Prediction of voluntary intake and digestibility of maize silages given to sheep from morphological and chemical composition, in vitro digestibility or rumen degradation characteristics
Ferret, A.; Gasa, J.; Plaixats, J.; Casanas, F.; Bosch, L.; Nuez, F.
Animal Science 64(3): 493-501
Eleven maize silages with crude protein (CP) and neutral detergent fibre (NDF) ranging from 77 to 93 and 359 to 542 g/kg dry matter (DM) respectively, were used to study the relationship between ear content, chemical composition, fermentative characteristics, in vitro DM digestibility and ruminal degradation characteristics, on the one hand, and the voluntary DM intake by sheep or in vivo organic matter apparent digestibility (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 measurement. The silages, in this case, were offered at a feeding level of 1.2 maintenance. OM digestibility and NDF apparent digestibility ranged from 0.622 to 0.757 and from 0.377 to 0.605, respectively. Rumen DM disappearance was measured by incubating samples in nylon bags in the rumen of three silage-fed rumen-cannulated wethers for 3, 6, 12, 24, 48 and 72 h and by fitting the exponential model y = a + b(1 - e-ct) to the 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 lt 0.01; residual s.d. = 3.9) and OM digestibility (r = 0.86; P lt 0.01; residual s.d. = 0.022) was achieved using the soluble fraction (a) and the insoluble but fermentable matter (B) and the insoluble but potentially degradable fraction (b), respectively. However, looking for a compromise between accuracy and simplicity, reliability and inexpensiveness, ear content is proposed as a predictor of OM digestibility (r = 0.85, P lt 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 lt 0.05).