Pgf2α

Cows between 39 and 64 DIM (mean ± SD = 45.2 ± 6.0) were submitted to a pretreatment for synchronization of ovulation, consisting of an Ovsynch + controlled internal drug-release insert (CIDR; Figure 1; Pursley et al., 1995) (link). Briefly, cows received GnRH (200 µg i.m.; Factrel, Zoetis) and a P4 intravaginal insert (Eazi-Breed CIDR; Zoetis). Seven days later, the P4 insert was removed, and prostaglandin F 2α (PGF 2α 25 mg i.m.; Lutalyse HighCon, Zoetis) was administered, followed by another PGF 2α 1 d later and a second GnRH 1 d after the second PGF 2α . Only synchronized cows with complete CL regression 2 d after PGF 2α (serum P4 < 1.0 ng/mL) and ovulation by 2 d after the last GnRH were used in the study (n = 64). The last GnRH of pretreatment was considered d 0 of the estrous cycle. After confirmation of synchronization, cows were randomly assigned to one of 3 treatments. Control cows (n = 22) did not receive any treatment except the synchronization protocol. Cows enrolled in the second treatment group (hCG7; n = 20) received an i.m. treatment with 3,300 IU of hCG (Chorulon, Merck Animal Health) 7 d after the last GnRH (d 7 of the cycle), and cows enrolled in the third treatment group (hCG7+13; n = 22) received 2 hCG treatments with 3,300 IU, one on d 7 and a second on d 13 after the last GnRH (d 7 and d 13 of the estrous cycle).

The reproductive status of nonlactating Holstein cows was assessed by transrectal ultrasonography and 20 cows with a detectable corpus luteum were subjected to a hormonal protocol to synchronize ovulation. On d -18 (day of expected ovulation = d 0), cows were injected i.m. with 25 mg of PGF 2α (Lutalyse, Zoetis, Florham Park, NJ) followed by 100 µg of gonadorelin (GnRH; Cystorelin, Merial Inc., Duluth, GA) on d -16. A second, identical injection of GnRH was given on d -9 and a progesterone-containing controlled internal drug release device (CIDR, Zoetis) was inserted intravaginally. At d -4, each cow was administered 25 mg of PGF 2α i.m. and the intravaginal device was removed. Another 25 mg of PGF 2α was injected at d -3 and 100 µg of GnRH was injected i.m. at d -2 (i.e., 24 h after PGF 2α ). Transrectal ultrasonography of ovaries was performed on d -4, -1, and 0 to confirm ovulation. A total of 15 cows were successfully synchronized and slaughtered at either d 0 (n = 4), 3 (n = 4), 5 (n = 3), or 7 (n = 4) relative to the day of ovulation. Cows within group were split into 2 groups that were slaughtered on 2 different days. Slaughter was by captive-bolt stunning and exsanguination at a commercial abattoir.

Cows had their estrous cycles synchronized for first TAI using a Double-Ovsynch protocol starting at 53 ± 3 DIM in herd A and 51 ± 3 DIM in herd B, as described by Souza et al. (2008) and later modified by Brusveen et al. (2009) . The GnRH (100 μg/dose of gonadorelin hydrochloride, Factrel) and the PGF 2α (25 mg/dose of dinoprost tromethamine, Lutalyse) were from Zoetis (Madison, NJ). Briefly, cows received the first GnRH treatment of the Presynch portion of the Double-Ovsynch, followed by a treatment with PGF 2α 7 d later and GnRH 72 h after PGF 2α . Seven days later, cows received a GnRH (G1) treatment followed by 2 PGF 2α treatments administered 7 and 8 d later, with the last GnRH (G2) treatment administered 56 h after the first PGF 2α treatment and AI 16 to 20 h later (Figure 1). Within each herd, cows (n = 800; n = 560 herd A; n = 240 herd B) were blocked by parity (primiparous vs. multiparous) and randomly assigned to serve as untreated controls (high-P4) or to receive a half dose of PGF 2α (low-P4; 12.5 mg of dinoprost tromethamine) 2 d before G1 (Figure 1). At each location, multiple sires with high genetic merit and proven fertility were used and were equally balanced between treatments.

Lactating Holstein cows (n = 1,100; 417 primiparous and 683 multiparous cows) diagnosed not pregnant were randomly assigned to 1 of 3 protocols for resyn-chronization of ovulation and TAI (Figure 1). Cows randomized to the first treatment received an Ovsynch protocol with a single PGF 2α treatment (control: 100 µg of GnRH; 7 d, 25 mg of PGF 2α ; 56 h, 100 µg of GnRH); cows randomized to the second treatment received an Ovsynch protocol with 2 PGF 2α treatments administered 24 h apart (GPPG: 100 µg of GnRH; 7 d, 25 mg of PGF 2α ; 24 h, 25 mg of PGF 2α ; 32 h, 100 µg of GnRH); and cows randomized to the third treatment received an Ovsynch protocol with a double dose of PGF 2α (GDDP: 100 µg of GnRH; 7 d, 50 mg of PGF 2α ; 56 h, 100 µg of GnRH). All cows received TAI approximately 16 h after G2. The GnRH (100 µg/dose of gonadorelin hydrochloride; Factrel) and the PGF 2α (25 mg/dose of dinoprost tromethamine; Lutalyse) were from Zoetis (Madison, NJ).