Degradation of Switchgrass Anatomical Tissue by Rumen Microorganisms

Abstract

Factors that influence rumen microbial degradation of switchgrass (Panicum virgatum L.) tissues are not well understood. Our objective was to measure and compare the anatomical degradation of leaf blades, leaf sheaths, and stems by tureen microorganisms. Two field‐grown switchgrass cultivars were harvested when three‐fourths of the inflorescence had emerged. Three‐millimeter portions of blade, sheath, and stem tissue were incubated in buffered rumen fluid for 0, 24, and 48 h, then removed and processed for light microscopy. Tissue composition and microbial degradation within each morphological component were measured with a computer‐based optical image analyzer. No differences in degradation were apparent between cultivars. The largest portion (35.7%) of blade cross‐sectional area was occupied by the mesophyll. After 48 h of incubation in rumen fluid, 32% of this tissue was partially degraded and 68% completely degraded. In contrast, leaf sheath parenchyma tissue was more resistant to complete degradation than that of the blade. In the sheath, 17.2% of tissues in the cross‐sectional area were at least 80% intact after 48 h of incubation; only 4.3% of the cross‐sectional area of the blade was this resistant to degradation. These differences in degradation resulted in lower (101 g kg−1) in vitro dry matter disappearance (IVDMD) in the sheath compared with the blade. Tissues (cortex, xylem, and bundle sheath) in which at least 80% of their area was intact after 48 h of incubation occupied 25.8% of the stem's cross‐sectional area. It is these resistant tissues that appear to cause the stem to have the lowest IVDMD of the three major morphological components of switchgrass. A detailed understanding of differences in degradation of anatomical tissues will result in the development of more digestible cultivars and morefficient forage utilization by livestock.

Relaciones entre estructura histológica y composición química en hojas de gramíneas y leguminosas

“…La composición de la pared celular interna de las epidermis equivale al mesófilo (Chesson et al, 1986;Twidwell et al, 1991), que es rápidamente digerido (Hanna et al, 1973;Wilson et al, 1991); lo anterior puede explicar la relación positiva entre la epidermis adaxial y la PC y la DIVMS, así como la relación negativa con la lignina y la FDN que se presentó en B. repens, especie en la cual el área de la epidermis adaxial explica el 61,4% de PC (P<0,05), en 57,5% la DIVMS (P<0,05), en 80,8% la lignina (P<0,05) y en un 57.2% el FDN (P<0.05). De igual manera, en los cortes se observó que la epidermis adaxial está fuertemente ligada a la estructura kranz por medio del esclerén-quima lo que dificulta su degradación.…”

Degradación microbiana in situ de tejidos foliares de gramíneas y leguminosas y su relación con indicadores de calidad nutricional

“…Se incubaron cinco fragmentos de 10 mm de lámina foliar de B. repens y B. pertusa y foliolos de S. scabra, D. barbatum y T. cinerea, colocados en bolsas de nylon en el rumen de 2 novillas Cebú, evaluando cinco tiempos de incubación; 0, 12, 24, 48 y 72 horas, siguiendo la metodología de Ørskov et al (1980). Luego de la degradación ruminal el material fue sometido a procesos de fijación con glutaraldehido al 5% (Twidwell et al, 1991).…”

“…Para el estudio anatómico de los fragmentos de forraje, se seleccionaron secciones por duplicado de lámina foliar y foliolo por especie época y tiempo de degradación. Para el procesamiento histológico de muestras de hojas con diferentes tiempos de degradación se utilizaron los protocolos de microtécnica de vegetales del Departamento de Biología de la Universidad Nacional de Colombia (Becerra et al, 2002) y la técnica descrita por Twidwell et al (1991), protocolos que fueron modificados en las fases de deshidratación, inbibición, infiltración, inclusión, y coloración debido a las características de degradación microbial de las muestras.…”

Lignin and fiber digestion

“…Consequently, degradability of plant tissues is variable and related to lignin concentration. Tissues with high lignin concentrations include the epidermis (grasses), xylem, and sclerenchyma (Akin et al 1990, Buxton and Redfearn 1997, Chesson et al 1986, Twidwell et al 1991. These tissues are relatively undegradable by rumen microbes (Grabber el al.…”

“…Because stems contain more lignified structural tissues and less metabolically active tissues than leaves, the digestibility of stems is generally much less than that of leaves (Akin 1989, Twidwell et al 1988. Using a lignin stain and image analysis, Twidwell et al (1991) characterized the anatomy of switchgrass leaves and stems. They reported that stems contained a greater proportion of structural and other lignified tissues than leaves and that these tissues were more resistant to degradation when incubated in buffered rumen fluid for 24 and 48 hours.…”