Number of calves produced at 4 years of age (NCP
). (A) Schematic representation of the reproductive cycle of Japanese Black cattle. At puberty, the heifer is artificially inseminated (AI) at the onset of estrus and becomes pregnant. After parturition (calving), the cow is again AI after the estrus cycle is re-established. Ideally, a cow produces a single calf each year. (B) The number of calves produced at 4 years of age (NCP4) is calculated from the following formula according to the method of the Wagyu Registration Association ; NCP4 = [4 - age at first calving (year)] / [average calving interval by t-age (year)] + 1. The t-age is the age at which the first calving occurs after the cow reaches 4 years of age. (C) The distribution of NCP4 in 15,225 cows in this study.