EVALUATION OF DIFFERENT CHROMIUM-MORDANTED WHEAT STRAWS FOR PASSAGE RATE STUDIES

Samples of untreated and ammonia-treated wheat straw were mordanted with sodium dichromate after being chopped, ground, or ground and washed in neutral detergent solution. The NDF content of the mordanted samples increased to 97 to 100% DM in those ground or ground and neutral detergent-washed, whereas the increase was lower (92% DM) in those chopped. Chromium content after mordanting was 4.0% DM in the samples washed in neutral detergent solution and 2.4 to 2.6% DM in those simply chopped or ground. There were no major differences due to ammonia treatment. Particle size distribution of ground samples showed significant differences in proportions of particles larger than 1mm with control samples less than ground and mordanted samples less than ground, neutral detergent-washed, and mordanted samples. There also were variable and significant effects of these treatments on functional specific gravity. Rumen DM disappearance after 48-h incubation in fiber bags was reduced greatly by mordanting but was negligible only with the previous neutral detergent treatment. The estimated rumen passage rates of mordanted samples of untreated straw differed significantly among treatments with chopped samples less than ground samples, which were less than ground and neutral detergent-washed samples, reflecting their differences in particle size and functional specific gravity. It was concluded that the mordanting procedure can affect greatly the physicochemical properties of feedstuffs, thus altering their passage rates.