Peripubrtal Plasma Progesterone Patterns in Ethiopian Menz Ewe Lambs

Abstract

Plasma progesterone concentrations were determined every 10 days for 38 grazing Menz ewe lambs from weaning (93 ± 7 d) until conception. Lambs were either fedextra supplementary concentrates and/or drenched for endoparasites. Inadequate nutrition delayed puberty onset by 4 to 5 months (P≤0.05). Progesterone concentrations, determined by the ELISA technique, were basal (≤1.0 ng/ml) before puberty. Subsequently, 63% lambs exhibited a ‘silent ovulation’ prior to first behavioural oestrus but, transient rises of progesterone were not observed in 45% of lambs conceiving at first mating. Further, first oestrus was unovulatory (non-pubertal) in 21.1% of animals which may bias estimates of puberty onset based only on first oestrous behaviour. 5% of lambs exhibited a gestational oestrus.