Evaluation of later timepoints for fixed-time artificial insemination of beef heifers and cows when using sex-sorted semen.

Two experiments were designed to evaluate later timepoints for fixed-time artificial insemination (FTAI) of beef heifers and cows, with the hypothesis that use of a later timepoint would allow a greater proportion of animals to express estrus prior to FTAI and result in greater conception rates among estrous females inseminated with sex-sorted semen. In Experiment 1, estrus was synchronized for 1640 heifers using the 14 d CIDR-PG protocol: insertion of an intravaginal progesterone-releasing insert (CIDR; 1.38 g progesterone) on Day -33 and removal on Day -19, and administration of prostaglandin F (PG; 500 μg cloprostenol sodium) on Day -3.

Inducing luteolysis prior to atresia of the first follicular wave by altering the interval to prostaglandin F administration after long-term progestin presynchronization.

A series of experiments was designed to evaluate treatment schedules for control of the estrous cycle in which luteolysis is induced prior to atresia of the first follicular wave following a long-term progestin presynchronization treatment in beef heifers. The overarching hypothesis was that the proportion of heifers undergoing luteolysis and expressing estrus following PG administration would be affected by the duration of treatment with an intravaginal progesterone-releasing insert (CIDR; 1.38 g progesterone) and/or by the interval from CIDR removal to prostaglandin F (PG; 500 μg cloprostenol) administration.