Genetic relationships of calving difficulty with birth measurements and carcass traits in Japanese Black cattle.

The objectives of this study were to compare the genetic parameters for calving difficulty (CD), which were treated as both a calf trait (CD_calf) and as a dam trait (CD_dam), and to clarify genetic relationships of these CDs with body size traits of calves at birth and carcass traits. In total, the CD records and calf body measurements of 2,258 Japanese Black cattle heifers were used in this study, in addition to the carcass records of 4,300 feedlot steers and heifers. Direct heritability of CD_calf (0.

Genetic associations between reproductive traits for first calving and growth curve characteristics of Japanese Black cattle.

The objective of this study was to estimate genetic parameters for first calving reproductive traits and growth curve characteristics in Japanese Black cattle. The Gompertz growth function was fitted to body weight-age data to obtain the mature weight (MWT) and rate of maturing (ROM) of cows. Data of reproductive traits including the first service conception rate (CR) for heifers, age at the first calving (AFC), and gestation length for the first calving were collected.