Abstract
Despite modifications in techniques and protocols used for multiple ovulation embryo transfer in recent decades, transferrable quality embryos (TQE) has remained relatively unchanged. The objective of this study was to evaluate the effects of endogenous progesterone during beef cow superstimulation on embryo quality and quantity. Thirty non-pregnant beef cows were sorted into 1 of 5 replicates and randomly assigned to one of two groups: High Progesterone (HP) or Low Progesterone (LP). All cows, were pre-synchronized utilizing a 5-d CO-Synch + CIDR protocol. Nine days after estrus (d 0) with a corpus luteum present, all cows received ultrasound-guided dominant follicle ablation (DFA) and were administered a CIDR with LP cows also being administered PGF2α. All cows began a timed, 13-d, superovulation CIDR-based protocol and were artificially inseminated (AI) twice. Embryo were recovered and evaluated on each replicate 7 days after first AI. Blood samples were collected to evaluate progesterone (P4) and estradiol concentrations daily when cows were handled. Greater number of total embryos were recovered from the HP than the LP cows (19.26 vs. 10.74, P = 0.01). The HP cows also had greater number Stage 4 embryos along with more Quality Grade 3 and 4 embryos than the LP group (5.76 vs 2.20 P = 0.002; 1.87 vs 0.61, P = 0.01; 8.22 vs 2.89, P = 0.01, respectively). However, LP cows had a greater percentage overall of freezable embryos with a higher percentage of Grade 1 embryos (58.22 vs 37.32, P = 0.03) and a greater percentage of Stage 7 and 6 TQEs (18.47 vs 1.22, P = 0.01; 10.37 vs 3.19, P = 0.03). Serum P4 concentrations were greater on d 2–3 in the HP cows (P = 0.002). In addition, HP cows had greater concentrations of estradiol (P < 0.0001) on d 6. Comparatively, estradiol was greater in concentration in the LP cows (P ≤ 0.04) on d 2–4. In conclusion, removal of endogenous progesterone during superovulation may decrease the total number of embryos but increase the percentage of Grade 1 embryos and percentage of Stage 6 and 7 TQE in a single recovery.
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