A MODIFIED METHOD FOR THE IN VITRO DETERMINATION OF DRY MATTER AND ORGANIC MATTER DIGESTIBILITY

Abstract

Several modifications were made to the two-stage in vitro fermentation techniques for dry matter and organic matter digestibility (IVDMD and IVOMD) determinations developed by Tilley and Terry (J. Brit. Grassland Soc. 18: 104–111, 1963) and Alexander and McGowan (J. Brit. Grassland Soc. 21: 140–147, 1966). These modifications included: (1) changing the buffer medium, which resulted in a pH of 6.8–7.0 in the fermentation tubes during the initial (stage 1) 48-h fermentation period, and (2) shortening the acid-pepsin incubation period from 48 to 24 h, and thus reducing time for estimation of both IVDMD and IVOMD by 24 h. Modification (1) eliminated pH adjustments during fermentation and acidification at the end of the fermentation period. Acid-pepsin digestion of substrates was completed within 24 h instead of 48 h. Both IVDMD and IVOMD values were obtained on the same substrates. These modifications were evaluated using 65 samples that arose from 13 forages, comprised of corn and grass silages and their mixtures, which had been dried by five different methods. IVDMD and IVOMD were determined on all samples, comparing the modified method with the parent methods. IVDMD and IVOMD coefficients within each method were not statistically different between the Tilley and Terry method and the modified method.