When treating pigs it can be difficult to remember which pigs were treated with what medication on which day. PQA Plus® guidelines require documentation of individual pigs or pens that have been treated, so make it easy for yourself and your employees. One method for identifying pigs at treatment is to have a color-coded marking system. Use different colors for specific days of the week (or medication used) then record the pen number (i.e., blue on Monday, red on Tuesday, etc.). Just remember to keep an updated chart with the correct colors and their meanings, and make sure everyone uses it.
Source: NEWS NOW from the Iowa Pork Industry Center (October 27, 2014 - Vol. 14, No. 14)