Effect of ensiling pomegranate pulp with solid additives on chemical composition, intake and digestibility by sheep

Abstract

Effect of ensiling pomegranate pulp (PP) with or without solid additives on composition and in vitro digestibility was assessed in glass silos. Ensiling of fresh PP solely, resulted in low DM content (185g/kg) and high fermentation losses (20% of DM). Notwithstanding, ensiling a mixture (on DM basis) of: 40% PP, 35% soy hulls and 25% corn silage, produced pomegranate pulp silage (PPS) characterized by low pH (3.86), appropriate DM content (34.7%), low fermentation losses during ensiling (5.58%) and similar in vitro DM digestibility (66.2%) compared with the raw material. Consequently, this PPS mixture was ensiled in two pressed bales (700kg each) wrapped with stretch polyethylene film, for measuring PPS intake and digestibility by sheep. A preliminary observation demonstrated that lambs refused to consume diet based just on PPS and soybean plus minerals and vitamins mix. Only after reduction of PPS level in the TMR to 51% of the DM while replacing part of the PPS with wheat hay, the PPS-hay diet was entirely consumed. Therefore, four male Assaf lambs housed in individual metabolic cages, were fed ad-libitum two total mixed rations (TMR) in a cross over design: The PPS TMR contained 51% PPS, 38% chopped wheat hay, and 11% soybean plus minerals and vitamins mix; The reference Hay TMR contained 89% chopped wheat hay plus 11% minerals soybean plus minerals and vitamins mix. This hay-TMR was used to calculate the apparent digestibility of the PPS component in the PPS+Hay TMR. Lambs fed the PPS+hay TMR ingested voluntary 1,129g DM/lamb/day including 580g PPS DM/lamb/day. Apparent in vivo digestibility values of the PPS component in the experimental TMR were: dry matter, 60.1%; organic matter, 65.6%; crude protein, 47.1%; and neutral detergent fiber, 46.8%. Notwithstanding, in vitro DM and NDF digestibility of the PPS was higher (67.5% and 52.3%, respectively). The lower in vivo digestibility values compared with the corresponding in vitro data is associated with occurrence of soluble phenolics that are considered entirely digestible in the in vitro system but actually form non-digestible phenol–protein complexes in the sheep gut that reduce in vivo NDF and DM digestibility.