Serum luteinizing hormone, progesterone, and estradiol levels in relation to broodiness in the turkey (Meleagris gallapavo).

Changes in nesting frequency, serum LH, progesterone, and estradiol were measured in relation to the onset of broodiness in turkeys. In each of two experiments the frequency of nest visits increased about four-fold in the 5 to 7 day interval before oviposition of the last egg associated with the onset of broodiness. In the 9 day period prior to oviposition of this egg LH levels declined from about 12 ng/ml to 6 to 7 ng/ml (Experiment 1) and from about 9 ng/ml to less than 5 ng/ml (Experiment 2). Progesterone levels declined during this same period going from about 2 to 2.5 ng/ml down to less than .5 ng/ml. In the 5 day period following the nadir in serum LH, which occurred on or a day or two after the last egg, levels of this hormone again rose substantially. Estradiol levels, assayed in Experiment 2, were generally low with many samples below detectability (less than 3 pg/ml). There were no consistent changes in serum estradiol until the day before oviposition of the last egg. On this day, and on the subsequent four days, mean estradiol levels were at a nadir (6 to 9 pg/ml) and rose to levels averaging over 11 pg/ml in the following five day period.