Inclusion of an intravaginal progesterone insert plus GnRH and prostaglandin F2 alpha for ovulation control in postpartum suckled beef cows

Four experiment stations (IL, KS, MN, and MO) conducted experiments to dete rmine effects of introducing a CIDR (controlled internal device release) in to an ovulation control program for postpartum suckled beef cows. Five hund red sixty cows were assigned randomly to two treatments: 1) 100 mug of GnRH (i.m.) followed in 7 d with 25 mg of PGF(2 alpha), followed in 48 h by a s econd injection of GnRH and one fixed-time insemination (Cosynch; n = 287) or 2) Cosynch plus one CIDR during the 7 d between the first injection of G nRH and PGF(2 alpha) (Cosynch+P; n = 273). Cows at three stations were inse minated at the time of the second GnRH injection (n = 462), whereas 98 cows at the fourth station were inseminated 16 to IS h after that injection. Bl ood samples were collected at d -17, -7, 0, and 2 relative to PGF(2 alpha) to determine concentrations of progesterone. Ultrasonography was used to mo nitor follicle diameter on d 2 and to determine the presence of an embryo a t 30 to 35 d after insemination. Pregnancy rates were greater (P < 0.05) fo r Cosynch+P- (58%) than for Cosynch-treated (48%) cows. No station x treatm ent interaction occurred; however, cows at MO (62%) and KS (60%) had greate r (P < 0.05) pregnancy rates than those at IL (47%) and MN (44%). Cows that had follicles > 12 mm on d 2 had greater (P < 0.01) pregnancy rates than t hose with follicles less than or equal to 12 min regardless of treatment. P regnancy rates were similar between Cosynch and Cosynch+P treatments when c ycling cows had elevated concentrations of progesterone at d 0, but pregnan cy rates were greater (P < 0.05) in the Cosynch+P (79%) than in the Cosynch (43%) treatment when cycling cows had low concentrations of progesterone o n d 0 (at PGF(2 alpha) injection). Similarly, among noncycling cows, pregna ncy rates were greater (P < 0.05) in the Cosynch+P (59%) treatment than in the Cosynch (39%) treatment. Cows in greater body condition at the onset of the breeding season experienced improved (P < 0.001) overall pregnancy rat es. Pregnancy rates for cows that calved > 50 d before the onset of the bre eding season were greater (P < 0.01) than those for cows that calved less t han or equal to 50 d. Thus, treatment of suckled cows with Cosynch yielded acceptable pregnancy rates, but addition of a CIDR improved pregnancy rates in noncycling cows. Body condition and days postpartum at initiation of th e breeding season affected overall efficacy of the Cosynch and Cosynch+P pr otocols.