Cardiovascular and metabolic adaptations in horses competing in cross-country events

The cardiovascular and metabolic response to two cross-country events (CC*: preliminary level and CC*** advanced level) were analysed in 8 male eventi ng horses (4 Angle-Hunter and 4 Anglo-Arabian). This study focused on the e stablishment of the main metabolic pathways involved in the muscle energy r esynthesis during the competitions. Heart rate (HR) was recorded throughout the CC events. Jugular venous blood samples were withdrawn before the warm -up period, immediately after the competitions and at 5 and 10 min in the r ecuperation period. The following haematological parameters were studied: r ed blood cells (RBC), packed cell volume (PCV), haemoglobin concentration ( Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mea n corpuscular haemoglobin concentration (MCHC), white blood cells (WBC), an d number and percentages of lymphocytes (LYM) and granulocytes and monocyte s (GRAN). One fraction of blood was centrifuged and, in plasma, lactate (LA ), total plasma protein (TPP) and the rate of LA disappearance were determi ned. The competitions induced significant increases in RBC, Hb, PCV, MCV an d TPP. Plasma LA response exceeded the anaerobic threshold of 4 mmol/l, rea ching a maximum level of 13.3 mmol/l. HR ranged from 140 to more than 200 b pm, peaking at 230 bpm, revealing a limitation in the oxygen supply to the working muscles. It was concluded that muscle energy resynthesis during a C C event is provided both through oxidative processes and glycolysis with LA formation. Therefore, both stamina and power exercises are required for ev enting horses.