Concentrations of oestradiol-17β in plasma and milk and progesterone in plasma during the oestrus cycle and in early pregnancy in goats

Abstract

Pre-ovulatory peaks in oestradiol-17β concentrations were observed on days 1 or 2 and post-ovulatory peaks between days 4 and 7, both in jugular venous plasma and defatted milk, day 1 being the day of the onset of oestrus in the goats. Mean values of the magnitudes of these concentration peaks and of their timing (relative to oestrus) during the oestrus cycle did not differ significantly ( P>0·05) from those when the goats were mated and became pregnant. Pre-ovulatory oestradiol-17β peaks were invariably greater than the corresponding post-ovulatory peaks, as were peak concentrations in plasma relative to those in defatted milk collected on the same day. Mean intervals between the pre- and post-ovulatory peaks in oestradiol-17β concentrations were respectively 4·2 days for plasma and 4·0 days for defatted milk. Concentrations of oestradiol-17β in jugular venous plasma and defatted milk were strongly correlated: rank correlation coefficients for the three goats studied were 0·871, 0·668 and 0·739. It is suggested that in goats, as in cattle, ovarian follicular oestradiol-17β secretion approaching pre-ovulatory level is restored by 4 days after oestrus and its rapid decline after this time may be due to the inhibitory influence of the rapidly rising plasma progesterone concentration.