The question of how many ribs a pig has does not have a single, fixed answer. The domestic pig, Sus scrofa domesticus, exhibits a notable range of variation in its skeletal structure, particularly in the number of vertebrae and corresponding ribs. This biological flexibility differs from mammals like humans, where the rib count is highly consistent. The variation observed in pigs is tied to both the animal’s breed and the long history of selective breeding by humans.
The Standard Rib Count and Expected Variations
The number of ribs in a pig is directly linked to the number of thoracic vertebrae, as each rib pair attaches to one of these vertebrae. The typical range for a domestic pig is between 13 and 17 pairs of ribs, totaling 26 to 34 individual ribs. Most common pig breeds fall into a tighter range of 14 to 16 pairs. For instance, Western breeds like Landrace and Large White often have 15 to 17 pairs, while some Chinese indigenous breeds typically have 13 to 15 pairs.
A higher rib count is closely correlated with the total number of thoracolumbar vertebrae. This results in a longer body length, which is an economically significant characteristic in pork production.
Anatomical Structure of the Porcine Rib Cage
Like other mammals, the pig’s rib cage is composed of ribs classified into three main types based on their anterior attachment point. The first few pairs are sternal ribs, or “true ribs,” because their costal cartilage connects directly to the sternum (breastbone). These ribs form a complete connection from the spine to the ventral midline of the chest.
Moving toward the rear, the next ribs are the asternal ribs, commonly called “false ribs.” These ribs do not connect directly to the sternum; instead, their costal cartilage fuses with the cartilage of the rib pair immediately superior to them, forming the costal arch. This arrangement provides structural support while allowing for greater flexibility.
The final pairs are the floating ribs, a specialized type of false rib. These short ribs only attach to the thoracic vertebrae posteriorly and terminate within the muscles of the abdominal wall without any cartilage connection to the sternum or other ribs.
Genetic Factors Influencing Rib Number
The variation in a pig’s rib count is a highly heritable trait that has been intentionally manipulated through selective breeding. Genetic factors strongly influence this anatomical feature, meaning breeders can reliably select parent pigs with higher rib counts to pass the trait on to their offspring.
The economic motivation for this selection is the direct correlation between a higher number of thoracic vertebrae and an increased carcass length. A longer pig yields more commercial cuts of meat, such as a greater number of pork chops and more bacon from the extended loin and belly sections. Specific genes, like the VRTN gene, have been identified as associated with the number of vertebrae and ribs.
Modern breeding programs actively select for these genetic variants to maximize meat yield. This practice has resulted in contemporary domestic pigs being noticeably longer and possessing more ribs than their wild boar ancestors.