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Title: Browsing cattle? Stable isotope analysis of cattle dung provides insights from a degraded pasture land in Northern Namibia
Authors: Radloff, FGT 
Van der Waal, C 
Issue Date: 26-Jun-2012
Abstract: In Namibia, the agricultural sector supports about 70% of the population directly or indirectly through income and employment. Livestock accounts for about 90% of all agricultural production and approximately 60% of households own cattle. About 57% of the Namibian population lives in the Northern Communal Areas (NCAs) together with approximately 1.04 million cattle, 25 895 sheep, and 774 000 goats. While Namibia produces a total of 85 000 tons of meat annually, very little of this is produced in the NCAs. Livestock in these areas are often in poor condition and thus seldom fetch acceptable market prices. Farmers in the NCAs thus have little incentive to sell livestock commercially. The poor condition of livestock in the NCAs to a large extend reflects the deteriorated state of rangelands in these areas. High livestock stocking rates and lack of effective rangeland management practices results in overgrazing of especially the desirable perennial grasses in the NCAs. In certain areas this has, in conjunction with the suppression of fires, resulted in the replacement of grasses by shrubs, trees and unpalatable forbs, thereby drastically changing forage conditions for herbivores in these systems. Cattle in these areas may have little choice than to increase the browse fraction (parts of trees, shrubs and forbs) in their diet to meet nutritional demands, in spite of being physiologically not adapted to subsist on browse. However, little information exists about the browse:graze diet composition of cattle in the NCAs. Information of how the natural resources are used by livestock is crucial for wise land use planning. If cattle are indeed dependent on browse resources, then feed supplementation, livestock management practises, and land use and veld restoration plans need to be adapted accordingly. Traditionally herbivore diets are studied through direct observation, which is time consuming and subjected to difficulties of quantification or intrusive measures. Recently, stable isotopes have been promoted and successfully used to study mammalian herbivore diets in tropical and sub-tropical environments. Terrestrial plants obtain carbon from atmospheric CO2. Almost all grasses and most sedges in dry tropical regions use the C4 photosynthetic pathway, while browse (trees, shrubs, and forbs) species use the C3 pathway. This results in grasses and browse plants having different isotopic signatures. The bimodal distribution of ᵹ13C between plants following the C3 and C4 photosynthetic pathways is faithfully recorded in the tissues of herbivores (teeth collagen, hairs and faeces) feeding on these plants. Cattle dung is useful markers of dietary variation because they offer insight at high-resolution time scales, i.e. in the order of several days, is easy to collect in the field, and sampling does not require interference through manipulation or slaughter of animals. Recent controlled feeding experiments of carbon isotopic fractionation have shown that large herbivore faecal ᵹ13C values correlate closely with the proportions of C3 browse and C4 grass fed to animals, with very small variations. We will present the results of a study where we used stable isotope analysis of cattle dung to quantify the relative proportions of browse and graze over a seasonal cycle in two of the Northern communal grazing areas. Both areas have high livestock stocking densities but diverse vegetation.
Description: Browsing cattle? Stable isotope analysis of cattle dung provides insights from a degraded pasture land in Northern Namibia JICSTDA: Joint International Conference on Science and Technology for Development in Africa, Cape Town, 26-28 June 2012
Appears in Collections:Appsc - Conference Papers

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