Ability of induced corpora lutea to maintain pregnancy in beef cows

Experiments were conducted in beef cows without a primary CL, in which preg nancy had been maintained with exogenous progestogen. In preliminary trials , replacement CL induced ipsilateral to the embryo and after, rather than b efore, d 36 of pregnancy, maintained more pregnancies after withdrawal of e xogenous progestogen (13/13 vs 2/6; P < 0.05). In Exp. 1, in cows with repl acement CL induced by treatment with hCG on d 28 of pregnancy, treatment wi th flunixin meglumine on d 31 through 37 did not increase maintenance of pr egnancy. Experiment 2 was conducted to evaluate directly the effects of con centrations of PGF(2<alpha>) and estradiol-17 beta during d 31 through 35 o f pregnancy on maintenance of pregnancy by replacement CL induced between d 28 and 31. In cows that maintained pregnancy while progestogen was provide d, maintenance of pregnancy after withdrawal of exogenous progestogen tende d to be greater with high (5/5) than with low (2/6; P < 0.10) concentration s of PGF(2<alpha>) and greater with low (6/7) than with high (2/6; P = 0.10 ) concentrations of estradiol-17 beta. Secretion of progesterone by replace ment CL was greater (P < 0.05) in cows with high than in those with low con centrations of PGF(2<alpha>) during d 31 through 35. Prostaglandin F-2 alph a may facilitate attachment of the bovine embryo (d 30 to 40) in a manner s imilar to that reported for implantation in other species. Cows that did no t form CL in response to hCG on d 28 to 31 responded well when retreated af ter d 36. Again, maintenance of pregnancy was greater when replacement CL w ere induced after (9/9) rather than before d 36 (8/16; P < 0.05).