A dog's reproductive system is designed to lactate only when she needs to produce milk, for a limited time before and after pregnancy. Usually you'll know she's lactating by looking at her before she delivers because her mammary glands will be enlarged, and perhaps leaking a trickle of milk. If you don't see those signs, you can check for yourself after she delivers.
Canine Mammary System
Even male dogs have a mammary system, but a female dog's is highly developed for the sole purpose of providing nourishment to her puppies. The system is comprised of two rows of mammary glands, containing between four and six mammary glands on either side of her abdominal midline. The glands are made of connective and glandular tissue, as well as secretive tissue that's present only while needed, during pregnancy and lactation, until the puppies are weaned. Each gland has a teat, or nipple, which accommodates approximately 7 to 16 ducts and openings to supply milk to a nursing puppy.
Four hormones stimulate milk production:
- Estrogen alerts the mammary tissue of the pregnancy, starting the production of the cells that will secrete milk.
- Progesterone depends on estrogen and helps maintain milk secretion during lactation.
- Prolactin prepares the mammary glands for milk production and helps maintain production throughout lactation; it also stimulates maternal behavior in the dog.
- Relaxin prepares the cervix, uterus and vagina for birth and encourages mammary development.
Milk letdown is prompted by oxytocin and prolactin when the puppies stimulate their mother's nipple. Oxytocin causes the mammary gland to tense and force milk into the teats while prolactin prompts milk to be released into reservoir areas.
Predelivery Lactation Signs
In the final two or three weeks before your dog delivers you will notice her mammary glands enlarge as they fill with milk. Her nipples will grow larger and darker and you may notice a milky discharge leak.
Checking Lactation After Delivery
When a dog begins labor, a puppy will press against her cervix, stimulating prolactin and milk production. As the puppies nurse and suck on their mother's nipples, her milk will begin to flow. If you want to be sure your dog is lactating, gently press or draw down on a nipple to produce milk. When you feel her mammary glands, they should feel supple, warm and soft, but not hard or hot, which may indicate mastitis. The puppies' behavior also provides clues about whether the mother is lactating. They should be nursing quietly. If any are cold or crying, they may not be getting enough milk or the mother may have mastitis.
Lactating dogs are vulnerable to potential complications, including:
- Mastitis, an inflammation or infection of the mammary glands, usually caused by a bacterial infection. Signs include swelling of the affected gland, heat, pain and abnormal milk, such as a greenish hue or tinged with blood.
- Agalactica, insufficient or lack of milk production.
- Galactostasis, a collection of unexcreted milk in the mammary gland, resulting in swelling and inflammation.
Any sign that a dog is not lactating normally requires veterinary attention, for the mother and puppies' health.