LAUSR

The objective was to compare the effect of corn type and tylosin inclusion on heifer growth performance, liver function, and carcass characteristics. Angus and Simmental × Angus heifers (n = 120; 188 ± 2.6 kg) were blocked by initial body weight (BW) and alloted to 8 pens. Pens were randomly assigned on d 0 to either be fed tylosin (T+) or no tylosin (T-). Heifers were adapted to the finishing diets utilizing a common adaptation proccess over 35 d. On d 36, pens were then assigned to a high moisture corn-based diet (HMC) or a dry-rolled corn-based diet (DRC) to achieve a 2 × 2 factorial design. Body weight was recorded and blood was collected on d 0, 35, and approximately every 28 d following. Rumen fluid and fecal grab samples were collected on a subset (n = 48) every 56 d. Treatment did not affect BW (P ≥ 0.14) or overall average daily gain (P ≥ 0.65) throughout the trial. No differences (P ≥ 0.21) were observed in overall dry matter intake. There was a diet × tylosin inclusion effect (P = 0.02) for estimated starch digestibility to be greatest for HMC/T+ heifers. On d 252, HMC heifers had greater (P = 0.03) ruminal pH before feeding compared to DRC. Heifers fed DRC/T- had the greatest (P = 0.01) blood urea nitrogen concentrations of all treatments. Aspertate aminotransferase was greater in T+ heifers compared with T- (P < 0.01). Heifers fed HMC had a larger (P = 0.04) longissimus muscle area than heifers fed DRC. Heifers fed HMC T+ had the most (P = 0.04) desireable yield grade. Although corn type and tylosin inclusion did not affect growth performance, corn type may affect starch digestibility, ruminal pH and blood markers of liver function.