Generate a delightful black and white vector illustration in pencil sketch style showing three happy cows with big smiles peering over a wooden fence. The entire composition must be purely monochromatic without any color elements, using only black lines on white background. Render each cow with distinct personality through expressive faces and slightly different poses. Create realistic hide patterns using varied cross-hatching techniques for different tonal areas. Show the wooden fence with detailed grain patterns, knots, and weathered texture. Capture the playful, friendly expressions with careful attention to the cows' large eyes and broad smiles. Include ear details with inner ear shading and natural positioning. The composition should be horizontal with the three cows arranged side by side creating rhythm. Use stippling for softer areas like muzzles and hatching for shadows. The artistic style should be whimsical yet realistic, evoking farm illustration traditions with contemporary charm.