Muscle development becomes an unmistakable separator by the fifth month. Pitbull puppies show clear muscle striations along the shoulder, quadriceps, and flank while still growing. Their abdomen features a distinct tuck-up behind the ribcage, resembling the silhouette of a sprinting sighthound wrapped in heavy muscle.
Bull Terrier puppies do not develop that high tuck-up. Instead, their bodies maintain a cylindrical, barrel-like profile from ribcage to loin. Their musculature looks smooth and compact rather than chiseled and vascular.
Coat patterns present another clear contrast. Pitbull puppies come in virtually every canine color pattern, from blue, fawn, red, and chocolate to intricate brindles and pied variations. Bull Terriers fall into two clean, standardized show classes: pure white (with or without head markings) and colored (often brindle, black-brindle, red, fawn, or tricolor, usually accompanied by white bibs and blazes). Merles never appear in purebred lines for either breed; the presence of merle patterning indicates crossbreeding with Australian Shepherds or Catahoula Leopard Dogs.
