Puppy Fetal Development

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Although puppy fetal development is not something that everyone needs to know, I find that it is a very interesting topic. Regardless of breed or size, puppy fetal development follows the same timeline and developmental milestones. In this article, we will look at this development, as well as what is going on with mom on a week to week basis.

When we look at puppy development, we count days from first breeding and usually look at the magic number of 63, although this is not 100% accurate. As ovulation can occur before or after that first breeding, pregnancy can range from 59 to 70 days. So while the average pregnancy is 63 days from ovulation, it may only be 59 days from time of the first breeding and so on.



0 to Day 21: Week 1 to 3

During the first two weeks, a lot is happening with the fetal puppy but not much is being seen with mom. She may have some temperament changes, may have a change in appetite (ie, eating more or less). Or she may simply be her usual self.

An interesting fact, and the reason that a pregnancy test can’t be done after breeding is that a female dog will produce the same hormones whether she is pregnant or not and is the reason why dogs exhibit false pregnancies.

Inside, things are happening! The eggs are fertilized and begin to develop into cell masses. They divide until they become a 16-cell mass, which is when the egg is officially an active embryo. Around 17 to 21 days, this embryo has made it’s way down and will implant on the uterine wall.

Once it has implanted, the placenta will develop and this will provide nutrients to the embryo and then the development into a puppy will begin.

Canine Fetus

Canine Fetus

Day 22 to Day 28: Week 4

Once it has implanted, the puppy begins to develop. Development begins on week 4, which is day 22 to day 28. During this time, puppy is still very small, and will only reach 1/4 to a 1/2 inch (5 to 10mm) by day 28. However, it is starting to take shape.

Over this week, the spinal cord begins to develop. In addition, the head portion of the embryo should be bending forward and the brain and the shape of the face will begin. Eyes will start to develop. Finally, the puppy’s limb buds should be developing.

For the mom, week 3, around implantation, and into week four, she may exhibit canine morning sickness, which is usually a loss of appetite, although some dogs will throw up. She may not show any outward signs at this point but a vet or experienced breeder may be able to palpitate for puppies, which feel like walnuts. (As a side, I do not palpitate as it can damage the puppies if you are not careful.)

The dam’s nipples may begin to darken and enlarge but again, this can be seen with false pregnancy. It can also be common for a dam to not show any outward signs, even at the end of the fourth week.

Canine Fetus Day 35

Canine Fetus Day 35

Day 29 to Day 35: Week 5

Over this week, the puppies will begin to look like puppies and by the end of the week, we will even have gender!

At this stage, the claws and individual digits are developed and can be seen. Originally, the puppy’s eyes were open but by day 32, the eyelid has developed and the eyes will be closed. They will remain closed until roughly 2 weeks after delivery (give or take a few days). As I mentioned, they are decidedly more dog like in appearance. The weight of the puppy at this stage is roughly 2 grams and he should measure about 30 to 35mm in length (slightly over an inch).

Whisker buds will develop and on day 35, they will move from being called an embryo to being a fetus.

For mom, changes can really differ depending on the condition of the bitch before breeding, and the breed. English Mastiffs have a lot of room for puppy so it may be harder to notice much of a change in the dam at this stage. However, there should be some swelling in the belly and some weight gain.

Also, her needs are changing and the shift to puppy food is done gradually during this week. Some dogs see a return in appetite while others may not have much of an appetite all the way through their pregnancy.

Canine Fetus Day 40

Canine Fetus Day 40

Day 36 to Day 42: Week 6

As I mentioned, by day 35, the sex of the puppy is clearly determined. In addition, the claws and individual digits are developed and can be seen. The fetus looks decidedly more dog like in appearance.

By the end of the week, the puppies should be about 44mm or nearly 2 inches! Weight should be at about 2 grams. Skin pigmentation is developing as well at this stage. Claws should be formed and the skeleton of the puppy should be solidifying. Most of what makes a puppy look like a puppy has developed at this stage and from this point on, most development will focus on growth.

For mom, she has reached the third and final phase of gestation. Her tummy should be getting larger and her pregnancy may be noticeable to others. It should be noted that this depends on the female and the breed. Some bitches, especially athletic, first time pregnant females, don’t show until close to delivery. During this week, the bitch may experience a loss of appetite and will need a higher nutritional level. Meals are increased to two or three a day.

Canine Fetus Day 47

Canine Fetus Day 47

Day 43 to Day 49: Week 7

Most of what makes a puppy a puppy has developed and now is the stage where puppies will gain the most growth.

Around day 45, the hair will begin to grow on the puppy. In addition, the coloration of the hair can be seen and the pigment of the skin is established. Proportion wise, the puppy is slightly off but that will correct itself within the next week or so.

Mom is usually uncomfortable by this stage, however, it does depend on the individual dog and also on the individual litter. She may vomit occasionally and may not be interested in eating her meals. Smaller, more frequent meals will help with the pressure that is against her stomach. Generally, the dam is tired by this week and is often looking for a place to whelp.

By week seven, especially near the end of the week, puppy movement may be felt, but again, it depends on the dog and litter. The dam’s nipples may be well-developed at this point and there may be some “first milk” being produced.

Again, these symptoms are all generalizations. Some dam’s do not produce first milk until the puppies are born, some are not tired, some eat fine, and some are tired earlier in the pregnancy.

Canine Fetus Day 57

Canine Fetus Day 57

Day 50 to Day 59: Week 8

We are getting close to the whelping date; however, any puppy born in this week are not likely to survive.This is week 8 and much like last week, the puppy is not developing in more ways than just growth. The puppies should have fur completely and they may be moving a lot as they prepare for birth in the upcoming week.

They are very crowded and the dam is usually very uncomfortable at this stage. One interesting fact is that by day 50, the puppies have fully ossified skeletons. Before this time, they were not visible in an x-ray, however, after day 50, they can be.

For the dam, she will be continuing to gain weight. She will also be looking for a place to whelp and will start whelping behaviors such as digging, finding a quiet place in the house (or on your lap) and preparing herself for the upcoming delivery.

Newborn Neapolitan Mastiff

Newborn Neapolitan Mastiff

Day 59 to Day 65: Week 9

This is the final week of pregnancy and is considered week 9. Puppies born before day 58 are less likely to survive. When we look at gestation, puppies are born 63 days from ovulation. Since breeding is not done at the exact moment of ovulation, we have a window of 59 to 65 days of gestation.

In regards to development, not much is happening for the puppies outside of some more growth before the big moment. Puppies are being positioned for delivery but you may not feel movement due to the cramped space and due to them resting before birth.

More than likely, the dam is uncomfortable and you will see this in her behavior. Often, as birth draws near, she will become anxious and restless. She might be introverted during the final week and spending time in quiet areas of the house. Some dogs become clingy during this stage to a specific human in the house while others will spend more time looking for a whelping area.

Appetite may drop, but again, this is dependent on the individual dog. Meals are often smaller as there is no much room with the puppies crowding her stomach and other organs. During this week, the dam may urinate frequently and should be monitored throughout the week.