In a bowl, cream shortening and sugar. Add eggs, one at a time, beating well after each addition. Beat in buttermilk and vanilla. Combine the flour, baking powder, baking soda and salt; add to creamed mixtures. Fold in apple and walnuts. Pour into a greased 8x4-in. loaf pan. Bake at 350° for 55-65 minutes or until a toothpick comes out clean. Cool for 10 minutes before removing from pan to a wire rack.