Chemical composition and in vitro ruminal fermentation of common tree forages in the semi-arid rangelands of Swaziland

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The aim of this study was to establish a database on nutrients and mineral profile, in vitro dry matter digestibility (DMD) and in situ ruminal degradability characteristics of leaves from 21 fodder tree species commonly fed to livestock in semi-arid and arid zones of Northern Pakistan. Leaves from 13 fodder tree species: Albizia lebbeck, Ailanthus altissima, Bauhinia variegata, Butea frondosa, Celtis australis, Ficus carica, Grewia oppositifolia, Leucaena leucocephala, Mallotus philippensis, Melia azedarach, Morus alba, Morus papyrifera and Ziziphus mauritiana were sampled from semi-arid zone. Leaves from 8 fodder tree species: Acacia modesta, A. lebbeck, Capparis aphylla, Olea cuspidata, Prosopis juliflora, Tecomella undulata, Ziziphus jujuba and Ziziphus mauritiana were sampled from arid zone. Within each ecological zone, leaves of each tree species were collected at four sub-locations, from three randomly selected trees. The results showed a large variation in the concentration of all measured chemical components, DMD and ruminal degradation characteristics among the tree species. The contents of crude protein (CP) varied from 8.76% (T. undulata) to 24.0% (M. alba); ash from 7.41% (O. cuspidata) to 22.4% (C. australis); and neutral detergent fibre from 20.6 (L. leucocephala) to 56.5% (C. aphylla). Except for T. undulata, leaves from all tree species had CP content of >10%, and 60% of the species had leaves with >15% CP, demonstrating that leaves from majority of tree species can be used as low-cost CP supplement. The mineral composition revealed that, except for C. aphylla, leaves from all tree species were rich sources of Ca, whilst most of the species were deficient in P, Na and Cu. The DMD of the majority (66%) of tree leaves were <50.0%, ranging from 33.1% (M. philippensis) to 67.6% (M. alba). The in situ data further showed that a large fraction of ruminal degradable dry matter was instantaneously degraded (soluble). The potentially rumen degradable (D) fraction and rate of degradation (k_d) was highly variable, ranging from 0.234 to 0.958 and 0.026 to 0.99/h, respectively. The effective ruminal dry matter degradability (ED_DM) was higher than the in vitro DMD, ranging from 0.34 to 0.84, at an outflow rate of 0.05/h. This information on nutrients and mineral profile, in vitro DMD and in situ ruminal degradability characteristics of leaves from 21 fodder tree species, obtained under well replicated and uniform experimental conditions can be used to optimize diet formulation in terms of nutrients supply to the animals that will ensure better utilization of this nutrients-rich feed resource and will increase economic profitability of subsistence livestock farmers in the region.

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Acacia karroo is one of the most widespread and abundant indigenous tree legume species in Southern Africa. The tree possesses positive attributes such as high growth rates, drought tolerance, adaptation to acidic infertile soils and resistance to large temperature variations. In the recent past, A. karroo was deemed to be a severe encroacher, which adversely affected land utilisation and rangeland productivity. Research attention has been diverted from its riddance as a weed to its utilisation as an animal feed. Widespread adoption of feeding strategies based on A. karroo was mainly impeded by the presence of thorns and tannins. Opportunities to minimise the adverse effects of these anti-quality factors are now well documented. A. karroo leaves have desirable fatty acid profiles, high N and mineral concentrations. At present, utilisation of A. karroo for beef production on rangelands is restricted by limited evidence regarding its feeding value. The current paper, therefore, demonstrates the potential of A. karroo to reduce worm burdens, and improve growth rates, carcass traits, beef quality and fatty acid profiles of cattle on rangeland. Economics of feeding A. karroo, strategies for incorporating it into feeding regimes for beef cattle and its relevance to sustainable livelihoods in low input production systems are outlined.

Citation Excerpt :

A range of Australian woody perennial plant species (n = 128 samples) were screened in vitro for overall fermentability and the capacity to induce favourable metabolic pathways in the rumen. Plants were tested in a batch rumen culture system, where gas pressure, pH and total volatile fatty acids were used as indicators of overall plant fermentability, and concentrations of methane, ammonia, acetate and propionate indicated changes in fermentation end products. In vitro fermentation of 52 of the plants yielded a gas pressure that was similar to, or higher than, the positive control (i.e., oaten chaff). Five plants produced less methane (mL/g dry matter supplied) without reducing total gas production, 54 reduced both methane and gas production, 47 reduced neither, and 22 reduced gas production but not methane production. All plants produced relatively low amounts of ammonia, while only 22 reduced the acetate: propionate ratio. Variability in response occurred at the genus and species level and plants with some favourable fermentative traits were identified. The screening of Australian woody perennial plants not previously considered for grazing systems illustrated the possibility of using some species to manipulate rumen fermentation, either as part of a mixed diet or to identify plant compounds associated with bioactivity in the rumen.