Serum cortisol and haematological, biochemical and antioxidant enzyme variables in horse blood sampled in a slaughterhouse lairage, immediately before stunning and during exsanguination.

The aim of the study was to determine changes of serum cortisol and biochemical, haematological and antioxidant enzyme variables in the blood of horses sampled during the pre-slaughter period (in the lairage and in the stunning box) and during exsanguination. A total of 24 Slovenian warm-blooded horses were observed. Blood samples for determination of serum cortisol and biochemical, haematological (red blood cell count, haematocrit, haemaglobin concentration) and antioxidant enzyme (whole blood superoxide dismutase and glutathione peroxidase) variables were collected by venipuncture of the left jugular vein in the lairage pen, 60 min before stunning (lairage) and immediately before stunning (stunning box). At exsanguination, blood samples were collected from the wound at the time of jugular vein sticking. During blood collection in the lairage pen and in the stunning box, horses were gently restrained with a halter. They were stunned using a penetrating captive bolt pistol impelled by air and were bled by jugular vein sticking. Horses were physically active in the lairage pen and in the race before entering the stunning box. After stunning, the horses showed paddling movements with their legs. In horses, the plasma lactate and glucose concentrations, the serum potassium concentration, the activities of the serum muscle enzymes aspartate aminotransferase and creatine kinase, and values of most of the other biochemical (Table 1) and haematological variables (Table 2), were significantly (P < 0.05) higher at exsanguination, than in blood sampled while they were in the lairage and in the stunning box. The serum concentrations of cortisol and chloride and the activities of alanine aminotransferase and antioxidant enzymes were not significantly different between the pre-slaughter period and exsanguination. All selected blood variables were not significantly different between the lairge and the stunning box sampling time, indicating no physiological stress responses of the investigated horses to stressors, such as novelty of the pre-slaughter environment and handling, present in the slaughterhouse between the lairage and the stunning box. However, the significantly higher values, at exsanguination, for the plasma lactate and glucose concentrations, serum muscle enzyme activities and haematological variables, than during the pre-slaughter period, might partially be attributed to stimulation of the sympathetic nervous system, caused by stunning and bleeding.