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T. J. Robinson

John Hammond died 16 years ago, and there are many of the younger generation to whom he is just a name. He became a legend in his time and his influence was enormous. He drew students from all over the world and these came to occupy key positions in animal science in many countries (Pl. 1, Fig. 1). We are a dying generation, but many of us have produced our own postgraduate students to whom some of the Hammondian philosophy has been transmitted, and they in turn are now producing their students.

The title of this address was suggested by a remark made to me many years ago by Professor 'Bunny' Austin. At an SSF meeting, I forget when or where, a group of us were talking about postgraduate training, and I remarked on the seeming casualness of Hammond. Practically all my discussions with him took place on Sunday over

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Five tests were conducted at intervals of 3 months to determine the seasonal variation in fertility following treatment with two types of intravaginal sponges impregnated with 30 mg of a synthetic progestagen (SC-9880; Cronolone, Searle). Sponges were prepared with 5 ml ethanol to release 20 mg SC-9880 over a 16-day period or with 1 ml ethanol to release 10 mg. Ewes were inseminated twice, 48 and 64 hr after withdrawal of the sponges.

There was a marked seasonal variation in all parameters associated with fertility and best results were obtained overall with the sponges releasing the higher dose. Treatment in the spring was followed by a low incidence of ovulation, a high incidence of 'silent heats' and few pregnancies following insemination (13·6%) ; most of the ewes that were not pregnant became anoestrous. Treatment in the autumn was followed by a high incidence of ovulation and oestrus, and a high pregnancy rate following a double insemination (82·5%), and few animals became anoestrous.

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An experiment is described in which spermatozoa were recovered from genital tracts of ewes either at the first oestrus following progestagen synchronization or at a normal oestrus.

Recoveries 1, 12, 24, 36 and 48 hr after the insemination of 500× 106 spermatozoa show that synchronization with intravaginal sponges impregnated with the synthetic progestagen 17α-acetoxy-9α-fluoro-11β-hydroxypregn-4-ene-3,20-dione (Cronolone, Searle) alters the numbers and distribution of spermatozoa throughout the female genital tract at the first oestrus after treatment.

One hour after insemination the total numbers of spermatozoa recovered, and their distribution between the various regions of the tract, differed little between progestagen-treated and untreated ewes. Thereafter the numbers recovered from treated ewes were significantly fewer than from untreated, and their distribution differed. Significant differences appeared in the vagina at 12 hr and in the cervix and uterus at 24 hr and thereafter this difference was maintained. The pattern in the Fallopian tubes followed that of the uterus. At 24 hr the mean numbers of tubal spermatozoa recovered were: synchronized—900; non-synchronized—8200 (P< 0·001).

Both transport and survival of spermatozoa may be deleteriously affected in the reproductive tract of the progestagen-treated ewe.

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D. T. Pearce and T. J. Robinson

Summary. Two experiments involving 24 and 54 Australian Merino ewes were conducted in which the establishment of a cervical population of spermatozoa and several endocrinological events were studied after several regimens for the synchronization of oestrus. Intravaginal sponges impregnated with 500 mg (Exp. 1) or 200, 400 or 600 mg (Exp. 2) progesterone resulted in the maintenance of plasma progesterone concentrations of 1·5–4·9 ng/ml over a 12-day insertion period compared with 1·9–6·9 ng/ml during dioestrus in control ewes. In Exp. 1 basal concentrations of ≤ 0·25 ng/ml plasma were attained by 4 h after sponge withdrawal and this decline was much more rapid than in normal luteolysis. This was associated with fewer spermatozoa recovered from the cervix 2 h after insemination, and PMSG had no significant effect. In Exp. 2 injection of a supplementary dose of progesterone at sponge withdrawal resulted in a rapid increase in plasma progesterone concentrations followed by an equally rapid decrease and an attenuation of the rise in plasma oestradiol-17β, the LH surge, and the onset of oestrus. The numbers of spermatozoa recovered 4 h after insemination were not increased, and PMSG had no significant effect. Two factors were significant, namely the dose of progesterone in the sponge (600 mg > 400 or 200 mg, P < 0·05) and stage of oestrus when inseminated (mid- or late oestrus > early). The data demonstrated that an adequate dose of progesterone/progestagen incorporated into intravaginal sponges and accurate timing of insemination relative to the LH surge are the most important factors involved in penetration of the cervix by spermatozoa.

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Eighty spayed ewes were used in a 4 × 4 factorial experiment (n = 5) in which four doses of oestradiol benzoate (0, 12·5, 25 and 50μg) were administered 48 hr after four progesterone regimens (0, 5, 10 and 20 mg/day for 12 days). Each ewe was inseminated 24 hr later with 0·15 ml undiluted semen (≥500 ×106 spermatozoa). After a further 24 hr, the ewes were slaughtered and the vagina, cervix, uterus and Fallopian tubes were flushed for spermatozoa. The population of spermatozoa in the cervix was highly dependent upon oestrogen (P<0·001) and appeared to be related to dose (P=0·1). There was no significant mean effect of progesterone but there was a significant interaction with oestrogen (P<0·05). High numbers of spermatozoa were associated with high doses of oestrogen and of progesterone. The numbers of spermatozoa in the vagina were not related to oestrogen and there was no relationship with the numbers in the cervix (r = −0·011). Penetration and maintenance of a cervical population of spermatozoa was related to the level of oestrogen and full expression required adequate progesterone influence preceding that of oestrogen.

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The numbers of spermatozoa recovered from the Fallopian tubes 24 hr after insemination, fertilization rate and lambing were measured in one group of 120 normal cyclic ewes and in three groups of 120 animals which had been synchronized with intravaginal sponges impregnated with 10, 30 or 90 mg Cronolone (Searle). Half of each group received 500 i.u. pmsg. Results were as follows:

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pmsg had no apparent effect on any one of the three parameters. Increasing dose of progestagen significantly increased the incidence of oestrus and was associated with an increasing ovarian response to pmsg. There was no evidence that embryonic mortality was greater in progestagen-treated than in untreated ewes.

Considering all parameters of fertility, ewes treated with intravaginal sponges containing 10 mg Cronolone yielded the fewest spermatozoa, the lowest number and percentage of fertilized eggs and the lowest percentage of lambing ewes.

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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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A. L. Poulton and T. J. Robinson

Summary. Rams and ewes of the Romney Marsh (N = 6), Dorset Horn (N = 8) and Australian Merino (N = 8) breeds were subjected to 4 successive periods of alternating 6 h light/18 h dark ('short' days) and 18 h light/6 h dark ('long' days) preceded by 16 weeks of 12 h light/12 h dark. The initial period was of 32 weeks (16 weeks 'short' days; 16 weeks 'long' days) and the next 3 were of 24 weeks (12 weeks 'short' days; 12 weeks 'long' days).

Rams of all breeds showed a cyclic pattern of growth and regression of testes associated with plasma testosterone concentration, influenced by the change in light regimen 15–19 weeks previously. Sexual behaviour was also cyclic but lagged by some 6–7 weeks. The changes were greatest in the Romneys and least in the Merinos in which a higher degree of sexual activity was evident even when the testes were regressed (P < 0·001). This was the major breed difference.

All ewes of the Romney and Dorset breeds showed marked seasonality related to the imposed light regimen, whereas only 1 of the 4 Merinos did so. The mean peak of ovarian activity in the former 2 breeds coincided with that of maximum sexual activity of rams housed with them; that is, some 6 weeks after maximum scrotal volume.

The rams and ewes were subjected to serial blood sampling episodes for plasma LH and testosterone and tested for plasma LH release following GnRH administration. There was little variation between breeds in LH concentration. Testosterone concentration varied greatly in the ram, highest levels associated with the developed phase of the testes and with maximum LH pulse frequency. The LH response to GnRH changed with respect to the state of the gonads. Maximal responses were observed in the developing phase of testicular growth although this variation was greater in the Romney and Dorsets than in the Merinos (P < 0·001). In the ewes, maximal responses were seen in the follicular phase (P < 0·001), with no difference between the luteal and acyclic phases. There were no breed differences.

Plasma pooled from the serial blood sampling episodes was assayed for prolactin. Rams of each breed exhibited a cyclic pattern of plasma prolactin concentration, directly related to photoperiod (P < 0·001) and inversely related to testicular activity (P < 0·001). All Romney and Dorset ewes, but only the 1 'seasonal' Merino ewe, displayed a cyclic relationship between plasma prolactin and photoperiod (P < 0·001). Mean prolactin concentrations were greater in the Romney and Dorset rams (P < 0·02) and ewes (P < 0·05) than in the Merinos.

It is concluded that, although these 3 breeds followed a similar endocrinological pattern, there was a marked difference in the 'ultimate' responses (i.e. libido and oestrus) with the Merino displaying the least constraint to the imposed light regimen. This could reflect the natural and artificial selection pressures upon the Merino for unrestricted (year-round) breeding.

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A. T. Sumner and J. A. Robinson

Summary. An integrating microinterferometer was used to measure the dry mass of sperm heads. The dry mass was found to be proportional to DNA content, and thus provides a useful method of estimating sperm DNA content.

Using this technique we have confirmed that human spermatozoa which show none and one quinacrine-fluorescent spot are X- and Y-bearing respectively. However, the measurements suggest that many of the spermatozoa with two quinacrine-fluorescent spots are not YY-bearing, as previously thought, but might be incompletely condensed Y-bearing spermatozoa.

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The activities of six oestrogenic substances were compared when given as a single injection, intravenously (i/v) or intramuscularly (i/m), to spayed progesterone-primed ewes. The following values for the ED50 for oestrous behaviour, with associated 95% fiducial limits, were obtained:

Oestradiol-17β (i/v) 16 —, 25 — 39; (i/m) 3 — 7 — 16

Oestradiol benzoate (i/v) 30 — 45 — 69; (i/m) 5 — 11 — 23

Oestrone (i/v) 48 — 96 — 194; (i/m) No data

Diethylstilboestrol (i/v) 6 — 10 — 18; (i/m) 6 — 10 — 18

Hexoestrol (i/v) 46 — 103 — 234; (i/m) 46 — 103 — 234

Methylethylstilboestrol (i/v) ∞ — ; (i/m) 130 — 279 — 600

They fell into three groups, with the following i/v : i/m ratios: natural oestrogens; oestradiol- 17β, oestradiol benzoate, 4 : 1: synthetic oestrogens; diethylstilboestrol and hexoestrol, 1 : 1 : pro-oestrogen; methylethylstilboestrol, ∞ : 1.

True oestrogens are presumed to accumulate in the reacting tissues with variable efficiencies. Pro-oestrogens, given i/v, are probably ineffective because they are not converted to oestrogens in a manner or at a rate suitable for such accumulation.