Reproductive performance of cows after fixed-time artificial insemination with ovulation synchronisation and re-synchrony in southern Australian dairy herds.

Objective: To describe reproductive performance of lactating dairy cows after fixed-time artificial insemination (FTAI) with ovulation synchronisation and re-synchrony in Australian dairy herds, and to compare reproductive outcomes with those of conventional mating programs.
Methods: The study was conducted in two seasonally calving dairy herds in which lactating dairy cows (n = 675) were enrolled into three treatment groups: group 1, oestrus detection and AI for 34 days followed by a natural service period; group 2, FTAI on day 1 followed by re-synchrony of all cows prior to ultrasound pregnancy diagnosis at day 31 and FTAI of cows diagnosed not pregnant at day 34, then a natural service period; group 3, FTAI on day 1 followed by oestrus detection and AI for 34 days, then a natural service period. First-service conception rate (FSCR), 6-week in-calf (6WIC) rate and proportions pregnant at the end of mating were compared using logistic regression with farm fitted as a fixed effect. Times from mating start date to conception were described using survival analysis with Kaplan-Meier failure functions.
Results: FSCRs (45.3%, 49.1% and 45.6% for groups 1, 2 and 3, respectively) and proportions pregnant at the end of mating (77.6%, 76.0% and 76.8% for groups 1, 2 and 3, respectively) were similar for all groups. The 6WIC rate in group 2 was similar to that in group 3 (70.4% vs. 67.2%; P = 0.486), but tended to be higher than in group 1 (70.4% vs. 62.0%, P = 0.066). The median days to pregnancy for cows that conceived was 1 day in groups 2 and 3 and 10 days in group 1.
Conclusion: Mating plans that use FTAI with ovulation synchronisation and re-synchrony during the AI period can achieve comparable reproductive performance to conventional mating programs in seasonally calving dairy herds.
(© 2018 Australian Veterinary Association.)