EVALUATION OF THE NUTRITIVE-VALUE OF GRASS HAYS FOR GROWING SHEEP

Data collected during 2 years on four grasses (three cultivars of timothy and one cultivar of bromegrass) harvested at four stages of growth were analyzed to identify variables that affect the nutritive value of grass hays for sheep. From 11 June, the day of the first harvest, to July 25, the percentage of crude protein (CP) decreased 0.17 unit/d (r2 = 0.86, P < 0.001) and the percentage of acid detergent lignin (ADL) increased 0.06 units/d (r2 = 0.74, P < 0.001). Over this period, dry matter (DM) intake decreased at a rate of 0.41 g kg-0.75 d-1 (r2 = 0.54, P < 0.001) and was negatively correlated with fiber content (P < 0.001). Delay of harvest caused a decrease in percent digestibility of 0.39 unit/d for DM (r2 = 0.86, P < 0.001), 0.38 unit/d for energy (r2 = 0.85, P < 0.001), 0.54 unit/d for CP (r2 = 0.77, P < 0.001) and 0.63 unit/d for NDF (r2 = 0.93, P < 0.001). Total digestible nutrients (TDN) decreased 0.35 unit/d (r2 = 0.86, P < 0.001). Date of harvest and % ADL were used to estimate energy value of hays. Digestible energy intake and TDN intake values decreased by 122.4 kJ kg-0.75 (r2 = 0.87, P < 0.001) and 6.6 g kg-0.75 (r2 = 0.89, P < 0.001), respectively, for each 1% increase in ADL of the hays. Equations were developed to estimate digestible DM intake and TDN intake, using NDF and ADF as independent variables. The predictive value of the equations was good when applied to data obtained from previous experiments (r2 = 0.87-0.91, n = 11, P < 0.001).