Findings, implications and lessons learned

• The case study demonstrates the importance of taking group effects (in this case herd) into account when selecting individuals from a heterogeneous group. Had this not been done the top 40 ranking cows will have mostly reflected herd performance. Thus, the top performing herds will have tended to provide the 'top producing cows'.
• Having attempted not to disadvantage the cows with lower than average lactation lengths by calculating a total yield based on a fixed lactation length, we see that it made little difference in fact to the overall results down to the first 30 or so ranked cows. Nevertheless by doing so it provides some reassurance to the researcher that little bias is introduced by using one method or the other.