|Jung, Hans Joachim|
Submitted to: Animal Feed Science And Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2003
Publication Date: 9/1/2003
Citation: Jung, H.G., Lamb, J.F. 2003. Identification of lucerne stem cell wall traits related to in vitro neutral detergent fibre digestibility. Animal Feed Science and Technology. 110:17-29. Interpretive Summary: Dairy cows need large amounts forage in their diet to maintain health of their four stomachs and to promote milk fat production. Unfortunately, forages are rich in fiber and forage fiber is poorly digested, limits feed consumption, and does not support high levels of milk production. In order to both protect dairy cow health and achieve high levels of milk production, the digestibility of forage fiber must be improved. In support of efforts to improve fiber digestibility of alfalfa stems (the part of alfalfa which has the most fiber) a study was conducted to identify the chemical components of alfalfa cell walls that control fiber digestibility. It was found that the total amount of stem cell wall material was the best predictor of how much alfalfa fiber was digested and how fast alfalfa fiber was digested. This result had not been observed previously in studies with grasses. The amount of lignin, a known inhibitor of fiber digestion, in alfalfa stems was negatively related to the amount of fiber which could be digested, but not how fast the alfalfa fiber was digested. Alfalfa cell walls contain a compound known as pectin which helps to stimulate milk fat production. It was found that more pectin in alfalfa stems resulted in more rapidly digested fiber. These results are being utilized to guide our group's on-going efforts to improve alfalfa through breeding and selection, and to identify specific gene targets for molecular approaches to improving alfalfa fiber digestion. Other groups with similar interest in improving the feeding quality of alfalfa for dairy cows will be able to utilize the information in their own efforts.
Technical Abstract: Genetic improvement of forage digestibility will require identification of biochemical traits and associated genes that impact digestibility. We undertook a study to identify cell wall traits of alfalfa stems that were consistently and strongly correlated with in vitro neutral detergent fiber (NDF) digestibility. Spring and summer harvested stem material from 24 plants in each of two germplasm sources were analyzed for 16- and 96-h in vitro NDF digestibility, and cell wall concentration and composition (cellulose, hemicellulose, and pectin monosaccharide constituents, and Klason lignin). Correlation coefficients were calculated for relationships among these cell wall traits and with in vitro NDF digestibility. Concentrations of the pectin monosaccharide components were all negatively correlated with total cell wall concentration. In contrast, glucose, xylose, and Klason lignin were not correlated or only weakly positively correlated with cell wall concentration. Cell wall concentration was consistently negatively correlated with both 16- and 96-h in vitro NDF digestibility. In contrast, Klason lignin concentration was strongly negatively correlated with 96-h in vitro NDF digestibility. Cell wall glucose and xylose concentrations were inconsistently correlated with fiber digestibility. Pectin components were consistently positively correlated with in vitro NDF digestibility. The results of this study indicate that genetic improvement of overall fiber digestibility of alfalfa stems should target reducing total cell wall concentration, perhaps by reducing the rate of xylem tissue deposition during maturation, and reducing Klason lignin and increasing pectin concentrations in the cell wall to improve potential extent and rate of fiber digestibility.