Gonadotrophin Levels and Ovarian Development in the Neonatal Ewe Lamb

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Abstract
Ovarian weight increases markedly in the newborn ewe lamb, and foctors which might contribute to this growth were examined. Follicle development was studied in the ovaries of 28 lambs age 0, 2, 4, 6, 8 and 10 wk. Plasma samples, pituitaries and 1 ovary were assayed for gonadotropin or steroid hormone content. No significant differences between age groups were found in pituitary LH [luteinizing hormone] concentration or mean plasma LH [luteinizing hormone]. Pituitary FSH concentration increased with age, except for a small decrease at 8 wk, but no significant changes were seen in plasma FSH. Ovarian progesterone and estradiol concentrations did not appear to be associated with follicular development. Growing follicles were most numerous at 2 wk while total vesicular follicles reached a peak at 4 wk. Most vesicular follicles were less than 1.4 mm in diameter. Advanced atresia in vesicular follicles became apparent by 4 wk although early signs were present in younger lambs. Fluctuations in gonadotropin levels do not appear to be responsible for variations in number and size of vesicular and growing follicles in the lamb ovary. Other possible explanations are discussed.

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