Source of Circulating Progesterone in Prepubertal Ewes

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Abstract
In ewe lambs peripheral progesterone increases for a 1-4 day period prior to puberty. The source of this increase was investigated in 15 spring-born ewe lambs. Ewes were checked twice daily with a teaser ram throughout the experiment but no signs of behavioral estrus were observed. Daily samples of jugular plasma were assayed for progesterone on the day of collection. Basal concentrations of progesterone (ng/ml; x ± SEM) averaged 0.3 ± 0.1 for all ewes and increased to 1.1 ± 0.1 during the first rise. The duration of the first rise in 5 ewes was 2.5 ± 0.5 days. Progesterone then decreased to 0.4 ± 0.1 for 4 ± 1 days and rose again to 1.9 ± 0.3 ng/ml.