PREDICTION OF VOLUNTARY INTAKE AND DIGESTIBILITY OF MAIZE SILAGES GIVEN TO SHEEP FROM MORPHOLOGICAL AND CHEMICAL-COMPOSITION, IN-VITRO DIGESTIBILITY OR RUMEN DEGRADATION CHARACTERISTICS

Eleven maize silages with crude protein (CP) and neutral detergent fib re (NDF) ranging from 77 to 93 and 359 to 542 g/kg dry matter (DM) res pectively, were used to study the relationship between ear content, ch emical composition,fermentative characteristics, in vitro DM digestibi lity and ruminal degradation characteristics, on the one hand, and the voluntary DM intake by sheep or in vivo organic matter apparent diges tibility (OM digestibility), on the other. The silages were offered ad libitum to mature ewes given a daily supplement of 85 g of soya-bean meal. DM intake varied from 41.1 to 68.6 g DM per kg M-0.75 daily. OM digestibility and NDF apparent digestibility were measured, using the same ewes in a period subsequent to that of voluntary intake measureme nt. The silages, in this case, were offered at a feeding level of 1.2 maintenance. OM digestibility and NDF apparent digestibility ranged fr om 0.622 to 0.757 and from 0.377 to 0.605, respectively. Rumen DM disa ppearance was measured by incubating samples in nylon bags in the rume n of three silage-fed rumen-cannulated wethers for 3, 6, 12, 24, 48 an d 72 h and by fitting the exponential model y = a + b(1 - e(-ct)) to t he results. Potential degradabilities (defined as a + b)for DM ranged from 728 to 815 g/kg. Accurate prediction of DM intake (r = 0.93; P < 0.01; residual s.d. = 3.9) and OM digestibility (r = 0.86; P < 0.01; r esidual s.d. = 0.022) tons achieved using the soluble fraction (al and the insoluble but fermentable matter (B) and the insoluble but potent ially degradable Junction (b), respectively However, looking for a com promise between accuracy and simplicity, reliability and inexpensivene ss, ear content is proposed as a predictor of OM digestibility (r = 0. 85; P < 0.01) and the pH and acetic acid concentration of the silages may be used as a predictor of DM intake (r = 0.80; P < 0.05).