A common observation we’ve made when reading breed standards is that some allow for bitches to be slightly longer in body than males, even in breeds described as ‘square’ or nearly square in proportion. It seems this allowance is not arbitrary, and much of it can be explained in an abstract entitled, “Morphometrics within dog breeds are highly reproducible and dispute Rensch’s rule.”
In a nutshell, Rensch’s Rule says that in animals, the size difference between males and females usually gets bigger as the species gets larger—if males are bigger. If females are bigger, the difference gets smaller as the species gets larger. A 2009 study conducted by Nathan B Sutter, Dana S Mosher, Melissa M Gray, and Elaine A Ostrander, however, refuted Rensch’s rule in the context of domestic dog breeds. The study examined over 1,100 purebred dogs from various breeds to see how well their physical measurements matched official breed standards and whether patterns of size differences between males and females (Rensch’s rule) applied to dogs.
They found that purebred dogs are remarkably consistent with their breed standards, meaning there’s little variation within each breed. Unlike many other animals, the difference in size between male and female dogs remains about the same regardless of whether the breed is large or small, so Rensch’s rule doesn’t really apply to dogs. They also noted that in many breeds, females tend to be slightly longer in body than males, likely due to reproductive needs.
Eureka. The last sentence very likely explains why, in breeds like the Tibetan Mastiff, Black Russian Terrier, Great Dane, Norrbottenspets and others, females are allowed to be slightly longer than males.
We find this subtle deviation in proportions a fascinating testament to the interplay between form, function, and selective breeding. It’s a reminder that breed standards are not just aesthetic checklists, but documents shaped by experience, and more recently, science.
What the study by Sutter et al. revealed is that the allowance for a slightly longer body in bitches is not merely a nod to reproductive practicality—it’s a consistent, measurable phenomenon across a spectrum of breeds. In a world where the “ideal” silhouette is often debated in the ring, next to the ring and over dinner after a dog show, this scientific validation underscores that the female’s extra body length is not a fault, but an adaptation. It appears to be a built-in accommodation for the demands of having puppies, seamlessly woven into the blueprint of breeds as diverse as the Great Dane and the Norrbottenspets.
For those who judge, breed, or simply appreciate dogs at a high level, this finding reframes the conversation: the slight elongation in bitches is not a compromise, but a feature—one that honors the biological reality of the female’s role. It’s a detail that bridges the gap between the written standard and the lived experience of the breed, reminding us that the best dogs are those that balance type, function, and the subtle signatures of sex.
Interestingly, veterinarian Dr. Bonnie V. G. Beaver opines that physical differences between dogs and bitches begin in the womb. Male pups are exposed to a testosterone surge which generates male characteristics, and puppies not exposed to this surge will be females. In pups, the dimorphic differences are very subtle, but emerge more noticeably after puberty. The biological foundation of Dr. Beaver’s statements is supported by primary research; studies published in journals such as Proceedings of the National Academy of Sciences and PubMed demonstrate that prenatal androgen (testosterone) exposure in dogs is responsible for the development of male-specific traits. For example, research has shown that treating female dogs with androgens in utero can eliminate typical sexual dimorphisms, confirming that these differences originate before birth3.
We end up where we started: Breed standards. So many are remarkable in that they were written before science could affirm the wisdom of breeders. But, as many of you will note, not all breed standards mention that females may be slightly longer than males. Why? We can only surmise that it may be due to historical reasons or a focus on the overall breed outline rather than sex-based differences. In some breeds, the difference is minimal or not considered important enough to specify, while others keep standards simple to avoid unnecessary detail. Even without explicit mention, experienced judges usually recognize and accommodate these natural variations. The omission typically reflects tradition, breed priorities, and the evolving nature of breed standards, rather than a rejection of the biological difference.
Image: Line drawing by kitahijrah5/Freepik