Effects of feeding alkali-treated olive cake on intake, digestibility and rumen liquor parameters

Abstract

Solvent-extracted screened olive cake (SESOC) is a very abundant lignocellulosic byproduct in the Mediterranean basin (3 million tonnes per year). It has a low digestibility (30–35% OMD) but rather high intake (100 g DM/day/W 0.75) among sheep. In the first experiment, SESOC was ensiled with different levels of sodium hydroxide and ammonia on a laboratory scale and chemical composition and in sacco digestibility determined. Maximum digestibility was achieved with 8% sodium hydroxide, and levels above 4% ammonia were not effective. In the second and third experiments, 4% sodium hydroxide-treated and pelleted SESOC and 2.5% ammonia-treated SESOC silage were given to sheep in order to determine the intake, digestibility, nitrogen balance and eating and ruminating behaviour. Pelleting of the untreated SESOC decreased the organic matter digestibility by about 6 percentage units, and significantly reduced the time spent eating and ruminating. Ammonia treatment increased the organic matter digestibility by 4 percentage units and the nitrogen retention by 6%. In a fourth experiment, 4 rumendashcannulated adult sheep received 4 rations (R1: hay, R2: untreated SESOC, R3: 4% NaOH-treated SESOC, R4: 2.5% ammonia-treated SESOC silage) in order to study the biochemical kinetics, protozoa counts, volume and rate of passage of the rumen liquid phase. Sodium hydroxide treatment increased rumen pH (6.89–7.02) and total volatile fatty acids (65–72 mM 1 −1) without any shift in the fermentation pattern. Dilution rates (0.154–0.174) were also significantly increased. Ammonia treatment increased rumen ammonia concentration by a factor of 5 and increased total volatile fatty acids concentration from 65 to 76 mM 1 −1 without any shift in the fermentation pattern or the other parameters. Neither alkali had a significant effect on protozoa counts.