The preference for warm drinking water induces hyperhydration in heat-stressed lactating goats.

The aim of this study was to determine whether lactating goats regulate their water intake when given a choice between warm (35 degrees C) and cold (15 degrees C) water. Six lactating goats were kept individually in pens. At 07.00 h one bucket was filled with warm water and another with cold water. Water consumption was measured at intervals until 18.00 h. Water temperature was not controlled at night. Two experiments were made, one at normal room temperature (18-19 degrees C) and the other at 39-40 degrees C from 10.45 to 17.00 h. At normal room temperature the goats drank 6.0 +/- 1.4 L of the warm water but only 1.7 +/- 1.3 L of the cold water (P < 0.001). The total water consumption, including the following night, was 9.2 +/- 1.6 L. This differed from control days, when only cold water was available (5.9 +/- 0.4 L; P < 0.05). Neither the plasma Na concentration nor the osmolality changed, which indicate that the goats regulated their fluid balance. In the experiments involving heat stress the goats drank 11.5 +/- 1.7 L of the warm water but only 2.0 +/- 1.0 L of the cold water (P < 0.001). In total, including the following night, they drank 16.2 +/- 2.6 L (P < 0.001 vs. control days). Goats drank repeatedly despite falling plasma Na and osmolality, proving that their thirst was not induced by water losses. Their abdomens became distended, indicating that water was stored in the reticulo-rumen and explaining why their body weights increased. The goats appeared distressed. It is concluded that goats prefer to drink warm water. Nevertheless, our results suggest that, if possible, warm drinking water should not be given to lactating goats under hot ambient conditions.