Do You Know “You” Actually Affect The Average Litter Size For Dogs? The Science Behind It!

Okay, you probably know the just of it. A male and female dog mate and then a few months later, you have a litter. It’s easy, nature does its own thing and, really, there isn’t a lot more that you need to know regarding litters.

However, that is not the case and, like everything with breeding, understanding the science of litter size is very important.

In fact, it can be extremely important, especially when it comes to planning your dog’s breeding career.

Understanding the important points of creating a litter will help you in determining when to breed, how often to breed and also what can affect litter size in you dog.

It is important to note that not everything can be planned for.

Even with the best knowledge and scheduling, you can end up with a small litter…or even a singleton…but having an understanding can also increase your odds of a healthy litter; both in size and overall health of your puppies.

So, let’s take the time and look at the science behind your dog’s litters and providing the best for your puppies even before they’ve been conceived.

What’s in a Litter and Litter Size?

Litter size can be affected by a number of factors.

Before we look at anything else regarding litter sizes, it’s important to look at what exactly goes into a litter and what the average litter sizes are.

First, a litter is the term used with a large number of animals to indicate a group of babies born to the same parents at one time.

We use this term for puppies, kittens and a number of other mammals. As an aside, many kennel clubs register a litter first before registering each individual dog.

Second, litter size does vary depending on the breed or size of your dam. However, with that being said, there is actually a good rule of thumb that many breeders follow.

Your dam will produce half as many puppies as she has teats. For example, if your mom has 9 teats, then she will have 4 or 5 puppies.

Of course, this rule is not hard and fast and dams with 10 teats can surprise us with 1 puppy or 15 puppies.

But, in general, dogs have between 5 to 6 puppies on average and most breeders plan for those numbers if they do not use other methods, such as ultrasounds and x-rays, to determine how many puppies are present.

Another factor that we need to look at is the size of the dam. Toy breeds usually have smaller litters on average and giant breeds tend to have larger litters.

To quickly recap, the following are the average litter sizes depending on size. Again, bear in mind that these are averages and every individual dam…and even breeding…will differ on the number of puppies in the litter.

Toy Sized Dogs:

Small Sized Dogs:

Medium Sized Dogs: 

Large Sized Dogs: 

Giant Sized Dogs: 

Bigger sized litters can be dangerous to the dam, especially if she is a smaller sized female. In addition, extremely small or large litters can lead to whelping complications that may result in a c-section.

It is interesting to note that the record holder for the most puppies in a litter is a Neapolitan Mastiff by the name of Tia. In 2004, she gave birth to 24 puppies.

Do Genetics Affect Litter Size?

Different breeds and different pedigrees can affect the size of your litters.

Okay, let’s face it, we aren’t going to all have a Tia in our breeding programs but we may have lines in our kennels that tend to produce larger or smaller litters. And that brings us to genetics and how they affect litter size.

The simple answer is that yes, genetics can affect litter sizes. In fact, it can affect litter size by as much as 15%. In addition, many other aspects of reproduction such as birthing problems and even lack of interest during mating, can be affected by genetics.

Many breeders, who have dealt with genetic reproductive abnormalities, will retire lines from their breeding kennel to prevent more problems with offspring.

Another option hat they will take is to bring in lines without the problems in an effort to breed them out.

In addition, I do know some breeders who will never keep a puppy from a bitch who consistently has small litters. The thinking on this is that small litters will be passed down to all of her female offspring.

While I am not sure of the validity of this claim, I kept a female out of a bitch who only had litters of one to three puppies. The daughter I kept happily whelped 13 puppies on her first litter, which makes me wonder if this idea is tried and true.

However, I understand the methodology behind this practice. The goal for most breeders is to produce average or above average sized litters so they have a bigger selection of puppies to choose from for their kennel.

In addition to the above points, there is one area of genetics that needs to be looked at and that is the coefficient of inbreeding. If you are not sure what coefficient of inbreeding is, it is a scale that looks at the number of related dogs in a pedigree.

Every instance of inbreeding, mating between family members, increases the coefficient percentage.

Inbreeding and line breeding are done for many reasons but one of the most common is to lock in a desired trait that you want your dogs to have.

For instance, perfect coat type can be locked in if you breed two related dogs with perfect coat type. Unfortunately, it can also lock in undesired traits.

So, what does this have to do with litter size?

Studies by the Institute of Canine Biology has shown that the higher the coefficient percentage is, i.e. the more related dogs in the pedigree and the closer the relation, the smaller the litter size is.

An example of this study can be found in the chart below.

Reduced litter size is seen with a high coefficient percentage.
Copyright The Institute of Canine Biology

As you can see, genetics can play a significant role in litter size and should be considered as you select your breeding dogs for your kennel.

Can Humans Affect the Size of a Litter?

Some things can be done to affect litter size but there is no sure-fire way that works 100%.

Now that we’ve touched on genetics, let’s look at how humans can affect the size of a litter.

Believe it or not, what we do with breeding management can affect how large a litter will be and we will look at different ways that humans can affect litter size.

Of course, there is no sure-fire way to ensure large litters sizes but there are things you can do to help increase the odds.

#1 Progesterone Testing

One of the first things that every breeder can do is use a little science when it comes to breeding. Progesterone testing is a great way to do this.

First, when a female dog goes into heat, a number of things happens with her hormones and you will see rises and drops in hormone levels.

Understanding these rises and drops will help you understand when your dog is ovulating. Hormones affected by a dog’s heat cycle are:



Luteinizing Hormone: 

Generally, vets will test the progesterone, which is a steady increase that they can mark.

They will usually start testing around day 7 or 8 depending on the breed, or individual dog and her past heats. Once progesterone rises to 5ng/ml (nanograms per milliliter), breeding can occur.

Vets can monitor hormones to determine when your dog ovulates, which will increase litter size.

By using progesterone testing, breeders can pinpoint the best time to breed their females to ensure that the most ovum are fertilized.

Levels that vets, including theriogenologists, look for are either calculated in ng/ml (nanograms per milliliter) or nmol/L (nanomoles Per Litre).

The levels that you should be aware of are:

3 nmol/L or 1 ng/ml (Level 1) :

6 to 8 nmol/L or 2.4 to 3.2 ng/ml (Level 2) : 

8 to 12 nmol/L or 3.2 to 4.8 ng/ml (Level 3): 

12 to 24 nmol/L or 4.8 to 9.6 ng/ml (Level 4) : 

24+ nmol/L or 9.6 ng/ml (Level 5) : 

Understanding hormone levels is important for breeding.
Hormone levels of a female in heat

And with those numbers, let’s look at the next way that humans can affect litter size.

#2 Timing

It's all about getting the perfect timing.

Obviously, timing is going to be an important part of affecting litter size. If you are going with progesterone testing, then you will just follow the breeding times recommended by your veterinarian. The common rule of thumb is 2 plus 2 plus 2 for breeding.

What this means is that ovulation occurs and you breed, then breed again 2 days after the first breeding and the final 2 days after that.

The reason behind this thinking is that eggs are not released all at once. The ovaries release eggs for 24 to 48 hours so that first breeding will catch the eggs that were released right at ovulation. Since it takes 24 to 48 hours for eggs to be ready for fertilization, you breed again two days after ovulation so that there is sperm waiting for eggs and also sperm being added after they are ready.

The final breeding will catch the eggs that are released closer to the 48 hour period.

Sperm can live up to 7 days in a female so the general rule is that you can breed 3 days before ovulation and up to 7 days after ovulation.

If you are not using progesterone timing, you want to look for physical and behavioral signs of the LH surge.

These include:

  • Less swelling in the vulva and vagina than at the start of the heat.
  • Bloody discharge lightens to a straw color.
  • Female may begin to flag, which is presenting her backend to the male and moving her tail to the side like a flag.
  • Softening of the skin around the vulva.

At this time, if you suspect an LH surge, ovulation should occur within 48 hours and you can start breeding at that time.

Generally, when you are not using testing of any kind, you will want to breed more times, however, still follow the same rule of 2 plus 2 plus 2.

When you get the timing just right, you will have a better chance of a larger litter size.

#3 Artificial Insemination

With advances in medicine, it shouldn’t be surprising that artificial insemination is becoming more and more popular.

In fact, more and more breeders are using AI because it is easier to get access to champion dogs around the globe instead of having to travel to a stud or use the ones close to you.

Unfortunately, AI does often produce smaller litters. In addition, the type of semen, whether it is fresh, chilled or frozen semen, can affect the litter size. Canine semen does not freeze that well and a lot of sperm will die. Also, quality can be affected greatly.

If you are choosing to do AI, be aware that your numbers can go down significantly, as can the chance of your female becoming pregnant. Still, many vets and breeders recommend AI and I wouldn’t rule it out completely.

#4 Post Breeding Management

Care for your female is as important during pregnancy as it is at any time.

Although your dogs should always have the best possible care, how you care for your dog after she has been bred can affect the litter size. First, dogs that are stressed or mistreated can end up absorbing or even aborting their litter. 

In fact, many dogs will absorb puppies, if not full litters, and it is quite common. When it is only a few puppies, it is usually due to nature making room for the puppies that are still viable. This type of absorption is normal.

However, if the dog has improper nutrition and housing, they can absorb puppies due to improper care. In addition, stressful situations can increase the likelihood of absorptions.

Be sure to keep mom happy and minimize the amount of stress she is under. Personally, I avoid visitors during the first month of pregnancy to reduce any risk of her absorbing the litter due to stress.

By giving her the very best care, you can help minimize the number of puppies she will absorb.

#5 Waiting for set Seasons

The American Kennel Club has noted larger litters in the spring than at any other times of the year.

Finally, while it is still up for debate, the American Kennel Club has noted that more puppies are born in litters whelped in the spring than at any time of year.

Further studies haven’t been done to determine why this is but for breeders who are planning litters, it may be better to breed for spring litters.

In addition, spring/summer litters are often easier to care for since you can get outside more often with the puppies than you can in the winter, especially if you live in cold climates.

While it may not be feasible to do, if it is, having a spring litter may boost your litter sizes.

Nutrition and the Effects on Litter Size

What your dog is eating can effect her fertility.

Nutrition is important for your breeding dogs throughout their entire life but when it comes to litter size, there is actually correlation to nutrition and the number of puppies that your dog has.

In fact, dogs who receive proper, high quality nutrition often have a larger number of puppies per litter than those who don’t.

Dams should be fed a high quality diet that is rich in protein and free of a lot of fillers.

In addition, foods that have a high level of pea fiber have also been linked to fertility problems in dogs, however, studies are still being done to determine how much it does affect dogs.

Another point that should be considered is the weight of your dog. Females should maintain an ideal body weight for their build and breed. Females that are too skinny or too overweight could end up with smaller litters or even failed pregnancies.

For these reasons, make sure that you always feed your dogs a good diet that maintains their weight.

The Aging Bitch and How it Affects Litter Size

Age of your mom can greatly affect litter size.

The final thing that we are going to look at is the age of the bitch and how it can affect litter size. In general, dogs should not be bred before they are 18 months to 2 years of age.

Before that time, they are considered to be too immature and could end up with complications.

After 2 years of age, your bitch can be bred up until her maximum age according to her age. For most breeder, that age is seven but it can also be younger or older. You can learn more about the how many litters your dog can have legally for each breed

With that in mind, however, the ideal age to breed a female is between age 2 and 5. Generally, the first litter of a dam will be the smallest with each mating having larger litters.

However, after the age of about 4, fertility does start to decrease, which could mean smaller litters or no litters at all.

Breeding your female between 2 and 5 means the best litter size and is also the healthiest time to breed your dog.

Just to note, sperm count and quality is reduced as your male dog ages and the ideal breeding age range for male dogs is 1.5 to 5 years of age.

As you can see, there is a lot of information to cover when it comes to litter size. How the dog is raised, the care she receives, her age and many other factors can affect how large or small her litters are.

By understanding all of the points above, you can ensure that your puppies are born healthy and that the odds of an average to above average sized litter will increase greatly.