Effect of polethylene glycol on gas production parameters and nitrogen disappearance of some tree forages

Abstract

The nine tree forages Carissa spinarum, Ficus roxburghii, Hippophae rhamnoides, Leucaena leucocephala, Melia azedarach, Quercus incana, Robinia pseudoacacia, Zizyphus jujuba, Zizyphus nummularia, and the three conventional forages paddy straw, wheat straw and mixed grass hay were analysed for chemical composition, phenolics, protein precipitation capacity (PPC), polyethylene glycol binding capacity (PEGBC) and rumen fermentation characteristics. The rumen degradability characteristics with and without polyethylene glycol (PEG) were studied in vitro by gas production. The crude protein content was more than 200 g/kg dry matter (DM) in H. rhamnoides, L. leucocephala, M. azedarach, R. pseudoacacia and Z. jujuba. The ash content (g/kg DM) was high in F. roxburghii (217) and paddy straw (178) while R. pseudoacacia and C. spinarum contained higher neutral detergent insoluble N and non-structural carbohydrates, respectively. Total phenolics (g/kg DM) ranged from six in paddy straw to 122 in H. rhamnoides, concurrent with the highest total tannin phenols (103) and hydrolysable tannins (89). The condensed tannins ranged from 0.2 in wheat straw to 56 in C. spinarum and H. rhamnoides, and C. spinarum had the highest PPC (0.593) and PEGBC (42.3%). In vitro gas production (ml/g) to 24 h ranged from 48.5 in Q. incana to 218.3 in M. azedarach. Addition of PEG increased gas volume and in vitro disappearing N, and decreased the partitioning factor in C. spinarum, H. rhamnoides, Q. incana, Z. jujuba and Z. nummularia. The in vitro true degradability of DM ranged from 0.337 in local grass hay to 0.820 in M. azedarach, which increased upon addition of PEG, except for M. azedarach and the conventional forages. Degradability values were negatively correlated with neutral detergent fiber, acid detergent fiber and lignin. Among the tree forages, the nutritional value of M. azedarach, L. leucocephala and Z. jujuba were ranked as very good on the basis of these parameters. Values of the in vitro gas production parameters determined in the presence or absence of PEG indicate the relative effects of tannins in these forages on substrate degradability and nutrient partitioning.