I keep a sheet on each cow. At the top it has her tag, her CCIA (govt tag), reg# if there is one. Date/year of birth, breed/description of cow, Dam/where we got her, Sire, BW, WW/ADG, date/year she left the herd, Other ID (metal tag, tattoo). Not all of this gets filled in for every cow.
Underneath all that I have a table for her calves that includes, Birthdate, CCIA(govt tag), Description,ID, Sex, BW, H/P (horned or polled), Assist, Sire, Date Weighed, WW, ADG, Kept/Sold, and Comments(where I record anything that concerned me.
On the back of the page, I made up another table to write down vaccinations and any other medicating we did. Date, Reason, Medication, Cost, Withdrawl and comments.
This way, I can just go through a binder and see pretty much everything a cow has done, as long as we have had her. I have progressively modified all this over the last 10 years, and I am pretty happy with how it works for me.
I can send anyone the template if they are interested. Just PM me your email