Effect of different drying procedures on the nutritive value of olive (Olea europaea var. europaea) leaves for ruminants

Fresh, freeze-, air- and oven-dried at 60 °C and 100 °C olive leaves (OL) were studied in order to determine the effect of different drying procedures on OL chemical composition, in vitro digestibility, ruminal degradability, and intestinal digestibility. The drying procedure affected all the parameters measured except for gross energy (GE; P=0.194). Protein-bound condensed tannins (CT) decreased (P=0.001) with freeze-, air- and 60 °C drying (from 1.25 up to 0.82 g/kg dry matter, DM). Total CT were only decreased (P=0.001) by drying at 60 °C (from 10.0 to 6.24 g/kg DM). The in vitro crude protein (CP) digestibility increased (P<0.001) with drying except for oven-drying at 100 °C up to 58%. Values for CP digestibility found in freeze- and air-dried OL were not different (P>0.05). No differences (P>0.05) were observed between CP digestibility in air- and oven-dried at 60 °C OL. Effective degradability of DM and CP increased from 0.53 to 0.62 (P=0.005) and from 0.46 to 0.64 (P=0.002), respectively after treatment. The apparent intestinal digestibility of undegraded CP in the rumen was only affected (P=0.046) by oven-drying, which increased it from 0.33 to 0.39. As air-drying did not have detrimental effects on the OL nutritive value it could be an appropriate, simple and low-cost procedure for olive-leaves preservation.