Prostaglandin F2a And Analogues

The best known luteolysin in farm animals is PGF2 a. It induces luteolysis when administered by intramuscular injection or when placed into the uterus, as early as four to six days after ovulation. Therefore, PGF2 a has been used widely in estrus-synchronization programs for cattle.

A single injection of PGF2a regresses the CL in approximately 50 60% of randomly cycling females. The CL is not responsive until after days 5 6 of the cycle. The percentage of females actually detected in estrus during five days after a single injection includes any in the responsive portion of the luteal phase at the time of injection plus those in the follicular phase that are coming into estrus spontaneously. If a second injection of PGF2 a is given 10 to 14 days after the first injection, females responding to the first injection (those recently in estrus and now in the luteal phase of their cycles) are responsive to the second injection and the remainder (those not responsive to the first injection) have a functional CL that is now responsive to PGF2a. Theoretically, estrus in all females may be synchronized after the second of two injections. Limitations to this theoretical potential include skills of those detecting estrus, luteolytic failure, or inadequate follicular development at the time of treatment. Prepubertal or early postpartum females without a functional CL are not affected by PGF2 a treatment. The estrus that occurs after one or two injections is equally fertile.

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