Quantification of the nutrition of grazing Arsi cattle through prediction of diet composition, feed intake and digestibility using plant wax markers

Abstract

Grazing land resources in the central highland of Ethiopia are shrinking due to deforestation, agricultural land expansion and continuous heavy grazing. Improved management of grazing lands necessitates the knowledge of the nutritional qualities of different pasture species, biomass yields, botanical composition and diet estimation. The use of plant cuticular wax hydrocarbons as diet composition markers has recently received increasing acceptance. The objectives of this study were: (i) to quantify changes in vegetation structure and aboveground biomass yield in response to traditional grazing land regimes; (ii) to evaluate chemical composition and in vitro ruminal fermentation parameters for forage species; (iii) to quantify plant wax profiles and evaluate the potential of using these compounds as markers; (iv) to validate feed intake and digestibility estimation by using n-alkane technique. Two traditional grazing land management practices, enclosure during wet season and the adjacent open access grazing land were selected in Kofele district, West Arsi Zone Oromia regional state, Ethiopia. Ten plots of 40 m x 40 m were established and sixteen 0.5 m x 0.5 m quadrats were nested per plot for sample collections. Chemical composition and in vitro fermentable parameters were conducted for 19 key forage species. Plant wax components from ten dominant forage species were evaluated. Finally, controlled in-door experiments were conducted using eight steers to validate the accuracy of the n-alkane method in intake and digestibility estimations. The results showed that mean aboveground biomass yield from enclosure area was higher (P<0.001) than open access grazing in the mid-highland agro-ecology. Forage species evaluated showed observable variation in chemical composition and in vitro fermentable parameters. Large variations in n-alkanes, carbon stable isotopes and alcohols were observed among the evaluated forage species which indicates the possibility of plant wax marker as diet estimations. Incomplete faecal recoveries were observed for the evaluated forage species. Dry matter intake was accurately predicted by using plant wax markers after faecal recovery correction. Dry matter digestibility was accurately estimated by using C35 alkane as internal marker after faecal recovery correction for the low intake group. Generally, it can be concluded that the information generated from this study could be used to design appropriate grazing land management practices to increase feed resource availability, environmental sustainability and productivity of the farming system in the study area.