Effects of hydration state on exercise thermoregulation in goats

In this study we asked how exercise affects sweating and panting and how dehydration affects exercise thermoregulation in goats. Six goats exercised (4.8 km/h, +10% slope) for 45 min at an ambient temperature of 35 degrees C when hydrated and after 48 h without drinking water. Hematocrit (Hct), plasma protein concentration (PP), and plasma osmolality were elevated by dehydration (P less than or equal to 0.05). Hct and plasma osmolality increased further during exercise in hydrated and dehydrated animals (P less than or equal to 0.05), but PP rose only in hydrated goats (P less than or equal to 0.05). The increase in central blood temperature (Tbl) during exercise was greater in dehydrated than in hydrated animals (P less than or equal to 0.001). Evaporation by panting (Eresp) and sweating were linearly related to Tbl during exercise. The relationship between Eresp and Tbl was not affected by dehydration, but dehydrated animals showed an increased Tbl threshold for sweating. We postulate that the elevation in threshold for sweating may be due primarily to increased body fluid osmolality, and that hypovolemia may not play a significant role in the thermoregulatory adjustments to exercise in dehydrated goats.