Forage quality of some Kalahari browse species and its ability to reduce enteric methane emission

Abstract

The nutritional value of browse foliage from shrub and tree species in the Kalahari region of the Northern Cape, South Africa is not well quantified and analysed. In this study, nineteen browse (shrub and tree) species were selected and their foliage harvested during April 2012, when the plants are at mid vegetative stage of growth in order to determine its chemical composition, nutritional values and its potential to reduce methane production. The foliage materials were analysed for crude protein (CP), ash content, dry matter (DM), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), total phenols and condensed tannins. The in vitro gas production technique was used to determine the volume of gas and methane (CH4) produced. IIn vitro organic matter digestibility (IVOMD), volatile fatty acids (VFA) and rumen ammonia (NH3-N) concentration were also determined. In the gas production study the forage samples were studied either in the absence or presence of polyethylene glycol 8000 (PEG) to determine the effects of tannin on various parameters of interest. Crude protein ranged from 70-320 g/kg DM, ash 40-210 g/kg DM, NDF 350-508 g/kg DM, ADF 270-530 g/kg DM, ADL 85-320 g/kg DM and neural detergent fibre nitrogen (NDFN) 47-93 g/kg DM. Total tannins ranged from 9-320 g/kg DM, condensed tannins 2-125 g/kg DM and hydrolysable tannins which ranged from 3-195 g/kg DM. The CP concentration of all 19 browse species included in the current study, except Olea europaea, Terminalia sericea and Monechma genistifoluim will meet the maintenance requirements of ruminants based on CP concentrations as indicated in the NRC (2007) guidelines. Among the shrubs and trees, Acacia luederitzii and Monechma incanum showed the best potential to decrease methane production by up to 90 % after 48 h of incubation. The secondary compounds (mainly tannins) of the browse species had no significant (p<0.001) effect on IVOMD and rumen ammonia concentration but the VFA, methane and gas production was decreased significantly (p<0.001). In the last experiment, an in vitro gas production experiment was conducted to evaluate the potential of 6 selected browse species (with high, medium and low condensed tannin concentrations) when supplemented to Eragrostis trichopophora. This was done in order to determine their potential as anti-methanogenic additives in the diet of ruminant animals. These browse species were supplemented with Eragrostis trichopophora at a ratio of 30:70. The effects of addition of these browse as a supplement, on rumen fermentation and methane production were studied. Of the six browse included in the current study, A. luederitzii and M. incanum decreased methane production by more than 50 %, but digestibility and VFA production was decreased. From these 3 studies, it seems that Boscia albitrunca and Rhus lancea has the best potential to be used as a feed supplement during times of drought, depending on the availability of these browse foliage, while A. luederitzii and M. incanum seems to have the best potential to consistently decrease methane production, but at the expense of digestibility. An in vivo feeding trail inside a methane chamber should be considered in the future in order to complement this study to determine the nutrient availability and degradability of these browse species and to estimate the actual potential reduction in enteric methane production.