Influences Of Timing Of Liver Abscess Control And Early Metabolizable Amino Acid Supplementation On Feedlot Growth-Performance And Digestive Function Of Calf-Fed Holstein Steers

Objective: Our objective was to examine the influence of timing of liver abscess control and early rumen-protected AA supplementation on cattle growth performance (Exp. 1) and digestive function (Exp. 2), and related responses on liver abscess incidence and AA supply to the small intestine of feedlot steers.Materials and Methods: In Exp. 1, a total of 200 calves were used in a 321-d experiment. Four strategies for liver abscess control using virginiamycin (VM; 16 mg of VM/kg of diet DM, Phibro Animal Health) were used: (1) 0% VM; (2) VM supplementation during the initial 168 d; (3) VM supplementation during the final 153 d; and (4) VM supplemented continuously for 321 d. During the initial 168-d feeding period, 2 levels of rumen-protected Met and Lys (Smartamine ML: SML; 0 vs. 0.6% DM basis, Adisseo) were supplemented across VM treatments in a 2 x 4 factorial arrangement. In Exp. 2, 4 Holstein steers (382 +/- 23 kg) with cannulas in the rumen and proximal duodenum were used in a 4 x 4 Latin square design to evaluate treatment effects on digestion.Results and Discussion: Cattle growth performance was not affected (P >= 0.18) by VM supplementation strategy. Moreover, VM supplementation did not affect (P >= 0.10) carcass characteristics. Liver abscess incidence was low (4%) and not affected (P >= 0.62) by supplementation strategy. Supplemental VM did not affect characteristics of ruminal and total-tract digestion (P >= 0.27). Supplementation of SML during the first 168 d decreased (P = 0.02) DMI during the last 153 d of the experiment, and tended to decrease (P = 0.07) overall (321-d) DMI. Smartamine ML supplementation did not affect (P >= 0.11) ADG, G:F, carcass characteristics, percentage of abscessed liver, or characteristics of ruminal and total-tract digestion.Implications and Applications: Timing of VM supplementation did not influence cattle growth performance or incidence of liver abscess, which was low (4%) regardless of VM treatment. Protected Met and Lys supplementation increased Met or Lys supply to the small intestine. However, MP and AA supplies of the basal diet, alone, were apparently adequate to achieve expected growth performance.