Deactivation Effects of Polyethylene Glycol (PEG) on in vitro Dry Matter Digestibility of Colophospermum mopane (Mophane) and Acacia Browse Trees in Botswana

Abstract

This trial evaluated the deactivation effects of PEG 6000 on in vitro dry matter digestibility (IVDMD) of Colophospermum mopane ( Mophane ) and acacia browse trees. Samples were collected from Sebele Content farm except for Mophane and were freezed dried before analysis. PEG was introduced into the digestion tubes at a rate of 160mg/g of sample in the form of a one milli liter of solution containing 80mg PEG before the addition of rumen fluid/buffer medium. It was found that plant species had an effect (P< 0.001) on IVDMD. Viscum verrucosum , mistletoe that attach on acacia trees, was found to have higher (576.6±27.7g/kg DM) while Mophane had the least IVDMD (350.5±31.0g/kg DM). IVDMD between PEG inoculated and control samples was similar (P>0.05). However, IVDMD values of PEG treated samples were numerically higher with those of Acacia nilotica approaching significance (P=0.083). Within the PEG treated samples, IVDMD was higher (P<0.05) for A. nilotica, A. tortilis and V. verrucosum and lower for Mophane samples. The low digestibility of Mophane may not be due to extractable condensed tannins (CT) because fresh Mophane leaves have been previously found to contain 27.0g/kg DM condensed tannins. Other anti-nutritional factors may be responsible for its low digestibility. Alternatively, phlobatannins which are a characteristic of heartwood of Mophane may be present in fresh leaves and may have formed an insoluble complex with PEG leading to an underestimation of IVDMD. It is concluded that PEG may not be an ideal deactivating agent to improve utilization of fodder trees by resource limited farmers and an alternative such as wood ash should be investigated.