In vitro nutritional evaluation of olive tree (Olea europaea L.) pruning residues and their fermentation characteristics in terms of ruminal microbial nitrogen, microbial biomass utilizing ¹⁵N-tracer

Nutritive values of the branches from Olea europaea trees cut at 25, 50, 75 or 100 cm distance from the tip were evaluated by determination of the microbial nitrogen (MN) and biomass (MBM) production after incubation with rumen fluid and '1'5N-tracer for 96 h in the absence or presence of polyethylene glycol (PEG, 6000). The characteristics of fermentation (initial gas produced from soluble fraction; a, gas production during incubation which produced from insoluble but fermentable fraction; b, potential gas production; a+b, fractional rate of gas production per hour; c) were assessed using an in vitro incubation technique with rumen fluid. Effective degradability (ED), partitioning factor (PF), and short chain fatty aids (SCFA) and predicted daily intake (Y) were also estimated in the experimental olive pruning branches. There was a negative effect of cutting length on all the studied nutritive parameters and fermentation characteristics. The values of MN, MBM, ED, Y, PF, SCFA, a + b and c declined with the increase in cutting length. The olive branches cut at 25 or 50 cm distance from the tip produced higher (P<0.05) amounts of MN (0.53 mg/g DM) than those cut at 75 and 100 cm lengths (0.30 mg/g DM). The values of ED, SCFA and PF, and the ratios of MN or MBM to effective degraded substrate were significantly higher (P<0.05) in the cutting olive branches at 25 cm length compared to other cutting lengths. There was a positive correlation between MN or MBM production and SCFA, PF, ED and a + b values. The greatest proportion of gas production occurred during the first 48 h of incubation. Microbial N and MBM production were positively correlated with a + b, SCFA, PF and ED. The addition of PEG to the plant samples incubated with rumen fluid at a ratio of 2:1 PEG: substrate increased the values of gas production, characteristics of fermentation, MN, MBM, SCFA and ED. The response of the olive pruning branches to PEG treatment in terms of increased gas production varied between cutting lengths and tended to decline as incubation progressed, with the highest increase (17%) during the first 24 h of incubation. On the basis of the studies nutritive parameters, olive pruning branches cut at 25 cm distance from the tip in diameter <3 mm were nutritionally well-suited as dietary supplements for ruminants (author).