Nutritional value of commercial broiler feed supplemented with olive mill waste fermented with probiotic Rhizopus oryzae strains

AIMS: The changes in chemical composition and metabolizable energy (ME) of both olive mill waste (OMW) upon fermentation by three potential probiotic Rhizopus oryzae strains and commercial feed (CF) upon its supplementation by fermented olive mill waste (FOMW) were investigated. The objective was to test whether there will be an enhancement in the nutritional value of OMW after fermentation and/or commercial broiler feed upon supplementation by potentially probiotic filamentous fungi. METHODS AND RESULTS: A three Rhizopus oryzae strains (92/1, 236/2 and 284) isolated from agricultural soil that were proven to have good probiotic properties (non‐toxic, antimicrobial activity, antioxidant capacity and gastrointestinal tolerance) were used to ferment OMW, then the chemical composition was analysed after 7 and 14 days of fermentation. The FOMW with the R. oryzae 284 strain, which gave the best results, was added to a commercial broiler feed at 20%, 30% and 40% supplementation ratios. Then proximal analyses were done to compare non‐supplemented with supplemented CF. Chemical analyses included dry weight, crude protein, crude fats, crude fibres, crude ash, sugars and starch, and then ME was calculated from the given values. CONCLUSIONS: Compared to non‐fermented OMW, the best results were obtained by the R. oryzae 284 strain allowing an increase in crude protein content by 23.4% after 7 days of fermentation, a decrease in crude fibre content by 9.8% after 14 days of fermentation and an increase in ME by 3.6% after 7 days of fermentation. Compared to non‐supplemented CF, the ME changes of 20%, 30% and 40% supplementation increased by 8.38%, 2.83% and decreased by 4.27%, respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: FOMW can be incorporated into broiler feed rations until 30% without causing any decrease in metabolizable energy. It can be a cheaper alternative with promising productivity and chicken health improvements.