Exploration & description

By weaning there were approximately half the number of DR lambs in the study compared with the DD lambs. These observations reveal an imbalance in the data. In particular, there were no RR and DR lambs in 1991 and the RD lambs were few in number during the last three years of the study. Since there were different numbers of lambs born for the different breeds in the different years, it is important to take year of birth into account in the analysis, since it is clear that the effect of genotype on weaning weight is partially confounded with year.