RUMINAL DISTRIBUTION OF ZINC IN STEERS FED A POLYSACCHARIDE-ZINC COMPLEX OF ZINC-OXIDE

Six Holstein steers (initial BW 335 kg) were used in a replicated 3 x 3 Latin square design to study the distribution of Zn in ruminal conte nts from a conventional Zn source (ZnO) or Zn sequestered to a polysac charide (PC-Zn). Treatments consisted of a basal diet (no Zn supplemen tation) and the basal diet supplemented with Zn from either PCZn or Zn O. Steers were provided with 208, 920, or 896 mg of Zn/d from basal, P C-Zn, or ZnO, respectively. On collection day, steers were dosed with 800 mg of Zn from each Zn supplement and whole ruminal contents (WRC) were sampled at 1, 2, 4, 6, and 8 h postdosing. The cell-free (soluble ) Zn concentrations in steers fed the PC-Zn or ZnO supplements decreas ed (P < .05) rapidly after dosing. Mean Zn concentrations of the cell- free fraction were considerably lower than either microbial or particl e fractions of WRC. Compared with ZnO, the PC-Zn source resulted in hi gher (P < .05) cell-free Zn at 1 and 2 h after dosing and higher (P < .05) Zn concentrations (micrograms/gram of DM) in the fluid- and parti cle-associated microbial and particle fractions. Compared with basal, fluid-associated microbial DM concentration tended to be higher (P < . 10) at 6 and 8 h with PC-Zn and ZnO. Results indicate a rapid disappea rance of Zn from the soluble fraction and a high concentration of Zn i n the DM of the microbial and particle fractions of WRC. Furthermore, PC-Zn resulted in higher levels of Zn in all fractions of WRC, and Zn supplementation tended to increase microbial DM production at later sa mpling times.