Of ultrasounds and due dates

For most of our shepherding years, we’ve had our ewes ultrasounded after breeding. When I first heard of ultrasounds for sheep, I thought back to my pregnancy ultrasounds, which were rather expensive. I was fairly certain that we couldn’t afford to do the same for our sheep — and have it done on our farm, no less! It seemed an outlandish notion.

Yet when I had time to look into it, I found a very good ultrasound technician right here in the Midwest, who would scan our ewes for only a few dollars each. I got on her schedule that year (maybe 2003 or 2004), and she has been coming here ever since. I have said many times that information is power, and ultrasounding gives me information I can get in no other way — and that allows us to better shepherd our flock.

There are limitations to ultrasound, however, and it has never been quite so obvious as it is for some of my ewes this year. We run our breeding season for about 6 to 7 weeks — if less, a good number of ewes may be left unbred; if more, I’ll be overwhelmed by exhaustion during lambing. Our rams wear a marking harness for the entire breeding period, so that when they mount the ewes who are in heat, they leave a telltale crayon marking on the back of the ewe’s coat, just above the tail stub. I check the flock for these markings daily and list each marking carefully in my records.

Once breeding season ends, I take the marking information I have collected and figure out due dates based on what I have recorded. I add 148 days to each date of Romney marking and 150 days to the Romeldale/CVM markings to get each ewe’s marking due date. It is not unusual for a ewe to be marked more than once. Sometimes they are extraneous markings, but at other times, it might signal that the ewe didn’t breed the first time or that she lost the pregnancy and was re-bred towards the end of the breeding season. Other ewes — like Grace this year — seem to be marked a lot for no discernable reason. Grace was marked every few days for a while, but I don’t know why the ram was so interested in her and why she was willing to stand for him so many times. It just happened, and I wrote it all down.

About 45 days after I pull out the rams, the ultrasound technician comes to our farm and, within about an hour, gives me information based on the scans. We learn which ewes are bred or open, how many fetuses each bred ewe carries, and the gestational age of the fetuses in days. Once the technician is gone, I convert the gestational age to a due date and enter the result onto the calendar. For example, if we scan the ewes on December 3 and the gestational age of a Romeldale’s fetus is 53 days, I subtract 53 from 150 (getting 97) and count out 97 days from December 3 to find a due date of March 10. If it were a Romney, I would use 148 days instead of 150, so her due date would be 95 days after December 3 (March 8). Then I can easily compare the marking due dates to the ultrasound due dates.

This is the point where many people get themselves into trouble. Because the ultrasound date comes from a “specialist” with some very expensive equipment, it’s easy to think that it’s more accurate than markings from a ram crayon. But this is not true. The very best due date always comes from the marking harness. Yet as mentioned above, there can be more than one marking harness date — so how do we decide? Well, it’s comprised of both science and art. If there is only one marking date and the due date from the scan is within a couple of weeks of that date, I use the marking due date as the date that the ewe will deliver, plus or minus a few days.

With multiple markings, of course, it isn’t that clear. This year, Romeldale Phoebe was marked twice with possible due dates on both March 7th and March 20th. Normally I would assume that the later date is the actual due date, but her scan showed her carrying triplets due on March 10. Because March 7th is closer to the scan date than the 20th, I decided to assume she was due the 7th — and locked her into the drop pen last Friday. I’d rather err on the side of caution and lock her in early than have her deliver triplets out in the snow.

Yet our drop pen is very crowded, and in looking at Phoebe today, it’s quite obvious that she is nowhere near ready to deliver her lambs; she looks as if she has around a couple of weeks to go. As a result, I moved her back into the general population of bred ewes, giving the other girls in the drop pen a bit more elbow room. It was a good thing I had all of Phoebe’s markings (and that tentative due date of the 20th) to verify what I was seeing in the barn!

I also have Romney Grace, who was marked with possible due dates of Feb. 21st, March 8th, March 10th, or March 17th. (I told you he liked her!) Her ultrasound showed her due on March 3, so I again locked her in for the earlier of the possible dates. She has enjoyed her time in the drop pen for these many days, and I now know she will likely deliver based on the March 8 or March 10 dates. She is finally getting close!

So for all of those shepherds who have had their ewes ultrasounded, beware of the gestational ages you are given with the scan — they may or may not be accurate. If you used a marking crayon during breeding, that is your best information by far. There is nothing better than careful observation and good record-keeping when it comes to shepherding!

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