It is very difficult to give hard and fast rules on interpreting egg counts, as there are so many variables to consider. These include:
Age of Animals:
Adult dry animals in good condition tolerate worms much better than young or poor animals.
Nutritional Status & Paddock Conditions: Well-nourished animals develop stronger immunity to worms faster and so withstand a worm challenge better than poorer animals. Sometimes moving animals onto a better paddock is as good as a drench.
Physiological Status: Are these animals young and growing, pregnant or rearing young? All these factors can place added stress on their systems and render them more susceptible to worm infestations. Young animals, such as weaners, are an important group to sample because they tend to be quite vulnerable to worms.
Weather Conditions & Outlook: Seasonal weather conditions need to also be considered and how they will impact your livestock and the worm numbers in the paddock. Warm, moist conditions can cause worm numbers to increase and become a problem very quickly.
Grazing & Management: Cross grazing can be an effective tool if you graze more than one species. Most worms are species specific and do not infect other types of animals. It can be a useful way of cleaning up the numbers of eggs and larvae on your pasture, as they do not survive in the second animal species. The only worms capable of infecting both sheep and cattle are Barbers Pole Worm and Stomach Hair Worm (T. axei)
Spelling paddocks can be useful but the length of time required will depend on weather conditions, pasture length and the types of worms present. Some worms can survive for a number of years. Short term spelling has little effect on worm control. Studies show a paddock would have to be rested for more than 10 weeks in the autumn and winter months to have a significant impact on reducing the numbers of worm larvae present.
If animals are to be mustered for some other reason, you may decide to drench based on egg count as well as convenience.
Worm egg counts considered with the other factors listed gives you the power to make an informed decision.
The table below offers a guide to egg counts. It is not hard and fast for many reasons, which include those stated above.
StockWatch suggests you contact your vet for the best advice.