Spread a thick layer of the buttercream over the cooled cakes. Using a palette knife, lightly peak the icing on 4 of the cakes.
Knead 75 g (3 oz) of the brown icing (wrap the remainder in clingfilm) on a work surface lightly dusted with icing sugar for the sheep. Reserve a small piece for the ears and roll the remainder into 4 balls. Flatten each ball into an oval shape and gently press on to the cakes thickly spread with buttercream. Shape and position small ears on each sheep.
Reserve a small piece of yellow icing for the ears and roll the remainder into 4 balls for the cows. Flatten into oval shapes as large as the cake tops. Gently press on to 4 more cakes. Shape and position the ears. Use the remaining brown to shape the cows' nostrils and horns, securing with a dampened paintbrush.
Reserve 25 g (1 oz) of the pink icing for the pigs' snouts and ears. Roll the remainder into 4 balls and flatten into rounds, almost as large as each cake top. Shape and position the snouts and floppy ears, pressing 2 small holes in each snout with the tip of a cocktail stick or fine skewer.
Use the white and black icing to make all the animals' eyes – their shape and size to suit each animal. Roll small balls of white icing and press tiny balls of black icing over them. Secure with a dampened paintbrush.
Use a fine paintbrush, dipped in the food colouring, to paint on additional features.