Effect of different drying systems for the conservation of olive leaves on their nutritive value for ruminants

Leaves obtained from olive trees (Olea europaea L.) were stored under various conditions for periods up to 42 months. Duration of storage had a marked effect on crude protein digestibility of leaves when fed to sheep. Protein appeared to be unavailable to animals fed leaves stored for 24 months or longer. The effect of storage on organic matter digestibility was less dramatic and due largely to the loss of soluble cell contents (r = 0.97). As a result, the proportion of water-insoluble dry matter and lignin present in leaves increased with duration of storage while the proportion of water or acetone-water (60:30 v/v) soluble material decreased. Despite being unavailable in vivo, cellulase digestion released protein from the water-insoluble residues of stored leaves in greater amounts than that released from freshly-dried leaves. It appears likely that protein released from stored leaves was in the form of a complex and remained unavailable to the animal. Hydrolysable and condensed tannins were not detected in fresh or dried leaves and could not have acted as complexing agents. The seco-iridoid glycoside oleuropein was found in fresh tissue (69.9 g kg(-1)) but concentrations decreased on storage in parallel with the observed decrease in crude protein digestibility (r = 0.80). ((C) Elsevier/Inra)