Did My Informal Lambing Calculator Backfire This Year?

Using a lambing calculator can help you better predict when ewes deliver spring lambs—and when you need to have supplies ready to care for the newborns.

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by Jana WilsonMarch 21, 2022
PHOTO: Tim Marshall/Unsplash

I will be the first to admit that my informal lambing calculator (done in my head) might not be the most scientific method of determining when my lambs are due.

In fact, as I let my hopefully pregnant ewes out a few days ago, I noticed one first-timer looked about ready to pop. She was even starting to bag up a bit.  Wait a minute, I thought. Weren’t my ewes due starting mid-April?

This seems a little early….

By the Calendar

I try to keep notes about my sheep, such as their vaccination and worming dates. However I do know from experience that if I don’t write such things down, I will forget!

And so, when I looked at my notes, I saw that, yes, I’d noted the ewes were due on or about April 15.  And that seemed fine. Except then I Googled lamb calculator and found a table that shows I may have been off a week or even two weeks!  While the average gestation period for a lamb is 147 days, it can range from 144 to 152 days.

I found a sheep gestation calculator and put in the date that my ram joined the ewes … November 8.  According to that calculator, my ewes could give birth anytime from March 26 to April 16.

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Read more: What do you need for lambing season? Here’s an overview of what you should have on hand.


Getting Ready

There are a few things you need to be ready for about a month before your lambing calculator predicts the arrival of lambs. So I figure I have slid in under the wire.

CDT Vaccination

First off: the CDT or overeating and tetanus vaccination. You need to administer that to your pregnant ewes in the last month —but at least two weeks—before they give birth. In this way, the lamb will receive passive immunity from the diseases when they nurse.

This immunity will last for about six weeks. At this time the lambs will be ready for CDT vaccines of their own.


Read more: Why vaccinate sheep? For an ounce of prevention.


Nutrition Notes

Secondly, nutrition becomes even more vital than ever in the last 40 to 45 days before lambing, when the majority of the fetal growth occurs. It’s important to ensure the ewes have top-quality hay and feed, and plenty of it, during this time as well as during the nursing phase after the lambs are born.

Purdue University has a great article about feeding the ewe flock that you might want to check out.

I lamb in the warmer months into the spring. So I don’t have to worry about an intensive setup for indoor lambing. My ewes will lamb just fine out in the pasture. I do, however, have some spaces set up for alone time between new moms and babies during the first 24-48 hours.

I had planned on cleaning out my sheds and setting up small lambing “jugs” (where ewe and lamb can bond) a little later in the month. But I’ll move that task up a few weeks as well.

I don’t use a harness on my ram to know when each ewe is bred exactly.  After all, I only have 10 ewes that may or may not be pregnant. But you can loosely consider that, because ewes come into heat about every 17 days, there will probably be a three-week span of time when my ewes will give birth.

I’m glad I re-checked my due dates for my lambs! I’ll move up the preparations just a bit, and I don’t anticipate any problems. However, the upcoming month will be a busy one. And, hopefully, at the end I’ll have a healthy flock of new mothers and lambs.

Glad I checked that lambing calculator!

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