It isn't just the fats that you will need to be concerned about; protein denaturation and damage may also be an issue. Some dairy proteins and immunoglobulins are very sensitive.
there may not be the problem of rancidity. the problem can be protein denaturation and immunoglobulins absorption due to irradiation treatment. please refer to this article www.ncbi.nlm.nih.gov/pubmed/18024765