Allometry of litter size in dog breeds.

Litter size varies among dog breeds and is related to body size. Generally, the relationship is described as small breeds having smaller litters, and larger breeds larger litters, though the trend does not extend to very large breeds. Allometric relationships are often log-log relationships. This study aims to investigate the relationship between body weight, body conformation, and litter size, with the hypothesis that: (1) body size and litter size are positively related with a power relationship and (2) breed-specific genetic characteristics, which impact body conformation, influence litter size. The present analysis addressed variation in litter size among 115 breeds and the effect of two breed-typical phenotypes, chondrodysplasia and brachycephaly. Log-log regression was used to investigate the relationship between litter size and body weight. A second-order relationship between log litter size and log body weight was observed. In conclusion, body size and litter size were strongly related. Brachycephaly had a significant negative effect on average litter size whereas litter size was unaffected by chondrodysplasia.