It is important to know which worm species are present because different species affect the growth and health of cattle to different degrees. In winter rainfall regions especially, the small brown stomach worm (Ostertagia ostertagi) has a major impact on growth and milk production. In summer rainfall and tropical regions, the barber’s pole worm (Haemonchus placei) can be a significant problem. The different species of small intestinal worm can all cause production losses, but two species, Cooperia pectinata and C. punctata, are more likely to cause scouring than C. oncophora.
In most worm species, high levels of larvae will build up on pasture under the right conditions, but the levels and timing will vary among farms and change from year to year with varying rainfall, temperature and the age of animals. Figure 1 gives an example of the seasonal occurrence of three different worm genera in heifers (weaner through to joining 5-14 months) on a farm in Tasmania. The figure highlights the value of regular testing as worm species do not all behave the same way at the same time.
Figure 1. Normal variation in worm egg counts of different worm genera detected in faecal samples from heifers on a Tasmanian farm monitored over 12 months. Data courtesy of Dawbuts.