Peripheral Plasma Progesterone Concentration of Cows During Puberty, Oestrous Cycles, Pregnancy and Lactation, and the Effects of Under-Nutrition or Exogenous Oxytocin on Progesterone Concentration

Abstract

SUMMARY Progesterone concentrations in the peripheral plasma of cows were measured by a protein-binding radioassay method. The mean concentration was lowest at oestrus (0·44 ng/ml) and then increased to a maximum of 6·8 ng/ml about day 14 of the 21-day cycle. The concentration decreased rapidly during the last 4 days of the cycle, reaching low levels on the day before oestrus. There were no significant changes in progesterone concentration during oestrus. After ovariectomy the plasma progesterone concentration decreased to a very low level (< 0·4 ng/ml). After hysterectomy, progesterone concentrations remained high for longer than in a normal cycle. At puberty, plasma progesterone concentrations indicated cyclic ovarian activity before the first observed oestrus. Daily treatment of cows with oxytocin (0·4 u./kg body weight) from day 2 reduced the oestrous cycle length to 9 days, but did not significantly alter the slow increase in plasma progesterone concentration during the first 5 days of the cycle. Plasma progesterone concentrations decreased again after day 5 to low values. Plasma progesterone concentration during early pregnancy was similar to the luteal phase value (4–6 ng/ml), declined during mid-pregnancy and then increased to a maximum (7–8 ng/ml) at about 240 days gestation. The concentration declined 2–3 weeks before calving. During lactation progesterone concentrations were very low until the resumption of cyclic ovarian activity. The first post-partum cycle, whether accompanied by observed oestrus or not, was usually preceded by a small increase in plasma progesterone concentration 3–5 days before the start of the cycle. Undernutrition significantly increased plasma progesterone concentrations in mid- and late pregnancy. Undernutrition of non-pregnant cows increased progesterone concentrations during the luteal phase of the first cycle, but reduced it in later cycles.

Response of cyclic and post-partum suckled cows to injections of synthetic LH-RH

“…These results support the view that the release of low levels of progesterone before normal cyclic activity may be important for the development of normal reproductive activity after anoestrus (Donaldson, Bassett & Thorburn, 1970;Yuthasastrakosol, Palmer & Howland, 1975). It is possible that the progesterone has a feedback action on the hypothalamus and/or pituitary to initiate a pattern of gonadotrophin secretion associated with normal cyclic ovarian function.…”

Plasma progesterone and gonadotrophin concentrations and ovarian activity in post-partum dairy cows

“…1 and in Cows 3 and 4 in Exp. 2 and preceded the onset of normal ovarian and oestrous cycles has been previously noted by a number of workers (Pope, Gupta & Munro, 1969;Donaldson, Bassett & Thorburn, 1970;Robertson, 1972;Tribble et al, 1973;Lamming & Bulman, 1976). The origin of this transient increase in peripheral plasma progesterone is not known, although it has been previously suggested that it originates from luteinized follicles (Tribble et al, 1973).…”

Progesterone Levels During the Oestrous Cycle and Pregnancy in the Cuis, Galea Musteloides

“…This is not the case in cavies where plasma progesterone levels during pregnancy can be divided into two phases (see above). (2) The highest progesterone concentration found in the plasma of the guinea-pig and cuis during pregnancy is certainly very much higher than those found in many other animals such as the pregnant hamster (25 ng/ml; Leavitt & Blaha, 1970), ewe (15 to 20 ng/ml; Bassett, Oxborrow, Smith & Thorburn, 1969;Fylling, 1970) and cow (8 ng/ml; Donaldson, Bassett & Thorburn, 1970). Thus, not to mention the high level of 513 ng/ml, even the progesterone concentrations (6-3 to 15 ng/ml) during the first 15 days in guinea-pigs Challis et al, 1971) and in G. musteloides (23 to 60 ng/ml) are, in fact, high levels and the progesterone requirement during the first 15 days' gestation in both species of cavy is, therefore, by no means low compared to these animals.…”