[Postnatal skeletal and body weight in beagles]

Unaltered sequence of dental, skeletal, and sexual maturity in domestic dogs compared to the wolf

BACKGROUND

It has been hypothesised that domestication altered the sequence of dental, skeletal, and sexual maturity of dogs when compared to their wolf ancestor. To test this we investigated a comprehensive sample of domestic dogs.

METHODS

We documented the timing of completed eruption of permanent dentition into occlusion (dental maturity) and the timing of growth plate closure at the proximal humerus (skeletal maturity) in ontogenetic series of wolves and 15 domestic dog breeds. Data for 137 domestic dog and 64 wolf individuals were collected based on radiographs and examination of macerated bones.

RESULTS

Our analyses show that domestic dogs exhibit a similar sequence of dental and skeletal maturity as the ancestral wolf. Although the absolute change of the age at attainment of sexual maturity is great in domestic dogs as compared to the wolf, the sequence of dental, skeletal, and sexual maturity is not altered as extensively, contradicting one previous hypothesis. Moreover, our data suggest that the chondrodystrophic dachshund attains skeletal maturity earlier than the non-chondrodystrophic breeds examined here.

CONCLUSIONS

Domestic dogs are more wolf-like in terms of the sequence of dental, skeletal, and sexual maturation than previously hypothesised. This implies that the domestication process and/or breed formation did not have a major impact on this sequence, although the absolute values of life history variables do have a greater range of variation than in the wild wolf.

Ontogenetic allometry of the Beagle

Background

Mammalian juveniles undergo dramatic changes in body conformation during development. As one of the most common companion animals, the time line and trajectory of a dog’s development and its body’s re-proportioning is of particular scientific interest. Several ontogenetic studies have investigated the skeletal development in dogs, but none has paid heed to the scapula as a critical part of the mammalian forelimb. Its functional integration into the forelimb changed the correspondence between fore- and hindlimb segments and previous ontogenetic studies observed more similar growth patterns for functionally than serially homologous elements. In this study, the ontogenetic development of six Beagle siblings was monitored between 9 and 51 weeks of age to investigate their skeletal allometry and compare this with data from other lines, breeds and species.

Results

Body mass increased exponentially with time; log linear increase was observed up to the age of 15 weeks. Compared with body mass, withers and pelvic height as well as the lengths of the trunk, scapula, brachium and antebrachium, femur and crus exhibited positive allometry. Trunk circumference and pes showed negative allometry in all, pelvis and manus in most dogs. Thus, the typical mammalian intralimb re-proportioning with the proximal limb elements exhibiting positive allometry and the very distal ones showing negative allometry was observed. Relative lengths of the antebrachium, femur and crus increased, while those of the distal elements decreased.

Conclusions

Beagles are fully-grown regarding body height but not body mass at about one year of age. Particular attention should be paid to feeding and physical exertion during the first 15 weeks when they grow more intensively. Compared with its siblings, a puppy’s size at 9 weeks is a good indicator for its final size. Among siblings, growth duration may vary substantially and appears not to be related to the adult size. Within breeds, a longer time to physically mature is hypothesized for larger-bodied breeding lines. Similar to other mammals, the Beagle displayed nearly optimal intralimb proportions throughout development. Neither the forelimbs nor the hindlimbs conformed with the previously observed proximo-distal order of the limb segment’s growth gradients. Potential factors responsible for variations in the ontogenetic allometry of mammals need further evaluation.

Correlation analysis of the skull and long bone measurements of the dog

In this study, a heterogeneous population of 42 dogs was examined for correlation between skull and long bone measurements. For this purpose, 17 craniometric measurements were carried out and used to calculate 12 indices and ratios. These indices and ratios were then subjected to a correlation analysis with long bone measurements. While a high significant negative correlation of p < 0.05 and p < 0.01 respectively was found for skull, cranial and facial I1, I2, LLI-2, BI and BI-1 indices, and the CFO and CFO-1 ratios respectively with respect to the non-indexed long bone measurements, a high positive correlation was found to exist between those indices and ratios, and the long bone indices (p < 0.01). The correlation coefficients for the skull indices and ratios to long bone measurements proved to be very similar for the long bones of front and hind legs. As a result of the correlation analysis, it was found that with an increase in skull tendency towards the dolichocephalic type, the long bone parameters also increase, while with the skull tending towards the brachycephalic type, the long bone parameters decrease. This finding of a long bone-related increase in dimensions and morphological skull expression favours the assumption of a close relation to the skull typology.