PHYSIOLOGICAL-RESPONSE OF ZEBU AND TAURINE OXEN TO DRAFT WORK

Four Zebu and four Simmental oxen were submitted to continuous and to graded draught work. Venous blood samples were taken before, during, a nd after exercise at intervals of 2-5 min. Anaerobic threshold was rea ched at a draught power of 1.6 +/- 0.06 kW for Zebu and 0.7 +/- 0.07 k W for Simmental. Corresponding plasma lactate concentrations were 1.7 +/- 0.2 mmol/liter and 1.6 +/-0.3 mmol/liter, respectively. Partial pr essure of oxygen (pvO2), carbon dioxide (pvCO2), and plasma free fatty acids (FFA) during and after work differed between breeds (P approxim ately .001) and individuals (P approximately .05). After work, an up t o 8-fold increase in FFA was found. Highest plasma lactate concentrati ons during continuous maximal draught were 3.75 +/- 1.76 (Zebu) and 6. 01 +/- 0.88 mmol/liter (Simmental). Acid-base-state during and after e xhaustive work remained stable. Heart rate in both breeds did not exce ed 190 min-1. It is concluded that 1) even during heavy draught work, anaerobic energy formation plays a minor role for cattle, 2) fatigue i n working oxen may be related to cardiovascular limitations, and 3) th e physical fitness of European beef-breed oxen is lower compared to mu ltipurpose African Zebu oxen. (C) 1993 Wiley-Liss, Inc.