The Namibian meat industry relies on the export of weaners to the South African feedlot industry while the largest part of the cattle population in the communal areas of Namibia remain underutilised. Producing a marketable cattle carcass for slaughter, which contributes the most to the Namibian economy, remains a challenge that needs a high level of understanding of all management variables under control by the rangeland manager. The nutritional requirements of cattle are one the important areas for maximising the return from the land and ensuring long term sustainability of the farming enterprise. A commercial farming enterprise, with the same climate and sandy soils that were predominantly found in the communal farming areas of Namibia, was chosen as experimental site. Three groupings of cattle were exposed to different experimental techniques and treatments over a 15 month trial period. The first grouping of cattle was 6 oesophageal fistulated cattle used, to collect veld samples selected by the cattle, every 3 weeks to estimate the contribution of the tree and shrub savannah towards the diet of the cattle. The second grouping was 110 cattle allocated to different nutrient supplementation treatments for slaughter at 28months of age. Five different nutrient supplementation treatments were chosen for 5 groups of 22 cattle, consisting of steers and heifers, for the duration of the period on an ad libitum basis. The 5 treatments were applied to illustrate the economic concept of diminishing marginal returns as the increasing feeding cost progressively deteriorated the amount of profit that would be expected. The optimal supplementation strategy would thus be identified according to the financial resources available to a farmer. Some of the treatments were also planned to progressively result in negative associative effects on forage intake, as energy containing raw materials in such treatments would replace the intake of natural available forage. The need for replacing forage was a common practice in droughts when the availability of forage was limiting or when the finishing of cattle during a short period before slaughter was planned. The cattle needed to be foraging less to conserve energy and thus increase protein accretion and fat deposition. The control of the experiment was the rock salt treatment group (RST) which only received a rock salt lick throughout the dry and wet seasons of the year. This was generally used for the supplementation of wildlife and cattle on rangeland in Namibia and it placed nearly no strain on the finances of a farmer. The remaining four treatments received commercially manufactured lick products with a diverse set of applications that were not strictly used according to the manufacturer's guidelines. During the wet season it was a well-established practice to only supplement with phosphorus and trace mineral containing licks due to the forage having maximum nutritional value during this time in which no additional benefit would be derived from the supplementation of protein and energy containing licks. All treatments, except for the rock salt treatment group (RST), were thus placed on a phosphorus and trace mineral lick during the wet season as part of the nutrient supplementation treatment programs. Different licks were made available to the cattle in the treatment groups, during the dry season, from which the treatment groups derived their names. One group was placed on a phosphorus and trace mineral lick for the duration of the trial, during the wet and dry season, and defined as the 6% phosphorus treatment group (6%PT). A maintenance treatment group (MTT) received protein in addition to phosphorus in the lick during the dry season. The production treatment group (PDT) received energy containing raw materials in addition to the minerals and protein as established in the MTT. The finisher treatment group (FST) received a larger amount of energy containing materials which diluted the mineral and protein concentration of the dry season lick even further than in the PDT. The third experimental procedure was to establish a group of 5 ruminally cannulated cattle that would individually be rotated every 3 weeks between the supplement fed treatment groups. The cattle would then be sampled for ruminal fluid, blood and faeces to observe the short term impact of the supplements during the different seasons on these variables and the diagnostic value of these parameters to indicate the nutritional status of cattle. The results clearly illustrated that the cattle had exhibited “nutritional wisdom”. The selection of higher quality plant material than what was on offer in the veld was highlighted in a review of previous oesophageal fistulated cattle research. The strong influence of rainfall on the forage quality (increased phosphorus and protein) was highlighted. During spring the phosphorus and protein reached their maximum concentrations. It was only during the wet season that animal performances were optimised when the quantity of high quality forage increased. The average daily ad libitum nutrient supplement consumption per animal on the different treatments was strongly influenced by these seasonal changes in forage quality and quantity. The lick intake increased as the dry season progressed and the quality of the forage the animals were able to select decreased. During spring the lick intake sharply decreased as the forage quality improved. The cattle adapted their intake level with the aim of maximising their energy intake, which resulted in the highest possible performance possible, from the forage and lick that was on offer to them. Monitoring the average monthly lick intake per animal would give valuable information to the farmer on the quality of the forage selected. The trends observed in average lick intake during the year could be used as an inexpensive indicator of veld qualit. An upper threshold could be set on lick intakes that would signal that a specific area was optimally grazed and that a camp rotation would aid in conserving the rangeland and optimise animal performance. The year round supplementation of rock salt lick group (RST), or alternatively no nutrient supplement, under these conditions had clearly shown a minimal contribution to the nutritional status of cattle and that this strategy would lead to certain financial underperformance or ruin of the cattle farmer. From the results presented, the year round supplementation with a phosphorus and trace mineral lick (6%PT) was indicated as the absolute minimum nutrient supplementation strategy that would need to be followed in all communal and commercial cattle farming areas of Namibia and probably similar farming locations around the world. Free access to phosphorus licks throughout the year to growing cattle must be ensured by the farmer to allow the cattle to select the correct amount that it would require to optimise performance. This strategy required the least amount of capital to implement and had the largest return on investment for a newly established farmer. If limited amounts of energy containing materials (molasses, maize, bran) were included in the nutrient supplement on offer it allowed the animal the opportunity to only consume the minimum amount of phosphorus that it required throughout the year to balance the shortages that occurred in the forage that it was selecting from. The finisher lick given during the dry season on the FST clearly illustrated that salt and phosphorus were poor regulators of supplemental intake if the cattle were able to increase their total energy retention by over consuming and probably excreting of minerals. The optimum nutrient supplementation strategy was the MTT that alleviated the primary phosphorus and secondary protein shortages during the dry season. This strategy had a much higher capital requirement and would be most suitable for the established cattle farmer that was able to afford this strategy or had access to credit. The PDT and FST were associated with higher supplementation costs that resulted in the highest turnover for the cattle farmer, although at lower profit than the MTT. The PDT and FST supplementation strategies would be more appropriate if the improved nutritional status of the cattle was utilised in a cow herd for improved reproduction or in stud farming when genetic expression of growth potential would offset the cost of supplementation. Copyright
Dissertation (MSc(Agric))--University of Pretoria, 2012.