90 The effect of removing tylosin from finishing diets with increasing roughage concentration on growth performance carcass characteristics and prevalence of liver abscesses of finishing cattle.

摘要

A trial utilizing 3,340 beef steers (initial BW = 387 ± 14.2 kg; DOF = 161 ± 7) was conducted to evaluate the effects of tylosin removal from finishing diets with increasing roughage concentration. A randomized complete block design with 8 pen replications (70 steers/pen) and 4 treatments were used. Dietary treatments were: 1) 7.1% corn stalks with tylosin (7.1TYL), 2) 7.1% corn stalks with no tylosin (7.1NT), 3) 13.1% corn stalks with no tylosin (13.1NT), or 4) 19.1% corn stalks with no tylosin (19.1NT). Corn stalks replaced steam flaked corn on a DM basis. Data were analyzed using the ANOVA procedure of Stata 15 with fixed effects of treatment and block and pen was the experimental unit. Categorical data (carcass grade distributions and liver scores) were analyzed using logistic regression (binreg; Stata 15). Single degree of freedom contrasts were used to compare 7.1TYL vs. 7.1NT; 7.1TYL vs. 13.1NT and 19.1NT; and the linear effect of increasing roughage without tylosin. Increased roughage resulted in a linear increase in DMI (P < 0.001). Increased roughage linearly reduced final BW, ADG, and resulted in poorer G:F (P ≤ 0.001). Final HCW was similar between 7.1TYL and 7.1NT (411 vs. 410 kg, respectively; P = 0.49); however, HCW linearly decreased as roughage increased (410, 408, or 401 kg, respectively; P < 0.001). Tylosin inclusion reduced liver abscess occurrence by 32.1% (13.03 vs. 19.18%, respectively; P = 0.001). Liver abscess occurrence decreased linearly with increased roughage (19.18, 11.88, or 14.40%, respectively; P = 0.009). Increased roughage did not improve liver abscess severity (P ≥ 0.13).These data indicate that replacing steam flaked corn with corn stalks in diets without tylosin may reduce liver abscess occurrence but not severity. However, decreased dietary energy led to increased DMI and lighter HCW in cattle fed to the same DOF.