Developmental competence of bovine embryos from heat-stressed ova

Abstract

Because multiple ovulation embryo transfer procedures are occasionally performed in cows experiencing heat stress, the goal of this study was to assess the developmental competence of otherwise morphologically normal embryos from heat-stressed ova. To this end, the ability of compact morulae from heat-stressed and non-heat-stressed bovine ova to undergo blastocyst development after culture at 38.5 or 41.0 degrees C was examined. It was hypothesized that heat-induced perturbations in the ooplasm carry over to increase the susceptibility of the preattachment embryo to heat stress. Initially, ova were matured at 38.5 or 41.0 degrees C. The consequences of heat stress did not include altered cleavage, but did reduce the proportion of 8- to 16-cell-stage embryos (55.3 vs. 50.6%; SEM +/- 1.9). Although proportionately fewer, compact morulae from heat-stressed ova were equivalent in quality to those from non-heat-stressed ova (2.1 and 2.1; SEM = 0.04). Culture of compact morulae from non-heat-stressed ova at 41.0 degrees C did not affect blastocyst development (71.9 and 71.5%; SEM = 3.0). Furthermore, the development of compact morulae from heat-stressed ova was similar to that of non-heat-stressed ova after culture at 38.5 degrees C (68.2 vs. 71.9 and 71.5%; SEM = 3.0). However, blastocyst development was reduced when compact morulae from heat-stressed ova were cultured at 41.0 degrees C (62.3 vs. 71.9, 71.5 and 68.2; SEM = 3.1). In summary, reduced compaction rates of heat-stressed ova explained in part why fewer develop to the blastocyst stage after fertilization. The thermolability of the few embryos that develop from otherwise developmentally challenged ova emphasizes the importance of minimizing exposure to stressor(s) during oocyte maturation.

Impact of Heat Stress Exposure During Meiotic Maturation on Oocyte, Surrounding Cumulus Cell, and Embryo RNA Populations

“…In vitro maturation, fertilization (IVF), and culture of resultant embryos were performed as previously described [23,25,26]. Briefly, cumulus-oocyte complexes were matured in Medium-199 containing Earle's salts, 10% fetal bovine serum, 50.0 μg/ml gentamicin, 5.0 μg/ml FSH, 0.2 mM Na pyruvate, and 2 mM Lglutamine) in a 5.5% CO2 humidified environment.…”

“…In summary, results described herein document the extent to which heat-induced perturbations occurring at the molecular level during meiotic maturation affect later stage embryos after fertilization. Previous efforts of Edwards et al [26] demonstrating that later stage embryos from heat-stressed oocytes are not as developmentally-competent as those from nonheat-stressed oocytes suggests that heat-induced alterations in RNA may not be without consequence. Demonstrated differences occurring at the molecular level in embryos from heat-stressed oocytes emphasizes the importance of minimizing stress exposure during meiotic maturation.…”

Factors affecting the in vitro embryo production in cattle associated to ovum pick up sistem

“…On the other hand, some findings provided evidence for bovine HSO to mature faster than non-heat-stressed counterparts (Edwards et al, 2005;Schrock et al, 2007; Andreu- Vazquez et al, 2010). In agreement with our results, oocytes heat-stressed during the germinal vesicle stage (bovine: Payton et al, 2004;mouse: LaRosa and Downs, 2007) or during maturation (bovine: Ju et al, 2005;Schrock et al, 2007;Edwards et al, 2009;Zhandi et al, 2009;Rispoli et al, 2011;Payton et al, 2011) have shown competence in overcoming the first cellular division similar to that found in non-HSO. In addition, we observed that HS treatment improved the ability of the oocytes to form blastocysts.…”

Effects of choice of month of treatment and parity order on bovine superovulation traits

“…It was reported that high temperatures decrease the oocyte maturation and reduces the number of embryos that cleave into two cells (Lenz et al, 1983;Rivera and Hansen, 2001). Heat stress was also reported to negatively affect the fertilization and embryonic development both in vitro and in vivo (Al-Katanani et al, 2002;Sartori et al, 2002;Hansen, 2007;Edwards et al, 2009); however, another study indicated no change during the summer (Ryan et al, 1993). Cerri et al (2009a,b,c) reported that the season affected the embryo development and number.…”