Age at first calving of dairy cattle in a multibreed population of Thailand

Age at first calving (AFC), 305-d accumulated milk yield (MY) and pedigree information of 1,024 cows, which born in the period of 1988 to 2000 in 75 farms located in the central part of Thailand, were used to estimate breeding value of each individual animal. The genetic prediction was done by solving mixed model equation and using an animal model that applied for a multibreed population. Least square means of phenotypic and estimated breeding values for AFC of the considering groups were compared. The results revealed that the average AFC in the studied population was 30.31 +/- 5.29 months. Heritability for AFC was 0.16. Range of EBVs for AFC was from -10.19 to +8.70 months compared to the population average. Phenotypic correlation between AFC and MY was not existed (-0.01) in this population, however, AFC was genetically correlated to MY (0.46). The variation of EBV for AFC of each animal (progeny) was affected by EBV of its' dam rather than its' sire. Cows born in the following year had phenotypic AFC (0.35 month per year) and genotypic AFC (0.11 month per year) shorter than those born in the previous year (P < 0.05). If the Thai dairy cattle population had structure as same as the population used in this study, the results of this study implied chance(s) to improve AFC in the population by selecting the parent animals from the population.