Guinea pigs, scientifically known as Cavia porcellus, are popular companion animals. Understanding their distinct anatomical characteristics is fundamental for providing them with proper care and supporting their overall well-being. Their unique physical structure necessitates specific considerations to maintain their health.
External Body Structure
A guinea pig has a stout, compact body, often described as “cobby.” Their eyes are positioned on the sides of their relatively large head, providing a wide field of vision for detecting threats. While they can perceive colors and movement, their direct forward vision is limited. Their highly developed sense of smell and sensitive whiskers around the nose, eyes, and mouth compensate for this, aiding in food selection and environmental navigation.
Guinea pigs have excellent hearing, capable of perceiving frequencies beyond the human range. Their limbs are short, with four toes on each front foot and three on each back foot, all equipped with claws that grow continuously and require regular trimming. Guinea pigs lack a visible tail, though a rudimentary tail bone is present internally. Near the base of their spine, a sebaceous or “grease gland” is present, more active in males and contributing to scent marking.
Specialized Dental Features
Guinea pigs have specialized dentition. All their teeth, including incisors and cheek teeth (molars and premolars), are “aradicular hypsodont.” This means their teeth are open-rooted and grow continuously throughout their lifespan. This constant growth necessitates consistent wear to prevent overgrowth.
Guinea pigs possess 20 teeth in total: four incisors and 16 cheek teeth (premolars and molars). They chew with a side-to-side motion, performing approximately 200 chewing movements per minute. A diet rich in abrasive fiber, such as hay, is essential for naturally grinding down these continuously growing teeth. Without adequate fibrous material, their teeth can become overgrown, leading to malocclusion, which causes discomfort and difficulty eating.
The Unique Digestive Tract
Guinea pigs are strict herbivores, consuming only plant matter. They are classified as “hindgut fermenters,” a digestive strategy where the primary site for breaking down fibrous plant material is located in the large intestine rather than the stomach. A significant component of their digestive system is the cecum, a large, thin-walled sac situated at the junction of the small and large intestines. This cecum can hold up to 65% of their gastrointestinal contents.
Within the cecum, a diverse population of bacteria and protozoa ferment cellulose and other complex carbohydrates from ingested plant material. This fermentation process yields usable nutrients, including short-chain fatty acids, B vitamins, and amino acids. To fully absorb these nutrients, guinea pigs engage in coprophagy, eating special droppings known as cecotropes. These soft, nutrient-rich pellets, distinct from regular feces, are consumed directly from the anus, allowing for a second pass through the digestive system to extract additional nutrition.
Distinguishing Males and Females
Differentiating between male and female guinea pigs, known as boars and sows, involves examining their genital area. From a top-down view, there are no immediately obvious external differences, though boars may be slightly larger on average. The most reliable method involves gently inspecting the area around the anus.
A female guinea pig, or sow, will have a Y-shaped genital opening. In contrast, a male guinea pig, or boar, has an “i” shaped genital opening, with the dot representing the penis. Applying gentle pressure just above the genital area in a boar can cause the penis to extrude slightly, confirming the sex. An important anatomical consideration for sows is that their pubic symphysis, the cartilaginous joint connecting the two halves of the pelvis, fuses with age, often by around 7-8 months. This fusion can complicate birth if a sow is bred for the first time after this age, leading to birthing difficulties.