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Premature regression of corpora lutea (PRCL) may adversely affect the outcome of hormonal ovarian superstimulation in small ruminants, and the total dose of exogenous gonadotropins used may be one of the causes of this condition. There were two major objectives of the present study: (1) to evaluate the effects of different superovulatory doses of porcine follicle-stimulating hormone (pFSH) on the biometry, blood perfusion (Doppler), and echotextural characteristics of luteal structures; and, (2) to determine the usefulness of biometric, vascular, and echotextural luteal variables, as well as measurements of circulating progesterone (P4) concentrations for early detection of PRCL in superovulated Santa Inês ewes. Twenty-seven Santa Inês ewes received an intravaginal P4-releasing device (CIDR) from Days 0 to 8 (Day 0 = random day of the anovulatory period). An IM injection of d-cloprostenol (37.5 μg) was given at the time of the CIDR insertion and withdrawal. On Day 6, all the ewes received 300 IU of eCG IM and were divided into three treatment groups (each n = 9): G100 (100 mg); G133 (133 mg); and G200 (200 mg of pFSH) administered IM every 12 h in eight injections. Transrectal ovarian ultrasonography and jugular blood sampling for serum P4 measurements were performed on Days 11 to 15. On the day of embryo recovery (Day 15), all the ewes underwent diagnostic videolaparoscopy and were classified, based on their luteal characteristics, into three response groups: nCL (ewes with normal CL only); rCL (ewes with regressing CL only); and ewes with both nCL and rCL following the superovulatory regimen. Our present results indicate that the total pFSH doses of 100 mg and 200 mg result in similar ovulatory responses and luteal function/biometrics, although the percentage of donor ewes with nCL was greater (p < 0.05) for G100 compared with the G200 animals. An application of 133 mg of pFSH was associated with diminished luteogenesis. Lastly, circulating P4 concentrations, ultrasonographic estimates of total luteal area, and CL pixel heterogeneity (standard deviation of numerical pixel values) are promising markers of luteal inadequacy in superovulated ewes.

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The present study was designed to study the follicular population dynamics followed or not by treatment with different doses of the GnRH antagonist in sheep. A total of 18 ewes were submitted to short-term oestrus synchronization protocol (Oliveira et al. 2009 Proc. Braz. Congr. Anim. Reprod.). The animals were 2 or 3 years old, multiparous, and had a body score of 3 to 3.5. On Day 7 after ovulation of synchronized oestrus, females were randomly divided into groups (n=6/group) according to the dose of the gonadotrophin-releasing hormone (GnRH) antagonist (Firmagon®, Ferring Pharmaceuticals) subcutaneously administered: G-control: placebo treatment (administration of saline solution); G-lower dose: 215 µg/kg; and G-higher dose: 235 µg/kg of bodyweight. B-mode ultrasound exams of the ovaries were conducted daily from 1 day before treatment with GnRH antagonist until the females showed oestrous behaviour. Ultrasound equipment (MyLab Vet®, Esaote) was used coupled to a transrectal linear transducer with a frequency of 6 and 8MHz to assess the ovarian population. Data were compared between groups, evaluation days, and their interaction by ANOVA with post hoc using Tukey’s test (P&lt;0.05). There was no interaction (P&gt;0.05) between the studied effects (treatments and evaluation days). The number of small follicles (2–3.49mm) was higher (P=0.0002) in the G-lower dose (5.4±0.4) compared with the G-control (4.1±0.3) and G-higher dose (3.5±0.2). The number of large follicles (≥4.5mm) was lower (P=0.01) in the G-higher dose (0.2±0.0) compared with the G-control (0.5±0.1) and G-lower dose (0.4±0.1). The number of medium follicles (3.5– 4.49mm) and the average diameter of the follicles in the 3 categories of diameter did not differ (P&gt;0.05) between groups. The number of medium follicles differed (P=0.0131) between Days 8 and 15 after synchronized oestrus ovulation. The number of large follicles on Day 6 differed (P=0.0002) of Days 8, 9, 10, 11, 12, 16, and 17. The average diameter of medium follicles differed (P=0.0095) between Days 8 and 10. The number of small follicles and the average diameter of small and large follicles did not differ (P&gt;0.05) between days. In conclusion, the administration of the GnRH antagonist at a higher dose in sheep suppressed the development of large tertiary or antral follicles, whereas at a lower dose, it led to an increase in the population of small follicles.