Peripubertal plasma progesterone patterns in Ethiopian Menze ewe lambs

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