Changes In The Bitch And Developing Foetus

submitted by Marj Brooks with thanks to Kevin & Donna Frizzell, DeSaix St. Bernards


Behavioural Changes: After mating a lively bitch may be quieter. As pregnancy progresses she will alternate periods of deep sleep with flurries of activity. Also a usually playful bitch can become quite grumpy with her playmates.

Dietary Changes: She may suffer from morning sickness and go off her food or only want certain types of food. This can start at the beginning of pregnancy and last for the entire time. It is very frustrating for the owner as the bitch requires extra top quality nutrition during this time. Conversely some bitches eat everything in sight and even steal food. They usually go off their food for a few days at around four weeks because at this point it time the expanding uterus folds in on itself.

Physical Changes: The most often noted change is nipple enlargement. This starts at around 4 weeks of gestation and the nipple take on a pinkish hue. The nipple enlarge at the base and become very protuberant as pregnancy advances. Mammary tissue does not increase until further into the pregnancy. The vulva remains slightly enlarged and may exude a thin clear mucus. It will continue to enlarge as pregnancy advances and in some cases even seem to hang down from the body like some sort of egg laying tube!

Milk Production: In the case of the maiden bitch milk does not appear until after the birth but a thin watery secretion may be present. In bitches who have had previous litters milk may be present for up to six days prior to whelping.


1 – 19 Days ~ The Period of the Egg: This lasts about 19 days. The fertilized egg begins development but is not yet attached to the uterine wall. It is nourished by uterine fluids often referred to as “uterine milk”.

20 – 30 Days ~ The Period of the Embryo: During this time the major regions of the puppies bodies become differentiated. An encircling placenta is formed which allows oxygen and nutrients to pass from the blood of the dam and waste products to be passed back to the dam from the foetus. however there is no mixing of blood of the mother and developing young. The blood like all its other tissues is formed during foetal development.

31days to Birth: 95% of all growth occurs during this phase.


Initially the fused cell of the zygote divides and subdivides repeatedly without there being any overall in crease in size. After about 4 days it leaves the uterine tube and continues to divide but then also increases in size. At this stage the ball of cells and all its membranes are referred to as a conceptus.

Initially the conceptus is free to move around the uterus and attachment to the uterine wall does not occur until about 18 days post fertilisation. This is relatively late as compared with other animals. It is supposed that the conceptuses find themselves evenly spaced throughout the uterine horns.

From about the 21st day each conceptus produces a visible bulge or swelling in the uterus and each swelling increases in size as pregnancy advances. The conceptus is now a recognisable embryo complete with an Amniotic sac filled with fluid and a larger outer sac also filled with fluid known as the Allantois. This is also surrounded by the Allantochorion. The umbilical cord passes through all the membranes to the placenta.

The outer surface of the Allantochorion is held tight against the lining of the uterus, initially by the pressure of the fluid within it; later the surface of the Allantochorion develops microvillus or small finger like projections that fit in similar sized depressions in the uterine wall (Interdigitation). The interdigitation between the villi and crypts is known as the Placenta. This placenta forms a band around the equator of the Allantochorion. At both edges of this band some of the blood vessels that supply this area rupture to produce a “marginal haematoma”. This is a continuous blood clot along the edges of the placenta. As this blood and its bile constituents decomposes during pregnancy a green pigment is formed and this is often seen during or after normal births. If any is seen prior to puppies being born veterinary advice should be sought without delay.

The placenta has two functions:

* physical stabilisation of the conceptus
* indirect contact of the foetus and its mother

The rudimentary heart is already beating by the 21st day. It sends blood down the developing umbilical cord in the umbilical arteries. When there arteries get to the Allantochorion they divide and subdivide until blood is flowing through tiny channels called capillaries. These thin walled vessels are massed into the villi of the Allantochorion and are side by side with the capillaries in the crypts of the uterus. The walls of these capillaries are porous and allow for the exchange of gases, nutrients and waste products. The capillaries of the Allantochorion conversely fuse to form larger vessels until they unite to become umbilical veins. Blood is returned to the embryo via these veins.

During the first 35 days or so the embryo does not increase in size very much because the cells in its body are still rearranging themselves and forming precursors of the body’s organs. Until this time each conceptus in the uterus of the bitch produces a firm spherical bulge in the uterus and is separated by a tight constriction of uterus from its neighbour.

After the 35th day growth is more rapid and is now classed as a foetus rather than an embryo. The Allantochorion also expands so the tight constriction is lost and the uterus becomes uniformly swollen. It also becomes less tense as because the volume of fluids does not increase with the expansion of the membranes. This means as the foetus grows the amount of fluid surrounding it decreases. In early pregnancy the fluid acts as a cushion to protect the developing young from movement of other body organs or crushing against it. As the foetus matures and develops its skeleton and skin it is less sensitive to these outside influences.

Foetal growth accelerates from this point on and extra food is required by the bitch to facilitate this growth period.

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