The distribution of healthy and atretic follicles on the ovarian surface of improved Valachian ewes 17, 24, and 32 days postpartum is reported in this study. The number of healthy follicles was higher on day 24 postpartum and their mean diameter tended to increase to day 32 ( ) with the greatest diameter of 5？mm. 78–81% of atretic follicles ≥3？mm in diameter was observed where apoptosis began in the follicular cells situated at the follicular cavity. The early atretic follicles are characterized by the presence of mitotic pictures. In one ewe 24 days postpartum, small regressive follicular cysts were observed. Contracting atresia is characterized by thickening of the theca interna even to 190？μm. Progesterone and oestradiol-17 concentrations were maintained at relatively low levels, but with no significant difference between the days postpartum. 1. Introduction Folliculogenesis progresses in the postpartum period of ewes similarly as in cows [1–3]. In our latitude (48° 40′ 0′′N), the first ovulation after parturition is determined by many factors and may occur 60–70 days at the earliest after lambing, but generally appears in the autumn mating season. Only a few hundred follicles mature throughout the life of an ewe and the others undergo atresia, which occurs in 99.9% of mammals [4–7]. Follicular atresia in themajority of mammals is primarily induced by programmed cell death or apoptosis of granulose and theca cells. Apoptosis is characterized by the fragmentation of internucleosomal DNA, reduction of cell mass, bubbling of the cytoplasmic membrane, and formation of apoptotic bodies [8]. Apoptosis of the granulose cells relates to imbalance between oestradiol and progesterone (E2↓, P4 ↑) in the follicular fluid [9–11], which stimulates the atresia formation [7, 12]. The concentration of IGF-I is the crucial factor deciding whether the follicle matures or undergoes atresia [9, 10, 13]. There are three basic types of atresia described in cattle—early, definite, and late [14–16]. Marion et al. [14] indicated some thickening of granulose and theca layers in various types of atresia in cattle, but there are no reports of this in ewes. The aim of this study was to observe the distribution of healthy and atretic follicles on the ovaries of ewes in the spring puerperal period, and to establish whether these parameters relate to thickening of the granulose and theca layers of healthy follicles and specific types of atresia, and with hormonal concentrations in the blood (progesterone, oestradiol- ). 2. Materials and Methods 2.1. Animals The experiments were
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