124 The NDF contents are lower. Compared to fresh grass, duckweed contains twice as much protein in the dry matter. Grass appears to be higher in NDF. Because of the high levels of nitrogen in duckweed, it is recommended that analysis be carried out on the nitrate content. The amino acid patterns correspond more or less to the levels that could be expected based on literature. The amino acid pattern of duckweed is comparable to that of fresh grass, with the exception of the low methionine content in duckweed protein. It cannot be ruled out that this is caused by a shortage of sulphur in the diet, although there is no indication of this from the water analyses in the duckweed pond. The fatty acids in duckweed consist of more than 60% linolenic acid, as is the case with grass. However, more than 90% of this essential omega 3 fatty acid is hydrogenated in the rumen. It could therefore contribute only to a limited degree in enrichening meat with omega 3. In the rumen, linolenic acid can reduce the production of methane, and after conversions to CLA, stimulate a more efficient build-up of meat. Compared to fresh grass, duckweed contains high levels of calcium, phosphorus and sodium. High phosphorus levels make it possible to apply other ingredients with low levels. Because the levels of sodium and potassium are high, the electrolyte balance should be taken into consideration if the amount of duckweed in the rations is increased. Of the trace elements, iron is of particular importance for the calves. To prevent the white meat of the calves getting too red a colour, it is important to moderate the content of iron in their feed. The high iron content in duckweed makes it unsuitable for white meat calves. VEVI is used as the measure for the net usable energy for beef cattle. To enable calves to grow quickly and efficiently, a high VEVI content per kg dry matter is important. VEVI content in duckweed is lower because of the greater ash content. The low VEVI in duckweed places a limitation on its usability. Duckweed is high in rumen degradable protein (DVE) and degraded protein (OEB). Too high an OEB in the overall diet has a deleterious effect on energy consumption and health. Of the nutrient costs of the diet, 65 to 70% consist of costs for VEVI and 20 to 25% of costs for rumen degradable proteins. Compared with fresh grass, the VEVI content in duckweed is significantly lower, which means that the dietary value of duckweed is lower too. This is due to a major degree to the higher levels of ash. On the other hand, the total protein and rumen degradable protein (DVE) content are higher, which means the dietary value of duckweed is overall similar to that of fresh grass, and greater than that of grass silage. Including duckweed in the diet leads to a decrease in the use of grass and soya. This has a favourable effect on the costs of the diet. However, the low dry matter content in the feed does require attention. To ensure the provision of sufficient energy to counter the protein-rich duckweed, a little more sugar beet pulp is being added to Pagina 131
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