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D. R. LINDSAY

Summary.

The sexual activity of groups of Merino, Dorset Horn and Border Leicester rams, from which weekly semen collections were made by artificial vagina, was studied at controlled temperatures from 27 to 43° C. Only Merino rams maintained sexual activity at the highest temperature (43° C). Dorset Horns recovered activity after the temperature was lowered but Border Leicesters did not. Semen motility was poor at high temperatures in all but two rams, both Dorset Horns. The Merino rams had shorter reaction times than the other breeds. There was no significant correlation between reaction time and number of ejaculates. The rectal temperatures of the Dorset Horn rams were 0·3 to 0·4° C lower than those of the Border Leicesters; Merinos were intermediate.

At a given ambient temperature, rams had lower rectal temperatures after severe heating than before, apparently owing to increased thermoregulatory ability. Mounting and ejaculation resulted in virtually no rise in rectal temperature.

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T. MARSHALL and D. R. LINDSAY

The experiment described in this paper initially aimed at developing a simple inexpensive method of pregnancy diagnosis for sheep. We considered that, if oestrus could be induced in the non-pregnant ewes in a flock (which may be in anoestrus) and this oestrus detected by the use of harnessed rams (Radford, Watson & Wood, 1960), a method of pregnancy diagnosis could be developed. Diamond & Young (1963) present evidence from a number of species that pregnancy prevents the virilizing effect of a range of exogenous steroid substances. Lindsay & Francis (1969) and Fels (unpublished data) have shown that ovariectomized ewes do not respond to oestrogen while under the influence of exogenous progesterone. Thus, endogenous progesterone could be expected to prevent oestrous responses in pregnant ewes. One
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P. B. Gherardi and D. R. Lindsay

Summary. Groups of 50 ewes were injected with serum from pregnant mares on 5 occasions, 3 months apart, and ovulation rate was estimated at laparoscopy. In Exp. 1, new ewes were used at each time and 3 dose rates (≡400, 630 and 1000 i.u. PMSG) were studied. In Exp. 2, the same ewes were used throughout and only 1 dose was given (1000 i.u.). In both experiments the response in ovulation rate of ewes varied significantly throughout the year, with the lowest response in spring (September) and the highest in autumn (March). The ewes in Exp. 2 were as responsive at the end as at the beginning of the experiment, indicating that the response was independent of the number of doses given. The results suggest that changes in the sensitivity of ovaries to gonadotrophin may be a factor controlling seasonal ovarian activity in sheep.

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D. R. LINDSAY and T. J. ROBINSON

Summary.

Seventy-two spayed crossbred ewes were used in a series of five successive tests, at intervals of 15 days, in a study of the actions and interactions of androgen, oestrogen and progesterone on behavioural and vaginal oestrous responses.

Androgen and oestrogen were additive in their action (128 vs. 62 services; P<0·001) on behavioural response, but androgen almost completely inhibited the expected vaginal response to oestrogen.

There was a significant linear decline in behavioural sensitivity from test to test; in the five successive tests, forty-eight, forty-three, thirty-seven, thirty-two and thirty ewes were served (P<0·001). This refractory condition was partly offset by progesterone pretreatment (P<0·001), but oestrogen was necessary to maintain a constant state of psychic reactivity to androgen (P<0·001).

A highly significant linear dose-response relationship was demonstrated with both testosterone and testosterone propionate (P<0·001).

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I. C. FLETCHER and D. R. LINDSAY

Summary.

The effect of rams on the duration of oestrous behaviour was studied with oestrogen-treated spayed ewes. Different degrees of association between ewes and rams influenced the duration of oestrus in two ways.

First, the duration of oestrus measured by teasing ewes with active rams once every 4 hr was shorter when ewes and rams remained together than when they were kept apart between observations. Continuous contact with rams appeared to limit the duration of oestrus by inhibiting the neural mechanism controlling the expression of oestrous behaviour.

Second, the duration of oestrus measured by teasing ewes individually every 4 hr and keeping them with rams between observations was longer than that measured when ewes were kept in continuous uncontrolled association with rams. Regular teasing probably resulted in a longer duration of oestrus because it eliminated competition between ewes and rams and overcame the apparent unwillingness of rams to continue to mate with the same ewes for the full duration of their oestrus.

The incidence, time of onset, and duration of oestrous behaviour all responded linearly to increasing doses of oestrogen, but the slopes of these dose-response relationships were not affected by the different methods of measuring oestrous behaviour.

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T. W. KNIGHT and D. R. LINDSAY

Summary.

Intravenous injection of oxytocin into rams immediately before collection of semen with an artificial vagina, resulted in an increase in the volume of semen and the number of spermatozoa per ejaculate. After 6 weeks, during which the rams received 35 i.u. oxytocin per week, the volume of semen and the number of spermatozoa per ejaculate declined to the level of the non-treated rams and this decline was maintained for the next 4 weeks. The percentage of abnormal spermatozoa in semen from rams treated with oxytocin increased significantly (P<0·001) in the 7th week. The concentration of fructose in the semen and the libido were not affected by oxytocin. When an electro-ejaculator was used for making collections, the volume of semen increased after oxytocin injection (P<0·05), with a maximum response at 10 i.u. oxytocin.

Oxytocin appeared to have an immediate stimulating effect on the ejection of spermatozoa and seminal plasma during emission and a long term adverse effect on spermatogenesis.

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D. R. LINDSAY and T. J. ROBINSON

Summary.

Three tests are described, two each with thirty-six entire and one with fifty-six spayed ewes, in which the action of clomiphene citrate was characterized in the sheep. It was found to suppress pituitary activity, to induce behavioural oestrus and to have a grossly stimulatory action on the uterus in that it induced a high incidence of hydrops uteri. It is concluded that clomiphene acts in the ewe as a weak oestrogen but differs qualitatively from true oestrogen in its effect on the uterus.

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P. D. MORGAN, G. W. ARNOLD and D. R. LINDSAY

Summary.

Observations were made of mating and pregnancy in intact Border Leicester × Merino ewes and in ewes with the senses of hearing, touch around the mouth and/or smell impaired. During November and December, almost all ewes with the sense of smell mated and became pregnant; less than half the ewes with smell impaired mated and became pregnant. It is suggested that rams stimulate oestrous activity in non-cycling ewes through olfactory receptors in the ewe.

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G. B. Martin, R. J. Scaramuzzi and D. R. Lindsay

Summary. Introduction of rams to ovariectomized ewes treated with oestradiol implants (N = 10) increased the frequency of LH pulses from 4·8 to 10·6 pulses per 12 h. This effect was reflected by increases in mean levels of LH and the basal levels upon which the pulses were superimposed. In ewes that had not been treated with oestradiol (N = 5), there was no significant increase in pulse frequency but mean and basal levels of LH increased slightly after the introduction of rams. In a second experiment, similar effects of the introduction of rams were seen in ovariectomized ewes treated with oestradiol or oestradiol + androstenedione (N = 16), but no significant effects of the rams were observed in untreated ewes (N = 8) or ewes treated only with androstenedione (N = 7). No preovulatory surges of LH were observed in the 30-h period after the introduction of rams.

It was concluded that the ram stimulus probably evokes the increase in pulse frequency by inhibiting the negative feedback action of oestradiol, and that the surge normally observed in entire ewes is dependent on the ovarian response to these pulses. However, the observation of responses in some ewes not treated with oestradiol also raises the possibility that the ram stimulus can act directly on the hypothalamic neurones that control the secretion of LH, and that this effect is enhanced in the presence of oestrogen.

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D. R. Lindsay, J. Pelletier, C. Pisselet and M. Courot

Summary. Groups of 6 Ile-de-France rams were housed in light-proof rooms and subjected in a factorial design to two light regimens, 180° out of phase, and two levels of protein in their diets. The daily duration of daylight was varied sinusoidally to produce 6-month years with 'winters' of 8 h light and 'summers' of 16 h light. The diets were formulated to supply 50 % above or 25% below maintenance requirements in protein. Testicular diameter and volume increased with decreasing light and decreased with increasing light but the diet had no effect. The frequency of LH pulses was measured monthly and was high (3/12 h per ram) when the daylight was being reduced and low (1/12 h per ram) when it was increased. At the extremes of the duration of dark or light the frequency of pulses was around 1 ·6/12 h per ram, regardless of the duration of light. The two diets had no effect on testicular dimensions but rams fed the 'high' protein diet had a total of 175 LH pulses, which was significantly higher (P < 0·05) than the 131 pulses recorded from rams on the 'low' protein diet.

It is concluded that, in these '6-month years', decreasing light stimulates LH pulsatility and testicular growth and increasing light is inhibitory. Pulsatility of LH appears to be influenced by the protein level in the diet.