Urinary oestrogen and plasma progesterone levels in non-pregnant mares
Palmer, E.; Jousset, B.
Journal of Reproduction and Fertility. Supplement 1975(23): 213-221
1975
ISSN/ISBN: 0449-3087 PMID: 1060781 Document Number: 89034
Eight mares were observed for 14 mth to detect oestrus and ovarian activity, and urinary oestrogens and plasma progesterone were measured. Cyclical ovarian activity occurred during 60% of the experimental period. Persistent luteal activity was found over 20% of the period, and for the rest of the time activity was absent. Cyclical activity was characterised by the alternation of periods of low and high progesterone levels corresponding to the follicular and luteal phases of the ovarian cycle. During the follicular phase, urinary oestrogen levels increased to a maximum of 463 plus or minus 296 ng/ml 2 days before ovulation. The duration of the interval from complete luteolysis to ovulation (6.3 plus or minus 2.7 days) was correlated with oestrone peak values (0.44) and with oestrone levels at the beginning of the low progesterone phase (-0.36). High oestrogen levels were recorded during persistent luteal activity, which occurred more frequently in summer than in winter. Ovarian inactivity was more frequent in winter and was characterised by very low progesterone and low oestrogen (<50 ng/ml urine) levels. Some individual and seasonal effects were studied.