Effect of the method and the period of oil extraction on in vitro digestibility of olive cake in northern of Morocco

In Northern Morocco, goat population is the most dominant livestock. His feeding is based on forest rangelands and characterized by strong seasonal variability responsible of low productivity. Therefore, it is necessary to diversify and improve its diet. Olive cake is an oil extraction by-product that is widely available and can be a ruminant feed. Olive cake is produced by three methods and for limited period. This work aims to determine the effect of oil extraction method and period on digestibility of olive cake. Twenty-seven samples were collected from 3 mills by each extraction method (mechanical pressure, centrifugation 2 and 3 phases) during three periods (November, December and January). In vitro digestibility was performed using gas production method of (Menke et al., 1979) improved by Menke and Steingass (1988). Samples were incubated in glass syringes that contained rumen fluid and incubation solution that conserved in water bath in 39°C during 72 hours. Gas production was recorded after 2, 4, 8, 12, 24, 48 and 72 hours. Studied digestibility parameters were dry and organic matter digestibility, microbial biomass production, partitioning factor and volatile fatty acid. Extraction method affected digestion kinetics and the digestibility parameters except partition factor and volatile fatty acids. Olive cake obtained by 2 phases method had the highest digestibility. For extraction period, gas production decreased significantly per period. Period had no effect on digestibility parameters except for volatile fatty acids. Two phases olive cake is most suitable for feed but has a reduced shelf life, which requires the development of a suitable conservation mode.