Abstract Production of an offspring in mammals is the culmination of many specific steps that must be completed successfully in both the male and female for pregnancy to occur and be maintained. Growth of the follicle precedes the female’s requisite contribution of an oocyte for fertilization. It has been well established in the literature that the follicular microenvironment is unique to develop a healthy and mature oocyte that is required for fertilization. It has also been well established that luteal production of progesterone is necessary to maintain pregnancy and concentrations of progesterone regulate changes in the uterine environment. Preovulatory estradiol from the ovulatory follicle; however, has more recently been reported to play a significant role in the establishment and maintenance of pregnancy. For example, follicular secretion of estradiol affects the oviductal or uterine environment by changing the pH of the uterus, by altering sperm transport and longevity, and changing uterine gene expression and indirectly by modulating progesterone action via induction of progesterone receptors in the uterus. Estradiol production by the dominant follicle is regulated in other species by local factors including GnRH, but GnRH was not identified in cattle follicular fluid by receptor binding assays; more recently, gene expression within the granulosa cells indicates that it is being produced. Could it be playing a role, even though literature says it is not there? Similarly, vaccinations play a critical role in herd health, and literature indicates there are no negative consequences for reproductive performance if the animal is not naïve to the vaccination. Recent studies have reported that vaccination with a modified live viral vaccine can have negative consequence on pregnancy success even when the animal has been vaccinated before. More specifically vaccination has been reported to disrupt luteal function and cause short estrus cycles. Thereby, not allowing an animal to conceive during that cycle and delaying the interval to pregnancy establishment. When research goes against published literature it can be difficult to pursue, but as technologies change, as techniques become more sensitive, an open mind must be kept, and research must objectively be evaluated. Are studies designed correctly with appropriate controls? Where does reinvestigating dogma lead us? It is important that scientific questions based on previous results lead research. Knowledge of what has been done in the past is critical in interpreting and evaluating results but should not limit scientific research.
George A Perry (Wed,) studied this question.