ANALYSIS OF THE PATTERN OF EJACULATION INSTALLIONS

M. TISCHNER, K. KOSINIAK and W. BIELA\l=N'\SKI

Agricultural Academy in Krakow, Institute ofApplied Physiology of Animals,30-059 Krakow, Al. Mickiewicza 24/28, Poland

(Received 5th February 1974)Summary. The emission of stallion semen was studied with the aid ofan `open' Krak\l=o'\w-72Model artificial vagina. The pattern of matingbehaviour was constant in all copulations observed : a mean number ofseven intravaginal thrusts was required to elicit ejaculation. Thepressure within the vestibule of the artificial vagina averaged 66 mmHgat the beginning of copulation, 142 mmHg just before ejaculation, and70 mmHg during the emission of semen. Emission appeared to be a morevariable process. Five to ten jets were observed; the mean number was

eight. The early jets occurred under high pressure in a stream with char-acteristic spatter. The later jets, accompanied by declining erectionand withdrawal of the penis from the vagina, were associated with lowpressure. Of the total time of ejaculation, 24% involved actual emissionof semen; the rest comprised intervals between successive seminal jets.The first three jets contained 80 % of the ejaculated spermatozoa. Thetotal number of spermatozoa, and the ergothioneine content, graduallydecreased in successive jets. No bacterial growth was found when thesperm-rich fraction was inoculated on solid media.

INTRODUCTIONIn stallions, as in other males, two main phases may be observed in matingbehaviour. The first phase is that of sexual excitation (libido) ; it is connectedwith stimulation of teloreceptors. The second phase (copulation) begins withcopulatory movements and ends with ejaculation. There is an extensive litera¬ture on the behavioural pattern ofstallions during the first phase (Wierzbowski,1959, 1962; Bielariski, 1972), but much less is known about the copulatorybehaviour during the second phase, especially the intravaginal events whichprecede ejaculation.

The aim of the present study was to elaborate methods which would providemore information about the copulatory and ejaculatory patterns in stallions.

MATERIAL AND METHODSTwo Anglo-Arab and two Oldenburg stallions (18 to 21 years of age) wereused. All four had been used previously for breeding, and all showed normal

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330 M. Tischner et al.

fertility and mating behaviour. A mare in oestrus was used as a 'teaser' forthree of the stallions, and a dummy was used for the fourth one.

The artificial vagina (AV), used in the experiments and referred to as theKraków-72 Model, has been modified several times. Its framework consistedof two rings, 14 cm in diameter, connected by means of two ribs. This frame¬work was covered with a rubber sleeve which constituted the outer wall of thewater-air chamber. This chamber was formed by placing another rubbersleeve on the frame and turning it down at both ends, as in the standard AV.The vagina was of the 'open' type, i.e. it had no semen collector. Instead, thesemen was collected directly from the external urethral orifice in a transparentfunnel connected to a series of test-tubes surrounded by a water-bath (36°C). Thetest-tubes were removed and replaced during ejaculation, so that each jetwas collected in a separate tube. In this manner, ten seminal fractions werecollected. The volume, sperm motility, number of spermatozoa, and ergothio¬neine content (Mann, Short & Walton, 1957) were determined for each jet.

Text-fig. 1. Diagrammatic representation of the equipment used for registration of theemission of stallion semen, a, Artificial vagina; b, air-cushion; c, air-pump; d, mano¬

meter; e, connection with the autographic recorder of the copulatory movements; f, airballoon for manual recording of seminal jets; g, time recorder; h, kymograph.

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The pattern of ejaculation in stallions 331The fractions resulting from the first jets ofsemen were examined bacteriologi-

cally by inoculation on a variety of solid media.Copulation and ejaculation were recorded kymographically and by filming.

A Zimmerman's kymograph was used and was provided with a Marey'sdrum connected by an air-hose with an air-cushion, which was inserted intothe water-air chamber of the AV round its vestibule. Before a collection was

started, the pressure in the air-cushion was regulated using an air pump andvacuum manometer. Ejaculation and the number of semen jets were recordedon the kymograph by pressing manually on a rubber balloon which had beenconnected by an air-hose to an additional Marey's drum (Text-fig. 1).

Two cameras were placed in front and at the side of the stallion. The courseand duration of each particular phase of ejaculation was determined by analysisof the film which was taken at 24 frames/sec and at an exposure time of 0-02sec.

RESULTSObservations of mating behaviour in stallions indicated that the ejaculatoryreflex results from the stimulus exerted by pressure and temperature on thepenile shaft, and not on the glans. About 200 ejaculates were collected fromthe four stallions; the average number of mounts per ejaculation was 1-6.

Copulation and ejaculation were recorded on the kymograph during thirty-three trials. An analysis of the number and pattern of copulatory movementsdemonstrated that these features of mating behaviour were fairly constant. Thenumber of intravaginal thrusts necessary to evoke ejaculation averaged 7(range 5 to 11) and their average duration was 10-5 sec (range 6 to 16 sec).

The pressure within the vestibule of the artificial vagina necessary to producecopulatory movements averaged 66 mmHg (range 40 to 80 mmHg). The pressureincreased with successive thrusts and reached its maximum value, average 142mmHg (range 100 to 240 mmHg), at the moment of maximal erection of thepenis just before ejaculation. With the onset of ejaculation, the pressure withinthe vestibule of the AV decreased to 70 mmHg (range 50 to 90 mmHg).

Ejaculation, both in particular sires and on particular days of observation,was a more variable process than copulation. Some stallions made arhythmicejaculatory movements. The average number of seminal jets was 8 (range 5 to10) and the average duration of ejaculation was 7-6 sec (range 6 to 14 sec),(Text-fig. 2, Table 1).

Direct observation as well as analysis by film of the pattern of copulatorybehaviour showed that ejaculation commenced when the penis reached thepoint of maximal protrusion. At this stage of copulation, about 10 to 15 cm ofthe glans penis was visible in front of the outlet of the AV. Successive pelvicthrusts resulted in gradual enlargement of the glans penis until the mushroom¬like formation could be seen just before ejaculation (PL 1, Fig. 1). The initialseminal jets were always emitted under high pressure. Film analysis showedthat the first seminal jet was expelled in a stream accompanied by a characteristicsplash of semen (PL 1, Fig. 2). The subsequent jets were emitted under lowerpressure, with a gradual decline of erection and withdrawal of the penis (PL 1,

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332 M. Tischner et al.

Stallion No. ISemen

32 ml

16 mi

Orni

120

40 I I I I I I I I_I_I_I_I_L30 ml

15 ml0 ml

150 ¬

Text-fig. 2. Typical kymographic curves during the course of copulation and semenemission by four stallions. The curves show the pressure in the vestibule of the AV. Thetiming of the period of ejaculation and the volume of seminal jets are also shown.

Fig. 2). It was calculated that the duration of the first jet averaged 0-61 sec;the next jet followed after an interval of 0-44 sec. In the terminal phase ofejaculation, the duration of particular jets as well as the volume of semen de¬creased, and the intervals between the jets lasted up to 2 sec in the final phase ofejaculation. Of the total duration of ejaculation, only 24% comprised semen

emission, and the remaining 76% consisted of intervals between successivejets (Table 2).

Individual jets of semen were collected for analysis into separate tubes duringtwo trials. The initial jets (1 to 3) were milky in colour and consistency andcontained 80% of the total number of spermatozoa ejaculated, while the laterjets (4 to 10) were mucinous in appearance. The volume, motility and con-

EXPLANATION OF PLATE 1Fig. 1. Collection of stallion semen by means of artificial vagina Kraków-72 Model.Inset A: the glans penis immediately before ejaculation.Fig. 2. The first jet of stallion semen (0-00 sec marks the beginning of ejaculation).Fig. 3. The fourth jet of stallion semen (mucous fraction).

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PLATE 1

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The pattern of ejaculation in stallionsTable 1. Kymographic records of copulatory behaviour in stallions

333

Stallionno.

No.of

obser¬vations

Total timeof

copulation(sec)

No.of

thrusts

Time ofsemen

emission(sec)

Mean no.

ofthrustsduring

emission

No. ofseminal

jets

Pressure inside artificialvagina (mmHg)

InitialBefore

moment ofejaculation

Semenvolume(ml)

8-92

10-2510-501218

5-9

7-37-18-2

607

8-098-108-16

Noobserved

thrusts0-61-75-2

8-2708-2

63

688062

130

144174141

41

494937

The values for the various parameters measured are expressed as average figures.

centration of spermatozoa were highest in the initial seminal jets. The firstjet contained 40%, the second 25%, and the third 15%, of the total number ofejaculated spermatozoa. The ergothioneine content of the successive jetsgradually decreased (Table 3).

No bacterial growth was observed in samples of fractions inoculated onsolid media.

Table 2. Duration of semen jets from four stallions and between-jetintervals timed by analysis of ciné-film

Jets ofsemen

IntervalsStallion No.

1Mean

1

2

3

4

5

6

7

8

9

10

I

II

III

IV

V

VI

VII

VIII

IX

0-710-420-370-500-420-620-420-790-331-000-371-290-291-250-26

0-710-200-460-540-420-830-420-830-251-500-251-330-12

0-500-540-500-870-290-500-421-330-330-330-331-460-461-580-33

0-540-620-620-790-460-960-421-170-420-750-371-620-172-080-201-670-201-980-29

0-610-440-480-670-400-730-421-030-330-890-331-420-261-640-261-670-201-980-29

Totalduration

Jets ofsemen

Intervalsbetween

jets

3-17

5-87

2-63

5-23

3-16

6-61

3-69

11-64

3-41

7-36

Time is expressed in seconds.

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M. Tischner et al.

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The pattern of ejaculation in stallions 335

DISCUSSIONIt may be inferred from the present study that the pressure by the air-cushionin the water chamber of the AV on the shaft of the penis is analogous to the pres¬sure of the circular muscles in the vaginal vestibular wall of the mare.

In the authors' experience, local anaesthesia of the glans penis, or injectionsof 5 to 7 ml of 5 % Polocaine (procaine hydrochloride) directly into the glanspenis, did not markedly alter the course of copulation and ejaculation installions. In this situation, some difficulties were observed only during theinsertion of the penis into the AV. These observations call for further investiga¬tions concerning the action of anaesthesia on different areas of the penilesurface.

The fact that the penis is maximally protruded at the commencement ofejaculation supports the hypothesis that during ejaculation the diverticulumurethrae of the penis is in close apposition to the external cervical orifice ofthe mare, and that semen is ejaculated under high pressure directly into theuterus. The final seminal jets ejaculated when erection is ceasing and the penisis being withdrawn are probably deposited in the vagina.

Wierzbowski (1959) observed 100 natural copulations of sixty-two stallionsand found that the sires achieved a mean number of 1 -4 mounts per ejaculation.Wierzbowski (1959) and Nishikawa (1959) demonstrated that with the use of an

AV the mean number of mounts per ejaculation increased to 2-2. When the AVKraków-72 Model was used, this index was closer to that recorded duringnatural mating (1-6). Intermittent semen collection over periods of 2 to 3 yearscaused no disturbances in the ejaculatory reflex of stallions. Furthermore, ourAV model enabled a more precise separation of the individual seminal fractionsthan was hitherto possible. The characteristics of the first three jets of the ejacu¬lated semen corresponded to the indices established by Mann et al. (1957) forthe so-called second fraction of the ejaculate in stallions. The terminal jets(from 4 to 10) with low concentrations of sperm cells and ergothioneine con¬sisted mostly of the so-called mucous fraction and corresponded to fractionthree described by Mann et al. (1957). The absence of micro-organisms in thesperm-rich jets was surprising, as semen samples from entire ejaculates had a

comparatively high degree of bacterial contamination.

REFERENCES

Bielanski, W. (1972) Rozrôd Zwierzat. [Reproduction in Animals], p.443. PWRiL, Warszawa.Mann, T., Short, R. V. & Walton, A. (1957) The 'tail-end sample' of stallion semen. J. agrie. Sci.,

Camb. 49, 301.Nishikawa, Y. (1959) Studies on Reproduction in Horses, p. 340. Japan Racing Ass., Tokyo-Minatoku.Wierzbowski, S. (1959) Odruchy plciowe ogierów. [The sexual reflexes of stallions.] Roczn. Nauk

roln. B, 73, 753.Wierzbowski, S. (1962) Badania nad zachowaniem plciowym ogierów i buhajów. [Investigations on

sexual behaviour of stallions and bulls.] Wydaw. wlasne Inst. Zoot. No. 154.

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