Technical note: use of slow-release estradiol and prostaglandin F2alpha to induce pseudopregnancy and control estrus in gilts.

We determined whether a single injection of slow-release estradiol-17β (SRE2) would induce pseudopregnancy in gilts and whether PGF 2α would regress the corpora lutea (CL) of pseudopregnancy. Crossbred gilts (n = 40) were induced to ovulate by treatment with 400 IU of hCG + 200 IU of eCG (PG600, Intervet, Millsboro, DE) given at 180 d of age (d = 0). On d 14, gilts were injected i.m. with one of five doses (n = 8 gilts/dose) of SRE2 (0, 12.5, 25, 50, or 100 mg). Blood samples were collected before SRE2 and twice weekly until d 73 to monitor serum progesterone (P 4 ) and estradiol (E 2 ). On d 59, gilts received (i.m.) 10 mg of PGF 2α (Lutalyse, Pharmacia Upjohn, Kalamazoo, MI) and were checked for estrus for 7 d. On d 62, mammary development was scored (0 = no development; 1 = some development; 2 = teat and gland development) by a neutral observer. Treatment with SRE2 increased (P .05) among doses of SRE2 in the percentage of pseudopregnant gilts that showed luteolysis after PGF 2α . We conclude that a single injection of SRE2 can induce pseudopregnancy and that the CL can be regressed with PGF 2α , providing a simple method for controlling estrus in gilts.