Abstract
Résumé
Introduction
Materials and methods
Results and discussion
Conclusion
Reference
G.O.Oyediji, M.O.Akusu¹ and G.N. Egbunike
¹ University of Ibadan, Nigeria
The response of ewes in oestrus to different stimuli was studied in five normocyclic West African dwarf ewes during five successive oestrous cycles. Sniffing around the perineum was significantly superior (P<0.05) to other stimuli in evoking the characteristic "looking-over-the-shoulder" behaviour of ewes in oestrus and was not affected by masking the ram's odour with an odoriferous substance. Visual stimuli by a dummy ram evoked the response in 896 of the ewes but acted synergistically with the auditory stimuli, when accompanied by a prerecorded ram's sexual vocalisation to increase the percentage response to 26. Olfactory stimuli with a linen, which was liberally rubbed on an intact ram, did not evoke the response.
It is concluded that oestrus detection in ewes may be possible using artificial stimuli in intensive sheep husbandry.
La réaction à différent stimuli a été étudiée au cours de cinq cycles successifs. Le reniflement du périnée s'est avéré significativement (P<0,05) plus eficace que les autres stimuli a déclencher /e comportement caractéristique de la brebis en chaleur, laquelle "jette des regards par-dessus l'épaule", Cette faculté fut conservée lorsqu'on a fait disparaître l'odeur du bélier avec des substances odoriférantes. L'utilisation d'un faux bélier déclenchait des réponses positives dans 8% des cas, chiffre qui montait à 26% lorsque celle-ci était synchronisée avec un stimulus auditif, en ['occurrence l'enregistrement des appels d'un mâle à l'acte sexuel. En revanche, l'utilisation, comme stimulus olfactif, d'un morceau de tissu qu'on avait précédemment passé sur le corps d'un bélier entier laissait les brebis d'une superbe indifférence.
Ces résultats montrent qu'il est possible, notamment en élevage ovin intensif, de détecter les chaleurs des brebis par des stimuli artificiels.
Oestrus behaviour is the most definite sign of oestrus in female animals and it has been reported for various species. The ewe does not exhibit oestrus behaviour in the absence of a ram (Terrill, 1975). It is therefore necessary to devise artificial teasers for oestrus detection in ewes under commercial or large flocks for the application of modern breeding techniques such as oestrus synchronisation and artificial insemination. This will involve identification of the stimuli involved in the "looking over the shoulder" which is characteristic of ewes in oestrus (Hafez et al 1969).
The objective of this study was to determine the characteristic behaviour of West African dwarf ewes and to identify the areas of the body of the ewe that evoke sexual arousal leading to the shoulder-looking behaviour of ewes in oestrus.
The experimental animals consisted of five normocyclic pluriparous WAD ewes aged 4-5 years and weighing 25-35 kg. Oestrus was synchronised with prostaglandin F2-alpha (UpJohn Company, Kalamazoo, USA) as described previously in the WAD goat (Akusu and Egbunike, 1984). Following the second PGF2-injection ewes were exposed to various stimuli as follows:
1. A dummy ram prepared with the skin of a 3-year old ram after slaughter (Stimulus A: Visual)2. A dummy ram as in (1) but accompanied with a pre-recorded ram's characteristic sexual vocalisation (Stimulus B: Visual/Auditory)
3. An intact apronned ram (Stimulus C: Tactile)
4. An intact apronned ram liberally bathed with an odoriferous substance (Perfekthion Bayer A.G., Germany) to mask the ram's odour (Stimulus D: Olfactory)
5. A linen which has previously been rubbed generously on an intact ram (Stimulus E: Olfactory).
The response of ewes to stimulus C was scored as described by Denenberg and Banks (1969) and Clayton et al (1981). The areas of the body investigated were the hindquarters, vulva, tail, abdomen and ears. A score of 1 was assigned to positive response (looking over the shoulder) while negative response was scored 0. For a comparison, stimuli responses were expressed as percentage of the observations.
Table 1. Comparative scores for the different erogenic areas of the ewe (x ± Sem).
|
Body area |
x ± Sem |
|
Hindquarters |
2.8 ± 0. 09a |
|
Vulva |
2.6 ± 0.13a |
|
Tail |
2.4 ± 0.16b |
|
Abdomen |
1.1 ± 0.17C |
|
Ears |
1.1 ± 0.17' |
Means with different superscripts are significantly (P < 0.05) different.
The relative positive response of the ewe to areas of the body investigated with stimulus C is summarised in Table 1. Responses to the ram's tactile stimulation of the hindquarters and the vulva were significantly superior to the stimulation of the tail (P<0.05) which was in itself superior (P<0.05) to stimulation of the abdomen and the ears.
The response of ewes to stimulus A was positive in 8% of observations. When accompanied with the ram's sexual vocalisation (Stimulus B), 26% of the ewes responded positively to the dummy. All ewes in oestrus elicited the response in the presence of an intact ram (Stimulus C) and this was not affected by masking the ram's odour with an odorifirous substance (Stimulus D). On the other hand, ewes in oestrus did not respond to the linen previously rubbed on an intact ram (Stimulus E).
The main sign of oestrus in the ewe observed in this study was "looking over the shoulder". This is in agreement with the report of Tomkins and Bryant (1974).
The hindquarters and the perineal region of the ewe may possess abundant tactile receptors in comparison to the abdomen and the ears. It is known that oestradiol-17B is responsible for the psychic manifestation of behavioural oestrus in domestic animals (Scaramuzzi, 1975; McDonald, 1977). However, Glengross et al (1981) observed that the mechanism of uptake of oestradiol by the hypothalamus could affect oestrus behaviour. It is therefore probable that the ewe produces less oestradiol-17B receptors during oestrus than other domestic animals such as the goat (Akusu, 1987) that displays behavioural oestrus characteristics in the absence of the buck.
Visual stimuli alone appeared to have a poor effect on the ewe in oestrus. However, response was improved by auditory stimuli and therefore both stimuli may be acting synergestically. The non-response to olfactory stimulus could not be explained. Pheromones of rams are located in the wool (Knight and Lynch, 1980). Hence, the non-response to the ram's odour may be due either to inadequate pheromones on the linen or the non-involvement of pheromones in the "looking-over-the-shoulder" response of ewes in oestrus. The latter suggestion is buttressed by the fact that response was unaffected by masking the ram's odour with an odoriferous substance. However, Baldwin and Meese (1977) and Alexander and Stevens (1982) reported that the scent of olfaction is very strong in the ewe. Therefore, it is possible that the ewe could discriminate the ram's pheromones from a variety of odoriferous substance.
This study has demonstrated that tactile, visual and auditory stimuli are important components in the characteristic "looking over the shoulder" behaviour of ewes in oestrus. It may be practicable to devise artificial oestrus detection stimuli consisting of blowing air around the perineum which simulate the ram's "nosing" around this area, a dummy ram and pre-recorded ram's sexual vocalisation.
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