Cardiovascular changes associated with dehydration and drinking in unrestrained, lactating goats

The aim of this study was to investigate if the alertness connected with seeing water increased arterial blood pressure and heart rate to the same extent as the act of drinking, and if ingestion of warm water caused a different effect compared with ingestion of cool water on these cardiovascular variables. Seven goats of the Swedish domestic breed (Capra hircus) were used in a cross-over design. The animals were dehydrated for 24 h. They were allowed to watch water being prepared for 11-16 min, after which they were given access to warm (35 degrees C) or cool (15 degrees C) water. The goats drank 6.86 +/- 0.36 l of the warm water and 4.54 +/- 0.35 l of the cool water (P < 0.05) within the first hour. The arterial blood pressure, heart rate and activity of the animals were registered by an implanted telemetric device. Dehydration did not affect the cardiovascular variables, except before feeding in the morning, when the heart rate accelerated faster in dehydrated goats. Heart rate increased abruptly when dehydrated goats saw water being prepared, remained at the increased level during drinking and then slowly declined. It increased again during the afternoon feeding, to a level similar to that on control days, but between 18.00 and 06.00 h the heart rate was higher than during control nights. Blood pressure did not change when the goats saw water, but increased when they drank. On the morning following rehydration, the rise in heart rate in response to feeding was delayed compared with that during control and dehydration periods. It is concluded that seeing water caused arousal in the goats, resulting in an accelerated heart rate. The additional rise in blood pressure during the act of drinking appears to be a combination of excitement and sensory inputs from the pharyngeal region, causing a temporary activation of the sympathetic nervous system.