Effects of Sire EPD, Dam Traits and Calf Traits on Calving Difficulty and Subsequent Reproduction of Two-Year-Old Heifers

A three-year study evaluated effects of sire birth weight EPD, heifer and calf traits on valuing difficulty and subsequent rebreeding of two-year-old cows. MARC II yearling heifers (n=550) were assigned for breeding to one of four angus sires with birth weight EPD of -2.1, -1.8, +6.3 and +5.9 lb. Of all heifer weights, only dam birth weight affected calving difficulty score. Heifers requiring caesareans had smallest pelvic areas. Calving difficulty increased as calf birth weight and external measurements increased. Low EPD sires produced calves with smaller head and foot circumferences and less dystocia. Degree of calving difficulty did not affect subsequent pregnancy rates, but did delay rebreeding conception date