Abstract
The financial impact of early embryonic loss in Australia may be as high as $137 million AUD/year. Embryos may be lost due to environmental conditions, or maternal factors such as nutrition or progesterone (P4) profiles. However, studies on the supplementation of P4 during early pregnancy have returned contradictory results, partly as a reliable method of detecting embryos in the early stages of gestation (<day 20) has yet be established. As such, Merino ewes (n = 62) were either not supplemented (control) or were given exogenous P4 at the time of insemination (day 0) or 3 days later (day 3). Transrectal ultrasound (TRUS) was performed on day 10, 12, 14, 17, 19 and 29 following laparoscopic artificial insemination. Transcutaneous ultrasound (TCUS) was performed on day 54 to confirm pregnancy and peripheral blood was collected for hormone analysis on day 19 to compare the accuracy of all three pregnancy diagnosis methods. Data were then analysed in developmental periods. The percentage of ewes detected as pregnant by TRUS during pre-, peri- and post implantation was 66% (41/62; day 12 and 14), 61% (38/62; day 17 and 19) and 58% (36/62; day 29), respectively. TCUS during established gestation recorded a pregnancy rate of 60% (37/62). The sensitivity of TRUS to correctly diagnose ewes as pregnant during pre-, peri- and post implantation was 68% (25/37), 89% (33/37) and 100% (36/36), respectively, while the sensitivity to correctly identify multiples was 49% (16/33), 60% (21/35) and 97% (34/35), respectively (P<0.05). The majority of embryonic loss occurred between pre- and peri- implantation (0.9±0.15 per ewe; P<0.001). No further loss was recorded after this point. Ewes that were given P4 at day 0 had significantly higher embryonic loss (77%) compared to the control (52%) and day 3-ewes (56%; P<0.05). These results show TRUS is a viable tool for investigating early embryonic loss and that the variability noted in previous P4 supplementation studies may be due to variation in time and length of treatment.
Highlights
Embryonic loss in sheep is a major source of reproductive wastage, accounting for significant economic losses to the industry
These losses were unable to be mitigated by the presence of additional exogenous progesterone (P4), which even increased embryonic loss when ewes were supplemented with P4 at artificial insemination or oestrus
The current study has shown that ovine embryos can be detected, with relatively high accuracy, as early as pre-implantation when using a 10MHz transducer for transrectal ultrasound
Summary
Embryonic loss in sheep is a major source of reproductive wastage, accounting for significant economic losses to the industry. The current technique for exploring early embryonic loss utilises ovulation rate, which is often used as a proxy for conceptus number This value is compared to traditional realtime ultrasound pregnancy diagnosis or lambing percentage [4]. This is a logical substitution for embryonic loss, due to the fact that sheep are generally believed to hold a high fertilisation rate and scarcely undergo late gestational losses [5]. This method does not represent accurate embryo loss data, especially considering that literature predicts the majority of loss to occur in sheep prior to implantation, which occurs at approximately day 14–16 [6, 7]. If embryos could be detected during early pregnancy (before or shortly after implantation), a more thorough and unambiguous means of studying early embryonic loss could be established but methods of prevention could be better evaluated
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