Lifelong Reproductive Performance and Fetal Development in Japanese Black Cows

Abstract

The present study was carried out to establish the reproductive performance of Japanese Black Cows in their lifetimes. The major results were summarized as follows. 1)Fetal development: Growth of fetal body weight and crown-rump length was characterized for conceptuses ranging 39 to 268 days of gestation. 2)Growth of female genital tract from birth to puberty: Heifers whose body weight reached 257-269 kg, had matured sexually. Uterine and cervical weights at puberty, distributed 78. 0-139.0g and 22. 0-85.0g, respectively. The body weight of heifers showed continual increase after puberty, while there were a little increase in the uterine and cervical weight, and no growth of the oviduct either in weight or length. 3) Uterine involution postpartum: Primiparous Japanese Black Cows were slaughtered at 18, 23, 29, 46 and 54 days postpartum to examine the histological patterns of involution of uterus. At 18 and 23 days postpartum, the uterine endometrium contained many phagocytes and nodular aggregations of lymphocytes. Capillaries located under the surface epithelium were not yet completely contracted. At 46 and 54 days postpartum, however, the endometrium contained only a little amount of lymphocytes and phagocytes, uterine glands evenly distributed with a tall glandular epithelium. It may be concluded that uterine involution was completed histologically at approximately 40 days or later postpartum. Using the ultrasonic linear scanner, it was confirmed that uterine involution was completed at approximately 40 days postpartum. 4) Lifelong reproductive performance of Japanese Black Cows: The mean duration for the first postpartum estrus was 67.7 days. Mean time interval from parturition to conception, that was days open, was 125.5 days, so mean calving interval was 417.5 days. First and final calving ages of the cows were 2.53 and 8.14 years old on average, respectively, and they produced 5. 4 calves on average in their lifetimes. Cows in which primiparous age ranged from 2.01 to 3.00 years old, produced more calves (over 6) in their lifetimes than those in which primiparous ages was under 2.00 or over 3.01 years old. Rate of culled cows at every calving number reached to 51 and 83 % of total cows after fifth and eight calving number, respectively. Seventy eight % of the culled cows were due to some reasons of reproduc-tive disorders. A reasonable age for beginning of calf production in Japanese Black Cows was estimated to be in the range from 15 to 20 months old, and economical limit of age for reproductive use was estimat-ed to be 9 to 10 years old when they will have more than 8 calves.