AI straws are the plastic straws that are filled with semen for insemination.  This semen can either be fresh or frozen in liquid nitrogen (cryogenic storage).  The AI straws listed here are bovine straws, but are also used for other animals such as dogs, cats and horses. Different colours are used to easily and quickly identify straws without the danger of thawing that comes from taking them out of the liquid nitrogen. Some customers make different colours breed specific, so the likelihood of inseminating with the wrong straw is reduced even if gets stored in the wrong location.