Potential Nutritive Value and Condensed Tannin Contents of Acorns from Different Oak Species

The potential nutritive values of acorns of Quercus suber, Quercus branti, Quercus coccifera, Quercus cerris and Quercus infectoria were estimated by chemical composition and in vitro gas production technique. Acorns collected at least 10 different trees in three experimental plots. There were significant (P<0.001) differences in the chemical composition among acorns obtained from different oak species. Crude protein (CP) contents of acorns ranged from 25.48 to 61.94 g/kg dry matter (DM). Neutral detergent fiber (NDF) contents ranged from 231.4 to 326.3 g/kg DM. Acid detergent fiber (ADF) contents ranged from 155.9 to 215.4 g/kg DM. Condensed tannin (CT) contents ranged from 7.2 to 26.7 g/kg DM. Starch contents ranged from 600.0 to 681.5 g/kg DM. Polyethylene glycol (PEG) addition significantly (P<0.001) increased the gas production and some estimated parameters of oak acorns. Although there is no significant (P>0.5) differences in the potential gas production of acorn among oak species when incubated in the absence of PEG, there is significant (P<0.001) differences in the potential gas production of acorn among oak species when incubated in the presence of PEG. Although the estimated organic matter (OMD) and metabolisable (ME) contents of acorn for Q. suber and Q. infectoria were significantly (P<0.001) higher than those for Q. branti, Q. coccifera and Q. cerris when incubated in the absence of PEG, the estimated OMD and ME contents of acorn for Quercus cerris and Q. infectoria were significantly lower than those for Q. suber, Q. branti and Q. coccifera when incubated in the presence of PEG. The improvement in gas production, OMD and ME in the presence of PEG emphasizes the negative effect of tannins on digestibility. As a conclusion, oak acorns have potential nutritive values for ruminant animals such as sheep and goat since acorns have high starch, OMD and ME but low level of CT contents. However these results obtained in the current study should be supported by in vivo feeding experiments.