Postnatal Development of the Urine Cortisol/Creatinine Ratio in the Dog

Abstract

The objective of this experiment was to study the age changes of cortisol to creatinine ratio in urine of growing puppies between birth and the age of 8 weeks. Beagle puppies (n = 14) of three litters were used. The puppies of litters 1 and 2 were from a research breeding facility and litter 3 from a dog breeder. They were nursed by their dams and obtained extra puppy food from the 4th week of age. The puppies were weighed weekly. Morning urine was sampled at the age of up to 48 h, and 7, 14, 21, 24, 35, and 56 days. Urine cortisol was measured using the RIA method, and creatinine was determined using a diagnostic kit. The urine cortisol to creatinine ratio (UCCR) was calculated. The body mass of puppies increased more than ten times. The UCCR for litters 1 and 2 as against litter 3 showed no significant differences and therefore the results were pooled. Thus no effect of the rearing environment upon this indicator was found. The UCCR values in puppies aged up to 48 h was 44.32 ± 30.47 × 10-6. Its following changes (a decrease to 30.52 ± 12.98 × 10-6 on day 7 and oscillations around these values until day 49) as well as an increase on day 56 were not significant. Characteristic features of the UCCR in puppies were values surpassing those reported for healthy adult animals, and a great inter-individual variability, presumably reflecting the maturation processes such as rapidly increasing body mass and skeletal musculature mass, changes in nutrition, locomotory activity and maturation of their excretory system. The specific features of this period should be considered when evaluating the UCCR in puppies.