Endogenous haematological rhythm in dogs

The present study was carried out in 2008 with the aim of analysing the various haematological variables in dogs submitted to different photoperiods. Six Collie dogs were divided into two groups and exposed to different photoperiods. One group received light-darkness cycle (LD) 10:14 and the other LD 24:00. In both photoperiods, blood samples were taken from the jugular vein at 2-h intervals over a 24-h period. All blood samples underwent erythrocyte, haemoglobin, haematocrit, leukocyte, lymphocyte, monocyte, neutrophil, eosinophil, basophil and platelet concentration tests. Haematological variables were measured with a haematological counter and analysed by repeated measures using ANOVA and Cosinor analysis. In those canines subjected to a natural LD variation, the environmental signals reset the period and biological rhythm phase daily and all the variables analysed showed chronobiological variations that adjusted to daily patterns. In free-running conditions, the erythrocyte, haemoglobin, haematocrit and platelet variables present ultradian variations, as well as a period variation range among individuals caused by lack of the synchronising geophysical phenomenon, while the biological rhythms for leukocytes, lymphocytes, monocytes, neutrophils and basophils are manifested in free-running conditions, revealing the endogenous biological clock action.