The text books advise that sheep gestation is 147 days, sadly sheep don’t read text books. With my flocks, and my system the mean gestation every year is 145 days. Very few reach the 147 day mark, and the latest I have recorded was 153 days, tho’ I cannot totally warranty her tupping date.
When was it tupped
This is very/pretty easy for sponged ewes as it will be within a 48-hour window if you have followed label instructions. My impression is that at least two thirds of ewes are covered in the first 24 hours. In the field, it is a little harder to be precise, all my ewes have numbers on their backs so, as I walk to check the flock each day, I note on my IPhone who has been covered on what date. This is pretty reliable though occasionally I misread a ewe number or miss a ewe in a large group. Also I am afraid I don’t refresh the raddle paint as often I should. One good smearing has to last 14/15 days and then I change colour. So towards the end of the 14 day period it is not as easy to pick up freshly covered ewes.
My tupping date is usually confirmed - roughly - by my scanner Stacey, who tells, me “80 days”, or “40-50” days. It’s a rough range which I reconcile with my own notes. Nearly always my notes and Stacey’s estimate are within five days of each other.
Some Impressions
Looking at over 10 years of lambing data I have the following impressions, note these are NOT statistically valid.
Some ewes consistently lamb earlier than others and vice-versa
Ewes with twins and triplets tend to lamb earlier than ewes with singles
As ewes get older they have a slightly longer gestation
Shearlings and ewe lambs (limited data on latter) tend to lamb earlier
Ewes carrying bigger lambs (ie better fed ewes) tend to lamb earlier
Lambs by the same sire often seem to lamb together
Any logic?
Is there an underlying logic to all this - I believe so. I recall reading some time ago that one of the triggers for parturition - the posh name for giving birth - is the internal pressure exerted on the cervix by the uterus with the unborn lamb (and behind that the rumen) is partially responsible for stimulating the birthing process. So ewes with bigger lambs or multiples will feel that pressure sooner; older ewes have a bigger rumen and roomier uterus so tend to lamb later. Some rams throw bigger lambs than others; and finally I believe hormones secreted by the lamb pre-birth are also part of the birthing signal.
Many thanks to Patrick Goldsworthy MBE (Webb Ellis and Heritage Flocks) for the use of this article. Further interesting and useful ponderings can be found on Patrick’s Bloggerama
