with Phil Rennie
Cooperia is the small intestinal worm regarded as being the most prevalent roundworm in New Zealand cattle. They are reddish in colour and quite small growing up to 10mm in length. Eggs in faeces may hatch in as little as 20 hours, while infective larvae can develop within four days. Like most parasites infective larvae are ingested by the host while grazing.
The importance of drenching against Cooperia is well-known in young cattle, as in certain conditions Cooperia can cause thin, scouring weaners that can die if not treated quickly. While this is one obvious undesirable form of the disease, productivity trial work has also shown that seemingly healthy yearling cattle can also be affected. Weight differences between groups were noted by Dave Leathwick and others at AgResearch in a study published in 2012. This study suggests even relatively low levels of Cooperia in healthy nine-month-old cattle may have a detrimental effect on growth. This challenges the traditional reputation that Cooperia parasites normally need to be present in high numbers to cause disease.
Dry seasons favour all parasites when autumn rain comes. Grazing animals’ natural immune defenses are weakened by drought and they are forced to graze low where the parasite larvae live. A wave of larval contamination can occur after a long dry spell and young cattle need to be drenched soon after decent rain.
When used on their own, the simple ‘pour on’ drenches – known as endectocides – are not highly effective at killing Cooperia. Levamisole however continues to have excellent effect against Cooperia, so using these drenches in combination is reasonable approach. The recommended practice of using combination drenches that contain levamisole is preferred, especially in cattle less than 15 months. Of some conciliation to stock is that by their second autumn – by around 12-15 months of age – the immunity of cattle against Cooperia is normally well established.