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

Abstract

The objective of this study was to determine the 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 all puppies increased more than ten times, and most of its increments from week to week were significant (p < 0.05 to p < 0.001). 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 x 10-6. Its following changes (a decrease to 30.52 +- 12.98 x 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 changes in body mass, nutrition, locomotory activity and maturation of their urinary system.The objective of this study was to determine the 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 all puppies increased more than ten times, and most of its increments from week to week were significant (p < 0.05 to p < 0.001). 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 x 10-6. Its following changes (a decrease to 30.52 +- 12.98 x 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 changes in body mass, nutrition, locomotory activity and maturation of their urinary system.