It is likely that this bias is caused by incorrect recording. This could include errors in parentage assignment on farm.

The scale of this bias has been increasing over time and it is reaching a level which is unacceptable by international standards.

NZAEL have developed a method of correcting the reproof bias. The correction is applied differently to individual bulls and is dependent on the following factors:

• Age
  A larger correction is applied to bulls that are further into the reproof phase.
• Breed
  There is a difference in the reproof bias seen in Jerseys and Friesians.
• Number of daughters
  The correction factor increases as a bull accumulates more daughters during reproof.

The reproof correction uses an internationally recognised and peer reviewed technique which significantly reduces the reproof bias.

Will this reproof correction affect any other animals?

Yes, any younger male or female relatives of these reproof bulls will have their BW altered upwards.

What are the steps?

• February 2016
  Reproof bias adjustment applied to all reproof bulls born between 2003 and 2006.
• June 2017
  Reproof bias adjustment becomes fixed for 2003 born bulls.
  Reproof bias adjustment updated for bulls born between 2004 and 2006 (inclusive).
  Reproof bias adjustment applied to all reproof bulls born in 2007 and 2008.
• November 2017
  Graduated reproof adjustment
  From June 2017 onwards the reproof bias adjustment will be gradually introduced into a bull's breeding values as he accumulates widespread daughters. By applying the bias adjustment throughout the season NZAEL will be able to stabilise the breeding values of bulls as they go through reproof.
• Ongoing research and development
  NZAEL will continue to research alternative methods which could be employed to account for this reproof bias. These include:
• Down weight data from non-verified daughters
• Exclude all non-verified data from Animal Evaluation (long term)
• Use DNA parent verified daughters to produce sire breeding values while using all data to produce evaluations for cows.