Abstract
Fourty repeat-breeder and anestrous Holstein heifers were treated with one of four methods using progesterone releasing intravaginal devices (PRIDs), prostaglandin F2α (PGF2α) analogue and synthetic gonadotropin releasing hormone (GnRH analogue). A PRID was inserted into the vagina for 7 or 12 days and a single injection of PGF2α analogue (500 μg) was administered one day before PRID removal. On the use of 12-day insertion, the estradiol-benzoate (E.B.) capsule containing 10 mg estradiol was excluded from PRID. The 12-day treatment of PRID without the E.B. capsule and a PGF2α analogue showed encouraging results in both estrus incidence (10/10; 100%) and the subsequent fertility (6/10; 60.0%) following fixed-time artificial insemination with frozen semen. Conception rate in heifers treated with two injections of PGF2α analogue 11 days apart was disappointed (3/10; 30.0%). The treatment of GnRH analogue (200 μg) and PGF2α analogue 9 days apart has showed a high conception rate (6/7; 85.7%) as well as the 12-days PRID treatment (9/10; 90.0%), when re-insemination in heifers returned to estrus within 24 days after treatment was involved. The present study indicates that the use of PRID combined with a PGF2α analogue is more effective for regulating the estrous cycle and the subsequent fertility of repeat-breeder and anestrous heifers than the two-injection regime of PGF2α analogue, and that the E.B. capsule may be unnecessary when a PGF2α analogue was administered one day before PRID removal.
