Domestic dogs typically have ten mammary teats arranged in five bilaterally symmetric pairs running from the axillary (chest) region to the inguinal (groin) region. Some individuals have as few as eight or as many as twelve. Teat count does not perfectly track litter size — a female may whelp a litter larger than her teat count, requiring pups to share or rotate.
The caudal (rear) mammary glands — particularly the inguinal pair — produce significantly more milk than the cranial thoracic teats. Studies in large litters show that the inguinal pair alone may account for 30–40% of total milk output. Consequently, the rear teats are the most competitive: dominant or heavier pups displace smaller littermates from these positions, potentially driving size divergence within the litter.
Unlike humans, dogs are born with a naive immune system — essentially no antibodies cross the placenta. All passive immunity must be transferred through colostrum (first milk) in the 24–48 hours after birth. Neonatal pup intestines can transport intact IgG molecules directly into the bloodstream during this brief window, after which gut closure prevents further bulk immunoglobulin absorption.
Milk ejection in dogs requires the neuroendocrine let-down reflex: pup suckling sends afferent nerve signals to the hypothalamus, triggering oxytocin release from the posterior pituitary. Oxytocin causes myoepithelial cells surrounding alveoli to contract, forcing milk into the lactiferous sinuses. Without this reflex, milk is not available regardless of how much milk the gland contains.
Dog milk is thicker and richer than cow milk, with a yellowish tint from carotenoids and fat-soluble vitamins. The high protein content (mainly casein and whey) gives it a slightly savory character. Lactose level is lower than human milk, so dogs are generally not acutely lactose intolerant to their own milk — but adult dogs may be to bovine lactose due to different β-galactosidase specificity.
Protein is disproportionately high relative to fat compared to human milk — reflecting the rapid muscle and connective tissue growth required in early canine development. Pups triple their birth weight in the first three weeks. The amino acid profile is rich in arginine, which supports the rapid cell division occurring in all tissues. Weaning typically begins at 3–4 weeks with introduction of solid food.
Calcium-to-phosphorus ratio is carefully balanced for bone mineralization. Iron in dog milk is relatively low — pups begin to draw on hepatic iron stores laid down before birth. Vitamin D, E, and the B-complex vitamins are present. The fat-soluble vitamin content reflects the mother's diet and can vary substantially between a well-fed domestic dog and a feral or malnourished one.
Dog milk contains a notably high concentration of immunoglobulins in colostrum — particularly IgG — compared to many other species. This is compensatory for the lack of transplacental antibody transfer. Additionally, lysozyme and lactoferrin levels are elevated, providing antimicrobial protection to vulnerable neonatal pups whose gastrointestinal tracts are being colonized in the first days of life.