Litter Size - Can we predict it?

Litter Size – What the research says

Litter Size - Can we predict it?

There is an ongoing paucity in the literature surrounding most dog matters, and that means dog knowledge is often based on anecdotes and experience instead of facts and figures. Dog breeding is no exception. Breeders will tell you that they get bigger litters if x, smaller litters if y, that they’ll never mate a bitch if z. While personal experiences can provide case studies, I am interested in much bigger data.

Enter a Norwegian study looking at 10,810 litters.

This study used data held by the Norwegian Kennel Club to look at every litter registered in 2006 and 2007, across 224 breeds. Statistical analysis was then done to determine all the wonderful figures summarised below.

The aim of this study was to determine what actually makes a difference in litter size. (Litter size being the number of puppies born, alive or dead.)

Firstly, an overall average had to be determined. For this data set, the average litter size, considering all breeds, was 5.4 puppies.

For those interested in average litter size by breed: The largest average litter size was in the Rhodesian Ridgeback with an average of 8.9 pups per litter. The Toy Poodle and Pomeranian had the smallest average litter size – 2.4 pups per litter. And the Border Terrier (because I’m biased) had an average litter size of 5.1 pups per litter.

This study found that litter size was influenced by the size of the breed, the method of mating, and the age of the bitch. Litter size was not affected by season of birth, or the number of litters a bitch had had.

Size of the breed

This study examined dogs based on average breed size. They were classed as miniature breeds (<5kgs), small breeds (5-10kgs), medium breeds (10-25kgs), large breeds (25-45kgs), and giant breeds (>45kgs). Bitches were recorded against the average size of a dog for their breed and not specifically on the size of that given bitch.

“When looking at all the … litters…, mean litter size increased with the size of the breed. The mean litter size was 3.5 in miniature breeds, 4.2 in small breeds, 5.7 in medium breeds, 6.9 in large breeds, and 7.1 in giant breeds.”

The feature of larger dog breeds having larger litters is not a new thing – this phenomena is consistent across other studies. But this study is different as it found that it wasn’t just size of the breed that mattered…

Age of the bitch

The first analysis of this data showed no significance with the age of the bitch, however, once breed size was taken into account, there were two trends apparent:

  • In small and miniature dogs, young and old bitches had smaller litters than the ages in between.
  • In larger breeds, increasing age corresponded with decreasing litter size. (Young bitches of larger breeds produced the largest litters – unlike small and miniature breeds.)

Predicted litter size by the age of the bitch for the five different breed size groups from Borge et al. study.These results are a little different to other studies, which have shown smaller litter sizes as bitches get older. (As in, the results this study got for larger breeds was seen in all breeds in previous studies.) It could be that smaller sample sizes in other studies may have missed this, or that other studies used larger breeds as their data set instead of small or miniature breeds. One suggestion is that small breeds may not mature as quickly as previously believed, and so they’re not able to reproduce until they reach that mark. (To me, this kind of makes sense – considering small breeds often live longer, then it’s likely that they mature more slowly, too.)

Method of mating

Like the age of the bitch, the first analysis on the data didn’t show a significance change in litter size based on mating method. However, when the data set was adjusted for breed, breed size, and age, naturally mated bitches had significantly larger litters than those who had been AIed (either fresh or frozen).

A decrease in mean litter size of 0.4 puppies would be expected for litters conceived with AI with fresh semen and 1.3 for AI with frozen semen, both compared to natural mating.

Things that didn’t matter

The number of litters a bitch had previously didn’t influence the size of her litter. (However, older bitches normally had had more litters – and their age did influence litter size.)

The season the litter was born in did not influence litter size.


Size of the breed, age of the bitch, and the method of mating are three factors that work together in determining litter size. It’s not one thing – it’s all three.

“… the size of the breed, the age of the bitch and the method of mating were found to influence litter size in purebred dogs when controlling for breed, with the size of the breed as the strongest determinant.”

This study is better than past studies in this area for its huge sample size, its variety of breeds, and the fact that it considers all puppies in a litter (not just those registered, as some past studies have done). In this way this study is unique. It is probably a pretty reliable data pool for purebred dogs, too, as 90% of purebred dogs in Norway are registered with their kennel club.

Things to consider regarding the vigour of the results:

  • It’s a retrospective study.
  • It does not include data from litters where all pups were born dead.
  • Calculating mean litter size is hard, because of the percentage made up of small or large breeds. Small breeds are currently popular, so could perhaps pull down the mean litter size seen in this study. Studies done in different countries, with different breeds being popular, are likely to result in different results.
  • There is a relatively small sample of bitches who were mated not-naturally in this study, so the results of assisted breedings should be interpreted cautiously, however the results are consistent with previous findings.
  • This study only groups dogs by weight – not by body shape. This might yield differences. (A neapolitan mastiff is really different to a greyhound.) And they group them by weight average of breed, not the weight of the individual bitch
  • This study looked at only two years and the researchers wonder if there might have been more variation in season of birth if there was more time taken into consideration.

In conclusion: Based on this study, breed size is the strongest determinant for litter size in a dog. The age of the bitch and the method of mating were also significant predictors of litter size. These three things interact, making litter size predictions difficult!


Borge, KS, Tonnessen, R, Nodtvedt, A, & Indrebo, A 2011, “Litter size at birth in purebred dogs – A retrospective study of 224 Breeds”, Theriogenology, 75, 911-919.

Thank-you to Waldwiese Kennels for the cover image – a litter of longhair weimaraner puppies.


How to Save a Swimmer Puppy


Phew. Okay, I just wanted to get that off my chest. For anyone who is googling for help for their swimmer puppy, the search results can be very dis-inspiring. I wanted to explain that it actually only takes a few days to a week to get a swimmer puppy to a mostly normal pup, and then several more weeks until the puppy is unrecognisable as a past swimmer.


What is a swimmer puppy?

A swimmer puppy is a very young puppy, normally 4 weeks of age or younger, who has legs that stick out to the side rather than underneath. Their chest is normally flat, and their back legs sometimes drag behind them. This often means that swimmer puppies struggle to walk, as their legs don’t push them off the ground, merely along it (‘swimming’ along the ground). It is important that a swimmer’s puppies legs are righted as soon as possible.


This is the swimmer puppy we had in our 2010 litter. He was born with some signs of being a swimmer. You can see that his legs stick out to the side instead of underneath or in front of him. Unfortunately, his condition was not recognised until a week later - but he still was walking normally by 8 weeks, and is not recognisable as a swimmer today.

This is the swimmer puppy we had in our 2010 litter, pictured at 3 weeks. He was born with some signs of being a swimmer. You can see that his legs stick out to the side instead of underneath or in front of him. Unfortunately, his condition was not recognised until a week later – but he still was walking normally by 8 weeks, and is not recognisable as a swimmer today.


What causes swimmer puppies?

Some puppies are undeniably born as ‘swimmers’, with legs that stick out to the side. However, whether this is genetic (caused by genes) or merely congenital (caused by in-utero-carriage) is hard to say. Many people report that puppies sometimes develop symptoms after being held in particular ways, as their bones are soft and pliable. From this logic, it’s not unfathomable that difficult birthing could also result in puppies that may be ‘pressed’ into a swimmer body shape.

However, a lot of swimmers are born as normal puppies and then become swimmers through their environment. One of the most significant causes of swimming is when litters are raised on surfaces with poor traction – particularly surfaces like newspaper.  These puppies can’t gain purchase on the floor, and end up ‘swimming’ instead of moving.  As noted above, some claim that puppies can become swimmers through routine poor handling (e.g. applying pressure to the pup’s chest when holding) and even one-off unfortunate incidents (e.g. a bitch laying on a pup).  Puppies in small litters (especially singleton puppies) are at risk of becoming swimmers from being overweight.


How do I fix a swimmer puppy?

They can be fixed!  The sooner you begin to implement some of these fixes, listed below, the faster you will begin to see improvements. (And the longer you leave it, the worse the condition can be.)

  • Make sure the bedding in your whelping box is easy for the puppy to grip on! Vet bed is great for this, but you can also use carpet, rubber matting, synthetic grass, etc.
  • Make the surface of the whelping box undulating. You can achieve this by putting egg carton, lumpy foam, or scrunched up newspaper underneath the bedding in the whelping box. This helps to encourage swimmer puppies to use their hind legs.
  • Place the puppy in sleeping positions that are helpful to recovery. Puppies that sleep on their chest will exacerbate the flatness on their chest, so place sleeping swimmer puppies onto their side at every opportunities. Also ‘tuck’ in the legs of these puppies, so they’re underneath the pup’s body and not out to the side. Obviously you can’t do this all the time, but even doing this occasionally will see improvements.
  • Be conscious of the way you hold the swimmer puppy. Don’t hold the puppy in a way that exacerbates the symptoms – so don’t place pressure on their chest, and don’t encourage the legs to stick out sidewards.
  • You can hobble the puppy. Basically, create ‘paw cuffs’ that pull the legs together using tape, a small child’s sock, or whatever may work. Obviously, make sure that the cuffs don’t cut off circulation. Even though this feels barbaric to do, the puppies I have done this to have not really objected to the process. (Click for photos of the puppy handcuff method.)
  • Let the puppy have sleeps in a sling (like an inside out pillow case hanging on a chair) in between feeds. (Ensure puppy is kept at an appropriate temperature.) Make sure the puppy’s legs are in the appropriate position before you leave them hanging – you don’t want to exacerbate their swimmer status! (Click for photos of the puppy sling method.)
  • Apply puppy-physio. Put puppy on your lap on their back, and gently massage their legs and ribs, and move legs in all directions – gently!
  • Encourage the swimmer puppy to move around, even by simply making them ‘walk to the milkbar’.
  • For obese swimmer puppies, restrict feeding times and especially get them to ‘walk to the milkbar’ (work off their meals!)
  • Some anecdotal evidence suggests that an overheated whelping box could aggravate the condition. Depending on your particular context, it may want to reconsider any external heating in the whelping box.


The same puppy at 9 months. This puppy had pretty much all the methods outlined applied from 4 weeks old, and was walking normally by 8 weeks.

The same puppy at 9 months. This puppy had pretty much all the methods outlined applied from 4 weeks old, and was walking normally by 8 weeks.

How do I prevent swimmer puppies?

Recognise the symptoms and act immediately! All the advice suggested above won’t hurt a puppy that is ‘normal’. Indeed, it’s just good sense to have a whelping box with good traction and try to manage the weight of young puppies. Starting early in swimmer rehab will see earlier results, and get the puppy normal sooner rather than later.

As there may be a genetic basis to swimmer puppies, seriously consider running on swimmer puppies for breeding purposes. This is particular true if you are consistently getting swimmer puppies in your litters, despite implementing high-traction surfaces and otherwise ‘doing everything right’ in terms of managing your whelping box environment.


Please share your successes with swimmer puppies. I would love to hear from you.


For more information, see the post Photographic Guide to Saving Swimmer Puppies.


This post is created with thanks to the Swimmer Pups thread on Dogz Online, and all the breeders who have contributed.