| dc.description.abstract | Objectives were to 1) evaluate the use of the CO-Synch + CIDR (COS-C)
protocol for synchronization of ovulation and timed AI (TAI) in Bos indicus-influenced
cattle, 2) compare cumulative pregnancy rates after COS-C synchronization and TAI to
those in a traditional management (TM) scheme, and 3) evaluate specific ovarian,
hormonal, and estrual events associated with COS-C. The COS-C regimen included
insertion of a controlled internal drug release device (CIDR) containing progesterone
and injection of GnRH (GnRH-1) on day 0, removal of the CIDR and injection of
prostaglandin F2a
(PGF on d 7, and injection of GnRH (GnRH-2) and TAI 48 h later. In
experiment 1 (Exp. 1), 335 females were stratified by BCS, parity and d postpartum
before random assignment to COS-C or TM. An additional 96 females in which TM
controls were not available for comparison also received COS-C. Conception rates to
TAI averaged 39% (n = 266). Cumulative pregnancy rates were greater (P < 0.05) after
30 and 60 d of the breeding season in COS-C than in TM (n = 170 and 165 females respectively). In experiment 2 (Exp. 2), 100 postpartum (F1) females were stratified as
in Exp. 1 within four replicates (25 each) and assigned randomly to receive either COSC
or COS (no CIDR) treatment. No differences were observed between treatments and
all data were pooled. Percentages of cows ovulating after GnRH-1, developing a
synchronized follicular wave, exhibiting luteal regression to PGF, and ovulating to
GnRH-2 were 40, 60, 93, and 72%, respectively. In experiment 3 (Exp. 3), primiparous
(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 ± 2.9, 99 ± 2.8, and 29 ± 2.2
h, respectively. Relatively low TAI conception rates (< 50%) were attributed to failure
of 40% of cattle to develop a synchronized follicular wave after GnRH-1 and to
inappropriate timing of TAI/GnRH-2. It may be possible to improve TAI conception
rates by delaying TAI/GnRH-2 to between 66 and 72 h, and by developing methods to
increase the number of ovulations after GnRH-1. | en |
