Prediction of the digestibility and digestible energy content of hay for horses using an enzymatic degradability method

The nutritive value of forage for horses is closely dependent on the digestibility of organic matter (OMD), which is typically measured in vivo. Researchers have developed a variety of prediction methods to estimate the digestibility value of hay. In ruminants, pepsin-cellulase degradability, expressed as dry matter enzymatic degradability (dCS) and organic matter enzymatic degradability (dCO), is a commonly employed method for predicting OMD in forage types. The objective of this study was to evaluate the feasibility of predicting the dry matter digestibility (DMD), OMD, energy digestibility (ED) and digestible energy (DE) content of hay through enzymatic degradability or a combination of enzymatic methods with other chemical composition parameters. For that purpose, a database of 43 hays harvested in a temperate zone (32 natural grassland hays, five grass hays and six lucerne hays) was constructed from studies carried out at the French National Institute of Agricultural Research. The dCS and dCO of each hay type were determined, as well as their in vivo digestibility in horses. The range of OMD across the entire dataset was between 0.42 and 0.63, and the range of dCS cellulase digestibility was between 41.0 and 62%. The results demonstrated that there were no significant differences (P > 0.05) between the slopes of the models obtained for the various forage types. The models used for the prediction of DMD, OMD, ED and DE from dCS and dCO were characterised by R² values between 0.87 and 0.91. The incorporation of chemical composition variables as independent variables into the prediction models did not result in a meaningful improvement in the model results obtained from dCS and dCO. The proposed models represent an alternative approach to the existing models for predicting the nutritive value and DE content of hay from their chemical composition.