Comparison of progestin-based protocols to synchronize estrus and ovulation before fixed-time artificial insemination in postpartum beef cows.
This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) after treatment with 1 of 2 protocols to synchronize estrus and ovulation. Cross-bred, suckled beef cows (n = 650) at 4 locations (n = 210; n = 158; n = 88; and n = 194) were assigned within a location to 1 of 2 protocols within age group by days postpartum and BCS. Cows assigned to the melengestrol acetate (MGA) Select treatment (MGA Select; n = 327) were fed MGA (0.5 mg x head(-1) x d(-1)) for 14 d, GnRH (100 microg of Cystorelin i.m.) was injected on d 26, and prostaglandin F2alpha (PG; 25 mg of Lutalyse i.m.) was injected on d 33. Cows assigned to the CO-Synch + controlled internal drug release (CIDR) protocol (CO-Synch + CIDR; n = 323) were fed a carrier for 14 d, were injected with GnRH and equipped with an EAZI-BREED CIDR insert (1.38 g of progesterone, Pfizer Animal Health, New York, NY) 12 d after carrier removal, and PG (25 mg of Lutalyse i.m.) was injected and the CIDR were removed on d 33. Fixed-time AI was performed at 72 or 66 h after PG for the MGA Select or CO-Synch + CIDR groups, respectively. All cows were injected with GnRH (100 microg of Cystorelin i.m.) at the time of insemination. Blood samples were collected 8 and 1 d before the beginning of MGA or carrier to determine estrous cyclicity status of the cows (estrous cycling vs. anestrus) before treatment [progesterone > or = 0.5 ng/mL (MGA Select, 185/327, 57%; CO-Synch + CIDR, 177/323, 55%); P = 0.65]. There was no difference (P = 0.20) in pregnancy rate to FTAI between treatments (MGA Select, 201/327, 61%; CO-Synch + CIDR, 214/323, 66%). There was also no difference (P = 0.25) between treatments in final pregnancy rate at the end of the breeding period (MGA Select, 305/327, 93%; CO-Synch + CIDR, 308/323, 95%). These data indicate that pregnancy rates to FTAI were comparable after administration of the MGA Select or CO-Synch + CIDR protocols. Both protocols provide opportunities for beef producers to utilize AI and potentially eliminate the need to detect estrus.
Schafer
D J
DJ
Division of Animal Sciences, University of Missouri, Columbia 65211, USA.
Bader
J F
JF
Meyer
J P
JP
Haden
J K
JK
Ellersieck
M R
MR
Lucy
M C
MC
Smith
M F
MF
Patterson
D J
DJ
D000034:Abortion, Veterinary; D000284:Administration, Oral; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D004343:Drug Implants; D004973:Estrus Synchronization / Q000187:drug effects / Q000379:methods*; D005260:Female; D005300:Fertility Agents, Female / Q000008:administration & dosage / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000662:veterinary; D008552:Melengestrol Acetate / Q000008:administration & dosage; D010060:Ovulation / Q000187:drug effects*; D049590:Postpartum Period; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000008:administration & dosage
D004343:Drug Implants; D005300:Fertility Agents, Female; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D008552:Melengestrol Acetate; D015237:Dinoprost; C010714:dinoprost tromethamine