**4. Early embryonic death (EED)**

nancy detection. The embryo initially appears as a short line (Day 20-22), later becomes Cshaped (Day 22-30), and finally, by Day 30-32 of gestation assumes an L- shape (Fig 2). Although the embryo can first be detected between Days 19 and 24 of gestation [Curran et al., 1986], it is most practical to scan females which are expected to have embryos that are >26 days of age. The bovine foetus can be visualized beginning at day 20 post breeding and continuing throughout gestation, however, because of its size in relation to the image field of view, the foetus cannot be fully imaged after 90 days using high frequency transducers.

146 Success in Artificial Insemination - Quality of Semen and Diagnostics Employed

**Figure 2.** Bovine embryo scanned on Day 26 of pregnancy using B-mode real time ultrasound with 5MHz linear array

Accuracy of diagnoses improves, however, by Day 18 (85%), Day 20 (100%) and Day 22 (100%) of pregnancy (Kastelic et al., 1989). Presence and vitality of the embryo can be con‐ firmed by the detection of a heartbeat as early as 19 to 24 days of gestation. Early pregnancy detection has a greater economic significance particularly for the dairy industry. When an accuracy of over 99% is achieved, it enables to rapidly identify fertility problems. The rate of detection of early embryonic loss is thus also higher with 10 to 16% of cows diagnosed preg‐ nant at 28 days post AI experience early embryonic loss by 56 days post AI. Cows diagnosed pregnant at 28 days post AI using ultrasound should, therefore, be scheduled for a subse‐ quent examination around 60 days post AI, when the rate of embryonic loss per day de‐

In situations where the exact dates of AI are known, ultrasonography is simply used as a confirmation of pregnancy or to validate that detection of a viable embryo within the first two weeks of pregnancy. In contrast, another study showed diagnosis of pregnancy in hei‐ fers on day 10 through day 16 of gestation resulted in a positive diagnosis for pregnant or non-pregnant cows in less than 50%. On from days 18 - 22 of gestation, accuracy of pregnan‐ cy diagnosis improved from 85% to 100% [Lamb and Fricke, 2005]. Although an embryonic vesicle is detectable by ultrasound as early as 9 days of gestation, accuracy of detection ap‐ proaches 100% usually after day 25 of gestation. For practical purposes, the efficiency (speed and accuracy) of a correct diagnosis of pregnancy should be performed in cows expected to

transducer

creases dramatically.

have embryos that are at least 26 days of age.

Prior to the development of ultrasound for pregnancy diagnosis in cattle, veterinarians were unable to accurately determine the viability or number of embryos or foetuses. Because the heartbeat of a foetus can be detected at approximately 22 days of age, one can accurately as‐ sess whether or not the pregnancy is viable. Studies in beef [Beal et al., 1992; Lamb et al., 1997] and dairy cattle [Smith and Stevenson, 1995; Vasconcelos et al., 1997; Szenci et al., 1998] have used ultrasound to assess the incidence of embryonic loss. The fertilization rate after AI in beef cows is about 90%, whereas embryonic survival rate is 93% by day 8 and only 56% by day 12 post AI [Diskin, and Sreenan, 1980]. The incidence of embryonic loss in beef cattle appears to be significantly less than in dairy cattle. Some reports [Beal et al., 1989; 1992; Lamb and Fricke, 2005] indicate a 6.5% incidence of embryonic loss in beef cows from day 25 to day 45 of gestation. In dairy cattle, pregnancy loss from 28 to 56 days after artifi‐ cial insemination may reach 13.5%, or 0.5% per day. Ultrasonography hence becomes a use‐ ful tool in the study of early embryonic death (EED), and to monitor the success of a breeding program, by determining pregnancy rates and embryonic death.

Ultrasonography also provides a tool to accurately differentiate between the failure of a fe‐ male to conceive and the incidence of embryonic mortality early after AI service [Beal et al., 1989]. At present, there is no practical way to reduce early embryonic loss in lactating dairy cows. However, recognizing the occurrence and magnitude of early embryonic loss may ac‐ tually present management opportunities by taking advantage of new reproductive technolo‐ gies that increase AI service rate in a dairy herd. If used routinely, transrectal ultrasonography has the potential to improve reproductive efficiency within a herd by reducing the period from AI to pregnancy diagnosis to 26 to 28 days with a high degree of diagnostic accuracy [Be‐ ghelli et al, 1986; Cheffaux et al, 1986; Baxter and Ward, 1997; Meyers, 2002].

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