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Effect of Shredding Alfalfa Stems on Fiber Digestion Determined by In Vitro Procedures and Scanning Electron Microscopy¹

US Dairy Forage Research Center, USDA, ARS, and University of Wisconsin, 1925 Linden Drive West, Madison 53706

ABSTRACT

Alfalfa stems were shredded using a rotary macerator, were ammoniated, or were left untreated (control). Shredding increased extent of NDF digestion over ammoniation and control at all times from 12 to 72 h of in vitro incubation. Shredding also increased rate of disappearance of potentially digestible NDF (.032 h^–1 for control, .045 h^–1 for ammoniated, and .089 h^–1 for shredded). Ammoniation increased extent of NDF digestion after 36 h. Computed time required for 95% digestion of potentially digestible NDF was 94 h for control, 66 h for ammoniated and 34 h for shredded stems. Scanning electron microscopy revealed that the most prominent effect of shredding was separation of lignified and unlignified cells. Shredding split stems into a number of fragments and damaged the external cuticular waxy layer and structural integrity. Ammoniation caused cracks in lignified vascular tissue. During in vitro incubations, shredded and ammoniated cell walls were heavily colonized by bacteria by 6 h. After 24 and 48 h, large masses of bacteria were still attached to the surface of pith and lignified vascular cell walls of shredded and ammoniated stems but not control stems. Lignified vascular tissue of control stems was not degraded and structural integrity was maintained.

¹ Mention of commercial products in this paper does not constitute endorsement by the USDA or the ARS.

² Present address: Department of Dairy Science, Kangweon National University, Chuncheon 200, Korea.

³ Present address: Department of Agronomy, Ohio State University, Columbus 43210.

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