Daily rhythms of 25 physiological variables in Bos taurus maintained under natural conditions

To further understanding of the multiple temporal relationships of the physiological process, we monitored simultaneously 25 different variables in individual cows. We used 6 Bruna Italiana non – pregnant and non – lactating cows from the same farm. The animals were housed individually in a 12 m2 box under natural 14/10 light/dark cycle. They were fed twice daily and water was available ad libitum. Locomotor activity and heart rate were recorded continuously. The rectal temperature, respiratory rate and blood samples were recorded every 4 hours for 24 consecutive hours. To describe the periodic phenomenon analytically we applied a trigonometric statistical model according to the single cosinor procedure. Twelve of the 25 variables studied showed a daily rhythm: locomotor activity, rectal temperature, respiratory rate, haemoglobin, glucose, creatinine, urea, total cholesterol, total lipids, non-esterified fatty acid (NEFA), phosphorus and magnesium.
Our results contribute to the understanding of the capacity for reaction and adaptation of animals to the environment, and to the improvement in their output by intervention in their environmental circumstances and in the breeding process.