Considerations About the Necessary Precision in Internal Parasite Egg Count in Ovine Faeces
Gastro-intestinal parasite infections (GPI) caused by nematodes constitute a health and economic limitation to sheep production in pastoral systems. Their control has relied on treatment with anthelmintic drugs, which has resulted in parasite resistance to such products. The consequences of GPI on sheep production are variable, depending on the severity of the effect of the parasite in question, the worm load, the sheep class, and the nutritional and physiological status of the sheep. Losses can reach tens of millions of dollars. The most widely used method to identify resistant sheep is by faecal egg count (FEC). The most commonly used precision when recording FEC is 100 eggs per gram of faecal matter, but there are no studies indicating whether the precision should be greater or if it could be smaller. Using properties of the uniform distribution, we estimated the precision with which FEC should be estimated for different values of the standard deviation of FEC and of the measurement error in relation to this latter parameter. We concluded that the precision with which laboratories measure FEC (100 eggs per gram) is more than enough. In genetic improvement programs, if there were surplus measurement capacity, increasing the number of animals recorded would be more beneficial than increasing measurement precision.