My milk cow Sandy was bred (via AI – artificial insemination) on September 26th.
And so I expect her to calve the first week of July.
The average gestation for dairy cattle is 283 days. Gestation for heifers (a heifer is a cow who has not yet had a calf) and smaller breeds is a few days less than average while gestation for older cows or larger breeds can be a week or more.
But a Jersey cow (which Sandy is) typically has a gestation period of 278 days – 5 days shorter than average.
And get this – there’s as much chance that a cow will calve at the average gestation (278 days) as there is that she’ll calve any time between the 271st day and the 285th day.* Statistics are wild like that.
Basically, just because the numbers suggest a specific due date doesn’t mean your cow is going to comply. (chuckle)
So – I’ll expect a calf sometime between July 1st (278 days) and July 8th (285 days), though it’s just as possible she could deliver as early as June 24th (271 days). It’s always a guessing game, but we’ll be prepared in any case.
A quick side note for comparison: the average human gestation is 280 days (40 weeks / 9ish months). And there aren’t that many women who deliver on their “due date” either!
How to calculate your milk cow’s due date
You could always calculate the due date manually (278 days after service/breeeding).
Or skip the math and do a quick internet search. There are LOTS of online calculators and calendars like this one from the Canadian Dexter Cattle Association (based on 283 days).
As I was getting ready to dry Sandy off (give her a 60 day “dry period” before her due date), I had a heck of a time remembering when I should stop milking and kept re-calculating and second-guessing myself (math is not my strong suit).
So I made my own gestation calendar and included not only the Breeding Date and Due Date, but the corresponding Last Milking date as well. Next time, all I have to do is consult my handy Milk Cow Gestation Calendar and circle the date (or you know, make a note in my phone’s calendar app since that’s how I keep track of things these days).
Because my milk cow is a Jersey, this is a Jersey-specific calendar (278 days gestation), but I made a note about adding days as needed depending on the breed of milk cow you have.
I’d love for you to skip the math and have your own copy.
Just enter your info below and you can download it right away. You’ll be surprised how often you need it.
You’ll reference it when your cow is in heat and ready to breed so you can know when she’ll be calving and make a plan for seasonal considerations.
For example, if it’ll be winter – you’ll need good shelter. If it’ll be in full summer – you’ll need to take her off pasture for a week or more ahead of time (for more on this pre-calving protocol and other calving info, download the Essential Guide for When Your Milk Cow Gives Birth).
You’ll check the Milk Cow Gestation Calendar as you’re getting close to drying her off so you can plan and implement protocols to lower her production and prep her for the full stop.
And you’ll look at it again (and again!) as her due date approaches and you’re on calf watch to be sure you’ve got all your ducks in a row.
*Copeland, Lynn. "Length of Gestation in Jersey Cows." Journal of Dairy Science. Vol 13.3. May 1930. DOI:https://doi.org/10.3168/jds.S0022-0302(30)93522-9.