Can you tell with an ultrasound weather or not a horses ovum or egg has been fertilize by the sperm?

Recently we had or mare fertilized she was at the breeders for only three days and they said that they could see her egg dropping with the ultra sound that she was right at the beginning of her cycle, so they began the fertilization process. Then two days later they said the egg was gone and they could see a yellow glow where the egg was traveling which would indicate that the egg had taken the sperm but it would be 14days before we could be 100% sure. does this sound right? And what is the yellow glow around the egg called? Thanks for your time.