A modified method for assessment of the morphological stage of development as a predictor of alfalfa herbage chemical composition and nutritive value

Abstract

SUMMARYThe aim of the current work was to investigate the possibility of modifying the existing mean stage by weight (MSW) system for evaluating the average development stage in alfalfa. The modification was performed with the aim of providing a simplified system that may be used to evaluate the alfalfa development stage and to predict its nutritive value for ruminants. The suggested modification consists of designating an MSW value on the basis of the fresh weight of all morphological stages in a fresh green plant, as opposed to the original method which is based on weighing all morphological stages dried at 65 °C. The investigation was done on 141 samples of one alfalfa cultivar, collected from the same location during the first three growth cycles: spring growth, the first and the second regrowth. On all collected samples the following characteristics were determined: MSW, modified MSW (mean stage by fresh weight (MSFW)), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), crude ash (CA) and in vitro organic matter digestibility (IVOMD). For these characteristics of chemical composition (apart from CA) and nutritive value the regressions were calculated for their prediction based on MSW and MSFW. The regressions were derived for individual growth cycles and all cycles combined. A trend for an increase in the coefficient of determination (R2) was identified as well as a decrease in root-mean-square error (RMSE) for all equations derived for all investigated characteristics from the spring growth to the second regrowth. A deviation from this trend was observed only in equations derived for IVOMD. A very high correlation was observed between MSW and MSFW (r=0·999). The determined R2 and RMSE were very similar within the same growth cycle in all regressions for prediction of chemical composition and nutritive value derived for MSW and MSFW. Based on the results of this investigation the MSFW appears to be a quick and accurate method for determining the average development stage in alfalfa which can therefore be recommended for both scientific research and practical field use, as well as for prediction of its chemical composition and nutritive value.