Plasma progesterone concentrations, ovarian and endocrinological responses and sperm transport in ewes with synchronized oestrus

Abstract

Two experiments involving 24 and 54 Australian Merino ewes were conducted in which the establishment of a cervical population of spermatozoa and several endocrinological events were studied after several regimens for the synchronization of oestrus. Intravaginal sponges impregnated with 500 mg (Exp. 1) or 200, 400 or 600 mg (Exp. 2) progesterone resulted in the maintenance of plasma progesterone concentrations of 1.5-4.9 ng/ml over a 12-day insertion period compared with 1.9-6.9 ng/ml during dioestrus in control ewes. In Exp. 1 basal concentrations of less than or equal to 0.25 ng/ml plasma were attained by 4 h after sponge withdrawal and this decline was much more rapid than in normal luteolysis. This was associated with fewer spermatozoa recovered from the cervix 2 h after insemination, and PMSG had no significant effect. In Exp. 2 injection of a supplementary dose of progesterone at sponge withdrawal resulted in a rapid increase in plasma progesterone concentrations followed by an equally rapid decrease and an attenuation of the rise in plasma oestradiol-17 beta, the LH surge, and the onset of oestrus. The numbers of spermatozoa recovered 4 h after insemination were not increased, and PMSG had no significant effect. Two factors were significant, namely the dose of progesterone in the sponge (600 mg greater than 400 or 200 mg, P less than 0.05) and stage of oestrus when inseminated (mid- or late oestrus greater than early). The data demonstrated that an adequate dose of progesterone/progestagen incorporated into intravaginal sponges and accurate timing of insemination relative to the LH surge are the most important factors involved in penetration of the cervix by spermatozoa.

Respostas endócrinas e ovarianas associadas com o folículo dominante da primeira onda folicular em ovelhas sincronizadas com CIDR ou PGF2alfa

“…Portanto, o eCG pode provocar hiperestimulação folicular, resultando em maior tamanho do corpo lúteo, evidenciando sua atividade luteotrófica (Evans & Robinson, 1980). Segundo Pearce & Robinson (1985), em um experimento com ovelhas Merino, houve aumento linear na taxa ovulatória quando aumentaram a dose de eCG de 300 para 600 UI. De forma experimental semelhante, Oyedipe et al (1989) observaram elevação também nas concentrações plasmáticas de P 4 em ovelhas Yankasa estabelecendo, possivelmente, a existência de uma relação direta entre a dosagem P 4 (ng/mL)…”

Seasonal Variation in the Timing of Estrous Behavior LH Surge and Ovulation Following the Treatment with Progesterone and PMSG in Suffolk Ewes.

“…It has been reported that ewes treated with progestagen intra-vaginal sponge and PMSG usually start to show estrus around 21-28 h after sponge withdrawal [8,9,12]. The time of estrous onset appears to be affected by the dose of progestagen and the timing of PMSG injection.…”

Cryopreservation of Sheep Produced Embryos – Current and Future Perspectives

“…Although allowing good estrus synchronization, the fertility is usually lower compared to natural estrus [55]. Several reasons have been raised to explain this lower fertility, including (a) the asynchrony between the beginning of estrus and the ovulation time [56], (b) a negative influence on the transport of spermatozoa [57], (c) the reduced expression of estradiol and progesterone receptors in oviduct and endometrial cells, (d) a reduced progesterone secretion by the corpus luteum (CL) [58], (e) an inadequate process of maturation and acquisition of competence by the oocyte [59,60], and (f) the development and lack of ovulation of large persistent follicles [53,[59][60][61] due to altered levels of progesterone after the first 6 days of treatment [62].…”