Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1997
Publication Date: N/A
Technical Abstract: To determine evaluation stability for productive life (PL), somatic cell score (SCS), and yield, Holstein bull predicted transmitting abilities (PTA's) from January 1994 through February 1997 were compared with theoretical expectations. Beginning in July 1994, released PTA PL included correlated information from type and yield traits, but an unreleased single-trait PTA PL was available for study. All PTA before January 1995 were adjusted downward to compensate for the genetic base change. Initial reliability was required to be 50-75% for PL, 50-75% for SCS, and 65-85% for yield traits; for all traits, final reliability was >95%. For PL, PTA were available for 125 bulls since January 1994 (single-trait PL) and for 98 bulls since July 1994 (multitrait PL). For SCS and yield traits, PTA were available for 130 and 186 bulls, respectively, since January 1994. Changes in PTA PL were negative instead of 0 as expected; mean multitrait PTA PL was .40 mo greater than mean single-trait PTA for the same 98 bulls. Regression of final PTA on initial PTA was expected to be 1.0 for all traits. Actual regressions were .74+/-.08 for single-trait PL since January 1994, .79+/-.08 for single-trait PL since July 1994, .88+/-.11 for multitrait PL, 1.16+/-.10 for SCS, .97+/-.06 for milk, 1.00+/-.05 for fat, and .97+/-.06 for protein. Standard deviations of observed changes as percentages of expected changes were 83% for single-trait PL since January 1994, 94% for single-trait PL since July 1994, 95% for multitrait PL, 131% for SCS, 123% for milk, 122% for fat, and 130% for protein. Early PTA generally were good predictors of later PTA; however, regressions for PL were low, and PTA for SCS and yield traits changed more than expected.