Summary

This case study explores the patterns in relationships of various factors with weaning weights of Red Maasai and Dorper lambs and their crosses, such as year of birth, sex, age at weaning and age of dam. In particular, different formulations of the relationship between age of dam and weaning weight are compared. Ways of subdividing the sums of squares in an analysis of variance to evaluate alternative parameterisations of the statistical model are described. Parameters describing the patterns with these various factors are then included in a model to compare the weaning weights of the different genotypes when adjusted for these factors. Finally, alternative forms of presentation of results from general least squares analyses of variance are discussed.

This case study is part of a larger investigation to compare the performance of these different genotypes when exposed to helminthiasis. Case Study 4 evaluates the genetic components of variation associated with a lamb's dam or sire.