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В течение 2 лет многоплодные овуляции определялись на основании исследования яичников после убоя у 1163 кобыл разного типа, в возрасте с 3 до 20 лет. Среди 585 кобыл, у которых отметилось присутствие желтых тел, у 17% (100 кобыл) выступили многоплодные овуляции. 64% многоплодных овуляции выступили на обоих яичниках, 20% — на левом, и 16% — на правом яичнике. Не доказано зависимости между очередными месяцами года и частотой многоплодных овуляций.
The ovaries from 173 mares were collected at the time of slaughter from September 1991 to September 1992 and follicles (5—20 mm in diameter) were isolated and dissected to obtain oocytes for culture. 669 oocytes were subjected to one of four different culture treatments: Gr. 1-medium with oocytes, Gr. 2-medium plus 3 X 10⁶/ml granulosa cells plus oocytes, Gr. 3-medium plus 0.3 X 10⁶/ml theca interna cells plus oocytes, Gr. 4-medium plus granulosa and theca interna plus oocytes. The oocytes were cultured for 24, 30, 36, 42 and 48 hrs. After culture cumulus cells the expansion and stage of nuclear maturition was determined. The majority of oocytes reached full nuclear maturition after 30 hrs. The best results — full dispersion of cumulus cells in 96% and 97% of the oocytes and metaphase II in 75% and 77% of the oocytes — were obtained after 36 and 42 hrs’culture of oocytes with theca interna cells, respectively.
Reducing the interval between generations would significantly advance the efficiency of genetic selection, which is mainly important in species characterized by late puberty, long pregnancy and single offspring. Oocytes for in vitro embryo production can be obtained from calves, lambs, goats, foals and gilts well before puberty, either after slaughter or by less invasive methods, such as laparoscopy and transvaginal aspiration under ultrasonograph guidance. The latter two can be applied to females without greatly affecting their health and are therefore the preferred methods when animals are to be retained for breeding purposes. However, the use of transvaginal aspiration is limited to larger animals, such as 6-month old calves. The quality of oocytes from prepubertal females seems to be lower than that of adults. Although hormone stimulation of the animals and the use of enriched media improve embryonic competence of prepubertal oocytes following in vitro maturation and fertilisation, the efficiency of embryo production remains low. The is probably due to the immaturity of their cytoplasm.
Prolactin (PRL) is known for the diverse role it plays in the preparation, maintenance and secretor activity of the mammary glands during lactation. It plays a role in processes such reproduction, fat metabolism, hair shedding and immune response. In humans, prolactin is able to inhibit GnRH secretion and has an antagonistic activity on ovarian function in comparison to GnRH. The role of prolactin during the estrous cycle has not been established, although there are few reports on increased follicular growth in anestrous mares, which have been administered prolactin. In mares, prolactin concentration is related to the length of daylight photoperiod periods, and its highest concentrations coincide with periods of maximum reproductive activity.
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