145 Factors Affecting Pregnancy Rate Following Timed Embryo Transfer Program in Cattle Under Field Conditions

Abstract

Hormonal estrus synchronization followed by heat detection of recipient animals is a widely used technique in embryo transfer (ET) programs around the world. However, the successful outcomes of ET rely heavily on appropriate heat detection of recipient animals. Additionally, limited availability of personnel and time to detect heat makes ET impractical at times. Therefore, pregnancy rates (PR) following a timed embryo transfer (TET) program were evaluated taking into account different variables of recipient cows, donor embryos, and season of transfer under field conditions in Argentina. Recipient cows were synchronized utilizing a progesterone (P4) intravaginal device (DIB, Syntex, Argentina) for 7 days. On Day 0 (day of DIB insertion) 2 mg of estradiol benzoate (EB) i.m. was administered and immediately after DIB removal on Day 7, 500 μg of D(+) Cloprostenol i.m. (PG, Ciclase, Syntex), 400 IU of eCG i.m. (Novormon, Syntex) plus 1 mg of cypionate estradiol i.m. (ECP; König, Agentina) were administered to all recipient cows. Fresh (n = 1746) and frozen (n = 2047) beef bovine embryos were nonsurgically transferred into recipient cows on Day 9 after PG. The effects of body condition score (1–9, BCS I: ≤5, n = 804 and BCS II: ≥6, n = 2989), corpus luteum (CL) score (CL1: prominent papilla, n = 932, CL2: small papilla, n = 2028, and CL3: asymmetric, n = 833), location of embryo placement in uterine horn (upper, n = 3566, and lower, n = 227), and type of recipient such as heifer (n = 487), lactating (n = 1010), or dry cows (n = 2296) on PR were evaluated. Additionally, stage of embryo development (4–7), quality (1–3), and season of transfer (spring, summer, fall, and winter) were included in the analysis. Pregnancy rate was confirmed by rectal palpation 60 days after ET. Data were first screened by chi square and then analyzed by Proc Logistic of SAS (SAS Institute Inc., Cary, NC). Overall PR was 54.7%. body condition score, CL, type of recipients, stage of embryo development, and year were not significantly (P > 0.05) associated with PR. As expected, cows that received direct fresh embryos had 1.49 times greater odds of conceiving (odds ratio, OR = 1.49, 95% CI: 1.22 to 1.82) than those receiving frozen embryos. Additionally, cows receiving embryos graded as quality 1 had greater probability to conceive (OR = 1.62, 95% CI: 1.34 to 1.95, or OR = 1.64, 95% CI: 1.25 to 2.21) compared to quality 2 or 3 respectively. Moreover, embryos placed into the upper portion of uterine horn were more likely (OR = 1.48) to conceive than those placed in the lower uterine portion. Regardless of embryos and recipient cow variables analyzed, there was a greater probability for cows to conceive during winter (OR = 1.41, 95% CI: 1.13 to 1.95) as compared with summer. In conclusion, synchronized recipient animals for a TET program resulted in acceptable PR for both fresh and frozen embryos. Results suggested that the quality and location of embryos (upper portion) in uterine horn were the most important variables associated with PR in recipient cows. Therefore, TET is a viable and practical option allowing a successful outcome for many beef operations where availability of personnel is limited.

Evaluation of the factors that affect the pregnancy rates during embryo transfer in beef heifers

“…The side of transfer (right or left) was recorded. Diameter of CL and type of CL (Purcell, Beal, & Gray, ; Scenna et al, ; Spell, Beal, Corah, & Lamb, ) were defined (Corpus luteum type: CLa = asymmetric, non‐embedded in ovary and soft texture, CLb = non‐embedded in ovarium, classic mushroom‐like and with cavity and CLc: prominent papillae, embedded in the ovary and compact texture). During the embryo transfer, three groups were formed according to cervix transfer score: easy (<60 s), moderate (60–80 s) and difficulty (>80 s).…”

Evaluation ofIn Vivo‐Derived Bovine Embryos

“…[15][16][17] These two groups of practitioners and scientists described the criteria that are, for the most part, still used today as a general guideline for embryo evaluation and prediction of potential pregnancy. The latest of those papers 17 described numerous parameters commonly used for embryo evaluation, including stage of embryonic development and structural features such as embryo size and shape, presence of extruded cells or degenerated cells, color characteristic, number and compactness of the cells (also called blastomeres) that comprise the early embryo, integrity of the zona pellucida, and presence or absence of vacuoles within the cytoplasm of the embryonic blastomeres.…”

“…Quality grade 1 and 2 embryos typically yield higher pregnancy rates than quality grade 3. One study 24 showed no difference in pregnancy rate among cows receiving grade 1 or 2 embryos (74.1% and 71.8%, respectively), whereas another study 16 showed that quality grade 1 embryos had a greater probability to conceive (odds ratio 1.62) compared with quality grade 2 or 3 embryos. Conception rate of quality grade 1 embryos was reported as 76% for fresh embryos and 64% for frozen embryos.…”