04044naa a2200253 a 450000100080000000500110000800800410001902400430006010000140010324501170011726000090023450006480024352025870089165300260347865300170350465300390352165300120356065300250357270000180359770000190361570000160363470000170365077301230366710613482020-09-25       2020    bl uuuu     u00u1 u    #d7 aDOI: 10.1016/j.livsci.2020.1042302DOI1 aCUNHA, F.  aAntral follicular count has limited impact in the selection of more fertile beef heifers.h[electronic resource]  c2020  aArticle history: Received 7 April 2020, Revised 20 July 2020, Accepted 25 August 2020, Available online 26 August 2020. Acknowledgments: This work was supported by the project ?Marcadores de Fertilidad para Ganado de Carne? of the National Institute of Agricultural Research (INIA). This research was partially supported by ARS Research Project 3040-31000-096-00D (RAC). The authors would like to acknowledge Pablo Cuadro from INIA and all the staff of the commercial farm ?Las Grutas?. We would also like to thank Pablo González for his contribution with statistic. Corresponding author: E-mail address: cvinoles@adinet.com.uy (C. Viñoles).  aABSTRACT: 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 (P<0.05); however, there was no difference in AFC between heifers inseminated in FTAI1 and FTAI2 (15.6 ± 0.4 vs. 16.7 ± 0.9 follicles, respectively; P = 0.3). Furthermore, conception rates did not differ statistically between heifers in FTAI1 and FTAI2 (P = 0.12). Antral follicle count influenced growth and carcass traits (P>0.05) and heifers in the High AFC class conceived approximately 1 week earlier than heifers in the Low and Medium AFC class (P<0.05). We conclude that pubertal heifers have less AFC, thus similar numbers were observed for heifers in both FTAI programs and no differences in pregnancy rate. Antral follicle count may allow for the selection of heifers that conceive earlier, but may result in a lower pregnancy rate.  aANTRAL FOLLICLE COUNT  aBEEF HEIFERS  aFIXED TIME ARTIFICIAL INSEMINATION  aPUBERTY  aREPRODUCCIÓN ANIMAL1 aCUSHMAN, R.A.1 aSANTA CRUZ, R.1 aDE NAVA, G.1 aVIÑOLES, C.  tLivestock Science, November 2020, Volume 241, Article number 104230. Doi: https://doi.org/10.1016/j.livsci.2020.104230