Reduced Immunolabelling of a Porcine Oocyte Membrane Protein Reflects Reduced Fertilizability of Porcine Oocytes Following Elevated Ambient Temperature

Decreased fertility in pigs is a common occurrence during summer months. An objective of the current experiments was to evaluate if elevated ambient temperature altered the oocyte plasma membrane including potential receptors for sperm. This would potentially contribute to reduced fertilizability. Treated gilts were exposed in vivo to 32°C for 12 h per day and 20°C for the remaining 12 h per day for 7 days; control gilts were exposed to 22°C for 12 h and 20°C for the remaining 12 h each day. Cumulus–oocyte complexes were also aspirated from ovaries obtained from gilts maintained at thermoneutral ambient temperature and matured in vitro at 38.5°C or 40°C. Relative abundance of a porcine oocyte membrane protein was examined by intensity of immunolabelling of the in vivo and in vitro matured oocytes evaluated with confocal microscopy; fertilizability of the in vitro matured oocytes was evaluated in in vitro fertilization assays. Oocytes obtained from gilts exposed to elevated ambient temperature for 7 days had reduced immunolabelling compared with oocytes from control gilts (p < 0.05). Similarly, oocytes matured in vitro for 44 h at elevated ambient temperature had reduced immunolabelling and reduced fertilizability compared with oocytes matured at 38.5°C (p < 0.01 and p < 0.05). These results suggest porcine oocyte quality is reduced by elevated ambient temperature and immunolabelling of oocytes with antibodies to specific membrane proteins may be effective to evaluate some aspects of oocyte quality.