Signs of Pregnancy
What you may notice about the Ewe Mother
Blackbelly are known for not "showing" their pregnancy (shown below are similar size ewes, Left to Right, a Painted Desert, an American Blackbelly, and a Yellow belly - similar hair sheep crossbred with Blackbelly).
You might be attentive to your sheep but since a good shepherd will be looking at his/her flock about every day, the slow changes in body shape/mass are hard to notice at times. They simply look like healthy and full figured sheep a majority of the time.
Most likely a ewe's first lambing will be a single lamb; genetics will dictate if this happens or not. From the pictures below it's easy to see that a ewe with a single lamb simply looks "well fed" and healthy, not even looking like she's as far along as she is. The ewe on the left (below) gave birth two(2) days later.
All ewes are 147 days pregnant
From Left to Right: Single, Twins, Triplets
Some signs that you should be looking for are 1) a slightly bloated belly, 2) more aggressive eating habbits at the trough, and 3) swollen utters during the last week or so. Even so, a change in diet might cause the same symptoms. While trimming hooves once I noticed (and this is just my opinion) that the best way to see if the ewe is pregnant at four months is to flip them on their back and feel their stomach. If pregnant the ewes belly will feel like a tight drum, more rounded, looking like a small ball instead of a flat belly; observable as early as 2 1/2 moths (10 weeks) but unmistakable at four (4).
Somewhere at about 3 - 4 weeks before birth you should begin to noticing that the ewe's utters are 'starting' to swell - not the teets, but the milk mammary glands (Utter).
They will increase more and more as they get closer to birth until the teets are pointing nearly sideways, rubbing on the rear legs of the ewe. At a week before birth the utters are unmistakably large, especially on ewes that have already given birth.
As stated earlier, you might notice that the ewes will be very obsessive about feeding time (if you feed them), pushing away others they wouldn't normally contend with because they are craving the protein being consumed by the lamb/s growth; which at this point is growing faster than the mother can keep up with. Before you get to this point your should have changed their diet for a higher protein source - the only way to know to do this is if you keep track of your rams.
Only experience will teach this (and it isn't fool proof), but a ewe carrying triplets will have a very broad and nearly flat back just prior to birth (like a horse's back - see pictures below) while a ewe carrying twins will simply look very fat and hang low to the ground. In both cases the mothers will start to develop sore backs and you might witness that quite frequently they'll extend their rear legs back as though they are stretching in order to relieve a little pressure.
Having triplets, this ewe is wide and her back is hurting
(147 days from inception)
In the last week you'll begin to notice the ewe's vulva (shown here as slightly reddish and inflammed) begin to swell and is more visible under the tail. Normally covered, it might be more visible when they defecate/urinate which may also seem more frequent (I must admit that this is somewhat subjective).
No, she wasn't happy when I did this. This shot was taken three weeks before birth. It will grow larger and more obvious before birth.