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In most litters, I will have lot of babies that look extremely similar. This makes it extremely difficult to tell the babies apart! Unfortunately, without marking them I cannot photograph babies, give them names, and list them as available because I will lose track of who is who. In order to solve this issue, many reputable breeders like me use humane "tattoo pens" to mark their animals for identification. Some breeders use other methods like clipping ears. I prefer marking under the tail because the ears are just way too pretty to alter! Tat-marks should remain on the underside of their tail for life.
Does it hurt the rat? A little. It is no different from giving a rat (or any animal) an injection of meds. It's very quick and most rats don't even realize they were marked. If I felt it was inhumane I would NEVER do it. In my professional opinion, it's a safe and humane method of identification. The marking usually only takes 15-30 seconds to complete.
Numbers: The method I use is numbering the underside of the tail near the base. Females will get a number between 1-6+ depending on how many are in the litter. Same goes for males. For example, "Jenna" will be marked 1, "Mika" will be 2, "Lilly" will be 3, and so on. The info for who has what number is recorded in specific book.
Rats will also get a W under the tail so I can make sure the rat can always be identified as a White Wolf Rattery Rat. The W will be close to the base with the number after it.
At what age do you tattoo the babies? It is done usually at 4-4.5 weeks old.
Tat-marks are also done to help prevent backyard breeders from pretending to be me and selling rats under my name.
Questions? I am happy to answer them. Email me: firstname.lastname@example.org
Pictured above is an example of my tat method. This photo was taken moments after this five week old female was tat marked "W 1" with special black tat ink. Her mark was completed in just 10 seconds.