| Summary: | Experiment 1 investigated whether sheep select between foods that differ in their effective rumen degradable protein (eRDP) content to achieve an estimated 'optimal' eRDP: fermentable metabolisable energy (fME) ratio. The foods offered were presented in a meal form to prevent chemical changes to the food ingredients that may occur during the pelleting process. However, as the food ingredients separated during the course of the experiment and the composition of the selected diet could not be sufficiently predicted, the results of the experiment were unclear. Experiments 2 and 3 re-asserted the hypothesis that diets selected by sheep would be those that meet the eRDP requirements of the animals and at the same time avoid excess consumption of rumen degradable protein (RDP). The sheep were given choices between pelleted foods differing in their urea content, which was used as an eRDP source. However, sheep selected a diet in favour of the urea-supplemented food regardless of the basal food to which the urea was added. This resulted in an excess consumption of RDP. The results did not support the hypothesis that sheep would avoid excess RDP when give a choice and suggest that eRDP may not be a relevant dimension in diet selection in the conditions of these experiments. It was thought that urea may have had other properties, such as a high buffering potential, that the sheep were selecting for when selectin a diet. Experiment 4 tested the hypothesis that the preference for and eRDP adequate food supplemented with urea would be reduced by the addition of a buffer (sodium bicarbonate (SB)) to both foods offered as a choice or offering <i>ad libitum</i> access to hay. In both cases urea may no longer be needed as a buffer and the preference for the urea-supplemented food would then be expected to be reduced or even disappear. Insufficient amounts of hay were consumed to reduce the preference for the urea-supplemented food.
|
|---|
