Administration of a GnRH analog on day 9 of a 14-day controlled internal drug release insert with timed artificial insemination in lactating beef cows.
Many estrus synchronization protocols aim to induce a new follicular wave to improve response and enhance pregnancy rate. Our objectives were to determine the effectiveness of GnRH analog administered d 0 and 9 during an extended controlled internal drug release (CIDR) protocol to produce 2 follicular waves, induce cyclicity in anestrus cows, and evaluate the efficacy of a single 50-mg dose of PGF2α to initiate luteal regression on CIDR removal. Lactating beef cows (n = 779) at 3 locations (n = 247, location 1; n = 395, location 2; n = 137, location 3) were randomly assigned to 1 of 3 treatments. Cows in the 14-d 50 PG treatment received a CIDR (1.38 g progesterone) with 100 μg GnRH analog intramuscularly (i.m.) on d 0, 100 μg GnRH analog i.m. on d 9, and CIDR removal concurrent with 50 mg PGF2α i.m. on d 14. Cows in the 14-d 6-h PG treatment were assigned the same protocol as the 14-d 50 PG treatment except that 25 mg PGF2α i.m. was given on d 14 plus 25 mg PGF2α i.m. 6 ± 1 h later. Cows in the control treatment, 5-d CO-Synch + CIDR (5-d CO-Synch), received a CIDR concurrent with 100 μg GnRH analog i.m. on d 9, CIDR removal concurrent with 25 mg PGF2α i.m. on d 14, and 25 mg PGF2α i.m. 6 ± 1 h after first F2α injection. Cows in all treatments received 100 μg GnRH analog i.m. and timed AI (TAI) 72 ± 3 h after CIDR removal. Pregnancy status to TAI was determined by ultrasonography 37 to 40 d after TAI. Averaged over all locations, pregnancy rates to TAI for 14-d 50 PG, 14-d 6-h PG, and 5-d CO-Synch treatments were 58.2%, 46.8%, and 41.9%, respectively. Pregnancy rates to TAI were greater (P < 0.05) in 14-d 50 PG treatment than 14-d 6-h PGF2α and 5-d CO-Synch treatments. Cycling status at 2 locations (n = 243, location 1; n = 391, location 2) was determined from blood collected on d -7 and 0; cows with serum progesterone concentrations >1 ng/mL at either (or both) bleeding date were considered cyclic. Averaged over the 2 locations, there was a tendency (P = 0.06) for a greater number of cyclic animals to become pregnant to TAI in the 14-d 50 PG treatment (64.4%) than 5-d CO-Synch treatment (50.2%). The 14-d CIDR with GnRH analog on d 0 and 9 and a single 50-mg dose of PG i.m. at CIDR removal was a more efficacious protocol to maximize TAI pregnancy rates than the standard 5-d CO-Synch.
Department of Animal Sciences, Colorado State University, Fort Collins 80523, USA.
R L
RL
Giles
J K
JK
Ahola
J C
JC
Whittier
J T
JT
French
P E
PE
Repenning
S G
SG
Kruse
G E
GE
Seidel
R K
RK
Peel
D000818:Animals; D002417:Cattle; D015237:Dinoprost / Q000008:administration & dosage / Q000494:pharmacology; D004343:Drug Implants; D004971:Estrus / Q000187:drug effects; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007273:Injections, Intramuscular; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology
D004343:Drug Implants; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D015237:Dinoprost