The objective of the present study was to assess the effect of egg yolk supplementation in solutions for either cooling or freezing of porcine embryos. In Experiment 1, porcine embryos collected on Day 3 to 7 (Day 0 = onset of estrus) were allocated to 12 experimental groups according to their developmental stages (four-cell to compact morula, early blastocyst to blastocyst, expanded blastocyst, and hatched blastocyst) and the concentrations of egg yolk (0, 5, and 10% (v/v)) for cooling to 0 degrees C. Whereas no embryos ranging from four-cell to blastocyst survived, the 10-min exposure to 0 degrees C despite egg yolk supplementation, expanded blastocysts and hatched blastocysts allocated to egg yolk-supplemented groups survived cooling to 0 degrees C. In Experiment 2, porcine expanded and hatched blastocysts collected on Day 6 or 7 were assigned to six experimental groups according to their developmental stages and the type of cryoprotectant used (10% glycerol, 11% Me2SO, and 10% propylene glycol) for freezing at -196 degrees C. All freezing solutions contained either 5 or 10% egg yolk. The embryos were equilibrated with one of the freezing solutions, cooled from 25 to -7 degrees C at 1 degree C/min, seeded at that temperature, then cooled to -36 degrees C at 0.3 degree C/min, and finally plunged into liquid nitrogen for storage. The frozen embryos were thawed by immersion in 37 degrees C water. After the cryoprotectants were removed by dilution, the embryos were cultured for 48 h to evaluate their viability.(ABSTRACT TRUNCATED AT 250 WORDS)