Efficacy of an injection of dinoprost tromethamine when given subcutaneously on luteal regression in lactating Holstein cows

The objectives of these studies were to evaluate the efficacy of a PGF(2alpha) (PGF) analog given through different routes on causing luteal regression in lactating dairy cows. In Experiment 1, lactating Holstein cows (n=118) at random stages of lactation were blocked by parity and days in milk (DIM) and, within each block, randomly assigned to receive PGF as an intra-muscular (IM) injection in the semimembranous/semitendinous muscle (CON), subcutaneous (SC) injection in the cervical area (SCN), or SC injection in the ischio-rectal fossa (IRF). Blood was sampled at 0, 12, 24, 36, and 48 h after treatment for assessment of progesterone concentration. In Experiment 2, a total of 379 lactating Holstein cows, 46+/-7 DIM, were blocked by DIM and, within each block, randomly assigned to receive treatment similar to CON or IRF groups from Experiment 1. Blood was sampled 0 and 48 h after treatment for assessment of progesterone concentration. Cows were classified as experiencing luteal regression when progesterone concentration was