Abstract
Résumé
Introduction
Materials and methods
Results
Discussion
Conclusion
References
M.O. Akusu, E. Nduka and B.A. Soyebo
University of Ibadan
Ibadan, Nigeria
Oestrus was synchronised with PGF2-alpha in four pluriparous West African Dwarf (WAD) goats and blood collected through jugular venupuncture. The length of the oestrous cycle and oestrus duration were observed in three successive cycles while peripheral plasma progesterone and oestradiol-17B levels were determined by the radioimmunoassay technique. The mean oestrous cycle lengths and oestrus duration were 19.4 ± 1.7 d and 33.3 ± 6.6 h, respectively. Progesterone levels were very low during the first four days of the cycle (day 1 = day of oestrous) with the lowest level of 0.3 ± 0.02 ng/ml being recorded on day 2 of the cycle. There was a steady rise in the levels during the cycle until day 15 when the highest level of 2.2 ± 0.05 ng/ml was recorded which was followed by a sharp decline on day 20 (P <0.05). The profile of oestradiol-17B was erratic during the cycle. Mean maximum and minimum concentrations were recorded on day 1 (152.6 ± 31.6 ng/ml) and day 2 (58.8 ± 22.6 ng/ml), respectively. These results showed that while progesterone and oestradiol profiles in the WAD goat followed the luteal and follicular phases of the oestrous cycle, progesterone profile is more reliable in assessing the phases of the oestrous cycle.
L'oestrus de quatre chèvres naines d'Afrique occidentale multipares a été synchronisé avec du PGF2-alpha; des échantillons de sang ont été collectés à travers la veine jugulaire. Les durées du cycle oestral et de l'oestrus de trois cycles successifs ont été mesurées, et les taux de progestérone et d'oestradiol-17B déterminés par radio-immunologie. La durée moyenne du cycle oestral était de 19,4 ± 1,7 jours et celle de l'oestrus de 33,3 ± 6,6 h. Très faible au cours des quatre premiers jours du cycle, la teneur en progestérone du sang périphérique atteignait son niveau minimum au deuxième jour du cycle, avec une valeur de 0,3 ± 0,02 ng/ml. Elle augmentait ensuite régulièrement jusqu'au 15e jour du cycle où elle atteignait le pic de 2,2 ± 0,05 ng/ml, avant d'enregistrer une chute brutale au 20e jour (P<0,05). Le taux d'oestradiol-17B a varié de manière erratique; les teneurs maximum (152,6 ± 31,6 ng/ml) et minimum (58,8 ± 22,6 ng/ml) ayant été enregistrées respectivement au premier et au deuxième jours du cycle oestral. Ces résultats montrent que, bien que les niveaux d'oestradiol et de progestérone suivent les phases lutéique et folliculaire, la progestérone est plus indiquée pour la détermination de la phase du cycle oestral à laquelle se trouve la chèvre naine d'Afrique de l'Ouest.
Progesterone and oestradiol-17B are ovarian hormones that have several practical biological applications in the management of reproduction in animals They are involved in oestrus manifestations, the ovulatory process, cyclic regression of the corpus luteum, establishment of pregnancy and parturition. Progesterone levers have also been used in the determination of the onset of puberty in cattle (Diaz et al, 1986), pigs (Shille et al, 1979) and sheep (Oyedipe et al, 1986) and verification of the accuracy of oestrus detection (Sawyer et al, 1986). A knowledge of the levels of these hormones can be of benefit for diagnostic and therapeutic purposes in cases of endocrine dysfunction involving normal sexual activity of the female.
The levels of these hormones during the oestrous cycle and pregnancy have been determined in several species of domestic animals, especially in sheep and cattle (Scaramuzzi, 1976; Adeyemo and Health, 1980; Voh et al, 1987). Compared to the other species, fewer reports are available for the goat (Mori and Kano, 1984; Akusu et al, 1989).
The objective of this study was to generate basal data on the levels and profiles of progesterone and oestradiol-17B during oestrous cycle of the West African Dwarf goat. This breed of goat is the most numerous of the ruminant species in the humid rainforest zone of southern Nigeria (FAO, 1966; Carew, 1982) and therefore represents the quickest means of increasing meat production for the populace through oestrous synchronisation and artificial insemination.
Four pluriparous WAD goats, aged 3-4 years and weighing between 15-20 kg were used for this study. They were managed intensively on concrete-floored pens in the small ruminant unit of the Department of Veterinary Surgery and Reproduction, University of Ibadan. Animals were fed on a corn-based ration (0.5 kg/d). Clean water and Giant Stargrass were constantly available.
Oestrus was synchronised with 10 mg PGF2 a as described previously (Akusu and Egbunike, 1984; Akusu et al, 1989). Animals were teased for oestrus five times daily at intervals of 4 hours between 08.00 and 24.00 h with an apronned sexually mature buck.
Animals were bled through jugular venupuncture and plasma stored at-20°C until assayed for progesterone and oestradiol-17B by radioimmunoassay techniques (Dada et al, 1984; Akusu et al, 1989). Hormone concentration was calculated from linearised logit-log plots of standard curves. Inter- and intra-assay variations for progesterone were 11.5% and 10.9%, the corresponding values for oestradiol-17B were 10.3% and 11.5%, respectively.
Blood was collected during the first five days of the oestrous cycle (day 1 = day of oestrus) and then on days 10, 15 and 20. The study was carried out during three successive oestrus cycles.
Oestrus was synchronised in all goats treated with PGF2-a The mean oestrus duration was 33.3 ± 6.6 h while oestrous cycle occurred at 19.7 ± 1.7 d.
Peripheral plasma progesterone and oestradiol-17B profiles are summarised in Figure 1. The levels of progesterone were generally lower than 1 ng/ml during oestrus and metoestrus (d 1-d 4). The lowest level of 0.3 ± 0.02 ng/ml was determined on d 2 of the cycle. -This was followed by a gradual rise in d 3 and d 4 (0.5 ± 0.03 ng/ml and 0.87 ± 0.02 ng/ml, respectively). D4 value was significantly higher than d 2 (P<0.05). There was a sharp rise on d 5 and remained stable up to d 10 and a further rise in progesterone level to a peak value of 2.2 ± 0.05 on d 15 followed by a sharp decline (P<0.05) by d 20. There were differences in the levels between the three cycles but the profiles were not affected (Figure 2).
Figure 1. Peripheral plasma levels of progesterone and oestradiol- 17ß of West African Dwarf goats during the oestrous cycle.
Figure 2. Peripheral plasma progesterone profiles during three successive oestrous cycles in WAD goats (X ± Sem).
Peripheral plasma levels of oestradiol-17B were highest on d 1 (152.6 ± 31.6). There was a rapid decline (P<0.05) on d 2. Thereafter, there were fluctuations in the levels but a gradual rise was observed Up to d 20 (131.7 ± 44.3 ng/ml). The profile of oestradiol was similar irrespective of the cycle (Figure 3).
Figure 3. Peripheral plasma oestradiol 17B profiles in WAD goats during three successive oestrous cycles.
The general profile of progesterone and oestradiol-17B of the West African Dwarf goat was similar to reports in various species of domestic animals (Shearer et al, 1972; Sarda et al, 1973; Perera et al, 1978; Arora and Pandey, 1982; Oyedipe et al, 1986; Danell, 1987). The mean level of progesterone of the WAD goat was lower than the values reported for other breeds of goats (Heap and Linzell, 1966; Thornburn and Schneider, 1972). This may be a breed characteristic which has been reported in the ewe (Bindon et al, 1979).
The individual variations in the peak values of progesterone and oestradiol-17B in the goats may be due to variations in individual traits that may be correlated with expression of overt heat signs and may serve as an index of selection (Perera, 1979). However, it was observed that all does had a common pattern with relatively levels Of progesterone during the luteal phase, a decline between the 15th and 20th d of the cycle and values approximating zero at and around oestrus. Similarly, the peak values Of oestradiol-17B generally corresponded with the follicular and luteal phases of the oestrous cycle. It showed a fluctuating level of between 58 and 92 pg/ml until the day preceding the onset of behavioural oestrus when an increase was demonstrated. The peak value was for a day and there was no subsequent rise. This was consistent with the report of Shearer et al (1972) and therefore suggested that the psychic manifestation of behavioural oestrus in the goat is the result of oestradiol acting on the central nervous system (McDonald, 1977; Hansel and Convey, 1983).
These results showed that while progesterone and oestradiol profiles in the WAD goat followed the luteal and follicular phases Of the oestrous cycle, progesterone profile is more reliable in assessing the phases of the oestrous cycle.
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