title: Ovarian dynamics in response to two modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocols designed for use in Brahman heifers.
abstract: The objective was to investigate the ovarian response of Brahman heifers to two modified ovulation synchronisation protocols developed to increase the proportion of normal synchronous ovulations. Experiment 1 characterised the growth of the ovulatory follicle in heifers (n=19) treated with an intravaginal progesterone releasing device (IPRD) and oestradiol benzoate (ODB), to determine the optimal time to induce ovulation. Using the findings from Experiment 1, Experiment 2 investigated the effect of reducing the duration of IPRD insertion and increasing the interval from IPRD removal to ODB treatment (modified protocol 1 - OPO-6; n=20), and omitting ODB treatment at the time of IPRD insertion (modified protocol 2 - PO-6; n=20). An IPRD (0.78 g progesterone) was inserted at Day 0 (OPO-8) or Day 2 (OPO-6 and PO-6) and all heifers also received 1 mg ODB i.m. Day 8: IPRD removed + 500 μg cloprostenol i.m. At 24 h (OPO-8) and 36 h (OPO-6 and PO-6) post IPRD removal: 1 mg ODB i.m. Fixed-time AI (FTAI) occurred at 54 h for OPO-8 and 72 h for OPO-6 and PO-6, post IPRD removal. After IPRD treatment all OPO-6 and OPO-8 heifers initiated a new follicular wave whereas 25% of PO-6 heifers failed. Diameter of the dominant follicle was larger at FTAI in the PO-6 (11.34 ± 0.50 mm) compared to the OPO-8 protocol (9.74 ± 0.51 mm; P<0.05), but similar to the OPO-6 protocol (10.52 ± 0.51 mm). Proportion of ovulations occurring 12 h prior and 24 h post FTAI was similar for the PO-6 (80%) and OPO-6 (75%) protocols but numerically lower in the OPO-8 heifers (60%). The apparent improvement in ovarian response in heifers treated with the modified protocols needs to be confirmed in larger field studies.
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia. Electronic address: s.butler@uq.edu.au.
authors.forename: S A A
authors.initials: SA
authors.lastname: Edwards
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia. Electronic address: pcatkinson@bigpond.com.
authors.forename: P C
authors.initials: PC
authors.lastname: Atkinson
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia. Electronic address: nanasatake@gmail.com.
authors.forename: N
authors.initials: N
authors.lastname: Satake
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia. Electronic address: g.boehansen@uq.edu.au.
authors.forename: G
authors.initials: G
authors.lastname: Boe-Hansen
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia. Electronic address: m.mcgowan@uq.edu.au.
authors.forename: M R
authors.initials: MR
authors.lastname: McGowan
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004973:Estrus Synchronization / Q000187:drug effects; D005260:Female; D010053:Ovary / Q000187:drug effects* / Q000502:physiology*; D010060:Ovulation / Q000502:physiology*; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: C074283:estradiol 3-benzoate; D011374:Progesterone; D004958:Estradiol
keywords: Bos indicus; Brahman; Fixed-time artificial insemination; Ovulation synchronization; Progesterone