title: Triennial Reproduction Symposium: influence of follicular characteristics at ovulation on early embryonic survival.
abstract: Reproductive failure in livestock can result from failure to fertilize the oocyte or embryonic loss during gestation. Although fertilization failure occurs, embryonic mortality represents a greater contribution to reproductive failure. Reproductive success varies among species and production goals but is measured as a binomial trait (i.e., pregnancy), derived by the success or failure of multiple biological steps. This review focuses primarily on follicular characteristics affecting oocyte quality, fertilization, and embryonic health that lead to pregnancy establishment in beef cattle. When estrous cycles are manipulated with assisted reproductive technologies and ovulation is induced, duration of proestrus (i.e., interval from induced luteolysis to induced ovulation), ovulatory follicle growth rate, and ovulatory follicle size are factors that affect the maturation of the follicle and oocyte at induced ovulation. The most critical maturational component of the ovulatory follicle is the production of sufficient estradiol to prepare follicular cells for luteinization and progesterone synthesis and prepare the uterus for pregnancy. The exact roles of estradiol in oocyte maturation remain unclear, but cows that have lesser serum concentrations of estradiol have decreased fertilization rates and decreased embryo survival on d 7 after induced ovulation. When length of proestrus is held constant, perhaps the most practical follicular measure of fertility is ovulatory follicle size because it is an easily measured attribute of the follicle that is highly associated with its ability to produce estradiol.
authors.affiliation: USDA-ARS Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301, USA. tom.geary@ars.usda.gov
authors.forename: T W
authors.initials: TW
authors.lastname: Geary
authors.forename: M F
authors.initials: MF
authors.lastname: Smith
authors.forename: M D
authors.initials: MD
authors.lastname: MacNeil
authors.forename: M L
authors.initials: ML
authors.lastname: Day
authors.forename: G A
authors.initials: GA
authors.lastname: Bridges
authors.forename: G A
authors.initials: GA
authors.lastname: Perry
authors.forename: F M
authors.initials: FM
authors.lastname: Abreu
authors.forename: J A
authors.initials: JA
authors.lastname: Atkins
authors.forename: K G
authors.initials: KG
authors.lastname: Pohler
authors.forename: E M
authors.initials: EM
authors.lastname: Jinks
authors.forename: C A
authors.initials: CA
authors.lastname: Madsen
mesh_terms: D000818:Animals; D002417:Cattle / Q000196:embryology* / Q000502:physiology*; D004622:Embryo, Mammalian / Q000502:physiology*; D047108:Embryonic Development; D030762:Estrous Cycle; D005260:Female; D005306:Fertilization / Q000502:physiology; D058751:Livestock / Q000196:embryology / Q000502:physiology; D009865:Oocytes / Q000502:physiology*; D006080:Ovarian Follicle / Q000502:physiology*; D011247:Pregnancy