A comparison of progestin-based protocols to synchronize ovulation and facilitate fixed-time artificial insemination in postpartum beef cows.
The experimental objective was to compare pregnancy rates after fixed-time AI in postpartum suckled beef cows following administration of two progestin-based protocols to synchronize ovulation. Cows (n = 424) at three locations (n = 208, 122, and 92 per location) were stratified by age, BCS, and days postpartum (DPP) and assigned randomly to one of the two treatment protocols. The MGA Select-treated cows (MGA Select; n = 213) were fed melengestrol acetate (MGA, 0.5 mg x cow(-1) x d(-1)) for 14 d and carrier for 8 d, and then GnRH (100 microg i.m. Cystorelin; d 26) was injected 12 d after MGA withdrawal, and PG (25 mg i.m. Lutalyse) was administered 7 d after GnRH. Cows assigned to the 7-11 Synch protocol (7-11 Synch; n = 209) were fed carrier for 15 d and MGA for 7 d, and then injected with PG on d 22 (d 7 of MGA), GnRH on d 26, and PG again on d 33. Artificial insemination was performed at fixed times for cows in both treatments at 60 or 72 h after d 33 PG for 7-11 Synch and MGA Select groups, respectively. All cows were injected with GnRH (100 microg of i.m. Cystorelin) at AI. There was no treatment x location interaction for age (P = 0.90), BCS (P = 0.64), or DPP (P = 0.93), and the results were therefore pooled for the respective treatments (age [7-11 Synch, 5.5 +/- 0.2; MGA Select, 5.5 +/- 0.2], BCS [7-11 Synch, 5.7 +/- 0.1; MGA Select, 5.6 +/- 0.1], and DPP [7-11 Synch, 41.1 +/- 1.1; MGA Select, 42.1 +/- 1.1]). Blood samples were collected 8 and 1 d before MGA or carrier to determine pretreatment estrous cyclicity (progesterone >or=1 ng/mL; 7-11 Synch, 59/209 [28%]; MGA Select, 54/213 [25%]; P = 0.50) and again on d 33 PG to evaluate treatment response as a percentage of cows with progesterone concentrations in serum >or=1ng/mL (7-11 Synch, 184/209 [88%]; MGA Select, 177/213 [83%]; P = 0.15). Pregnancy rates resulting from fixed-time AI did not differ (P = 0.25) between treatments (7-11 Synch, 128/209 [61%]; MGA Select, 142/213 [67%]), nor did pregnancy rates (P = 0.77) at the end of the breeding season (7-11 Synch, 198/208 [95%]; MGA Select, 204/213 [96%]). These data indicate that pregnancy rates were comparable after fixed-time AI, following administration of the 7-11 Synch and MGA Select protocols. Both protocols provide opportunities for beef producers to use AI and eliminate the need to detect estrus.
Bader
J F
JF
Department of Animal Science, University of Missouri, Columbia 65211, USA.
Kojima
F N
FN
Schafer
D J
DJ
Stegner
J E
JE
Ellersieck
M R
MR
Smith
M F
MF
Patterson
D J
DJ
D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D004973:Estrus Synchronization / Q000187:drug effects / Q000379:methods*; D005260:Female; D005938:Glucocorticoids / Q000008:administration & dosage / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation; D016015:Logistic Models; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000494:pharmacology*; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000097:blood; D011453:Prostaglandins / Q000008:administration & dosage; D011897:Random Allocation; D013997:Time Factors
D005938:Glucocorticoids; D011453:Prostaglandins; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D008552:Melengestrol Acetate; D015237:Dinoprost; C010714:dinoprost tromethamine