Luteinizing Hormone, Oestrogen and Progesterone Levels in Peripheral Serum of Anoestrous and Cyclic Ewes as Determined by Radioimmunoassay

Abstract

Summary. Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean \ m=+-\ S.E. value of 2\m=.\3\ m=+-\ 0\m=.\9 ng/ml. High LH values of 20\m=.\0, 41\m=.\2and 137\m=.\5 ng/ml were observed in three ewes on Day \m=-\24of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0\m=.\11 \ m=+-\ 0 \ m= . \ 0 1 ng/ml) before Day \m=-\25of anoestrus. A major rise occurred on Day \m=-\12 of anoestrus and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4\m=.\40 \ m=+-\ 0\m=.\1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5\m=.\2\ m=+-\ 0\m=.\3 pg/ml. A wel l \x=req-\ defined peak of 13\m=.\3\ m=+-\ 0\m=.\7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day \m=-\25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.

Release of LH in anoestrous and cyclic ewes

“…The progesterone concentrations of Ewes 1, 3 and 4 were <0·5 ng/ml at all times during anoestrus but the level of 0-38 ng/ml in the first sample collected from Ewe 2 on Day -9 had increased to 1 -32 ng/ml by the end of the 24-h collection period, perhaps indicating that luteinization had begun. These data lend further support to previous findings that episodic releases of LH occur in the anoestrous ewe (Cicmanec & Niswender, 1973;Akbar et al, 1974;Yuthasastrakosol et al, 1975). Foster et al (1975) also observed pulsatile releases of LH in ewe lambs as they approach sexual maturity, but like us, they were unable to detect any marked change in the release pattern or peak amplitude before the first ovulation at puberty.…”

Changes in LH pulse frequency and serum progesterone concentrations during the transition to breeding season in ewes

“…These results support previous demonstrations that brief increments in progesterone occur just before the first full-length luteal phase of the breeding season (Yuthasastrakosol et al, 1975;Walton et ai, 1977). In addition, the present results demonstrate that one or more of these brief rises in progesterone can occur within 1-4 weeks before the first full-length luteal phase, the same time interval as the previously-defined transition period, during which one or more increases in LH pulse frequency were observed.…”

Development of preovulatory follicles expected to form short-lived corpora lutea in beef cows

“…Short-lived corpora lutea are observed after the first ovulation after parturition in cows (Lamming et al, 1981;Humphrey et al, 1983) and sheep (Wise et al, 1986) and after the first ovulation of the breeding season in sheep (Yuthasastrakosol et al, 1975;Walton et al, 1977). Additionally, the first ovulation at puberty in heifers (González-Padilla et al, 1975), ewes (Berardinelli et al, 1980) and primates (Young & Yerkes, 1943;Wentz, 1979;Resko et al, 1982) is frequently followed by a short luteal phase.…”