The central hypothesis of this project is that gilts demonstrating tertiary follicle development on their ovaries earlier in life are more likely to achieve puberty at a younger age compared to their counterparts. The objective of this project was to identify physiological markers and specific time-points during pre-pubertal development that could be utilized as valid indices to predict age of first puberty. Five time points (days 75, 85, 95, 105 and 115 of age) were used and at each time point from which phenotypic measures (vulva length, vulva width, and body weight) and blood were collected. These time points represent specific days in age that observations can be made to distinguish gilts with high and low probability of achieving puberty by 200 days of age. Identification of pre-pubertal markers that correlate to age of first puberty will assist producers in making earlier gilt replacement decisions.