Voluntary consumption and digestion of diets high in endophyte-infected fescue by growing Holstein steers.

Holstein steers (112 to 258 kg BW) were fed diets high in endophyte-infected fescue (80 to 100%) in 15 latin square experiments to determine the relationships among BW, forage composition, voluntary consumption and digestion. Fescue DM intake (kg/d) increased linearly (P less than .05) with increasing BW (-.513 + .0275 BW; R2 = .69). Regressing log fescue intake (DM) on log BW resulted in a BW exponent of 1.1034 (R2 = .66) but did not account for any more variation in intake than the simple regression did. The percentage NDF in fescue was not related (P greater than .10) to fescue intake (kg/d) and was correlated only slightly with fescue intake as a percentage of BW (r = -.13; P less than .10). Adding the percentage of fescue in the diet or NDF in the fescue to the regression of DM intake on BW did not increase explained variation. Organic matter intake (kg) and digestibility (%) were not related (P greater than .10). Based on standardized partial regression coefficients, differences in voluntary intake accounted for 60% of the variation in the total quantity of OM digested, whereas differences in digestibility accounted for 40%. In conclusion, ingestibility of endophyte-infected fescue hay in relation to changing BW did not vary greatly. Concentrations of chemical constituents such as NDF and ADL in fescue were poorly correlated with feed consumption and digestibility.