Some abstracts do not have video files because ASAS was denied recording rights.
1118
Effect of a progesterone-based estrous synchronization program for timed AI (TAI) on reproductive performance in a seasonal pasture-based dairy production system
The aim of this study was to investigate the effect of progesterone-based TAI programs on fertility in seasonal-calving pasture-based dairy herds. At 10 days before the mating start date (MSD), 840 lactating dairy cows on 3 seasonal-calving farms were blocked based on days in milk (DIM) and parity and randomly allocated to one of three treatments: (i)Control: no treatment, inseminated at detected estrus; (ii)P4-Ovsynch: cows received a 7-day progesterone-releasing intravaginal device (PRID®Delta) with 100 mg of GnRH analogue (Ovarelin®) at PRID insertion, 25 mg injection of PGF2α (Enzaprost®) at PRID removal, GnRH at 56h after device removal and TAI 16h later; (iii)P4-Ovsynch+eCG: same as P4-Ovsynch, but cows received 500 IU equine chorionic gonadotropin (eCG; Syncrostim®) at PRID removal. At trial initiation all cows that were ≥30 DIM were ultrasound scanned to assess presence/absence of a corpus luteum (CL) and Body Condition Score (BCS) was also recorded. Pregnancy diagnosis was performed by transrectal ultrasonography 30-35d after insemination. Binary data were analysed using the GLIMMIX procedure of SAS, and time-dependent data were analysed using survival analysis. Overall, conception rate was not different between groups (51.0%, 52.0% and 51.8% for Control, P4-Ovsynch and P4-Ovsynch+eCG, respectively; P=0.9), but the 21-day pregnancy rate was increased by the synchronization protocols (38.6%, 58.6%, and 53.6%; P<0.0001). Supplementation with eCG at PRID removal did not affect pregnancy rate (53.3 vs. 52.5, P4-Ovsynch vs. P4-Ovsynch+eCG, respectively; P=0.9). Compared to the Control group, synchronization treatments significantly reduced the interval from MSD to conception (36.7, 24.0 and 27.1 days, respectively; P<0.001), and consequently reduced the average days open (87.0, 75.0 and 78.0 days, respectively; P<0.001). Across all treatment groups, DIM at start of synchronization had a significant effect on conception rate (44.3%, 51.1% and 59.5% for <60, 60-80 and >80 DIM, respectively; P<0.05), but parity (49.7%, 51.5% and 53.9% for parity 1, 2 and ≥3, respectively; P=0.7), BCS (44.9%, 51.6% and 58.6% for ≤2.50, 2.75 – 3.25 and ≥3.50, respectively; P=0.2) and presence of a CL (51.7% vs. 51.7%; P=0.9) did not have significant effects on the likelihood of pregnancy per AI. Additionally, there were no two-way interactions detected (P > 0.05) between treatment and DIM, parity, BCS or CL status category. In conclusion, the use of TAI accelerated pregnancy establishment of cows in a pasture-based system by reducing days open, but eCG supplementation at PRID removal did not affect pregnancy rate.
Keywords: eCG, progesterone, synchronization, timed AI