Study design

The purpose of the experiment was to compare the genetic resistance to helminthiasis of the two indigenous breeds of sheep - Dorper and Red Maasai, together with their crosses. Throughout six years from 1991 to 1996 Dorper (D), Red Maasai (R) and Red Maasai - Dorper crossed ewes were mated to Red Maasai and Dorper rams to produce a number of different lamb genotypes.

In the first year 12 Dorper and 12 Red Maasai rams were mated to Dorper and Red Maasai x Dorper ewes (Red Maasai genes coming from the sire (ram) and Dorper genes coming from the dam (ewe). Red Maasai ewes were not available in this year and the study formed what is known in the discipline of genetics as a partial diallel design.

A full diallel design involves the mating of sires and dams from both breeds.

In subsequent years 12 Dorper and 12 Red Maasai rams were mated to Red Maasai ewes as well with about seven or eight new rams being used each year. This is a full diallel design.