Endocrine, estrous and pregnancy response to varying dosages of Luprostiol in beef cows

Multiparous lactating beef cows were observed for estrus and randomly assigned to one of four Luprostiol (13, thia-PG-F(2)alpha analog) treatment groups receiving 3.8 (LI), 7.5 (LII), 15 (LIII) or 30 (LIV) mg Luprostiol, respectively, or to an untreated control group (C), or to a positive control group (E) receiving 500 mcg Estrumate. Cows received their respective treatments in a single dosage on Day 7, 8 or 9 of the estrous cycle (estrus = Day 0) and were artificially inseminated 12 h following the subsequent estrus. Blood samples were collected from all groups immediately prior to treatment and at 12-h intervals to 48 h post treatment and analyzed for progesterone (P(4)). Blood samples were collected at 3-h intervals from 24 to 72 h post treatment for animals in Group LIII and for 48 h (or observed estrus) starting on Day 19 of the estrous cycle for animals in Group C. These samples were analyzed for estradiol-17beta(E(2)), follicle stimulating hormone (FSH) and luteinizing hormone (LH). Treatment with Luprostiol at doses >/= 7.5 mg resulted in a synchronous estrous response during the first 5 d post treatment in 75 to 95% of cows treated. Luteal function, as evaluated by systemic P(4) concentration, paralleled results observed for estrous response. Treatment with a 15 or 30 mg dose of Luprostiol resulted in greater overall pregnancy rate at synchronized estrus. No biologically significant differences were found in blood levels of E(2), FSH or LH around the time of estrus between cows in Groups C and LIII. Results from these studies indicate treatment with Luprostiol at doses >/= 7.5 mg resulted in a synchronous estrus during the first 5 d after treatment. Pregnancy rates and endocrine changes were similar to those observed in control and Estrumate-treated cows.