Embryonic development in progestogen-supplemented cows administered prostaglandin F2a

An experiment was performed to examine the effects of elevated concentrations of prostaglandin F_2α (PGF_2α) on embryonic development in cows supplemented with exogenous progestogen. Cows were inseminated artificially at estrus (day 0) and 12 h later. A synthetic progestogen (melengestrol acetate; 4 mg/cow*day^-1) was supplemented in feed from days 3 through 8. Cows were allotted randomly to receive either 15 mg PGF_2α (TRT; n=14) or saline (CON; n=10) at 0600, 1400 and 2200 h from days 5 through 8. Blood samples were collected at 0600 and 2200 h from days 5 day 8 for determination of progesterone and 13,14-dihydro-15-keto- PGF_2α, (PGFM) . Single embryos were recovered on day 8 by flushing the uterine horn ipsilateral to the corpus luteum (CL) as determined by ultrasonography on day 5. Each embryo was assigned a quality score of 1 (excellent) to 4 (poor), and stage of embryo development was recorded. Concentrations of progesterone were lower from days 5 to 8 in TRT versus CON cows (0.3 ± 0.14 vs 2.01 ± 0.16 ng/mL, respectively; P=0.0001). Overall, PGFM concentrations from days 5 to 8 were elevated in TRT cows (553.2 ± 42.1 pg/mL) compared to CON cows (13.2 ± 50.1 pg/mL; P=0.0001). Embryo quality scores were elevated in TRT cows compared to CON cows (2.9 vs 1.6, respectively; P=0.059). Percentage of embryos considered transferrable (quality scores 1, 2, and 3) was decreased by administration of PGF_2α (Fisher's exact test, P=0.003). Nine of fourteen (64%) TRT embryos were retarded in development at day 8, whereas four of fourteen (29%) TRT embryos developed to expanded blastocyst. All CON embryos developed beyond the morula stage; eight of ten (80%) developed to the expanded blastocyst and two of ten (20%) reached the blastocyst stage upon recovery (Fisher's exact test, P=0.003).

In conclusion, treatment of progestogen-supplemented cows with PGF_2α reduced quality and retarded development of embryos prior to the blastocyst. Decreased fertility in conditions elevating PGFM concentrations may be a result of retarded development or reduced quality by PGF_2α.