Bartlewski PM

Beard AP

Rawlings NC

Eight February-born Suffolk ewe lambs underwent transrectal ovarian ultrasonography every 2 weeks (from 6 to 38 weeks of age) and during seven 10-day periods, with starting dates every 5 weeks (from 6 to 36 weeks of age), to study antral follicle development. Blood samples were taken at 2 and 4 weeks of age, and before each ultrasonographic examination, for radioimmunoassay (RIA) of serum FSH and estradiol, and daily, from 30 weeks of age, for measurement of progesterone. Six ewe lambs reached puberty (defined as an elevation in serum progesterone concentrations ≥0.1 ng/ml for ≥7 days) between 32 and 36 weeks of age (mean \ub1 S.E.M.: 34.0 \ub1 0.5 weeks). The total number of all follicles ≥2 mm in diameter/ewe lamb increased from 12 to 14 weeks, declined from 24 to 28 weeks, rose from 28 to 32 weeks, and then decreased after 32 weeks of age (n = 6; P &lt; 0.05). The diameter of the largest follicle increased from 8 to 14 weeks, declined from 14 to 22 weeks, and finally increased between 32 and 36 weeks after birth (P &lt; 0.05). Mean serum FSH concentrations peaked at 30 weeks and increased again from 14 to 4 weeks before attainment of puberty (P &lt; 0.05). There were 2.4 \ub1 0.09 peaks in the daily serum FSH concentrations and 0.8 \ub1 0.1 emerging follicular waves per lamb (follicles attaining ovulatory diameters of ≥5 mm; P &lt; 0.05) over each 10-day scanning period. The frequency of FSH peaks and follicle wave emergence did not change significantly throughout the study. Mean circulating concentrations of estradiol increased gradually (P &lt; 0.05) from approximately 6 weeks of age until puberty. It was concluded that antral follicle recruitment and growth increased after the first 8 weeks of age and just before puberty in February-born ewe lambs. A rhythmic pattern of increases in daily serum FSH concentrations, as seen in adult ewes, was present in the ewe lambs of all ages but the pattern of follicular wave emergence was not fully established in pre- and peripubertal ewe lambs. \ua9 2005 Elsevier B.V. All rights reserved

Ultrasonographic study of antral follicle development during sexual maturation in ewe lambs

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