grazing platform and assigning a risk value to it, then grazing appropriately, can help you decide how you use your paddocks and reduce the risk of heavy parasite burden year-on-year.

The survival of larvae depends largely on temperature. Survival over winter can be higher in cold conditions, particularly under snow. After three weeks, these newly acquired infections will result in an adult population of worms that start to lay eggs. These eggs deposited on pasture in spring develop slowly to the third larval stage. As temperatures increase from April to June, development time shortens, larvae develop within 3⁠–6 weeks at temperatures of around 10°C and within one week or less when temperatures are 15 to 23°C.

Infective larvae need moisture to leave the dung and make their way onto herbage, where they are more likely to be ingested by cattle.

By mid-July, there is an abundance of larvae on the pasture.

So, while some ill-thrift can occur in the first two to three months after turnout, the risk of significant loss of weight and scouring is greatly increased from July onwards.