Many factors determine litter size in dogs, but many may not be under people's control.
For instance, litter size may be based on the number of eggs produced by the dog's ovary during a given heat cycle.
It can also depend on the viability of the male dog's sperm and the number of spermatozoa available to fertilize the female dog's eggs.
In the old days, the practice was to count the number of nipples the female dog had to come up with an average number of puppies to expect in a litter (the so-called one-half nipple rule), but this practice turned out being inaccurate for many reasons.
Becoming aware of the factors that influence litter size in dogs can be helpful, but the only way to more accurately determine litter size in dogs is through a veterinarian.
Picking the Right Date
While several of the above factors may not be under the breeder's control, several others are.
For instance, breeders can pick a date for breeding that can up the chances for a large litter.
Margaret V. Root Kustritz, a veterinarian specializing in reproduction, suggests that the optimal time for mating female dogs is two days (48 hours) after ovulation if there will be a natural breeding or artificial insemination with fresh or chilled semen.
In the case of artificial insemination using frozen semen, instead, the ideal time for mating female dogs would be 3 to 4 days after ovulation. The chances for success tend to be higher if the dog is bred twice within the estrus cycle.
While this formula may seem easy, determining exactly when ovulation takes place can be a bit challenging, but the best way to do this is by measuring progesterone levels with the help of a vet.
"It has been well demonstrated that litter size is optimized by breeding on optimal breeding day..Litter size can be maximized by inseminating twice during a given heat cycle... two and four days after ovulation with natural service, fresh or chilled semen, and three and four days after ovulation with frozen-thawed semen." ~Margaret Kustrtiz, DVM360
Nature Knows Best
The type of breeding, method and frequency may also play a role in litter size in dogs.
Records from the American Kennel Club suggest that natural breeding service yields larger litters when compared to artificial insemination.
According to a study conducted in Sweden, the most significant decrease in litter size was seen in dogs who were artificially inseminated with frozen semen.
The litter in these dogs was 30.5 percent smaller than females inseminated with fresh semen. Litter size increased though with the number of artificial inseminations.
How dogs are artificially inseminated also seems to play a role in what determines litter size in dogs.
Generally, dogs artificially inseminated by depositing the semen directly into the uterus had larger litter sizes (5. 4 pups) compared to dogs artificially inseminated by depositing semen through the reproductive tract (4.0 pups).
Intrauterine insemination is a successful technique though requires general anesthesia and can be attempted only once during a heat cycle. Transcervical insemination is another procedure that can be done when the dog is awake and several attempts can be made within a heat cycle.
A Matter of Breed
The breed of dogs selected for mating, and thus, reproducing has surely an impact on the number of puppies produced. Generally, smaller breeds give birth to smaller litters compared to larger breeds.
The number of puppies produced therefore tends to increase the bigger the dog, but this isn't a a black and white statement.
There are many cases of large dog breeds producing very small litters. Within a breed there are therefore variances and this may be due to genetics.
Some lines may produce fewer eggs when they ovulate than others. There are chances that dogs can be selectively bred for producing larger litter sizes.
The Age Factor
Age is also a big factor. The dogs who produce the largest litters are middle-aged dogs, while very young dogs and the old tend to produce smaller litters.
And of course, as male dogs age, their sperm quality and count decreases too.
Health and Diet
Finally, the overall health and diet of the female dog may also play a role in litter size. Before mating male and female dogs, they should be determined healthy and they should pass a brucellosis test.
When it comes to diet, it's important that female dogs selected for breeding receive the right proportions of protein and essential fatty acids to deliver healthy litters.
According to Association of American Feed Control Officials (AAFCO) the minimum level of crude protein on a dry matter basis for a pregnant dog's diet is 22 percent.
Lower that optimal levels of protein in pregnant dogs has led to smaller litter size. When it comes to essential fatty acids, the right proportions are also important. Consult with your vet or veterinary nutritionist for the best diet for your breeding dog.
"(Female dogs) consuming an omega-6/3 fatty acid ratio of 5:1 produced larger litters, fewer stillbirths, and fewer misconceptions compared to (female dogs) consuming an omega-6/3 fatty acid ratio of 20:1. ~Dr. Waltraud Off
- J Reprod Fertil Suppl. 1993;47:313-23. Results of 527 controlled artificial inseminations in dogs. Linde-Forsberg C1, Forsberg M.
- Fédération Cynologique Internationale (FCI), Effect of fatty acids on dogs and their offspring, retrieved from the web on July 21st, 2016
- Considerations for the Use of Frozen Semen George F. Seier, Jr. D.V.M. retrieved from the web on July 21st, 2016
- DVM360, Decreased litter size in the dog (Proceedings)retrieved from the web on July 21st, 2016
- K. Borge et al.Litter size at birth in purebred dogs - a retrospective study of 224 breeds. Theriogenology (2011)