Harold D. Johnson

TL;DR: Hormones in plasma as they relate to stressor effects and milk production are important as potential indicators of the physiological state of a cow and reflect the physiological compensations a cow undergoes at various lactation intensities and/or stress exposure.

TL;DR: Prolonged exposure to heat of Guernsey heifers increased plasma progesterone on days 2 to 19 of the first cycle and only on days2 to 8 of the second cycle, but heat stress depressed plasma cortisol in both cycles and reduced the correlation coefficient between these steroids relative to specific stages of the estrous cycle.

TL;DR: Data show a high and sustained adrenosympathetic activity (indicated by increases in epinephrine and norepinephrine) during heat acclimation and a transient increase in plasma glucocorticoids, which then declined even though body temperatures remained elevated during long heat exposures.

TL;DR: The reduction in thyroxine and triiodothyronine of plasma and the decline in excretion of thyroxines and Triiodothyronsine suggested that environmental heat reduced synthesis of both hormones.