title: Animal-level factors affecting ovarian function in Bos indicus heifers treated to synchronize ovulation with intravaginal progesterone-releasing devices and oestradiol benzoate.
abstract: The primary objective of this study was to investigate the impact of animal-level factors including energy balance and environmental/management stress, on the ovarian function of Bos indicus heifers treated to synchronize ovulation. Two-year-old Brahman (BN) (n = 30) and BN-cross (n = 34) heifers were randomly allocated to three intravaginal progesterone-releasing device (IPRD) treatment groups: (i) standard-dose IPRD [Cue-Mate(®) (CM) 1.56 g; n = 17]; (ii) half-dose IPRD [0.78 g progesterone (P(4)); CM 0.78 g; n = 15]; (iii) half-dose IPRD + 300 IU equine chorionic gonadotrophin at IPRD removal (CM 0.78 g + G; n = 14); (iv) and a control group, 2× PGF(2α) [500 μg prostaglandin F(2α) (PGF(2α))] on Day -16 and -2 (n = 18). Intravaginal progesterone-releasing device-treated heifers received 250 μg PGF(2α) at IPRD insertion (Day -10) and IPRD removal (Day -2) and 1 mg oestradiol benzoate on Day -10 and -1. Heifers were managed in a small feedlot and fed a defined ration. Ovarian function was evaluated by ultrasonography and plasma P(4) throughout the synchronized and return cycles. Energy balance was evaluated using plasma insulin-like growth factor 1 (IGF-I) and glucose concentrations. The impact of environmental stressors was evaluated using plasma cortisol concentration. Heifers that had normal ovarian function had significantly higher IGF-I concentrations at commencement of the experiment (p = 0.008) and significantly higher plasma glucose concentrations at Day -2 (p = 0.040) and Day 4 (p = 0.043), than heifers with abnormal ovarian function. There was no difference between the mean pre-ovulatory cortisol concentrations of heifers that ovulated or did not ovulate. However, heifers that ovulated had higher cortisol concentrations at Day 4 (p = 0.056) and 6 (p = 0.026) after ovulation than heifers that did not ovulate.
authors.affiliation: The School of Veterinary Science, The University of Queensland, Gatton, Qld, Australia. s.butler@uq.edu.au
authors.forename: S A A
authors.initials: SA
authors.lastname: Butler
authors.forename: N J
authors.initials: NJ
authors.lastname: Phillips
authors.forename: G B
authors.initials: GB
authors.lastname: Boe-Hansen
authors.forename: G A
authors.initials: GA
authors.lastname: Bo
authors.forename: B M
authors.initials: BM
authors.lastname: Burns
authors.forename: K
authors.initials: K
authors.lastname: Dawson
authors.forename: M R
authors.initials: MR
authors.lastname: McGowan
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D001786:Blood Glucose; D002417:Cattle / Q000502:physiology*; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D006854:Hydrocortisone / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D010053:Ovary / Q000502:physiology*; D010060:Ovulation / Q000187:drug effects* / Q000502:physiology; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*; D015430:Weight Gain
chemical_list: D001786:Blood Glucose; C074283:estradiol 3-benzoate; D011374:Progesterone; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D006854:Hydrocortisone