Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/23/2004
Publication Date: 7/25/2004
Citation: Norman, H.D., Powell, R.L., Wright, J.R., VanRaden, P.M. 2004. Genetic relationships of milk yield for different parities between bulls and their sons [abstract]. Journal of Dairy Science. 87(Suppl. 1):413. Interpretive Summary:
Technical Abstract: This research was done to determine how daughters of bulls differ in their rate of maturity. The 305-day milk records for Holsteins having first parity calving dates between 1960 and 1998 were used to calculate three Predicted Transmitting Abilities (PTA) for each bull. The first set of genetic evaluations included only first lactations on daughters and contemporaries (PTA1). The second and third sets included the first two and three lactations available, PTA1-2 and PTA1-3, respectively. The contribution from individual parities, two (PTA2) and three (PTA3), were approximated using a weighted average of the (single trait) evaluations, PTA1, PTA1-2, and PTA1-3. Weights were based on number of daughters with a second (or third) lactation. Bulls (2864) with >=500 daughters ranged from + 295 to - 290 kg in difference between PTA1-3 and PTA1, with a SD of 85 kg. In contrast, when the same bulls were ranked on the differences between their contribution to separate parities, they ranged from + 555 to - 610 kg, for PTA3 - PTA1 with a SD of 179 kg. To determine if these difference were transmitted, comparisons were made across a generation. Expected regressions for 16,643 sons' with >=40 daughters on sires' PTAs calculated within sire's and son's years of birth (YOB) were 0.44 (derived from sons'mean reliability x 0.5). Actual regressions for PTA1, PTA1-2, PTA1-3, PTA1-2 - PTA1, PTA1-3 - PTA1, and PTA1-3 - PTA1-2 were 0.44, 0.43, 0.43, 0.43, 0.43, and 0.42, most with standard errors (SE) = 0.01. Regressions were also derived on the bulls' specific contribution to second and third parities. Actual regression calculated within YOB for PTA2, PTA3, PTA2 - PTA1, PTA3 - PTA1, and PTA3 - PTA2 were 0.42, 0.44, 0.44, 0.45, and 0.43, most with SE = 0.01. These results suggest that differences observed in high reliability bulls as their daughters mature is transmitted to their sons' daughters. Modeling separate PTAs for each parity should increase accuracy of, and reduce unnecessary oscillation in, genetic evaluations when number of records per daughter changes.