Correlation of indices of stress with intensity of electrical shock for cows.

Electrical shock is commonly used as a paradigm of stress. Cows have a higher tolerance to electrical shock than other species. To test this tolerance, seven lactating cows were shocked biweekly for 10 s: 0, 2.5, 5.0, 7.5, 10.0, then 12.5 mA, 60 Hz. At lower mA, cows became tense and showed limited movement. As mA increased, cows became more agitated. The experiment was terminated because of the severity of behavioral responses. Heart rate immediately after shock increased with mA and was significantly different from baseline at 10 mA (+17 beats/min) and 12.5 mA (+30 beats/min). Prolactin and glucocorticoids were unaffected by shock; however, both increased pronouncedly following a single recannulation prior to blood sampling. Norepinephrine was unaffected by shock or recannulation. Epinephrine doubled in two exceptional cows at 10 mA. The two exceptional cows showed consistent glucocorticoid responses, had consistently elevated baseline heart rates and prolactin, and were the only cows not shocked at 12.5 mA due to severe behavioral responses. The dramatic behavioral responses displayed by cows subjected to electrical shock were not correlated with significant or prolonged physiological responses. This dichotomy, although probably exaggerated in cows, suggests that electrical shock may not be a good paradigm of "stress".