Ovarian, hormonal, and reproductive events associated with synchronization of ovulation and timed appointment breeding of Bos indicus-influenced cattle using intravaginal progesterone, gonadotropin-releasing hormone, and prostaglandin F2 alpha.

摘要

The objectives of this study were to (1) compare cumulative pregnancy rates in a traditional management (TM) scheme with those using a synchronization of ovulation protocol (CO-Synch+CIDR) for timed AI (TAI) in Bos indicus-influenced cattle; (2) evaluate ovarian and hormonal events associated with CO-Synch+CIDR and CO-Synch without CIDR; and (3) determine estrual and ovulatory distributions in cattle synchronized with Select-Synch+CIDR. The CO-Synch+CIDR regimen included insertion of a controlled internal drug-releasing device (CIDR) and an injection of GnRH (GnRH-1) on d 0, removal of the CIDR and injection of PGF2 alpha (PGF) on d 7, and injection of GnRH (GnRH-2) and TAI 48 h later. For Exp. 1, predominantly Brahman x Hereford (F1) and Brangus females (n=335) were stratified by BCS, parity, and day postpartum (parous females) before random assignment to CO-Synch+CIDR or TM. To maximize the number of observations related to TAI conception rate (n=266), an additional 96 females in which TM controls were not available for comparison also received CO-Synch+CIDR. Conception rates to TAI averaged 39+or-3% and were not affected by location, year, parity, AI sire, or AI technician. Cumulative pregnancy rates were greater (P<0.05) at 30 and 60 d of the breeding season in CO-Synch+CIDR (74.1 and 95.9%) compared with TM (61.8 and 89.7%). In Exp. 2, postpartum Brahman x Hereford (F1) cows (n=100) were stratified as in Exp. 1 and divided into 4 replicates of 25. Within each replicate, approximately one-half (12 to 13) received CO-Synch+CIDR, and the other half received CO-Synch only (no CIDR). No differences were observed between treatments, and the data were pooled. Percentages of cows ovulating to GnRH-1, developing a synchronized follicular wave, exhibiting luteal regression to PGF, and ovulating to GnRH-2 were 40+or-5, 60+or-5, 93+or-2, and 72+or-4%, respectively. In Exp. 3, primiparous Brahman x Hereford, (F1) heifers (n=32) and pluriparous cows (n=18) received the Select Synch+CIDR synchronization regimen (no GnRH-2 or TAI). Mean intervals from CIDR removal to estrus and ovulation, and from estrus to ovulation were 70+or-2.9, 99+or-2.8, and 29+or-2.2 h, respectively. These results indicate that the relatively low TAI conception rate observed with CO-Synch+CIDR in these studies was attributable primarily to failure of 40% of the cattle to develop a synchronized follicular wave after GnRH-1 and also to inappropriate timing of TAI/GnRH-2..