DIFFERENCES IN THE BIOLOGICAL STRESS RESPONSES OF 2 CATTLE BREEDS TO WALKING UP TO MOUNTAIN PASTURES IN THE PYRENEES

The aim of this experiment was to study the biological responses of Pi renaica and Parda Alpina cows (2-4 years old, n = 32) and their calves (2-4 months old, n = 32) to the physical exercise of climbing to moun tain pastures in spring. These two breeds have a different sensitivity to stress-induced myopathy, the Pirenaica calves being highly sensiti ve. The animals walked 14 km with an elevation increase of 600 m, in a pproximately 3 h. Blood samples were obtained the day before, immediat ely after the move to the mountain pastures and the following day. The plasma cortisol levels in Pirenaica cows were significantly higher th an in Parda Alpina cows under basal conditions, but disappeared in lat er samples. There were also significant differences in the hematologic al parameters. Under basal conditions, the red blood cell counts, pack ed cell volume, and hemoglobin content of blood were higher in Parda A lpina than in Pirenaica cows, but calves of both breeds did not differ . On the other hand, the calves of both breeds were more sensitive tha n their darns to the exercise, as shown by the large increase in white blood cell counts with a reversal of the lymphocytes:neutrophils rati o, a consequence of cortisol secretion. In calves the largest differen ces were observed in the muscle enzyme activity levels measured in ser um (creatin kinase, lactic dehydrogenase, aspartate amino transferase and alanine amino transferase), which were always higher in the Pirena ica carves both under basal conditions and after exercise. These biolo gical changes reflected the sensitivity of Pirenaica calves to muscula r problems when they walk up to the pasture. it was concluded that gen etic factors and age might play essential roles in the neuroendocrine and metabolic adaptation to this unusual physical exercise.