Ultrasonographic Characteristics of Ovulatory Follicles and Associated Endocrine Changes in Cyclic Ewes Treated with Medroxyprogesterone Acetate (MAP)‐releasing Intravaginal Sponges and Equine Chorionic Gonadotropin (eCG)

Abstract

The aim of this study was to assess the ultrasonographic characteristics of ovulatory follicles in cyclic Western White Face ewes (December) that had received intravaginal sponges containing medroxyprogesterone acetate (MAP; 60 mg) for 12 days, with or without an injection of 500 IU of equine chorionic gonadotropin (eCG) at sponge removal. We hypothesized that quantitative echotextural attributes of the follicles in ewes treated only with MAP would differ from those in MAP/eCG-treated ewes, reflecting the increased antral follicular growth and secretory function under eCG influence. Digital images of ovulatory follicles obtained at 0 and 24 h after MAP sponge removal and at 24 h before ovulation in the eCG-treated (five ewes, 13 follicles) and control (six ewes, 9 follicles) animals, were subjected to computerized analyses. The mean diameter of ovulatory follicles increased (p < 0.001) 24 h after eCG treatment. The mean pixel intensity and heterogeneity of the follicular antrum (p < 0.001), as well as mean pixel intensity of the follicular wall and perifollicular ovarian stroma (p < 0.05), were greater in eCG-treated animals compared with control ewes 24 h after sponge removal and at 24 h before ovulation. Mean serum concentrations of oestradiol-17beta tended to increase (p = 0.06) 24 h after eCG treatment and the eCG-treated ewes exceeded (p < 0.05) control animals in progesterone concentrations from days 9-15 after ovulation. Our results support the hypothesis that large antral follicles in eCG-treated ewes exhibit distinctive echotextural characteristics. Follicular image attributes in eCG-treated ewes appear to be indicative of the changes in follicular morphology and secretory activity caused by the administration of the exogenous gonadotropin, which has both FSH- and LH-like activities.

Evaluation of the ultrasound image attributes of developing ovarian follicles in the four follicular waves of the interovulatory interval in ewes

“…No trend in NPV was seen for Waves 1 and 2. Echotexture of the follicular wall is dependent on the thickness of the wall, degree of vascularization in the theca layer, vascular blood flow, and the amount of lipid in steroid-producing granulosa and theca cells [16,17,19,25]. Investigations in cattle revealed that hypertrophy and proliferation of granulosa and theca cells, as well as development of the dense connective tissue of vascular walls, were reflected as brighter images with increased NPV [16,17,26].…”

“…It has been suggested that echotextural characteristics of the follicular wall are indicative of the steroidogenic activity of the theca and granulosa cells in cattle [16]. In ewes given equine chorionic gonadotropin (eCG), high NPV for the follicular wall was associated with higher serum progesterone concentrations after ovulation and CL (corpus luteum) formation [25]. Based on the current echotextural analysis of the follicular wall in cyclic ewes, we speculated that follicles emerging after the middle of the interovulatory interval may be more adapted for ovulation and CL formation.…”

Efeito do tempo da aplicação de prostaglandina na resposta folicular em ovelhas durante o ciclo estral

“…Na espécie ovina, o conhecimento dos mecanismos que regulam a dinâmica folicular tem recebido especial atenção, principalmente por duas razões: o interesse do melhoramento da fertilidade, sincronização do estro com maior precisão e aumento da resposta superovulatória mediante administração de gonadotrofinas exógenas; e o fato de a fêmea ovina ser um excelente modelo experimental para o estudo do recrutamento, seleção e dominância folicular, apresentando diversas raças e variedades genéticas com variadas taxas de ovulação e altos índices de prolificidade (Fabre et al, 2006;Liu et al, 2007).…”

“…Os métodos mais utilizados para a sincronização do estro e estimulação do crescimento folicular em pequenos ruminantes envolvem prostaglandinas (Weems et al, 2006;Uribe-Velásquez et al, 2008a), progesterona e/ou progestágenos e a administração intramuscular de eCG (López-Sebastian et al, 2007;Holtz et al, 2008;UribeVelásquez et al, 2008b).…”

Use of B-mode Ultrasound and Grey-Scale Analysis to Study Uterine Echogenicity in the Pig

“…Alternatively, grey-scale analysis (GSA) is used, which is based on computer-supported pixel quantification and is thus a more objective procedure. In large animal species, GSA has mostly been used to define echogenicity patterns of reproductive tissues such as of testes and accessory glands in growing bulls and rams [1,2], as well as of ovarian structures in mares [3], cows and heifers [4,5], and ewes [6,7]. Also, GSA has been employed for studying endometrial echogenicity in pregnant vs. non-pregnant cows [8][9][10] and the European roe deer [11], and has been advocated as an appropriate procedure for the delineation of uterine diseases in mares [12].…”