Timing of artificial insemination in postpartum beef cows following administration of the CO-Synch + controlled internal drug-release protocol.
This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) at 54 or 66 h after administration of the CO-Synch + controlled internal drug-release (CIDR) protocol. Cows (n = 851) at 2 locations over 2 yr (yr 1, n = 218 and 206; and yr 2, n = 199 and 228 at the 2 locations, respectively) were stratified by age, BCS, and days postpartum to 1 of 2 FTAI intervals. Cows were administered GnRH (100 mug, i.m.) and were equipped with a CIDR insert (1.38 g of progesterone) on d 0. Controlled internal drug-release inserts were removed 7 d later at the time PGF(2alpha) (25 mg, i.m.) was administered (d 7). Continuous estrus detection was performed at location 2 by using the HeatWatch Estrus Detection System; the transmitters were fitted at the time of PGF(2alpha) and removed at the time of AI. Artificial insemination was performed at predetermined fixed times [54 h (FTAI 54; n = 424) or 66 h (FTAI 66; n = 427) after PGF(2alpha)] and all cows were administered GnRH (100 mug, i.m.) at AI. Two blood samples were collected on d -10 or -8 and immediately before treatment initiation to determine the pretreatment estrous cyclicity status of cows [progesterone >/=0.5 ng/mL (FTAI 54, 288/424 = 68%; FTAI 66, 312/427 = 73%; P = 0.07)]. Pregnancy rates were greater (P < 0.01) among cows that exhibited estrus than among those that did not (123/163 = 76% and 150/270 = 56%, respectively). There were no treatment x location interactions within year (P > 0.10) for age, days postpartum, or BCS; thus, the results were pooled for the respective treatments. Pregnancy rates were greater for FTAI 66 than FTAI 54 (P = 0.05; 286/426 = 67% vs. 257/424 = 61%, respectively). Pregnancy rates resulting from FTAI did not differ between year (P = 0.09), farm (P = 0.80), AI sire (P = 0.11), or technician (P = 0.64). There was no difference between pregnancy rates resulting from FTAI based on pretreatment cyclicity status (P = 0.30), and there was no difference between treatments in final pregnancy rates (P = 0.77). In summary, pregnancy rates resulting from FTAI following CO-Synch + CIDR at 66 h were greater than those resulting from FTAI at 54 h.
Busch
D C
DC
Division of Animal Science, S132 ASRC, University of Missouri, Columbia 65211, USA.
Schafer
D J
DJ
Wilson
D J
DJ
Mallory
D A
DA
Leitman
N R
NR
Haden
J K
JK
Ellersieck
M R
MR
Smith
M F
MF
Patterson
D J
DJ
D000818:Animals; D002417:Cattle / Q000502:physiology*; D016009:Chi-Square Distribution; D003692:Delayed-Action Preparations; D015237:Dinoprost / Q000008:administration & dosage; D004973:Estrus Synchronization / Q000187:drug effects / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation; D008297:Male; D049590:Postpartum Period; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000097:blood; D013997:Time Factors; D016216:Ultrasonography, Prenatal / Q000662:veterinary
D003692:Delayed-Action Preparations; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D015237:Dinoprost