Also, heat stress alters follicular dynamics in cattle and therefore could alter the ability of the oocyte to produce viable embryos after ovulation and fertilization. This effect could be short term, affecting fertility in the current cycle, or could be long term, perhaps contributing to the less than optimum fertility that has been reported in the fall season. Evidence that heat stress can affect the oocyte before ovulation is presented in the following paragraphs, which discuss studies in superovulated cattle.