Qualitative intake and certain rumen parameters of beef cattle in north western parts of Namibia

Abstract

Beef production is known to be the most important livestock related activity in Namibia (Just over 2 million cattle in Namibia in 2009) with the majority of weaners being exported to the South African feedlot industry. Extensive beef production requires a sound knowledge of management practices, genetics and nutrition. The nutritional requirements of cattle remain one of the most important factors for maximizing return and profitability of the farming enterprise. The purpose of this study was to quantify the nutritive value of two veld types in the north western part of Namibia. The thorn bush savanna was assigned as treatment K whilst the mopane savanna was assigned as treatment M. For the oesophageally collected samples there were differences between the two years (2007 and 2008) for all the parameters as well as differences between the two veld types (treatments) and periods. Crude protein (CP) had a large seasonal variation in both treatments, with treatment K having higher CP concentrations for the majority of the trial period compared to treatment M. Phosphorous (P) also tended to show seasonal variation with higher concentrations during the wet season. The CP requirements for a 400kg cow were not met during the time when the cow is expected to be pregnant, however during lactation and early gestation the CP requirements of a 400kg cow are met from the intake of forage alone. The P requirements of a 400kg cow were met during the majority of the year except during the last trimester of gestation where the forage alone is not able to supply the P requirements of a 400kg cow. Treatment K had higher concentrations of calcium (Ca), zinc (Zn) and copper(Cu) compared to treatment M, whilst Treatment M had a higher concentration of manganese (Mn) during the majority of the trial period. The Mn concentration of the forage was shown to be adequate during most parts of the year and was able to supply the Mn requirements of a 400kg cow during gestation and lactation for both treatments. However, Cu, Zn and Mg were deficient especially during the winter months and intake from forage alone was not able to supply the Cu, Zn and Mg requirements for a 400kg cow during both gestation and lactation. The Ca concentration of both treatments was high, and caution should be taken to ensure that the high intake levels of Ca through feed and water do not cause mineral imbalances. The in vitro digestible organic matter (IVDOM) concentrations increased from the winter to the summer months. The neutral detergent fibre (NDF) and acid detergent lignin (ADL) concentrations varied between treatments as well as throughout the trial period. The rumen cannulated animals showed differences between years, treatments and periods for total volatile fatty acid (VFA) concentration and rumen NH3-N. The rumen ammonia-N concentrations increased during the periods of higher rainfall whilst the total VFA concentration showed no distinct seasonal pattern. The faecal CP results indicated that protein supplementation is necessary especially during periods of lower rainfall. whilst the faecal P results fell within the normal range. The relationship between faecal CP and diet CP concentration was not so strong and faecal CP concentration should be used with caution to predict the CP concentration of the forage. The relationship between faecal P and diet P concentration was also not strong when both treatments and years were combined which confirms that such relationships need to be tested under specific conditions.