ABSTRACT:The selection of replacements using applications such as reproductive tract scores and antral follicle count may be useful to eliminate less fertile animals before breeding. Previously, we reported that heifers with increased numbers of follicles achieved puberty earlier than heifers with diminished numbers of follicles. We, therefore, hypothesized that heifers that achieved a reproductive tract score ?4 earlier in the breeding season would have greater numbers of follicles than heifers that achieved a reproductive tract score ?4 later in the breeding season. The uterus and ovaries of three hundred and fifty beef heifers from a commercial farm were evaluated by transrectal ultrasonography 20 days before breeding and parameters of growth and development were recorded. The antral follicle count (AFC) of both ovaries was recorded and the heifers assigned a reproductive tract score (1 to 5). Only heifers with a reproductive tract score ?4 entered to two fixed timed artificial insemination (FTAI) programs. The first group (FTAI1 , n = 269) started the day of the beginning of the breeding period and the second group (FTAI2 , n = 61) one month later. The rest were naturally mated (no FTAI, n = 20). Serial pregnancy scanning was performed throughout the breeding season and 45 days after bull removal to estimate the day of conception. Data indicative of growth and development were analysed using the REG and GLM procedures of SAS with FTAI (0, 1 and 2), AFC (low, medium and high), and the interaction as the independent variables. Reproductive tract development was negatively associated to AFC (P>0.0001). There was no interaction between FTAI and AFC (P>0.11). Heifers inseminated at FTAI1 were heavier and taller, had greater deposition of fat and muscle, and conceived earlier than those inseminated at FTAI2 (P0.05) and heifers in the High AFC class conceived approximately 1 week earlier than heifers in the Low and Medium AFC class (P