Plasma progesterone in heifers treated with prednisolone during the oestrous cycle

Four heifers that had showed oestrus with regular intervals, were treated daily with 30 mg prednisolone per 100 kg body weight from the day after ovulation to slaughter. Two of the heifers were slaughtered on day 13 after oestrus for histological examination of the corpora lutea, and the remaining two were slaughtered on day 26 after oestrus. Three other heifers served as controls. Plasma progesterone was determined in all heifers during the period of treatment, and in one heifer during the cycle preceding. The normal increase of plasma progesterone in metoestrus was inhibited, and the plasma progesterone levels in dioestrus were found to be low in the prednisolone treated heifers compared to the controls. The corpora lutea of the two treated heifers slaughtered in dioestrus did not differ histologically from normal. The effects of prednisolone treatment on the development and function of corpus luteum, on prostaglandin secretion from uterus and on LH release, are discussed.