Abstract
Proximate nutrient composition (crude protein, non-fiber carbohydrates, crude fiber, and ash), fiber fractions (neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin), and both macro (calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), sodium (Na), and sulfur (S)) and trace (copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn)) mineral profiles were quantified in mixed pasture samples collected during the wet (n = 8) and dry (n = 15) seasons in north central Uganda. Metabolizable and Net Energy values for dairy production were estimated based on standard calculations, and samples were compared seasonally. Crude fat (p = 0.05) and lignin (p = 0.01) values were lower in the dry compared with the wet season, linked with reduced plant growth. Crude protein (13.0% of dry matter (DM)), fiber fractions, and calculated energy content did not vary seasonally in this data set, and reflected chemical components of a grass-dominated system that appeared energetically limiting for production livestock. Mineral constituents varied more dramatically by season, with Ca, Mg, Cu, and Mn lower (all 0.05) and K higher in the dry season. Sodium was deficient in these pastures, whereas Ca, P, Mg, S, Cu, and Zn concentrations may have been only marginally sufficient, particularly to meet needs for lactation, dependent on season. These limited data suggest that a high-energy mineral supplement may prove beneficial in meeting nutritional and production needs of multiple grazing ruminant species in this region, particularly during dry seasons.
Highlights
Carrying capacity of rangelands utilized in the Ankole grazing system in Uganda has been previously modeled [1], and has been found to be highly dependent on rainfall patterns, subject to strong seasonality
Pasture nutrient resources—measured as either average dry matter production [1] or crude protein content [2]—were highly variable; cattle body condition and productivity decline with the dry season and recover during wet seasons
This study provides baseline information on proximal nutrient and mineral constituents of pastures utilized by grazing livestock during dry season compared to wet season in the Bbale district of central Uganda
Summary
Carrying capacity of rangelands utilized in the Ankole grazing system in Uganda has been previously modeled [1], and has been found to be highly dependent on rainfall patterns, subject to strong seasonality. Animals can respond to lower available forage in the dry season behaviorally through selective feeding and browsing, pasture provides primary nutrition year-round. Both quantity and quality characteristics must be considered in order to optimize nutritional strategies, including the need for supplementation.
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