In-vitro Dry Matter Digestibility, an Alternative Method for Silage Quality Assessment

Canadian dairy farmers rely heavily on silage as the primary feed ingredient and strive for optimal quality. Relative feed value (RFV) is a common index used within industry to compare forage quality and prices however it has been suggested that RFV may be a better reflection of plant maturity rather than digestibility. To improve the accuracy of silage quality assessment, an analytical technique which reflects the silages biological value is required, such as in-vitro dry matter digestibility (IVDMD). Between 2018-2020, samples of first cut legume, grass, and legume-grass mixed silages were collected from bunkers, piles, wrapped bales, and vertical silos across Canada (n=274). Subsamples were collected and sent for wet chemistry analysis of neutral detergent fiber (NDF) and acid detergent fiber (ADF) and values were used to calculate digestible dry matter (DDM) and dry matter intake (DMI) with the following equations, DDM= 88.9 – (0.779 x %ADF), DMI = 120/(%NDF). DDM and DMI were then used to calculate RFV with the following equation RFV= (DDM x DMI) / 1.29. IVDMD was conducted via the ANKOM DAISYII method with 48-hour incubation and NDF ending. RFV for grass, legume, and mixed silages at mid maturity were 96, 136, and 110 respectively while IVDMD was 55%, 66%, and 61% respectively. These results indicate RFV favours legume forages as grass and legume-mixed forages had considerably lower RFV while IVDMD values showed similar digestibility among the three forage types, indicating IVDMD is a more accurate comparison of silage quality than RFV as it represents the amount of dry matter available for digestibility. Incorporating IVDMD into the livestock and feed industries would allow for a more accurate comparison of forage types across regions not only for economic purposes but efficiency in allocating forages to specific group of animals.

Key words: silage quality, digestibility, relative feed value.

Presented at the 2022 Animal Nutrition Conference of Canada. For information on the next edition, click here.