Forage Quality: Techniques for Testing

Abstract

Forage quality refers to how well animals consume a forage and how efficiently the nutrients in the forage are converted into animal products. Six major factors affecting forage quality: maturity (harvest date), crop species (differences between grasses and legumes), techniques of harvest and storage, environment (moisture, temperature and amount of sunlight), soil fertility, variety or cultivar. Also, weeds, insect pests, plant diseases and presence of bacteria, molds, and/or some of their metabolites, e.g. mycotoxins can negatively affect forage quality. Recommended tests for determining forage quality are: dry matter (DM), pH, crude protein (CP), available protein, amoniacal nitrogen (as % NH3/TN), acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin and ash. Energy values such as total digestible nutrients (TDN), net energy (NE) and relative feed values (RFV) can be calculated from these core analyses. There are two methods used to analyse such variables: the traditional chemistry analysis and the newer, near infrared reflectance spectroscopy (NIRS) analysis. Currently, the quality of a forage has been evaluated only through those chemico-fermentative parameters. However, recent studies propose to incorporate the analysis of microbiological parameters such as fungal propagule counts, the presence of Aspergillus fumigatus and mycotoxins (aflatoxins and deoxynivalenol) as decisive parameters of forage acceptability. Forage quality information is important for formulating nutritionally balanced rations, evaluating forage management practices (growing conditions, timing of harvest, and handling from harvesting to utilization) and marketing and pricing forages.