Effects of feeding high manganese rice straw on the mineral status of beef cattle

Abstract

The objective of this study was to determine the effects of feeding rice straw containing high concentrations of manganese (Mn) to beef cattle on liver Mn concentration and its potential to interfere with other minerals. Open, crossbred cows (N=12) in good health were randomly assigned to one of three treatment group diets: oat hay (control), rice straw containing 550 ppm Mn and rice straw containing 770 ppm Mn. High quality alfalfa hay was supplemented at the same amount to each group to ensure adequate energy and protein intake. Blood, serum and liver samples were taken from each animal at day 0, 49 and 93 and analyzed for trace mineral and heavy metal content. Liver Mn concentrations for the group receiving 770 ppm Mn rice straw were significantly higher than for the control group at both day 49 and day 93 (P<0.05). Liver Mn concentrations for the 550 ppm Mn group were significantly higher than for the control group at day 93 (P<0.05). Liver Mn concentrations among the two rice straw treatments were not significantly different from each other. Serum sodium (Na) levels in cows fed the 770 ppm Mn rice straw were significantly higher than the animals fed 550 ppm rice straw at day 49 (P<0.05); however, there appeared to be no significant difference at day 93. There was no significant difference among treatment groups for other trace mineral and heavy metal concentrations. While it appeared cattle fed rice straw maintained higher liver Mn concentrations relative to control cattle, these concentrations were within the reference range of 2-6.5 ppm. There were no significant differences among treatment groups for average daily gain. No practical impact on the mineral status of cattle fed high Mn rice straw was observed over the 93-day period.