title: Progesterone (CIDR)-based timed AI protocols using GnRH, porcine LH or estradiol cypionate for dairy heifers: ovarian and endocrine responses and pregnancy rates.
abstract: The overall objective was to compare the efficacy of GnRH, porcine LH (pLH) and estradiol cypionate (ECP), in a modified Ovsynch/fixed-time AI (FTAI) protocol that included a controlled internal drug [progesterone] release (CIDR) device. In Experiment 1, heifers received a CIDR on Day -10, and PGF (25mg) on Day -3. At CIDR insertion, heifers received 100 microg of GnRH (n=6), 0.5mg of ECP (n=6), 5.0mg of pLH (n=6) or 2 mL of saline (n=7); these treatments were repeated on Day -1, except for ECP, that was repeated on Day -2, concurrent with CIDR-removal. The 5.0 mg pLH was the least effective with a longer interval to ovulation than the other groups combined (102 versus 64 h; P<0.05). Overall mean LH concentrations (1.6 ng/mL) and area under the curve (AUC) did not differ among treatments, but mean peak LH concentration was lower in heifers given 5 mg of pLH compared to all other groups (4.5 versus 10.3 ng/mL; P<0.05). In Experiment 2, heifers on CIDR-based Ovsynch protocols were given 12.5mg pLH (n=6; pLH-low), 25.0 mg pLH (n=6, pLH-high), or 100 microg GnRH (n=5; control). Heifers in the pLH-high group had greater (P<0.01) plasma LH concentrations (between 12 and 20 h) than GnRH-treated heifers, but the pLH treatments did not differ (P>0.10). Area under the curve for LH (ng/32 h) was at least 50% greater (P<0.01) in pLH-treated heifers compared to GnRH-treated heifers (mean, 41.3, 56.3 and 20.3 for pLH-low, pLH-high and GnRH, respectively). Ovulation occurred in 15 of 17 heifers. Progesterone concentrations were higher on Days 9 and 14 in heifers given 25mg of pLH, suggesting enhanced CL function. In Experiment 3, 240 heifers were assigned to CIDR-based Ovsynch/FTAI protocols. The first and second hormonal treatments (with an intervening PGF treatment on Day -3) were GnRH/GnRH (100 microg), ECP/ECP (0.5 mg), pLH/pLH (12.5 mg) or GnRH/ECP, respectively; pregnancy rates were 58.7, 66.1, 45.9 and 48.3%, respectively (ECP/ECP>both pLH/pLH and GnRH/ECP; P<or=0.05). In conclusion, CIDR-based Ovsynch/FTAI protocols using either GnRH/GnRH or ECP/ECP yielded pregnancy rates about 20% points higher than previously reported for dairy heifers bred to Ovsynch/FTAI in the absence of a CIDR.
authors.affiliation: Livestock Development Division, Alberta Agriculture Food and Rural Development, Suite 205, 6903-116 Street, Edmonton, Alta., Canada T6H 5Z2. divakar.ambrose@gov.ab.ca
authors.forename: J D
authors.initials: JD
authors.lastname: Ambrose
authors.forename: J P
authors.initials: JP
authors.lastname: Kastelic
authors.forename: R
authors.initials: R
authors.lastname: Rajamahendran
authors.forename: M
authors.initials: M
authors.lastname: Aali
authors.forename: N
authors.initials: N
authors.lastname: Dinn
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002417:Cattle; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007986:Luteinizing Hormone / Q000008:administration & dosage* / Q000097:blood; D010062:Ovulation Induction / Q000662:veterinary; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage* / Q000097:blood
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; C007630:estradiol 17 beta-cypionate; D007986:Luteinizing Hormone