Soluble and Structural Components of Alfalfa (Medicago sativa L.) and selected Reed Canarygrass (Phalaris arundinacea L.) Clones1

Abstract

Abstract‘Vernal’ alfalfa (Medicago sativa L.) and two clones of reed canarygrass (Phalaris arundinacea L.), varying markedly in acceptability to lambs, were analyzed for soluble carbohydrates, soluble nitrogen, hexosans, pentosans, and crude lignin. A continuous digestion trial, in which forages were harvested at successive stages of maturity, and an ad libitum grazing trial provided the forage material. Whole plant samples of the top growth were obtained before and after the ad libitum grazing trial, while samples were obtained daily throughout the trial by the use of esophageal‐fistulated lambs.Samples from the continuous digestion trial contained the highest levels of both soluble carbohydrates and soluble nitrogen at the early head stage with no consistent differences noted among forages. Alfalfa samples obtained from esophageal‐fistulated lambs contained significantly more soluble carbohydrates than either of the two reed canarygrass clones, while nonsignificant increases were obtained in the case of whole plant samples. Alfalfa had consistently higher soluble nitrogen levels than the two clones. Only slight differences existed between clones in the soluble constituents determined.Analysis of samples from both trials indicated that alfalfa contained significantly less pentosans than either of the two reed canarygrass clones. Differences among forage treatments in percent hexosans were only apparent in samples before the ad libitum grazing trial. Hexosans, pentosans, and crude lignin of all forages increased with maturity. Significant chemical differences among reed canarygrass clones were not apparent despite the fact that in vivo acceptability differences existed. It is hypothesized that the lower pentosan content of alfalfa, as compared to reed canarygrass, has a favorable effect on in vivo cellulose digestion.