Effects of Supplement Type on Growth and Pregnancy Rate of Yearling Brahman-Crossbred Heifers

Abstract

The effects of winter supplement type on growth and pregnancy rate of fallborn, yearling heifers was investigated over 2 consecutive yr. During both years, heifers were stratified by breed (Braford and Brangus-crossbred) and BW and randomly assigned to one of two treatments consisting of 1) wheat middling-based range cube or 2) molasses-cottonseed meal slurry (n = 34 and 24 heifers per treatment for yr 1 and 2, respectively). Supplements were fed at rates to achieve a target of 1.47 and 0.34 kg of supplemental TDN and CP daily, respectively. Four limpograss (Hemarthria altissima) pastures were utilized each year (n = 2 pastures per treatment; 0.71 and 0.51 ha per heifer for yr 1 and 2, respectively). All heifers were allowed free-choice access to stargrass (Cynodon nlemfuensis) hay during periods of limited pasture forage availability. During a 70-d breeding season, heifers were combined by group and exposed to mature Angus bulls. Bulls were rotated among pastures each week. Individual heifer BW and hip height were collected at the start of supplementation and at the start and end of the breeding season. Pregnancy rate was determined by transrectal ultrasonography in late April of each year (minimum of 40 d after the end of breeding). There were no treatment × year, breed × treatment, or breed × year interactions for heifer ADG (P>0.10). Supplement type did not affect heifer ADG (0.44 and 0.47 kg/d for molasses-slurry and range cubes, respectively). Heifers consuming molasses-slurry had a greater (P<0.01) overall pregnancy rate compared with heifers consuming range cubes (76.3% vs 49.2% pregnant). Regardless of treatment, Brangus-crossbred heifers had a greater pregnancy rate (P<0.01) than Braford heifers (73.2% vs 46.8%). These data indicate that yearling heifers supplemented with molasses-cottonseed meal slurry may have increased pregnancy rates compared with heifers supplemented with a wheat middling-based range cube. This response appears to be independent of heifer ADG.