Predictive Equations of Forage Nutritive Value for Use Under Quebec's Environmental Conditions.

Using simple field measurements, equations were developed in the United States to predict the forage nutritive value of alfalfa-grass mixtures with the objective of helping producers in making harvest decisions. These predictive equations, however, are for the spring growth only and have not been tested in Quebec. Our objectives were 1) to determine if equations developed in New York State for the spring growth can be used in Quebec and 2) to develop equations specific for Quebec that could be used to predict a larger number of forage nutritive attributes for both spring growth and first summer regrowth. Our results demonstrate that equations developed in New York State for the spring growth predicted satisfactorily (r² = 0.81) the neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations of alfalfa-grass mixtures grown in Quebec, as well as Relative Feed Value (RFV) and Relative Feed Quality (RFQ) (r²= 0.78 and 0.80). New equations developed in Quebec predicted satisfactorily forage NDF (r² = 0.82) and ADF (r² = 0.81) concentrations, the in vitro digestibility of the NDF (r² = 0.82), the true digestibility of the dry matter (r² = 0.84), and RFV and RFQ (r² = 0.80) of both the spring growth and the first summer regrowth but not crude protein concentration. Newly developed equations were finally validated using samples collected on commercial farms from 12 regions of Quebec. This validation demonstrated that some equations, mostly those including the proportion of grasses, can be used across Quebec to predict NDF concentration (r² = 0.80) and RFV (r² = 0.75) but the proportion of grasses must be precisely determined.