The Virginia opossum has 13 teats arranged in a horseshoe pattern with one central teat. This is one of the highest teat counts among mammals. Only joeys that attach to a teat survive.
Marsupial milk composition changes dramatically through lactation — early milk is dilute and carbohydrate-rich for tiny neonates, shifting to high-fat, high-protein milk as joeys grow. Each teat can be at a different lactation stage simultaneously.
Opossum joeys are born after just 12–13 days of gestation, weighing approximately 0.13 grams — about the size of a honeybee. They must crawl to the pouch and attach to a teat to continue development.
Unlike kangaroos, the Virginia opossum has only a rudimentary pouch — a shallow skin fold rather than a deep pocket. The teats and attached joeys are partially exposed rather than fully enclosed.
Marsupial milk undergoes dramatic compositional shifts. Early-phase milk is dilute with high carbohydrates for bean-sized neonates. Late-phase milk becomes fat- and protein-rich, resembling eutherian milk. Each teat independently tracks its own phase.
Opossum milk contains potent antimicrobial peptides called cathelicidins that protect immunologically naive joeys. These compounds are effective against a broad spectrum of bacteria, compensating for the neonate's undeveloped immune system.
A mother opossum can nurse joeys of different ages simultaneously, with each teat producing milk of a different composition matched to the developmental stage of the joey attached to it.
Individual milk volumes are minuscule — fractions of a milliliter per bout — but the continuous nature of marsupial nursing means joeys receive a steady supply. Total daily output across all teats is only a few milliliters.