Effect of growing beef replacement heifers on wheat pasture before and during breeding on reproductive performance

ABSTRACT Reproductive performance of heifers grazing wheat pasture before and during breeding was compared with heifers grazing wheat pasture until approximately 3 wk before breeding. In each of 2 yr, 40 Angus and crossbred heifers were placed on wheat pasture in December and assigned to treatment groups in mid March. Group 1 (WP; n = 20) remained on wheat pasture through estrus synchronization and fixed-time AI (FAI). Group 2 (DL; n = 20) was placed in drylot and fed a corn-based growing ration (11.1% CP) through estrus synchronization and FAI. Heifers were exposed to bulls 10 d after FAI for 45 d. Conception after FAI was determined at 32 d post-AI by ultrasonography. Weekly blood samples starting 5 wk before FAI were obtained to describe luteal activity before estrus synchronization and for analysis of urea nitrogen concentrations before and during estrus synchronization and FAI. Percentage of heifers with luteal activity was 75 and 55% for WP and DL, respectively. The DL heifers were heavier than WP heifers (408 vs. 394 kg ± 4.49) at AI but were similar in final weight on native range (417 vs. 414 kg ± 5.26). Conception rate to FAI (53 vs. 43%) and final pregnancy rate (95 vs. 88%) were similar for WP and DL. Concentrations of urea were less (5.77 vs. 29.15 mg/dL) for DL heifers during all weeks after treatments were imposed. Reproductive performance of heifers grazing wheat pasture during estrus synchronization and FAI was similar to that of drylot heifers consuming a corn-based growing diet.