dairy: how long can a cow lactate?

This question from a fellow farmer:

Hi, Doughertys! Thanks for your book. Question: I have a dairy cow (Jersey, five years old) that I didn't get bred last year and she's been lactating for 14 months now. She's producing about two gallons a day right now, on grass. Can I keep milking her? I mean, is there a problem with milking longer than a year? I'm planning on getting her A.I.'d this month, but I'd like to keep milking her until I have to dry her off for calving -- we love milk! -- Darcy

Hi, Darcy,

Good to hear from you. Aren't dairy cows great? Magic food. No, there's absolutely no problem with milking a cow just as long as she'll make milk for you. More than once we've had a cow that for one reason or another wasn't bred and we kept her in milk for two years between calvings. I've got a 12-year-old in stanchion right now that's been lactating since last September (2021) and she won't calve until next August.