Dog Pregnancy | Canine Fetal Development
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Canine Fetal Development



Canine Fetal Development: Puppies develop from a fertilized egg to a viable fetus over a very short period of time - about nine weeks

Puppies develop from a fertilized egg to a viable fetus over a very short period of time - about nine weeks (58 – 63 days on average). This period is called “gestation.” Gestation ends when parturition (birth) occurs. Anyone breeding a litter should become familiar with the stages of fetal development so that they can take all steps necessary to attend to the needs of their pregnant dog and her future offspring. Here’s a snapshot of what goes on inside a dog once she has been bred successfully:

Average Day After Breeding

Fetal Developmental Stage




Fertilization of egg by sperm (now called an ovum); chemical reaction causes outer layer of ovum to harden and form a protective barrier, making it impervious to other sperm


Ovum divides (cleaves); becomes a 2-celled embryo


2-celled embryo moves to oviduct (between ovary and uterine horn); cells divide


4-celled embryo forms; female going out of heat


8-celled embryo becomes 16-celled embryo; cells divide


16-32-celled embryo (now called a morula); cells divide


32-64-celled morula enters uterine horn; fluid accumulates inside morula; morula develops a defined fluid-filled inner cavity (now called a blastocyst)


Blastocyst floats free in uterus; multiple blastocysts space out evenly along uterine horns; grow from ~¼ mm to ~2 mm in diameter; embryos resistant to insult from chemicals or radiation


Blastocysts implant; uterine lining forms band-like structure around each embryo that becomes the placenta


Body of embryo starts to form; linear thickening of cells (the “primitive streak”)


Primitive body parts start to form (called “somites”)


10 or more somites formed; primitive brain and spinal cord starting to develop; head area of embryo bends forward


Limb buds form; embryo grows from ~5 mm to ~10 mm in length


Limb buds become paddle-like; uterine lining swells at each implantation site as embryos grow; skilled practitioner may be able to palpate


Pigmentation develops in retina of eyes; body taking form; face starting to take shape


Facial features become more defined; nipples develop; embryo now ~14-15 mm long


Toes take shape; whisker buds become visible; umbilical cord forms; embryo ~18 mm long


Details of face and legs become recognizably dog-like; embryo 24 mm long (now called a “fetus”); organogenesis ends; beginning of mammary development


Male and female sexual characteristics can be differentiated; fetus ~24 mm long


Toes and toenails differentiate; eyelids close; fetus ~30 mm long


External and internal body parts grow and differentiate; skin pigmentation visible; fetus ~45 mm long


Beginning of ossification (formation of bone)


Continued fetal growth and differentiation


Fetal movement detectable with abdominal palpation

Birth of puppies is the end result of a complex chain of events known as “whelping.” “Parturition” is the medical term for the act or process of giving birth.

Source: PetWave


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