Predicting forage nutritive value from height and maturity of alfalfa in Saskatchewan, Canada

Several authors have shown that fiber levels can be predicted from plant height and maximum maturity in alfalfa (Medicago satvia L.). These estimates have been used to predict animal performance without any reference to error terms. This study evaluates the equations for predicting chemical characteristics from field measurements of plant morphology, and some equations for predicting animal performance from chemical characteristics. Finally, predicting forage utilization directly from field measurements of plant morphology was evaluated. Six sites were chosen from irrigated alfalfa fields in southwestern Saskatchewan. The chemical characteristics measured were neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), acid detergent lignin (ADL), ash, acid detergent insoluble nitrogen (ADIN), neutral detergent insoluble nitrogen (NDIN), and ether extract (EE). Only ADF and NDF showed predictive value from height and maximum maturity (R2 = 0.86, and R2 = 0.90, respectively). Weiss developed a theoretical model for estimating net energy based on summing the true digestibility of each of the components. This model did not predict digestibility well (R2 = 0.23). A model was developed to predict in-vitro dry matter digestibility directly from height and maximum maturity, however this model only performed moderately well (R2 = 0.61). This shows that in-vitro digestibility is predictable directly from height and maturity, although not without significant increases in error compared to prediction of ADF and NDF. Caution would be advised when using these estimates for further prediction