Treatment with prostaglandin F and an intravaginal progesterone insert promotes follicular maturity in advance of gonadotropin-releasing hormone among postpartum beef cows.

An experiment was designed to evaluate treatments to promote ovarian follicular maturity in advance of administration of exogenous gonadotropin-releasing hormone (GnRH; 100 μg gonadorelin) for control of the bovine estrous cycle. We hypothesized prostaglandin F (PGF; 500 μg cloprostenol) followed by an intravaginal progesterone-releasing insert (CIDR; 1.38 g progesterone) would induce greater follicle size and serum estradiol at the time of GnRH administration.

Comparison of long-term progestin-based protocols to synchronize estrus prior to natural service or fixed-time artificial insemination in Bos indicus-influenced beef heifers.

This experiment was designed to evaluate breeding strategies involving natural service or fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers (n = 1456) when there were field-type management conditions. Body weights and reproductive tract scores (RTS; Scale 1-5) were obtained for heifers before assignment to one of five treatments: 1) Non-synchronized control exposed for natural service (NS), n = 299; 2) melengestrol acetate + natural service (MGA + NS; 0.5 mg/heifer/d), n = 295; 3) 14-d controlled internal drug release insert + natural service (CIDR + NS), n = 289; 4) 14-d MGA-prostaglandin F (PG) + FTAI, n = 295; or 5) 14-d CIDR-PG + FTAI, n = 278.

Altering duration of the presynchronization period in a long-term progestin-based estrus synchronization protocol for timed artificial insemination of beef heifers.

An experiment was designed to evaluate the effect of extending duration of the presynchronization treatment in a long-term progestin-based estrus synchronization protocol. Heifers were assigned to either an 18 d (Day 0-18) or 14 d (Day 4 to Day 18) CIDR treatment (1.38 g progesterone controlled internal drug release insert; Zoetis, Madison, NJ), with prostaglandin F (PG; 250 μg im cloprostenol sodium) administered 16 d after CIDR removal (Day 34).

Evaluation of split-time artificial insemination following administration of a long or short-term progestin-based estrus synchronization protocol in beef heifers.

Fixed-time and split-time AI were compared following the melengestrol acetate (MGA) prostaglandin F (Experiment 1) and 7-d CO-Synch + controlled internal drug release (CIDR) protocols (Experiment 2). Heifers in Experiments 1 (n = 524) and 2 (n = 456) were assigned within pen to balanced treatments based on weight and reproductive tract score (RTS; Scale 1-5). In Experiment 1, MGA (0.

Evaluation of SexedULTRA 4M™ sex-sorted semen in timed artificial insemination programs for mature beef cows.

An experiment was designed to compare fertility of SexedULTRA 4M™ sex-sorted semen and conventional, non-sex-sorted semen following either fixed-time artificial insemination (FTAI) or split-time artificial insemination (STAI) of mature suckled beef cows. Units of sex-sorted and conventional semen were produced using contemporaneous ejaculates from three commercially available sires. Units of conventional semen were generated with 25.