DETECTING GENETIC-DIFFERENCES BETWEEN GROUPS OF SHEEP DURING PARASITEINFECTION

When experiments are established to compare parasitological difference s between genetic groups of animals, sampling of families within group s and individuals within families are both important. Many parasitolog ical measurements are quite variable, so relatively large numbers of a nimals are required to detect small differences. Calculations are pres ented which show, for example, that 100 animals per genetic group sill only have an 80% chance of detecting a difference in faecal worm egg counts as significant (P < 0.05) if the real difference between the gr oups is about 3-fold, When sampling genetic groups such as flocks or b reeds, it is preferable to represent as many families as possible. (C) 1997 Australian Society for Parasitology, Published by Elsevier Scien ce Ltd.