Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: February 25, 2011
Publication Date: July 12, 2011
Citation: Boyd, J.A., Mertens, D.R. 2011. Comparison of alternative methods, sample grinds, and fermentation times for determining indigestible neutral detergent fiber. Journal of Dairy Science. 94(E-Supplement 1):454. Technical Abstract: The objectives of this study were to evaluate the effects of sample grind, fermentation method, and time on the determination of indigestible neutral detergent fiber (iNDF). Samples of: 1) alfalfa hay and silage, 2) corn stalks and silage, and 3) ryegrass and mixed grass hays were ground through 2-mm and 1-mm screens in a cutter mill and a 1-mm screen in a cyclone mill. Both 1-mm ground samples were fermented in flasks in vitro (IV) or in F57 filter bags in a rotating jar system for 0, 48, 72, 96, or 144 h. In-situ (IS) samples were fermented for 0, 48, 72, 96, 144, 240, and 288 h in animals fed either total mixed ration (TMR), alfalfa silage, or grass hay, and these same donors were used to make a composite inoculum for the in vitro and rotating jar fermentations. For in situ, 2-mm samples were fermented in Ankom in situ bags, and 1-mm cyclone samples were fermented in F57 filter bags. Fermentation residues were extracted in neutral detergent using crucibles with silica sand for IV or using the A200 fiber analyzer for all bags. Only samples fermented for >96 h were evaluated as estimates of iNDF. Data were analyzed using Proc MIXED of SAS with Run within Method and Rep within Run as random variables. Across all samples, 288 h IS obtained the smallest iNDF for the 1- and 2-mm grinds, and they were not different (P<0.05) from 1- and 2-mm grinds of 240 h IS or from both 1-mm grinds for 144 h IV. Bags appeared to impede measurement of iNDF. At 144 h, the IV results of both grinds were lower (P<0.05) than both grinds in F57 bags in the rotating jar system and the 1-mm cyclone grind in F57 bags fermented IS. The 2-mm grind fermented in IS bags at 144 h IS were not different from IV results at 144 h. In general, IS fermentation took nearly twice as long to obtain iNDF similar to IV results. Differences in iNDF among treatments were greater for more slowly fermenting substrates (corn stalks and mixed grass hay). In summary, measurement of iNDF is affected by time and fermentation system, but less so by grinding through 1- or 2-mm screens.