Technical note: Use of slow-release estradiol and prostaglandin F-2 alpha to induce pseudopregnancy and control estrus in gilts

We determined whether a single injection of slow-release estradiol-17 beta (SRE2) would induce pseudopregnancy in gilts and whether PGF(2 alpha) 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, gil ts 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 twi ce 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(2 alpha) (Lutalyse, Pharmaci a Upjohn, Kalamazoo, MI) and were checked for estrus for 7 d. On d 62, mamm ary development was scored (0 = no development; 1 = some development; 2 = t eat and gland development) by a neutral observer. Treatment with SRE2 incre ased (P < .05) peak E-2 concentrations, duration of luteal function, and ma mmary gland score. There were no differences (chi-square, P > .05) among do ses of SRE2 in the percentage of pseudopregnant gilts that showed luteolysi s after PGF(2 alpha). We conclude that a single injection of SRE2 can induc e pseudopregnancy and that the CL can be regressed with PGF(2 alpha), provi ding a simple method for controlling estrus in gilts.