Characteristics of plant cell walls affecting intake and digestibility of forages by ruminants.

Abstract

Even under the intensive concentrate feeding systems of ruminant animal production in the United States, forages continue to represent the single most important feed resource. Cell-wall concentration and digestibility limit the intake potential and energy availability of forage crops in beef and dairy production. Identification of cell-wall characteristics that should be targets of genetic modification is required if plant breeders and molecular biologists are to successfully improve forages for livestock feeding. As the forage plant cell develops, phenolic acids and lignin are deposited in the maturing cell wall in specific structural conformations, and in a strict developmental sequence. Lignin is the key element that limits cell-wall digestibility, but cross-linkage of lignin and wall polysaccharides by ferulic acid bridges may be a prerequisite for lignin to exert its affect. Lignin composition and p-coumaric acid in the wall are less likely to affect digestibility. Voluntary intake of forages is a critical determinant of animal performance and cell-wall concentration is negatively related to intake of ruminants consuming high-forage diets. Cell walls affect intake by contributing to ruminal fill. A simple model of cell-wall digestion and passage in which ruminal fill is a function of rates of digestion and passage, as well as the indigestible fraction of the cell-wall indicates that cell-wall concentration and rate of passage are the most critical parameters determining ruminal fill. Plant factors that affect rate of passage include those that affect particle size reduction by chewing and those that affect particle buoyancy in the rumen. The latter is primarily affected by 1) the ability of the particulate matter to retain gases, which is probably related to plant anatomy and rate of digestion of the plant tissue, and 2) the rate at which the gas is produced, which is affected by the potentially digestible fraction of the particulate matter and the rate of digestion of this fraction. Increasing rate of digestion should increase rate of passage by diminishing the gas produced and increasing density over time. A reduction in the indigestible cell-wall fraction is beneficial because this will decrease fill and increase digestibility. Animal production and economic benefits from reduced cell-wall concentration and increased digestibility are significant. Because of the high cell-wall concentration and large digestible cell-wall fraction of grasses, reduction in cell-wall concentration would probably be of greater value than improving digestibility in these species. Legumes represent the opposite situation and may benefit more from improvements in the digestibility of their cell walls.

Nutritional diversity of agricultural and agro-industrial by-products for ruminant feeding

“…The low digestibility of NDF in the by-products of G1 for rice hull and parchment coffee was mainly due to the high concentration of LIG, as LIG is one of the main limiting factors of fibrous carbohydrate digestion (Jung and Allen, 1995).…”

The filter bag versus the conventional filtration technique for the determination of crude fibre and Van Soest cell wall constituents

“…Moreover, they are common parameters in practical feed evaluation for the prediction of voluntary intake (Van Soest et al, 1978;De Brabander et al, 1987;Jung and Allen, 1995), digestibility and energy value (De Boever et al, 1996 as well as the physical structure content . However, these parameters are considered more or less arbitrary because their procedure is rather empirical and no primary fibre standard is available.…”

Características produtivas, agronômicas e nutricionais do capim-tanzânia em cinco diferentes idades ao corte

“…Com o desenvolvimento da forrageira, esses compostos substituem os espaços na matriz da parede celular ocupados por água, aumentando a rigidez da parede celular (Giger-Reverdin, 1995). As ligninas afetam a digestibilidade da matéria seca por se ligarem aos componentes da parede celular, sendo a ocorrência dessa interação aumentada com a maturidade da forrageira, seja pelo aumento da concentração de LIG e/ou pela modificação na composição dos compostos fenólicos (Jung, 1989;Jung e Allen, 1995;Wilson e Hatfield, 1997). Na Tab.…”

“…O primeiro grupo, formado pelo capimtanzânia cortado aos 42 dias, ocorreu a maior taxa de produção de gases em torno de 24 horas em relação às taxas apresentadas pelos demais tratamentos. Esse fato pode ser atribuído ao maior conteúdo celular na célula vegetal em idades mais jovens, o qual é fermentado mais rapidamente no rúmen (Jung, 1989;Van Soest, 1994). O segundo grupo é formado pelo capimtanzânia cortado aos 63 dias, com aumento nas taxas de produção de gases após as 24 horas, sendo estas mais altas que as da forrageira cortada aos 84, 107 e 126 dias, e superando o corte aos 42 dias a partir das 48 horas de incubação.…”

“…A parede celular apresentou maior taxa de fermentação em períodos mais tardios. As ligninas ligam-se aos componentes da parede celular, tendo a ocorrência dessa interação aumentada com a maturidade da forrageira, seja pelo aumento da concentração de LIG e/ou pela modificação na composição dos compostos fenólicos, que afetam a extensão da degradação da forrageira (Jung, 1989;Jung e Allen, 1995 (Jung, 1989;Jung e Allen, 1995). Tal afirmação é comprovada pelo estudo de correlação entre os resultados obtidos para a composição agronômica, composição bromatológica e volume acumulado de produção in vitro de gases às 24 (G24) e 48 horas (G48), de incubação do capim-tanzânia.…”