Background Blood biochemistry and reference intervals help to differentiate between healthy and ill dogs as well as to provide information for the prognosis, evaluation, and monitoring; however, these intervals are often obtained from adult animals. It is essential to understand that puppies and adults are physiologically different, which justifies the need to obtain age-specific biochemical reference intervals. The aim of this research was to assess the potential effect of age, sex, body size, and their interaction on routine biochemical analytes and physiological constants (body temperature, heart rate, and respiratory rate). To carry out the research, we selected 197 healthy dogs of both sexes and different body sizes (small, medium and large) classified by age: group I (4–8 wk), group II (9–24 wk), group III (25–52 wk), and group IV (> 52 wk). The biochemical analysis included the measurement of the enzymatic activity of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP), and the concentrations of cholesterol, triglycerides, total proteins, albumin, globulins, glucose, urea, and creatinine. Statistical analyses used analysis of variance (ANOVA) and a general linear model (GLM), which allows the comparison of multiple factors at two or more levels (p < 0.05). Results The results of this study showed that ALT, total protein, albumin, globulin, urea, creatinine, and body temperature levels were lower in puppies than in adult dogs of group IV (p < 0.05), while the enzymatic activity of ALP, LDH, glucose concentration, and heart rate were higher. Whereas sex, body size and the interaction did not show a significant effect (p > 0.05). Conclusions Some biochemical components are influenced by age. For this reason, this manuscript contributes with additional data for the clinical interpretation of blood biochemical results in puppies.

Background: Blood biochemistry and reference intervals help to differentiate between healthy and ill patients as well as to provide information for the prognosis, evaluation, and monitoring of a patient; however, these intervals are often obtained from adult animals. It is essential, hence, to understand that puppies and adults are physiologically different, which justifies the need to obtain age-specific biochemical reference intervals. The aim of this research was to assess the potential effect of age, sex, breed, and interaction on routine biochemical analytes and physiological constants (body temperature, heart rate, and respiratory rate) in addition to establish age-specific reference intervals. In order to carry out the research, we selected 197 healthy dogs of different sex and breed classified by age: group I (4-8 wk), group II (9-24 wk), group III (25-52 wk), and group IV (>52 wk). The biochemical analysis measured the enzymatic activity of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP), and concentration of cholesterol, triglycerides, total proteins, albumin, globulins, glucose, urea, and creatinine. Statistical analyses used the Analysis of Variance (ANOVA) and General Linear Model (GLM), which allows the comparison of multiple factors at two or more levels (p < 0.05). Results: The results of this study showed that ALT, total protein, albumin, globulin, urea, creatinine, and body temperature levels were lower in puppies compared to adult dogs (p < 0.05) while the enzymatic activity of ALP, LDH, glucose concentration, and heart rate were higher. Moreover, in small breeds, the serum creatinine levels were lower (p < 0.05) whereas sex and interaction did not show a significant effect (p > 0.05).Conclusions: Some biochemical components evince influence by age. For this reason, this research offers specific reference intervals to help the veterinary clinician to interpret the biochemical results of puppies with accuracy.