Physiological response of Zebu and taurine oxen to draught work.

Four Zebu and four Simmental oxen were submitted to continuous and to graded draught work. Venous blood samples were taken before, during, and after exercise at intervals of 2-5 min. Anaerobic threshold was reached at a draught power of 1.6 +/- 0.06 kW for Zebu and 0.7 +/- 0.07 kW for Simmental. Corresponding plasma lactate concentrations were 1.7 +/- 0.2 mmol/liter and 1.6 +/- 0.3 mmol/liter, respectively. Partial pressure of oxygen (pvO2), carbon dioxide (pvCO2), and plasma free fatty acids (FFA) during and after work differed between breeds (P approximately .001) and individuals (P approximately .05). After work, an up to 8-fold increase in FFA was found. Highest plasma lactate concentrations during continuous maximal draught were 3.75 +/- 1.76 (Zebu) and 6.01 +/- 0.88 mmol/liter (Simmental). Acid-base-state during and after exhaustive work remained stable. Heart rate in both breeds did not exceed 190 min-1. It is concluded that 1) even during heavy draught work, anaerobic energy formation plays a minor role for cattle, 2) fatigue in working oxen may be related to cardiovascular limitations, and 3) the physical fitness of European beef-breed oxen is lower compared to multipurpose African Zebu oxen.