Evaluation of Pregnancy Rates of Dairy Heifers Receiving IVP Embryos with or without Supplemental Progesterone

Pregnancy rates after the transfer of frozen-thawed, in vitro produced (IVP) embryos are less than ideal. The objective of this study was to determine whether the addition a controlled internal drug release (CIDR) device at the time of transfer of IVP embryos influenced pregnancy rates of dairy heifers. A total of 439 Holstein heifers (479 ± 33 d of age) were included in this study. Estrous cycles of heifers were synchronized and those detected in estrus with a viable corpus luteum each received a frozen-thawed IVP embryo 7.1 ± 0.47 d after detected estrus (d 0). At the time of transfer, heifers were stratified by the donor flush group of the embryo they received, and then randomly assigned to 1 of 2 treatment groups: 1) received no supplementation (control; n = 211), or 2) received supplemental progesterone via a CIDR device from d 7 (immediately after transfer) until d 19 post-estrus (CIDR; n = 228). Transrectal ultrasonography and rectal palpation were performed at approximately d 30 and d 60 post-estrus, respectively, to determine pregnancy status. Developmental stage, grade, and parentage of all embryos were recorded. Data were analyzed using the GLIMMIX procedure of SAS; means are presented. Overall pregnancy rates were 27.5% on d 30 but were reduced by d 60 to 23.3%. Supplementation of progesterone did not affect pregnancy rates on either d 30 (P = 0.467; 26.5 vs 28.1%, for control and CIDR, respectively), or d 60 (P = 0.417; 24.9 vs 21.5%, for control and CIDR, respectively). Embryo parentage, grade or developmental stage or BCS of recipient heifers did not influence (P ≥ 0.105) pregnancy rates. In conclusion, supplemental progesterone via a CIDR device did not alter pregnancy rates after the transfer of IVP embryos. Further research is necessary to elucidate mechanisms to increase the viability of IVP embryos.