You cannot do DNA hair roots or blood for the testing of your Azteca foal if the only thing on file for the Andalusian parent is bloodtype. The lab cost to do hair roots testing is the same as for blood testing. The lab starting in January of 2001 will no longer process Bloodtype results, they will now only process DNA from Hair Root or Blood samples. That sample belongs to the registry that processed it. With DNA there is no minimum age.
Cleanliness is the watch word here.
Do not use a comb or brush on the horse that has been used on a previous animal as you could contaminate the sample. Wash the area that you are going to pull from. Brush out any debris first. If the hairs are too long to fit into the DNA hair root kit they can be trimmed to 6 inches, as long as it is the hair roots that are sent in for testing. Wrap the hairs around your finger or other object and yank.