422 Evaluating the relationship between anogenital distance, reproductive tract score, and fertility to timed-artificial insemination in commercial Bos taurus beef heifers.

Abstract Previous studies have found an inverse correlation between anogenital distance (AGD) and beef and dairy cattle fertility, with greater fertility observed in females with short AGD. It has been previously demonstrated that heifers with mature reproductive tracts, as assessed by reproductive tract scores (RTS), have improved fertility to artificial insemination programs. The objective of this study was to explore the relationship between AGD, RTS, and conception rates to timed-artificial insemination (TAI) in Bos taurus commercial yearling beef heifers (n=884). All heifers were assigned to RTS on a scale from 1 to 5 at least two days before the beginning of the TAI protocol. Reproductive tract scores were determined based on uterine horn diameter and uterine tone, where 1=immature, <20mm diameter and no tone; 2=20-25mm diameter and no tone; 3=20-25mm diameter with slight tone; 4=30mm diameter with good tone; 5= >30mm diameter with good tone. Heifers from 8 different locations in the states of Kansas and Tennessee were utilized during the years of 2023 and 2024. All heifers were enrolled in a controlled internal drug release (CIDR)-based estrus synchronization protocol and received TAI. Pregnancy status was determined by transrectal ultrasonography approximately 45 days post TAI. The AGD was defined as the distance from the middle of the anus to the base of the clitoris, and was assessed using digital calipers at CIDR insertion, withdraw, TAI, or pregnancy diagnosis based on location. Results indicate a moderate correlation between RTS and AGD (r=0.32; P< 0.0001). Additionally, there was an effect of Location (P< 0.001) and RTS (P=0.003), but no effect of AGD (P=0.151) on conception rates to TAI, and there was no difference in average AGD between heifers that were diagnosed as pregnant or open to TAI (P= 0.1935; 83.2mm, and 84.2mm, respectively). We conclude that RTS is a more accurate assessment of beef heifer fertility to TAI than AGD.