Preheat the oven to 375°F (190°C or 175°C for a fan or convection oven).
Grease a muffin pan with 12 cups or line them with paper muffin cases.
In small bowl, combine the buttermilk and baking soda. The milk may foam up a little, so be sure the bowl is big enough to accommodate an increase in volume.
In a medium bowl, stir together the flour, oat bran and salt. Set aside.
In a large bowl, cream the butter and sugar together until light and fluffy.
Add the beaten eggs.
Stir in the grated orange rind.
Gradually add the flour mixture alternately with the buttermilk.
Add the pecans, raisins and carrot and stir until well combined. Do not beat.
Divide the muffin batter between the muffin cups.
Bake for 20 minutes or until a skewer inserted in the centre of the muffins comes out clean.
Cool on a wire rack for a few minutes before eating.
Once any leftover muffins are completely cool, store them in an airtight container at room temperature for 3 to 4 days.