Bìol. Tvarin, 2016, vol. 18, no. 1, pp. 77–86

OVARY MORPHOLOGY IN EWES IN DIFFERENT MONTHS OF YEAR

I. Lobachova

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The Ivanov’s Institute of Animal Breeding in Steppe Regions «Ascania-Nova»,
1 Chervonoarmiiska str., Ascania-Nova, Chaplynskyi district., Kherson region, 75230, Ukraine

The morphology of ovary of domestic sheep (Ovis aries) of Ascanian Merino breed in different month of year was studied in 2 experiments. In the first (1999–2013) the ovaries in 145 ewes were post-mortally or laparoscopically examined to define the borders of estrous season. Diameter of the greatest follicle, presence of corpus luteum and proliferation in surface layer were estimated. Data were grouped according to calendar month of inspection. In the second experiment the tracing of the change of ovaries morphology in transient from anoestrus to oestrous period was carried. For this purpose 10 ewes of the same flock since July 6thto revealing of a typical corpus luteum were subjected to weekly laparoscopic examination.

During the period from September to March quantity of animals which had corpus luteum in ovaries varied within 67–100 %. In April the corpus luteum was not observed, in May, July and July it was revealed in 2.6, 11.8 and 11.1 % of animals. Intensification of proliferation in surface layer was noted in April–May, August and October. The noticeable increase of diameter of the greatest follicle occurred in April and September. The seasonal difference is noted between morphology of cells of germinal epithelium — in animals in anestrus the cells were flat, in July they got cubic form, and in August in the majority of animals they became columnar and showed the presence of cilia. During the transition to estrous season the characteristic changes were observed in surface layer. In particular, from the middle of June the ovary surface in majority of animals became dense and whitish and remained such mainly till the end of July–beginning of August. From the middle of July–beginning of August on a surface the small (less 0.5 mm) white specks were appeared. To the middle of August the amount of such formations decreased but among them the part of spots with enlarged (up to 2 mm) diameter increased and the small spots in the form of bagel appeared. Occurrence of specks in the majority of animals preceded intensification of proliferation in ovary surface layer. In the end of August specks disappeared.

By results of experiences it was concluded that anestrous period in Ascanian Merino sheep corresponds to April–July. Also it is assumed that formation and the subsequent transformation of white specks in the end of anestrous period represents one of components of sequence of restoration of cyclicity of sexual activity in sheep and is connected with luteinization of preantral and small antral follicles.

Keywords: SHEEP, SEASONALITY, OVARY, MORPHOLOGY, CORPUS LUTEAL, FOLLICLE

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