Julia Topmöller 1, Kristina Merhof 1, Eva Packeiser 1, Marion Schmicke 2, Holger Andreas Volk 1, Johanna Rieder 1

Background
Hypoadrenocorticism in dogs, though relatively rare, can manifest in juveniles and often presents with nonspecific symptoms. Diagnosis is challenging in young dogs due to age-related physiological variations. This study aimed to assess the normal growth of adrenal glands in Beagle puppies via ultrasonography and to examine the relationship between adrenal size and basal serum cortisol levels, which may aid in distinguishing normal development from pathological conditions like hypoadrenocorticism.

Methods
A prospective longitudinal study was conducted in ten healthy Beagle puppies (five males, five females) from two litters, aged 6 to 12 months. Adrenal gland measurements—longitudinal length, and diameters of caudal and cranial poles—were recorded monthly using ultrasonography. Concurrently, basal serum cortisol levels were assessed using chemiluminescence immunoassay. Statistical analysis included repeated-measures ANOVA and Spearman correlation to evaluate growth trends and relationships between variables.

Results
All adrenal dimensions increased significantly over the study period, with adult-like sizes reached by ten months of age. The right caudal pole showed the highest growth (27.7%), while the left adrenal longitudinal length had the smallest increase (8.3%). No consistent sex differences were observed except for a slightly longer left adrenal in females at 12 months. Basal cortisol concentrations were highly variable but showed no correlation with adrenal size or age. Most cortisol values were low-normal, and seven values (12%) were below the 22 nmol/L threshold used to screen for hypoadrenocorticism, though none of the dogs exhibited clinical disease. Correlation was found between age and body weight, and between several adrenal dimensions, but not between cortisol levels and any adrenal measurement.

Limitations
The study included a small, homogeneous sample (Beagle puppies only), which limits generalizability. ACTH stimulation testing—the diagnostic gold standard for adrenal insufficiency—was not performed. The study focused on basal cortisol, which may be affected by stress and does not conclusively rule out hypoadrenocorticism. Additionally, only a six-month window was studied, without extending into earlier puppyhood.

Conclusions
Adrenal glands in Beagle puppies grow significantly between 6 and 10 months, reaching dimensions comparable to adults by the end of the observation period. Low-normal cortisol levels were common and not predictive of adrenal size. Therefore, in young dogs, small adrenal glands or low cortisol alone should not lead to a premature diagnosis of hypoadrenocorticism; follow-up imaging or further diagnostic testing is advised to distinguish normal development from pathology.

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