Serum concentrations of progesterone and oestradiol during the ovarian cycle of Syrian Awassi ewes

An experiment was conducted on adult Awassi ewes to characterise the oestrous cycle, activity of the corpus luteum and to determine normal serum concentrations of progesterone and oestradiol during the different phases of the oestrous cycle using radioimmunoassay. Eighteen indigenous cycling Syrian Awassi ewes, aged about 3 years, and weighed an average of 57.6±4.5 kg were used during the normal breeding season for two consecutive oestrous cycles. Results showed a cyclic pattern in the progesterone concentration curve which was coincident with the activity of the corpus luteum. Average length of 36 oestrous cycles was 17.0±0.7 days (range: 16-18 days), divided into: 3.7±0.8 days (2-5 days), where progesterone concentration was low averaging 1.03±0.93 nmol 1-1 (range 0.01-3.14 nmol 1-1), followed by a sharp increase in progesterone secretion, coinciding with the presence of active corpora lutea, which lasted an average of 9.8±1.0 days (range:8-12 days), with a mean progesterone concentration of 8.98± nmole 1-1 (range: 3.24-38.89 nmol 1-1)(luteal phase), followed by a sharp decline in progesterone concentration, coinciding with an inactive corpora lutea (follicular phase), which lasted an average of 3.5±0.8 days (range: 0.01-2.77 nmol 1-1) Mean maximum progesterone concentration during the luteal phase was 11.66± nmol 1-1 and occurred at around day 11 of the oestrous cycle. As for oestradiol, its concentration was slightly high during the first 3 days of the oestrous cycle (22.91, 26.97, 35.27 pmol 1-1), followed by a concentration of about 20 pmol 1-1 (18.73-21.37 pmol 1-1) for a duration of 10 days, and then, followed by an increase in the concentration which reached a maximum of 58.5 pmol 1-1 one day before the end of the cycle. The latter peak was followed by a sharp decrease in the concentration. The lowest and highest oestradiol concentrations during the oestrous cycle were 7.2 and 150.67 pmol 1-1, respectively, while the overall mean concentration was 30.67±13.42 pmol 1-1. A negative and significant correlation (r=-0.563, p>0.05) was found between blood serum progesterone and oestradiol concentrations during the different phases of the oestrous cycle. It was possible, for the first time, to characterise hormonally and precisely the oestrous cycle of the Syrian, Awassi ewes, and to determine normal progesterone and oestradiol concentrations during the different phases of oestrous cycle. It is concluded that progesterone and oestradiol concentrations showed a cyclic pattern during the oestrous cycle, in addition, a negative and significant correlation between the concentrations of the two hormones was found.(author)