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R. Gonzalez, P. Poindron and J. P. Signoret

Summary. The response of sexually experienced Ile-de-France rams to the presentation of oestrous females in October at sunrise (Subgroup S) or at 11:00 h (Subgroup N) was studied and compared with unstimulated controls (Subgroup C). Animals (12 per group) were bled for 7 h at 20-min intervals, starting 3 h before stimulation by oestrous females (3 per group). Eight rams from Subgroup S showed an increase of LH pulse frequency and only 3 in Subgroup N (P < 0·03). In Subgroup S the introduction of females led to 2- and 3-fold increases in LH pulse frequency during the stimulation period compared with values in Subgroup C or before the stimulation period (3, 1·6 and 1 peaks/rams/6 h respectively; P < 0·05). The presence of females also led to an increase in mean testosterone concentrations, and small increases in basal and mean LH values. No differences were found in LH peak amplitudes. In Subgroup N only inconsistent evidence of increases in mean LH and testosterone values was found. No differences between Subgroups S and N in behavioural patterns during stimulation were detected. We conclude that the presence of females affects LH pulse frequency at sunrise but not at noon during the breeding season and this effect is at least partly independent of sexual behaviour. These results suggest a possible circadian variation in CNS sensitivity involving the hypothalamic regulation of LH secretion in response to the presence of oestrous females.

Keywords: temporal variations; LH; testosterone; ram; female effect; teasing

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Isabelle Delcroix, R. Mauget and J. P. Signoret

Summary. Reproductive events were recorded in two groups of female wild boars kept in semi natural conditions. The first group had been kept for 2 consecutive years with a male. Most farrowing took place within 4–5 days: 6/7 in the first year and 8/9 for the second. A second group of 5 females was kept for 13 months in the absence of a male, and oestrous cycles were monitored by weekly measurement of plasma progesterone concentrations. All the females experienced summer–autumn anoestrus and resumed cycling in the same week of December. This accurate synchronization of reproduction may result from stimulation amongst females belonging to the same social unit.

Keywords: reproduction; synchronization of oestrus; social group; wild boar

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M. LEMON, J. PELLETIER, J. SAUMANDE and J. P. SIGNORET

I.N.R.A.-Laboratoire de Physiologie de la Reproduction, Nouzilly, 37380 Monnaie, France

(Received 29th May 1974)

The concentrations of a number of reproductive hormones found in the peripheral plasma of the cow around the time of oestrus have been measured by numerous authors: plasma concentrations of progesterone throughout the oestrous cycle (Stabenfeldt, Ewing & McDonald, 1969), LH (Schams & Karg, 1969), oestrogen and progesterone (Henricks, Dickey & Hill, 1971) and LH and progesterone (Henricks, Dickey & Niswender, 1970). These and other reports have paid little attention to the precise onset and duration of oestrus, behaviour being checked at various intervals (usually two or three times a day) before the expected onset.

To obtain a more precise pattern of hormone concentrations around oestrus, we have measured simultaneously LH, oestradiol-17β and progesterone in samples of plasma taken at 2-hr intervals from cows over a period of 5 days. The cows were maintained with a

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J. P. SIGNORET, F. du MESNIL du BUISSON and P. MAULÉON

Mating has been shown to have effects on ovulation in a number of species which ovulate spontaneously, such as rats (Aron, Asch & Asch, 1961; Aron, Asch & Ross, 1966; Zarrow & Clark, 1968) and sheep (Parsons, Hunter & Rayner, 1967; Van der Westhuysen, Van Niekerk & Hunter, 1970). In the sow, the results obtained by Pitkjanen (1955) and Lebedev (1957) suggest that mating hastens ovulations and shortens the time during which ova are liberated. Direct inspection of the ovaries by coelioscopy (Locatelli, 1971) allows rapid and accurate determination of the time of ovulation and causes minimal trauma. By this technique, the earlier results have been confirmed in a preliminary experiment (Signoret, 1970).

The present experiment was designed to show by how many hours mating advances ovulation and shortens its total duration.

Fifty-nine Large

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J. Cohen-Tannoudji, C. Lavenet, A. Locatelli, Y. Tillet and J. P. Signoret

Summary. In anoestrous ewes, male chemosignals elicit rapid increases in luteinizing hormone (LH) secretion that can ultimately lead to ovulation. To assess the possible involvement of the accessory (vomeronasal) olfactory system in the mediation of those chemical cues, we destroyed this pathway by vomeronasal organ electrocauterization (Exp. I) and vomeronasal nerve section (Exp. II). Neither of these lesions inhibited the LH response of ewes to the odour of the male. These results suggest that the vomeronasal system is not necessary to mediate the neuroendocrine response of the ewe to the male odour. As both surgical methods spared the main olfactory system but destroyed the vomeronasal system, it is likely that the main olfactory system is involved in the LH response to chemical stimulation in sexually experienced ewes.

Keywords: sheep; male effect; chemosignals; vomeronasal system