We pulled the last of the rams out of their breeding groups on Thursday, November 6th, which started the imaginary ultrasound clock ticking. Ultrasounding our sheep allows us several benefits for a small fee: we know how many lambs to expect from that ewe, we can confirm our due dates, and because we learn the number of lambs for each ewe, we can feed each girl according to her gestational needs without worrying about over- or under-feeding.
In the end, it is this last point that provides us the funds to ultrasound here on our farm; the saved cost of feed essentially pays for the testing, so we gain a lot of information for very little outlay. Although human pregnancy scans costs between $200-$300 for each scan (based on the Healthcare Bluebook prices in May 2014), getting our ewes scanned costs us less than $5 each. We can save that much on feed costs over the remaining approximately three to four months of their pregnancies, bringing the benefits of the ultrasound well above the costs.
The ultrasounding of sheep is very similar to my own pregnancy experience: the technician uses a gel to lubricate the skin over the uterus, then presses a probe against the lubricated skin. For our sheep, this is the area of the rear flanks, the area of the belly against which the rear legs lie. This area is normally fairly clean of wool, allowing for good contact by the ultrasound probe. The ewe is brought up to the technician and held in place while the lubricant is applied and the probe is run across the skin. In seconds, the technician brings up the image on the screen, and she can both count the number of lambs and measure the size of each fetus, allowing for a calculation of gestational age.
There are limitations to this scenario, however – which leads us to that fictional ultrasound clock. For the first weeks of pregnancy, the embryo is too small to pick up on the ultrasound. Assuming that at least one ewe was bred on the last day with the ram, the changes within her uterus won’t be significant enough to detect pregnancy until at least day 30 – and the ultrasound cannot pick up how many fetuses are present until about day 45 – so the ideal first possible ultrasound date is reached when the ultrsound clock ticks over to day 45. We have compromised this date in the past and ultrasounded a bit before this date, acknowledging the fact that we might not know exactly how many lambs that last ewe or two is/are carrying. The 30-day cut off is firm, however: we do not ultrasound our ewes before 30 days after we have pulled the rams.
This sets the earliest date for ultrasounding, but there is also a last good ultrasound date, too. As the fetuses grow in size, the ability to accurately count their number becomes more difficult. When they are the ideal size, you can count all of the spines or all of the skulls essentially within the frame of the image on the screen. If there are triplets, you can see and count three separate skulls, for example, on the screen’s view. When the fetuses pass about 90 days of gestational age, they become so large that the probe must be moved to get each one onto the screen. This means, for example, that the tech sees the first spine and must then move the probe to the second one, and then knows there are two lambs. Yet, if the technician must again move the probe and finds another spine in another place, is that because the first lamb moved and is now in another place? Or is this a third lamb, as yet uncounted? After about 90 days, the accuracy of the data we get as far as numbers of lambs in each ewe is greatly reduced, so this sets the last desired ultrasound date for our fictitious clock: we mark 90 days after the day the rams were put into their breeding groups and won’t ultrasound unless the technician can come before that date.
So, for our flock this year, our rams were put into their groups on Sept. 19th, so our last good ultrasound date is Dec. 18th. We pulled our rams on Thursday, Nov. 5th, putting our 30-day cut-off on Saturday, Dec. 5th, and our ideal 45-day date on Dec. 20th. Obviously, since this latter date is past our 90-day cut off, we will have to compromise a bit this year in setting our ultrasound window. We will set up our ultrasound for sometime between Dec. 5th and Dec. 18th, in hopes that when the technician schedules us, it will be later within that window. This will mean that we might not know how many fetuses the last two ewes bred (Kiera and Oyster, both on Nov. 1) are carrying if we scan before about Dec. 15th or 16th, but that’s OK. I know Oyster will go into the top nutrition group because of her age, and Kiera comes from a line that generally twins, so will likely go into the lower nutrition group for at least the start of our segregated feeding.
Feeding on the day of ultrasounding should be carefully considered. It is important that the ewes not have full bellies at the time of the scan, so the advice is usually to hold off on feeding them for at least the eight hours prior to the ultrasound. The problem, however, is that the ewes are bred and we don’t want to keep them hungry for too long, possibly impacting both their fetal nutrition and their wool production. Here at our farm, we make sure to feed them the night before the scan, and since our technician usually comes later in the day, we clear away all remaining hay about eight to ten hours before she is scheduled to appear. Since we only feed once each day, the sheep aren’t too hungry, but also are empty enough for an accurate ultrasound.
It is necessary that the technician have access to the left rear leg (if the tech is right-handed, or the other rear leg if left-handed) to do the scan. Our tech sets up her station in a pen where the ewes await her arrival – big enough that the sheep can move around and lie down, but small enough that we don’t have to chase them far to catch them. I usually get a number of high school helpers to catch the ewes and bring them forward for the scan, marking their coats with marker or crayon when they are done. This way, we can tell at a glance which ewes have already been scanned and which still need to be caught. One person stands with a clip-board and records the number of fetuses and the fetal age – or “open” if the ewe didn’t settle. Any adult ewe who scans with three or more or any ewe lamb who is bred is immediately moved through a gate right next to the scan. We collect them in this area and move them into the high nutrition group immediately following the ultrasounds. Our system has developed to the point that we can do fifty ewes in about 45 minutes once we start with the first girl.
I am happy to answer questions about ultrasounding in the comments to this blog. Our technician is not taking new clients, so please don’t ask for contact information for her. She is trying to retire and is even having trouble finding someone to train to take over the business. If you know someone who might be interested, however, and is anywhere between Wisconsin and Idaho, please let me know and I will pass along contact information! It would be a shame to lose such a resource simply because our technician couldn’t find another interested person to take over for her when the time comes!