This research was carried out on five clinically healthy Sella Italiana horses to determine the daily rhythm of total proteins and their fractions, to establish if these rhythms are endogenously generated and to assess the role of light as synchroniser of these rhythms. Blood samples were collected from each subject every 3 h over a period of 48 h, starting at 9:00 on day 1 and finishing at 9:00 on day 3, into vacutainer tubes without an anticoagulant via intravenous cannulas inserted into the jugular vein. Total serum proteins, albumin, α1-, α2-, β1-, β2- and γ-globulin concentrations were assessed in all samples. The application of two-way ANOVA showed a significant effect of the time of day on total proteins, albumin, β1- and β2-globulins, and of the experimental conditions on total proteins α1-, α2-, β1-, β2- and γ-globulins. No statistical modifications were observed on the A/G ratio. Daily rhythmicity was exhibited only by total proteins and albumin during the L/D cycle. We can claim that the fluctuation of serum total proteins and albumin concentrations are daily and not circadian and that they are driven by the L/D cycle.
