Effects of twice daily compared with split-time estrous detection on pregnancy percentage in recipient beef cows.

Objectives were to compare pregnancy percentages per embryo transfer (P/ET) in recipient beef cows following twice daily compared with split-time estrous detection and to determine associations of dominant follicle diameter, CL volume and progesterone concentrations. All cows (n = 695) were treated to synchronize time of estrus among cows using a CIDR + Select-Synch treatment regimen and randomly assigned to twice-daily or split-time estrous detection (CS-DEET or CS-SEET, respectively). Cows in the CS-DEET group were observed twice daily (eight times) for estrus until 96 h after the time of PGF2α administration, whereas cows in the CS-SEET group were observed twice (64 and 84 h after PGF2α). In 280 recipient cows, blood sampling (for progesterone) and ultrasonographic assessment of dominant follicle diameter were conducted 48 h after the time of PGF2α administration. At 7 d after estrus, the CL was imaged and there was transfer of a frozen-thawed embryo into cows with a CL ≥ 1.5 cm. There were positive correlations between follicle diameter and CL volume (rs = 0.827; P < 0.001) and CL volume and progesterone concentration (rs = 0.680; P < 0.001). Progesterone and CL volume differed between cows in CS-SEET and CS-DEET groups P < 0.05), however, percentage P/ET for cows in the CS-SEET and CS-DEET groups did not differ (P > 0.1). Dominant follicle diameter, CL volume and progesterone concentrations were greater in pregnant compared with nonpregnant cows. In conclusion, percentage P/ET did not differ when there was twice daily and split-time estrous detection highlighting the value of this approach in beef enterprises.