Effects of the dietary incorporation of untreated and white-rot fungi (Ganoderma resinaceum Boud) pre-treated olive leaves on growing rabbits

Abstract

The aim of this study was to evaluate the effects of the level of inclusion of olive leaves and its pre-treatment with Ganoderma resinaceum Boud on growth performance, nutrient digestibilities and caecal fermentation. A total of 48 rabbits were kept in individual cages and divided in 4 groups of 12 animals. Animals were fed ad libitum with one of four diets based on a basal feed for growing rabbits – Control diet (basal feed without olive leaves; OL0), basal diet with 50g/kg or 100g/kg of olive leaves (OL5 and OL10), and a basal diet with 50g/kg of G. resinaceum pre-treated olive leaves (OL5F).The inclusion of olive leaves (OL0 vs. OL5 and OL10) had no effect on growth performance or feed intake. However lower feed intakes (P=0.038) were measured at 100g/kg of inclusion when compared to 50g/kg level of inclusion. Organic matter, neutral detergent fibre, crude fat and crude protein digestibilities were lower (P<0.05) for diets with the inclusion of olive leaves (OL0 vs. OL5 and OL10). Although the caecal volatile fatty acid (VFA) concentration was not affected by treatments there was an increase in caecum dry weight contents (P=0.004) in animals fed diets with olive leaves (OL0 vs. OL5 and OL10). Simple phenolics were completely removed by the pre-treatment with G. resinaceum and the concentration of flavonoids and iridoids were reduced by 85%. No effects of the pre-treatment with fungi (OL5F) were observed on the performance of growing rabbits compared to OL5 treatment. The pre-treatment with G. resinaceum increased (P=0.02) crude fat digestibility (0.829 vs. 0.886) and decreased (P=0.006) starch digestibility (0.987 vs. 0.973). Animals fed OL5F diet had lower caecum dry weight contents (−21%; P=0.002), higher caecal valeric acid concentration (+50%; P=0.046) and a trend (P=0.054) for a higher caecal acetic acid concentration (increase of 12%), compared with OL5 treatment.In conclusion, this study showed that increasing amounts of olive leaves in the diet decrease nutrient digestibility. However, fungal treatment of olive leaves seems to alleviate the effect of olive leaves inclusion.