title: Oxygen and steroid concentrations in preovulatory follicles of lactating dairy cows exposed to acute heat stress.
abstract: Maternal heat stress reduces oocyte competence for fertilization and post-fertilization development, but the mechanism is unknown. The present experiment investigated two potential mechanisms: (1) reduced oxygen delivery to the preovulatory follicle (due to increased thermoregulatory vascular perfusion of skin and respiratory tract); (2) reduced follicular steroid synthesis. These hypotheses were tested by measuring the fractional concentration of oxygen and concentrations of estradiol-17beta and progesterone in follicular fluid of the preovulatory follicle of lactating Holstein cows. Estrous cycles were synchronized using GnRH on Day -9 and PGF(2alpha) on Day -2. On Day 0, all cows without a CL and with a large preovulatory follicle were assigned to control or heat stress treatments for 1d (beginning at 1030 h). Between 4 and 6 h after treatment (1430-1630 h), follicular fluid was aspirated by transvaginal puncture, and fractional oxygen concentration in follicular fluid of the dominant follicle was determined with a fluorometric fiber-optic oxygen sensor. There was no significant effect of heat stress on follicular fluid P(O2) or concentrations of estradiol-17beta or progesterone among cows that had follicular fluid steroid concentrations considered typical of a preovulatory follicle. Follicular oxygen concentration was 6.9+/-0.4% for control cows and 7.3+/-0.3% for heat-stressed cows. Oxygen concentration tended to be inversely correlated to follicular diameter (P=0.09). In conclusion, it was unlikely that reduced oocyte competence due to acute heat stress was caused by reductions in follicular concentrations of oxygen, estradiol-17beta, or progesterone.
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville, FL 32611-0910, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: de Castro E Paula
authors.forename: J
authors.initials: J
authors.lastname: Andrzejewski
authors.forename: D
authors.initials: D
authors.lastname: Julian
authors.forename: L J
authors.initials: LJ
authors.lastname: Spicer
authors.forename: P J
authors.initials: PJ
authors.lastname: Hansen
mesh_terms: D000208:Acute Disease; D000818:Animals; D001831:Body Temperature; D002417:Cattle / Q000502:physiology; D003612:Dairying; D004780:Environment, Controlled; D004958:Estradiol / Q000032:analysis; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry; D005498:Follicular Phase; D012739:Gonadal Steroid Hormones / Q000032:analysis*; D018882:Heat Stress Disorders / Q000473:pathology*; D007774:Lactation; D009994:Osmolar Concentration; D006080:Ovarian Follicle / Q000737:chemistry* / Q000473:pathology; D010100:Oxygen / Q000032:analysis*; D011247:Pregnancy; D011374:Progesterone / Q000032:analysis; D012007:Rectum / Q000502:physiology; D013997:Time Factors
chemical_list: D012739:Gonadal Steroid Hormones; D011374:Progesterone; D004958:Estradiol; D010100:Oxygen