PSI-5 Pregnancy and calving rates following fixed time AI in beef cows: A comparison between two estrus synchronization protocols.

Abstract Fixed-time artificial insemination (FTAI) has been widely utilized by beef industry as their ability to provide chances for the females to be inseminated on a predetermined time, while also decreasing the time and labor for estrus detection. Presynchronization was applied as a method to improve estrus response before FTAI. Our aim was to compare estrus responses and FTAI outcomes in beef cows using two different synchronization protocols: 7&7 Synch (7&7) and 7-day Co-Synch+CIDR® (7dCSC). One hundred and eighteen Angus cows from 3 farms, two in eastern/middle region of Georgia, (cows only, GLEN, n=39 and COBB, n=42), and one in middle GA (FVSU, n=37; 25 cows, 12 heifers) were used. Cows from GLEN and COBB farms were assigned to 7dCSC protocol and received GnRH and CIDR insertion on Day 0, prostaglandin F2α (PG) injection and CIDR removal on Day 7. Cows from FVSU farm were assigned 7&7 protocol and administered PG and CIDR insertion on Day − 14, GnRH on Day − 7, and CIDR removal and PG on Day 0. For both protocols, FTAI conducted with GnRH 66 h after second PG. Estrus detection patches were placed on all animals at CIDR removal and second PG injection. Body condition score (BCS) was recorded at AI. Estrus indicators include estrus patch status (color change or missing), the color of vulva mucus membrane (pink vs pale), texture of the cervix (hard vs soft), and the status of insemination (easy vs hard) were also reported. Pregnancy was determined by ultrasonography at 3 months after FTAI. Differences in estrus responses and pregnancy rates between the two protocols were analyzed by Chi-square, Fisher’s Exact testing, and general linear mixed models (GLIMMIX) test using SAS. Significant difference was set at P< 0.05. The results showed that pregnancy rate following FTAI was higher for 7&7 than 7dCSC one (64.9% vs. 50.6%, respectively), however the difference was not significant. Among estrus indicators, we found that estrus patches had color change or missing in 90.9% of cows in 7&7 compared to 30.3% in 7dCSC protocols (P< 0.001). No significant differences were observed in other indicators between the two protocols. In FVSU farm, cows showed higher (P<0.05) pregnancy rates than heifers (76.0% vs. 41.7%, respectively). Furthermore, calving rate to AI was higher (P< 0.05) for cows than heifers (66.7% vs 20%, respectively). Animal BCS score was higher (P< 0.001) for COBB (4.9±0.06) and FVSU (5.0 ±0.07) farms than GLEN one. Among the 3 farms, FVSU had the highest (P< 0.03) calving rates to AI (76±0.2%) than other 2 farms. In conclusion, effectiveness of estrus synchronization protocol depends on a cow’s physiological status and 7&7 protocol showed higher estrus response and pregnancy rate and calving rate to AI compared with 7dCSC.