Abstract.
Plasma cortisol variations have been determined by radioimmunoassay in 5 stallions during mating and in 2 teasers during oestrous female exposure. In all the animals, cortisol plasma levels consistently increase (71.1 ng/ml vs 44.0 and 63.0 ng/ml vs 35.1, in the stallions and in the teasers, respectively) 7–30 min after female exposure; 120 min after exposure, cortisol concentrations are again low.
Androstenedione concentrations in both plasma and milk were higher than those of testosterone throughout pregnancy. Testosterone concentration increased during pregnancy; the levels in milk were always lower than in plasma. Androstenedione concentrations increased in plasma and milk during pregnancy but the values were twice as high in milk as in plasma after Day 90. This change in androstenedione distribution suggests that the mammary gland could be active in the uptake of androstenedione from plasma to milk or that the mammary gland itself might synthesize this hormone.
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