The postnatal development of the ovary and uterus of the Merino lamb

Abstract

The growth and development, between birth and 33 wk of age, of the ovaries, uterus and pituitary of Merino lambs were studied at monthly intervals. The ovarian weight at 4 and 8 wk of age was 6.8 and 10.8 times, respectively, the ovarian weight at birth. At 12 weeks, it had declined significantly and then remained relatively constant to 33 wk. The uterine weight at 4 wk was approximately twice the weight at birth, but it did not increase significantly again until 33 wk. There was a small increase in pituitary weight between 4 and 8 wk but no significant change thereafter. The mean numbers of growing and vesicular follicles in the ovaries were 455±62 and 935±208, respectively, at birth. They increased significantly at 4 wk, then declined significantly in older lambs. Mean diameters of the largest follicle per ovary and per animal increased steadily from birth to 33 wk. Estradiol 17α was detected by thin layer chromatography in the urine of all newborn lambs and estradiol 17β was detected in the urine of one newborn lamb. After birth, estrogens were not detectable in urine until 33 wk when estradiol 17α was found in two lambs and estradiol 17β in another.