Effect of Electrocautery of Nonovulated Day 1 Follicles on Subsequent Morphological Variation among Day 11 Porcine Embryos1

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Abstract
One hundred and thirteen crossbred gilts were used in three experiments to examine the relationship between the pattern or sequence of ovulation and subsequent variation in the morphology of Day 11 embryos. In the first experiment, the percentage of follicles that had ovulated was determined in individual gilts at 26, 30, 34, or 38 h after the onset of estrus (n = 20) and 39, 41, 43, 45, or 47 h post-injection of human chorionic gonadotropin (n = 25; hCG, 1000 IU). The second experiment consisted of observing the percentage of follicles ovulated in 52 additional gilts at 34 h after the onset of estrus (Day 0). In the third experiment, the morphological variation among littermate embryos was compared on Day 11 between sham-operated control gilts (n = 8) and gilts whose nonovulated follicles were destroyed by electrocautery (n = 8) on Day 1. Results of these experiments indicated that the pattern of ovulation in gilts was skewed (p less than 0.01). Ovulation, induced with hCG, appeared to occur in a majority of follicles during a short period of time, whereas the remaining ovulations occurred over a longer interval. Of the 57 gilts observed at 34 h after natural estrus, ovaries of 25 gilts contained corpora hemorrhagica (CH) and follicles; one gilt had 1 CH and 17 follicles, and 24 others had 10-17 CH with 1-4 follicles remaining. Destruction of these nonovulated follicles resulted in a more (p less than 0.01) uniform group of Day 11 embryos and with fewer (p less than 0.05) small embryos. These data demonstrated that the pattern of ovulation may affect morphological variation in embryonic development such that some of the later ovulating follicles may represent smaller embryos within a litter.