The heifer we thought was safe

Dot is a Hereford mix. First-time heifer. Her mother, Eyelashes, is the only cow in our herd allowed to have horns — everyone else gets dehorned, but the horn line stayed with Eyelashes and it stayed with Dot.
We had moved Dot into what we affectionately call the No Kids Club — our safe heifer pasture. Wire-fenced. Virgin heifers only. No bull was getting in there.
Last time I was at the ranch, she was walking around like she was about to have a baby. Some drippage. All the signs.
I looked at my mother. Did a bull ever get in? How would she have been exposed? Do we think she is actually pregnant? My mom said, I can't imagine. Maybe she's just coming into her body differently.
A couple of days later, she started calving. I had already had to head out; Mom and Dad were the ones there to help her deliver. Pulled the calf. She got up. Started feeding. Everyone was okay. New little Hereford baby heifer.
Then I went to HerdBook and worked backward from the calving date. About nine months earlier — right in the impregnation window — Dot was still out in the main pasture with the herd bull. She had not been pulled yet. Which means the bull is her father. Which means her calf's father is her father.
Teenage pregnancy. Just not good.
But we knew, immediately, and we knew for good. HerdBook wrote it down. Dot can never be in a pen with that bull again. Her calf can never be with him. We don't have to remember every time. It's just in the record now, on her profile, in her lineage tree. Anyone who ever manages this herd — future us, someone we hire, the person who buys her calf someday — will see it the second they open her page.
A herd is a lot of things to remember, and a rancher's memory is a lot of places to keep them. A notebook in the house. A text thread with a sibling. That one thing your mom said out in the pasture last October. Some of it, you can afford to lose track of.
This wasn't one of those things.