Efficacy of Timed Embryo Transfer with Fresh and Frozen In Vitro Produced Embryos to Increase Pregnancy Rates in Heat-Stressed Dairy Cattle

Abstract

Our objective was to determine whether pregnancy rates in heat-stressed dairy cattle could be enhanced by timed embryo transfer of fresh (nonfrozen) or frozenthawed in vitro-derived embryos compared to timed insemination. Ovulation in Holstein cows was synchronized by a GnRH injection followed 7 d later by PGF2α and a second treatment with GnRH 48h later. Control cows (n=129) were inseminated 16h (d 0) after the second GnRH injection. On d 7, a fresh (n=133) or frozen-thawed (n=142) in vitro-derived embryo was transferred to cows assigned for timed embryo transfer after categorizing the corpus luteum by palpation per rectum as 3 (excellent), 2 (good or fair), 1 (poor), and 0 (nonpalpable). Response to the synchronization treatment, determined by plasma progesterone concentration (ng/ml) ≤1.5 on d 0 and ≥2.0 on d 7, was 76.2%. Mean plasma progesterone concentration on d 7 increased as the quality of corpus luteum improved from category 0 to 3. Concentrations of progesterone in plasma were elevated (≥2.0ng/ml) at 21 d in 64.7 (fresh embryo), 40.3 (frozen embryo), and 41.4 ±0.1% (timed insemination) of cows, respectively. Cows that received a fresh embryo had a greater pregnancy rate at 45 to 52 d than did cows that received a frozen-thawed embryo or timed insemination (14.3>4.8, 4.9 ± 2.3%). Body condition (d 0) of cows influenced the pregnancy rate and plasma progesterone concentrations. In summary, timed embryo transfer with fresh in vitro-produced embryos in heat-stressed dairy cattle improved pregnancy rate relative to timed insemination.