Annual changes of some metabolical parameters in dairy cows in theMediterranean area

The seasonal rhythms reflect the ability of the endogenous adaptive mechanism to react in advance to the regular environmental changes associated with the seasons. It seems that these biochemical parameters are often influenced by a change in physiological status. The aim of this study was to assess the trend of annual variations of some biochemical parameters in dairy cows. The experimental subjects were ten dairy cows and the start of the experimental period coincided with the last month of pregnancy. These animals were monitored for one year and blood samples were collected every month. From the obtained sera, total bilirubin, blood urea nitrogen (BUN), creatinine, total cholesterol, non-esterified fatty acids (NEFA), tryglicerides, β-hydroxybutyrate, total proteins, calcium and phosphorus were assessed by means of an automated spectrophotometer. All the results were expressed as mean ± standard deviation (SD). Data were normally distributed (P<0.05, Kolmogorov- Smirnov test). One method of repeated measurement, the Analysis of Variance (ANOVA), was applied to determine the effect of time during the experimental period (12 months) and P values of <0.05 were considered statistically significant. Using cosinor rhythmometry, three rhythmic parameters were determined: mesor (mean level), amplitude (half the range of oscillation) and acrophase (Φ, time of peak). A significant effect of time (P<0.0001) was shown for all the parameters, except for NEFA. After application of cosinor rhythmometry, only total bilirubin, creatinine, triglycerides and β-hydroxybutyrate showed a seasonal rhythm. In conclusion we can affirm that our results supplement the current information available about the circannual changes in the metabolic activity of these animals and help us to evaluate the adaptation of these animals to environmental changes, together with the metabolic effect of calving and lactation.