Nutritive Value of Crownvetch Forage as Influenced by Structural Constituents and Phenolic and Tannin Compounds1

Abstract

AbstractTwo experiments were conducted to evaluate the nutritive value of crownvetch (Coronilla varia L.) forage by in vitro dry matter disappearance (IVDMD). Structural constituents [neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (lignin)] and secondary compounds (tannin and phenols) were determined and were related to IVDMD.In experiment I, leaves were discarded from 40 clones and the stems were separated into tops and bottoms. A regrowth of leafy forage was also harvested. Clonal differences in IVDMD were greater in the stem tissue than in the leaves. Increased quality of crownvetch appeared possible through plant selection; however, selection for increased IVDMD would probably result in late flowering clones that had low spring vigor.In experiment II, six crownvetch clones varying in internode length, leaflet size, and date of flowering were separated into component parts (stems, leaflets, petioles, and flowers) at different growth stages in different years. Mature stems were considerably lower in percentage IVDMD (47.7) than either leaflets (66.1) or petioles (64.7). However, IVDMD of immature stems was almost equal to those of leaflets and petioles of the same harvest (72.0, 77.9, and 78.9%, respectively). Both cell solubles (100‐NDF) and ADF predicted IVDMD of stems (r2 = 0.96**), while only ADF showed any relation to IVDMD of petioles (r2 = 0.80**) or leaflets (r2 = 0.44**). Total phenol and tannin fractions of leaflets were negatively associated with IVDMD. Total phenols accounted for 59% of the variation, and tannins, 30%. Of the six clones evaluated, highest, but similar, total phenol concentrations were found in leaf tissues of clones 4 and 6. However, IVDMD percentages for clone 6 were not as drastically affected (62.7 to 71.9%) as were those of clone 4 (53.6 to 61.6%). When both structural constituents (ADF) and secondary compounds (total phenols and tannins) were considered, 77% of the variation in leaf IVDMD was accounted for. The importance of the leaf portion in altering the nutritive value of crownvetch is apparent when considering that the total‐plant dry matter, when averaged over the six clones and three harvest dates, consisted of 38.5% leaflets, 45.9% stems, and 10.1% petioles.