Development of the Timed Re‐Insemination (TRI‐synch) program re‐inseminating 24 days after the initial service in dairy cows

For the timed re‐insemination at the minimal interbreeding interval, cows were treated with a progesterone (P(4))‐releasing intravaginal device from Days 13–15 to 21 post‐insemination (Day 0 = estrus), followed by plasma P(4) assay on Day 23 and then subjected to the Experiments 1 and 2. In Experiment 1, of 18 cows, 6 cows were determined as luteolysis with low (<1 ng/ml) plasma P(4) concentrations on Day 23 and ovulated on Days 24 (3 cows), 25 (1 cow), and 26 (1 cow) except a cow affected by ovarian quiescence. In Experiment 2, all cows were treated with GnRH on Day 23. Cows with low (<1 ng/ml) plasma P(4) concentrations on Day 23 were diagnosed as non‐pregnant and subjected to the re‐insemination in the morning of Day 24 irrespective of estrous signs. Of 36 cows, 15 cows were diagnosed as being non‐pregnant on Day 23. Fourteen cows of the non‐pregnant animals were re‐inseminated in the morning of Day 24 irrespective of estrous signs and the pregnancy rate of re‐insemination was 36%. The conception rates of initial and re‐inseminations were 50% (18/36) and 36% (5/14), respectively. The overall pregnancy rate by adding the rates of initial and re‐inseminations was 64% (23/36).