Chemical composition and in vitro ruminal fermentation of selected grasses in the semiarid savannas of Swaziland

ArticleinAfrican Journal of Range and Forage Science 26(1):9-17 · February 2009with15 Reads
DOI: 10.2989/AJRFS.2009.26.1.2.697
Abstract
Little is known about the grass species type, composition and nutritive value in the semiarid savannas that sustain most of Swaziland's cattle population through the seven-month-long dry season. This study was conducted to investigate the nutritional characteristics of grasses collected from two grazing areas (Big Bend and Simunye), which differed mainly in soil types. Mature grass species were harvested and evaluated for chemical composition (organic matter, neutral detergent fibre [NDF], acid detergent fibre [ADF], crude protein [CP] and minerals) and in vitro ruminal fermentation (in vitro gas production, in vitro organic matter degradability and partitioning factors). The most common grass species in the Big Bend grazing area were Bothriochloa insculpta, Cenchrus ciliaris and Urochloa mosambicensis. In the Simunye grazing area the most common species were B. insculpta, U. mosambicensis, Heteropogon contortus, Panicum deustum and P. maximum. For grasses harvested from Simunye, the most (P < 0.05) degradable (532 mg g−1 dry matter) was B. insculpta, which also had the least fibre (597 g kg−1 NDF and 351 g kg−1 ADF) and the highest CP content (79.8 g kg−1). The most common grass species harvested from the Big Bend area did not differ (P > 0.05) in their Mg, P, Cu, Fe, Zn, CP and NDF content. However, U. mosambicensis had the highest (P < 0.05) ADF content. The least fermentation efficiency (partitioning factor = 2.2 mg degradable organic matter [DOM] ml−1 gas) was observed for U. mosambicensis as a result of low DOM coupled with high cumulative gas production. It was concluded that all the grasses investigated in this study show a deficit for Ca, P and protein. Therefore, supplementation is needed to ensure maximum forage utilisation and to satisfy nutrient requirements of ruminant livestock.
    • "Of the seasons, forage plants in summer might have a ratio beyond the critical limit. Contrasting to this result, several studies in semi-arid African rangelands reported Mg levels of grass species that fall within the grazing animals requirement (Moleele, 1998; Mutanga et al., 2004; Tefera et al., 2009; Beyene and Mlambo, 2012a). In the Lowland area, winter forages across all landscapes may not meet the Mg (0.5-1 g/kg) and P (0.9-1.3 g/kg) requirements of grazing animals. "
    [Show abstract] [Hide abstract] ABSTRACT: Semi-arid African rangelands are characterized by heterogeneous topography and distribution of grazing forages. In these ecosystems, grasses are the main sources of livestock feed with few species contributing to the bulk of the nutrient intake. Forage yield and elements availability play a significant role in determining the adequacy of nutrients intake and fodder flow plan, but limited information is available on their dynamics for the semi-arid South African communal rangelands. There is also little data on factors influencing concentrations of forage minerals throughout the year. We investigated the standing crop yield (DM) and element concentrations of major forages and evaluated their spatial and temporal variations. We conducted the study in two semi-arid (Highland and Lowland) communal rangelands in the Eastern Cape province, South Africa. Herbages for major forage species were harvested from three landscape positions (upland, slopping and bottomland) over four seasons (summer, autumn, winter and spring) in 2012/2013 to determine DM, macro and micro element concentrations. Our results confirm great variations in DM and mineral contents between grass species, across landscapes and seasons. Compared to the Lowland, more elements in the Highland showed interaction effects between species, landscape or seasons. While species variations are attributed mainly to biotic and anthropogenic factors, spatial and temporal variations may be due to topographic, edaphic and/or climatic variations. Minerals most likely to be found deficient were P, Mg, Zn, Cu and K, but this depends on seasons and landscapes. Their amendments through supplementation may deserve utmost consideration.
    Full-text · Article · Jan 2016
    • "On their study around watering points, Fensham, Holman & Cox (1999) and Beukes & Ellis (2003) also concluded that there is a general trend for reduced forage biomass with increasing distance from water points. Both DM yield and estimated G.C reported in this study were extremely low compared with the study of Tefera et al. (2009) in Swaziland, but similar to the report of Abule, Snyman & Smit (2007) in Ethiopian semi-arid rangelands. Based on an inference from the long-term average rainfall of the study area (500 mm), which was also recorded during the study period, the mean DM yield, and hence G.C was extremely too low to carry the potential number of animals that this area should support. "
    [Show abstract] [Hide abstract] ABSTRACT: This study examined rangeland condition and degradation characteristics of the semi-arid savannahs of Swaziland in response to distance from dip-tank points in three soil types. Eight dip-tanks, three each in sandy and loamy, and two in stony soils, were selected. Two transects (1 km) radiating from each dip-tank were established. Total herbaceous yield (range: 176-363.8 kg DM ha(-1)) and grazing capacity (47.5-111.5 ha LSU-1) were very low throughout the studied areas. Palatability and ecological values of grasses were 18.7-67.6% and 43.2-64.1%, respectively. Most sites were dominated by woody seedlings and saplings (<0-2 m). Most vegetation variables did not respond considerably to distance, soil types and sites within soil types. When all measured variables were combined, the results showed a generally poor range condition scores across distance points from the dip-tank. A holistic restoration programme with full involvement of communal farmers, experts, policy makers and extension workers is recommended.
    Full-text · Article · Jul 2014
    • "Tropical forages are generally characterised by a low CP and high NDF content (Preston, 1982; Wassmann and Velk, 2003) with season of sampling (dry or rainy) having an important effect on the chemical composition (Machado et al., 2007; Miller and Thompson, 2007). In the long dry season, the CP content of forages may fall to less than 70 g/kg DM (Tefera et al., 2009), which is considered to be limiting for an optimum rumen microbial growth and fermentation (Van Soest, 1982; Leng, 1993). The chemical compositions and the species richness of forage diets used in the present experiment (Table 1) resemble the type of diet animals would consume in the dry and rainy seasons. "
    [Show abstract] [Hide abstract] ABSTRACT: A feeding experiment was conducted to measure the faecal recovery rates of n-alkanes and to evaluate molasses-based alkane boluses for feed intake and digestibility estimations in cattle consuming low-quality tropical roughages. The experiment was performed in a cross-over design with four experimental diets, four 21-day feeding runs and eight bulls. The animals received a measured amount of the experimental diets that resulted in little refusal throughout the experiment. After seven days of adaptation, the animals were dosed with molasses-based alkane boluses (each containing 200 g C32 and 150 g C36) twice daily at 07:00 and 18:00 h. Concurrent with the alkane dosing, faecal spot samples were taken twice daily until the end of each run. In addition, total faecal collections were performed over the last 5 days of each run. The mean faecal recovery rate of both natural and dosed n-alkanes ranged between 0.61 and 0.86, with the recovery showing an upward trend with increasing carbon-chain length. The recovery rate of dosed alkanes was considerably higher than that of adjacent odd-chain alkanes. Whilst diets did not differ (P≥0.23) in the recovery of even-chain n-alkanes, an effect of diet (P≤0.01) was observed in the recovery of odd-chain n-alkanes. The faecal concentration of dosed alkanes reached equilibrium 3.30 days into the alkane dosing. On the assumption of similar faecal recovery of adjacent n-alkanes, intake was underestimated by 12% (P<0.001) when C31/C33 and C33/C32 alkane pairs were used and by only 1.5% (P≥0.42) when C35/C36 was used. Correction for differences in the faecal recovery of adjacent n-alkanes considerably improved the intake prediction when C31/C32 and C33/C32 pairs were used. Digestibility of diets was accurately predicted using either C36 as external marker or C35 as internal marker corrected for incomplete recovery. The results showed that molasses-based boluses administered twice daily are suitable, and that knowledge of the faecal recovery rates of adjacent n-alkanes improves the reliability of the predictions.
    Full-text · Article · Nov 2012
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