Onset of puberty and estrous cycle phenomena in Yankasa ewes as monitored by plasma progesterone concentrations

Abstract

Blood samples for plasma progesterone determination were collected every other day from 10 Yankasa maiden lambs beginning at 3 months of age through two estrous cycles following the first behavioural estrus. Estrus was checked twice daily (a.m. and p.m.) using vasectomised rams. Age and body weight at puberty averaged 238±23.4 days and 18.4±0.4 kg respectively. Short luteal phase progesterone profiles which were not accompanied by overt signs of estrus were observed prior to the onset of puberty. Following puberty, mean estrous cycle length and duration of estrus were 18.1±2.7 days and 25±2.2 h respectively. Progesterone concentrations ranged from nondetectable levels on the day of estrus to a peak 1.86±0.38 ng/ml at mid-cycle. The study shows the occurrence of short cycles during the prepubertal period and normal estrous cycles following puberty.