AIPL Changes to Evaluation System - November 2001


Productive life in discontinued herds

National productive life (PL) evaluations have included observed months in milk for dead cows and projected months in milk for cows still alive, those sold for dairy purposes, and those in herds that discontinued testing. Improved procedures were introduced to detect discontinued herds. With flexible milk recording rules, such records may not be labeled with the correct termination code (code 2) because dairy records processing centers (DRPC's) may not know that a particular herd has stopped testing. Many cows are not reported as sold or died and have no further milk records. After 12 months without a new record or indication of sale or death, a cow was assumed to have died immediately after her last recorded milk yield. For data since 1990, projected herd life will replace observed herd life if the last herd test date is less than 12 months after the cow's last recorded yield data. In herds that have discontinued testing, most cows will now have a projected herd life instead of a herd life ending on the last test. As a result, the mean PL for cows born in 1995 (the base cows) increased from 23.9 mo in the August 2001 evaluation to 24.4 mo for the November 2001 evaluation. Only cows with an opportunity to reach 36 months of age have PL projected. Using the last herd test date instead of the current date to determine the status of cows for PL calculation resulted in some cows not 36 months at the last herd test date being excluded from the analysis, although they were 36 months old by the current date. For some bulls, the number of daughters for productive life declined slightly due to this change. The reported reliability for some bulls may also decline slightly due to the change in number of daughters and the replacement of some observed herd life records with projected herd life.