Heritability and Repeatability Estimates for Reproductive Traits of Japanese Black Cows

Data preparationAll historical pedigree data and reproductive records were obtained from Wagyu Registry Association.Every year approximately 480,000 calves of Japanese Black are produced from 600,000 breeding cows in Japan.For each birth the parents of the calf, dates of insemination and birth, owner of cow, etc. are kept as reproductive records.Out of the whole database, 65,276 reproductive records from 17,303 Hyogo cows and 59,553 records from 15,612 Shimane cows registered after October 1990 were chosen for analysis because of changes in body condition scoring system.The records covered animals born from 1990 to 2001.Firstly the cows, which have been used as ET donors or recipients, were excluded because egg collection disturbs their estrous cycles.Then age at first calving (AFC), gestation length (GL), days open (DO) and CI were calculated.In Japan AI produces more than 90% of progenies, and producers sometimes postpone AI to sell calves at appropriate ages.It mostly occurs in the area where the calf market is held only once or a few times per year.Consequently such cows must show longer DO.Meyer et al. (1990) emphasized that ignoring open cows may foreclose the most variable information on genetic difference because they are likely to be genetically worst.However the cows with longer DO in AI breeding system due to their poor reproductive ability cannot be distinguished from the cows with longer DO due to Heritability and Repeatability Estimates for Reproductive Traits of Japanese Black Cows