Artificial insemination (AI) following a detected estrus results in decreased fertility when compared to hormone-based fertility programs. It is unclear at what stage of gestation pregnancy failure occurs and why it occurs in a greater proportion following AI to a detected estrus. The objective of the present dissertation was to investigate the current fertility potential of high-producing lactating dairy cows. A novel methodology of serial measurements of pregnancy-specific protein B (PSPB) allowed for pregnancy evaluation as soon as day 19 of gestation. Reduced antral age of the pre-ovulatory was associated with greater steroidogenic capacity and more intense estruses. Cows detected in estrus ovulated follicles with greater diameter in comparison to cows synchronized with Double-Ovsynch. Follicle diameter was positively associated with 17β-estradiol to progesterone (E2 to P4) ratio, but the ratio was not a predictor of conceptus attachment in estrus cows. Cows that received AI to a detected estrus had decreased fertility at conceptus attachment and pregnancy diagnosis performed between days 31 and 49 post-AI in comparison to Double-Ovsynch. Pregnancy losses occurring prior to this period did not differ between treatments. Hormonal intervention enhanced intrinsic fertility of cows that had at least 2 estrus events detected prior to 1st AI. Induction of accessory corpora lutea post-AI did not improve fertility of cows treated with timed AI programs. The models utilized herein enabled the endocrine, behavioral, and fertility characterization of high-producing dairy cows detected in estrus.
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