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N. Ayalon

Introduction

Embryonic mortality, strictly interpreted, should refer to fertility losses during the embryonic period, i.e. the period extending from conception to completion of the stage of differentiation which, in the cow, occurs at approximately 45 days (Committee on Reproductive Nomenclature, 1972). However, many authors have included under this term, fertilization failure, as well as death after fertilization. Since the present review was written for presentation within the framework of a symposium on reproductive efficiency in domestic animals, it was considered necessary to include data on fertilization rates, for a more complete picture of fertility losses.

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N. AYALON and M. SHEMESH

A preovulatory rise in peripheral plasma progesterone concentration has been reported in women, monkeys, rats, mice, hamsters, guinea-pigs and rabbits (Kazama & Hansel, 1970). In the cow, a preovulatory rise in plasma progesterone levels was not found when blood samples were collected once daily (Shemesh, Lindner & Ayalon, 1971) every 2 to 3 hr for 10 to 12 hr, starting with the onset of oestrus (Henricks, Dickey & Niswender, 1970), or every 6 hr from the onset of oestrus until ovulation (Kazama & Hansel, 1970). The latter authors noted the possibility that a transient rise and fall in plasma progesterone concentration may have been missed due to infrequency of sampling during the pro-oestrous period. The present investigation was undertaken to examine this possibility.

The blood samples examined were aliquots from the same collections of jugular

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M. SHEMESH, H. R. LINDNER and N. AYALON

Summary.

The non-steroidal phyto-oestrogens, coumestrol and genistein, were able to compete with oestradiol-17β (Oe2) for binding sites on a macromolecular component of the uterine cytosol from 6-day-pregnant rabbits. Binding affinity for these compounds was related to their reported oestrogenic potency: approximately one part by weight of Oe2, seventy of coumestrol and 175 of genistein produced equivalent inhibition of the uptake in vitro of [3H]Oe2 by this uterine receptor. Biochanin-A, formononetin, 12-O-methylcoumestrol, sativol and medicagol did not significantly inhibit Oe2 binding, suggesting that free hydroxyl groups in both position 7 and 12 (= 4') of coumestans and isoflavones are essential for effective interaction with the oestrogen receptor. The 7- and 12-methoxy-coumestans and isoflavones tested appear to be pro-oestrogens, able to bind to the uterine receptor only after O-demethylation in vivo.

A rapid competitive protein-binding radioassay for phyto-oestrogens in the blood that makes use of the uterine cytosol receptor is described. Its useful range is 0·5 to 40 ng for coumestrol and 2·5 to 200 ng for genistein. Prior chromatographic separation is required to discriminate between plant-derived and endogenous steroidal oestrogens. Coumestrol was present in the blood of goats (2·0 to 3·9 ng/ml) after feeding alfalfa hay at a rate supplying 12 mg coumestrol/24 hr/animal.

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M. SHEMESH, N. AYALON and H. R. LINDNER

Progesterone levels in jugular venous blood are being measured by us in cycling (unmated) and inseminated (pregnant or non-pregnant) cows as part of a comparative study of cows with normal and difficult breeding histories. Hawk, Wiltbank, Kidder & Casida (1955) reported a high incidence of embryonic death in cows during the period 16 to 25 days after insemination. The 3rd week of gestation may indeed be a critical phase in the regulation of luteal function, since towards the end of this week regression of the corpus luteum normally occurs in the absence of a conceptus. This note records that in a herd of normal Friesian cattle with a cycle length of 21·2 days±1·5 s.d. the presence of a conceptus in the uterus first exerted a significant

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M. Shemesh, N. Ayalon and T. Mazor

Summary. Plasma and milk progesterone concentrations in pregnant sheep (18–22 days after mating) were similar, about 3·7 ng/ml whereas values in non-pregnant sheep were <1 ng/ml. Lambing results indicated identical accuracy for both methods (82 and 84% in 2 flocks). The accuracy was 92–100% for ewes diagnosed non-pregnant in the breeding season, but for ewes tested in the non-breeding season the diagnosis of non-pregnancy according to milk progesterone levels was only 50% accurate.

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M. SHEMESH, H. R. LINDNER and N. AYALON

Summary.

A rapid radiometric assay based on thin-layer-chromatography and the competition by progesterone for binding sites on the corticosterone-binding globulin of human plasma was used to determine changes in the level of progesterone in peripheral bovine plasma during the oestrous cycle. The blood level (ng/ml, mean ± S.E.) of the hormone was minimal (0·6± 0·15 to 0·8± 0·20) from Day −2 to +2 of the cycle (Day 0 = day of oestrus), rose steeply between Day 3 and Day 7, and either continued to rise very slowly or maintained a plateau fluctuating about a mean of 5·4± 0·16 for 8 to 10 days, before declining; the most abrupt fall in plasma progesterone concentration occurred on Day −4 or −3. The results agreed well with control data obtained by sequential paper- and gas-chromatography (r = 0·93).

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M. Shemesh, F. Milaguir, N. Ayalon and W. Hansel

Summary. Bovine blastocysts were collected at Days 13, 15 and 16 and placed in TCM-199 supplemented with 5% fetal calf serum; some blastocysts were immediately frozen while the others were cultured for 48 h and then frozen. Samples (tissue + medium, 5–12/group) were thawed, homogenized and analysed by radioimmunoassays. Measurable amounts of progesterone were found in all blastocysts but values were higher (P < 0·01) after culture. Testosterone was not found in the cultured or uncultured blastocysts at Day 13, but was detectable on Days 15 and 16 and in greater amounts (P < 0·05) in the cultured blastocysts. PGF and PGE-2 were increased (P < 0·05) in the cultured blastocysts on all 3 days. Oestradiol was measurable in some but not all blastocysts. It is suggested that PG synthetase and enzymes capable of synthesizing progesterone, testosterone and, possibly, oestradiol are present in these early bovine blastocysts.