Diurnal variations in blood gases and metabolites for draught Zebu and Simmental oxen.

In previous articles it has been shown that blood parameters may be useful to assess physical fitness in draught cattle. The aim of the present study was to detect possible variations in baseline values for the key metabolites: lactate and free fatty acids (FFA), and for blood gases in samples drawn from a catheterized jugular vein. Sampling took place immediately after venipuncture at intervals of 3 min for 1 hr in Simmental oxen (N = 6) and during a period of 24 hr at intervals of 60 min for Zebu (N = 4) and Simmental (N = 6) oxen. After puncture of the vein, plasma FFA and oxygen (pvO2) were elevated for approximately 15 min. All parameters returned to baseline values within 1 hr of the catheter being inserted. Twenty-four-hour mean baseline values for all measured parameters were significantly different (P < or = 0.001) between Zebu and Simmental. All parameters elicited diurnal variations which were mainly related to feed intake. The magnitude of these variations is comparable to the responses to light draught work. It is concluded that a strict standardization of blood sampling, at least in respect of time after feeding, is required for a reliable interpretation of endurance-indicating blood parameters measured under field conditions.