Livestock ear tags were developed in 1799 under the direction of Sir Joseph Banks, President of the Royal Society, for identification of Merino sheep in the flock established for King George III. the first batch of sheep ear tags was made of tin.
 

Although ear tags were developed in Canada as early as 1913 as a means to identify cattle when testing for tuberculosis, the significant increase of use of ear tags appeared with the outbreak of BSE in the UK.

Ear tags come in all different colors, and farmers often have meaning behind the colors they use and which ear the tag is in.  Some use blue for bull calves and pink for heifer calves.  Others use the placement as a gender id ear tags in the calf’s left ear mean it’s a heifer (girl) and in the right ear means it’s a bull(boy).  I had the idea to tag all the calves born in the first 21 days with a certain color and then the next 21 days a different color. That idea bombed with management!  I guess you can get a bit carried away with the whole color-coding calves.

Since we’re a cow-calf farm and our calves are born on our farm, we give them ear tags when they’re first born, this helps to keep the right calf with its mother, especially when it’s time to go to pasture.

There are quite a few ways to do your numbering and identification the International letter for calves born in 2020 is H,  Last year calves were G and calves born in 2021 will be J. 

Letters  I O Q and V are not used because they can easily be mistaken for numbers.

Some people will number in the order there were born, so at the end of the season, you can see if calf #1 is larger than calf #25. I guess this will work if you always keep this group together and don’t try to sort to go to different pastures.    I wouldn't want to consult my calving book to try and match up pairs all the time.

Of course, most of the ear tag id is useless if it’s not recorded somewhere.  At the Extension office, we offer two different Cow/calf record books.  The first is printed at KSU, it has lots of helpful stuff in it,  you can record up to 220 calves.  It has a gestation chart, an International lettering system, all the calving ease scores, udder scores, docility score, and body condition scoring.  The second is the NCBA book which includes a calendar that some find helpful. There’s room to record 425-600 calves, it contains all of the above plus a calendar for 2020, pasture usage, performance charts, AI records and a chart for keeping track of supplements. 

Besides these about every Breed registry has its own calving record books.  There are about as many options as to how to tag your calves!