Quality of two veld types in the Northern Cape as quantified in grazing sheep

Abstract

The purpose of this study was to quantify the nutritive value of two veld types in the Northern Cape and also to identify limitations regarding animal production directly from the natural pasture. The two veld types were identified as Grassveld and Ranteveld. Three sheep were fitted with oesophageal fistulae and allowed to graze each veld type for three days every month for two years. Analysis was done to determine the crude protein (CP), phosphorus (P), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), molybdenum (Mo), In-vitro organic matter digestibility (IVOMD), neutral detergent fibre (NDF), acid detergent insoluble nitrogen (ADIN) and metabolizable energy (ME) content of the two veld types. Six sheep fitted with rumen cannulae were allowed to graze each veld type for six days every month for two years. Rumen fluid was collected and analysed for volatile fatty acids (VFA) and rumen ammonia-nitrogen (NH3-N). Blood was also collected for blood urea nitrogen (BUN) analyses and faecal samples were drawn to test faecal phosphorus and faecal crude protein as nutritional indicators. For the oesophageally collected samples there were differences between Year 1 and Year 2 for all of the parameters. There was also differences between Grassveld and Ranteveld for all of the parameters. Crude protein was shown to have large seasonal variation in both Ranteveld and Grassveld, with Grassveld having lower CP concentrations for most of the year compared to Ranteveld. The crude protein content was low during winter and was identified as the first limiting nutrient during dry periods. Phosphorus had low concentrations in both veld types with large seasonal variation. The mineral balance of the two camps differed widely with Ranteveld having higher concentrations for Ca, Cu, Mg, Mn, Fe and Zn compared to the Grassveld. Calcium, copper, magnesium and manganese were found in concentrations that were acceptable for most applications of animal production. There was a deficiency of Zn and Mo in both the veld types. The Fe concentration of both veld types was very high. The calcium concentration of the selected diets was high and caution should be taken to ensure that the high intake levels of calcium through feed and water do not disturb mineral balances in livestock. The IVOMD concentrations for both veld types were similar throughout the trial period. The IVOMD concentration dropped during the dry winter months. The NDF concentrations was higher in the Grassveld than in the Ranteveld for most of the trial period. Acid digestible insoluble nitrogen (ADIN) did not have a seasonal trend and would further lower the nitrogen available to animals throughout the year. The rumen cannulated animals showed differences between years and veld types for VFA's and rumen-NH3-N. Total VFA concentration showed seasonal variation with few differences between months. Acetic acid concentrations was high with relatively low concentrations of propionic and butyric acid. Rumen NH3-N had large seasonal variations. Rumen NH3-N was low during the dry months and would not support optimal rumen function and animal performance. BUN was shown to be an indicator of diet crude protein. Faecal phosphorus and faecal crude protein was not a reliable indicator of diet phosphorus or diet crude protein content.