title: Pregnancy rates after fixed-time artificial insemination of Brahman heifers treated to synchronize ovulation with low-dose intravaginal progesterone releasing devices, with or without eCG.
abstract: The objective was to determine whether eCG in an ovulation synchronization protocol with an intravaginal progesterone (P(4))-releasing device (IPRD) containing a low dose of P(4) improves pregnancy rate (PR) to fixed-time AI (FTAI) in Bos indicus heifers. Day 0, 2 y old Brahman heifers were allocated to either eCG+ (n = 159) or eCG- (n = 157) treatment groups. All heifers were weighed, body condition scored (BCS), and ultrasonographically examined to measure uterine horn diameter and presence of a CL. On Day 0, all heifers received a low-dose IPRD (0.78 g P(4)) and 1 mg of estradiol benzoate (EB) im. On Day 8, the IPRD was removed, all heifers received 500 μg cloprostenol im, and those in the eCG+ treatment group received 300 IU of eCG im. On Day 9, all heifers received 1 mg EB im. All heifers were FTAI 52 to 56 h after IPRD removal. Ten days after FTAI, heifers were exposed to bulls. Heifers were diagnosed as pregnant to FTAI, natural mating, or not detectably pregnant (NDP) 65 d after FTAI. Treatment with eCG+ as compared to eCG- did not affect PR to FTAI (28.9 vs 30.6%; P = 0.590), natural mating (51.3 vs 47.7%; P = 0.595), or overall (65.4 vs 63.7%; P = 0.872). Mean live weight gain from Days 0 to 65 d post-FTAI was higher in heifers pregnant to FTAI (72.29 ± 4.26 kg; P = 0.033) and overall (66.83 ± 3.65 kg; P = 0.021), compared to heifers that were NDP (60.03 ± 3.16 kg). Uterine diameter group, 9-11, 12-13, and 14-20 mm (26.2, 31.3, and 33.3%; P = 0.256), presence and absence of CL (29.8 vs 29.4%; P = 0.975), AI technicians 1, 2, and 3 (32.6, 28.8, and 22.4%; P = 0.293) and sires A, B, and C (23.9, 36.0 and 27.0%; P = 0.122) had no effect on PR to FTAI, natural mating, or overall. In conclusion, treatment of primarily cycling Brahman heifers with 300 IU eCG in conjunction with a low P(4)-dose (0.78 g) IPRD and EB to synchronize ovulation, did not improve PR after FTAI, natural mating, or overall.
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia. s.butler@uq.edu.au
authors.forename: S A A
authors.initials: SA
authors.lastname: Butler
authors.forename: P C
authors.initials: PC
authors.lastname: Atkinson
authors.forename: G B
authors.initials: GB
authors.lastname: Boe-Hansen
authors.forename: B M
authors.initials: BM
authors.lastname: Burns
authors.forename: K
authors.initials: K
authors.lastname: Dawson
authors.forename: G A
authors.initials: GA
authors.lastname: Bo
authors.forename: M R
authors.initials: MR
authors.lastname: McGowan
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D001823:Body Composition; D002417:Cattle / Q000502:physiology*; D006063:Chorionic Gonadotropin / Q000008:administration & dosage / Q000494:pharmacology*; D003008:Cloprostenol / Q000008:administration & dosage / Q000494:pharmacology; D005260:Female; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*; D015430:Weight Gain
chemical_list: D006063:Chorionic Gonadotropin; D003008:Cloprostenol; D011374:Progesterone