was recorded when the increase for each mare, at any 30-min interval after the stimulus application, exceeded the mean baseline concentrationsq 2 = intra-assay coefficient of
variation.
3. Results
3.1. Experiment 1 For the evaluation of responses to teasing, teasing periods before mating were also
included. All oestrous teasings were accompanied by a display of oestrous behaviour such as posturing and clitoral winking; while during all dioestrous teasings, the mares
demonstrated aggressive behaviour and rejected the stallion. Teasing caused a significant Ž
. Ž
. P - 0.05 increase in OT concentrations in both oestrus and dioestrus Fig. 1 . There
Ž .
was no significant difference P 0.1 either between the number of mares responding Ž
. Ž
. to teasing with increased OT release in oestrus 6r10 and dioestrus 3r5 or in the
magnitude of response. In both dioestrous and oestrous teasing periods, except those followed by mating, mean OT concentrations declined to baseline values within 30 min
Ž .
Fig. 1 . On three occasions, an OT peak was observed immediately prior to the initiation of teasing, coinciding with the entrance of the stallion into the mare’s visual
field. Although teasing had no significant effect on mean PGFM concentrations in Ž
. oestrus Fig. 1 , elevations were observed in two of the five sampling periods after
teasing. None of the dioestrous mares released significant amounts of PGF at teasing
2 a
Ž .
Fig. 1 .
Ž .
Ž .
Ž .
Fig. 1. Oxytocin and PGFM
at teasing in 10 oestrous mares and in 5
Ž .
dioestrous mares. Note that only 5 oestrous mares were sampled after teasing. Asterisks represent a
Ž .
significant increase from baseline concentrations y30–0 min .
3.2. Experiment 2 All five mares had a positive OT response during natural service and mean stimuli
Ž .
Ž .
values were significantly higher P - 0.05 than baseline values Fig. 2 . Furthermore, in two mares in which false mounting occurred without intromission prior to successful
mating, an oxytocin peak was observed. Mean OT concentrations after mating declined to baseline values within 30 min after the application of the stimulus. Mating had no
Ž .
significant effect on mean PGFM concentrations Fig. 2 , but minor elevations were observed in three of the five mares after mating. There was no detectable PGFM in the
Ž .
samples collected 16–18 h after natural service data not shown . 3.3. Experiment 3
Manipulation of the genital tract consisted of three distinct stimuli to which the OT and PGFM response varied. Active massage of the clitoris and external genitalia
Ž .
significantly P - 0.05 increased OT concentrations in two of the four mares. Both
Ž .
distension of the vaginal walls and cervical stimulation significantly increased P - 0.05 mean OT concentrations. In only one of the mares did PGFM levels reach statistical
significance when compared to mean baseline concentrations in response to manipula- tion of the genital tract. In all mares, mean OT concentrations returned to baseline levels
Ž .
within 1 h of the application of the stimuli Fig. 3 . Mean PGFM concentrations in the one responding mare did not return to baseline levels by the end of blood sampling, 2 h
after the application of the stimuli.
Ž .
Ž .
Fig. 2. Oxytocin clear bars and PGFM shaded bars in 5 oestrous mares around mating. Asterisk represents a Ž
. significant increase from baseline concentrations y30–0 min .
Ž .
Ž .
Fig. 3. Oxytocin clear bars and PGFM shaded bars levels around manipulation of the genital tract in 4 Ž
. Ž
oestrous mares. Active massage of the vulva and clitoris stimulus 1 , distension of the vaginal walls stimulus .
Ž .
2 and cervical manipulation stimulus 3 are noted. Asterisk represents a significant increase from baseline Ž
. concentrations y30–0 min .
3.4. Experiment 4 The intrauterine infusion of 500 ml PBS provoked a significant OT response
Ž . Ž
. P - 0.05 Fig. 4 . Mean OT concentrations returned to baseline levels within 30 min
from the time of infusion. There was a positive PGFM response in only one mare.
Ž .
Ž .
Fig. 4. Oxytocin clear bars and PGFM shaded bars in 5 oestrous mares after intrauterine infusion of 500 ml Ž
. PBS. Asterisk represents a significant increase from baseline concentrations y30–0 min .
4. Discussion
