It is widely believed that stimulation of the phosphoinositide pathway and production of 1,4,5-inositol trisphosphate (IP₃) underlies the oscillatory changes in the concentration of intracellular free calcium ions ([Ca² ]_i) seen during mammalian fertilization. IP₃ promotes Ca² release in eggs by binding to its receptor, the type-1 IP₃ receptor (IP₃R-1, also known as ITPR1), a ligand-gated Ca² channel located in the membrane of the endoplasmic reticulum, the main Ca² store of the cell. While IP₃R-1 has been shown to mediate all Ca² release during mouse fertilization, whether or not it plays such an essential role in fertilization-induced Ca² release in large domestic species such as bovine and porcine is presently not known. Accordingly, we have generated metaphase II bovine eggs with a ∼70%–80% reduction in the number of intact IP₃R-1 by inducing receptor down-regulation during oocyte maturation. We did so by injecting the nonhydrolyzable IP₃ analogue, adenophostin A. Functional Ca² release analysis revealed that IP₃R-1 is the predominant Ca² release channel in bovine eggs, requiring as little as 20% of total intact receptor to mount persistent [Ca² ]_i oscillations in response to fertilization, expression of PLCζ (also known as PLCZ1), and adenophostin A. However, lower concentrations of IP₃ and near-physiological concentrations of porcine sperm extract were unable to trigger [Ca² ]_i oscillations in this reduced IP₃R-1 model. Furthermore, we present evidence that the sensitivity of bovine IP₃R-1 is impaired at the first embryonic interphase. Together, these results demonstrate the essential role of IP₃R-1-mediated Ca² release during fertilization in bovine eggs, and identify cell cycle regulatory mechanisms of [Ca² ]_i oscillations at the level of IP₃R-1.