By John Byrd, DVM
Horsemen’s Laboratory often gets this question and we have determined that exposure to oxygen is the main factor. If samples are packed firmly so that the eggs are exposed to very little oxygen then they are fine.
Eggs need oxygen for the larvae to develop and hatch, once the eggs hatch the larvae disintegrates fairly rapidly therefore no evidence of eggs exist. However, if there is a lack of oxygen in the sample then the eggs can appear just as they were passed for at least 2 weeks.