6. Twins or Singles
Producers who run Merino ewes in self replacing or first cross enterprises will, on average, have no fewer than four to five times as many single-bearing ewes as twin bearing ewes in their flock after joining each year and no fewer than twice as many lambs born from single-bearing ewes as from twin-bearing ewes.
Much more attention should and needs to be focused on single-bearing ewes because management practices aimed at saving their lambs are easier to put into place, cost free after scanning and more likely to be successful than is the case for twin-born Merino and first cross lambs.
The decision not to scan for twins because there are too few of them can be the wrong decision and is arrived at because of a focus on twins that is somewhat misplaced. Indeed the lower the twinning rate the more single lambs that there are to be kept alive by relatively simple management practices. (Link; Save more lambs).
The significance of this misplaced focus on twin-bearing ewes becomes more alarming when examined from a national perspective. There are about 41 million ewes in Australia and about 28 million of them are Merino and Merino type ewes. The proportions of non pregnant, single bearing and twin bearing ewes in the Australian flock and the survival rates of lambs born are well documented (Alexander 1975, Fowler 2007).
When these proportions are examined with regard to the national flock, it becomes clear that after joining each year, about 19 million Merino ewes are pregnant with one foetus, about 5 million are pregnant with two or more foetuses and there are about 4 million ewes that are not pregnant. Merino ewes that are pregnant with one foetus far outnumber those with two or more foetuses.
The lambs that are marked from single bearing Merino ewes, amount to about 15.6 million which represents a loss of lambs between birth and marking of about 3.4 million lambs. Twin-bearing Merino ewes give birth to about 10 (9.9) million lambs and the number of lambs marked from these ewes is about 6 (6.3) million lambs, a loss of 3.6 million lambs. Many more lambs are born as singles than are born as twins and just as many single lambs die between birth and marking as do twin lambs.
Furthermore, where there are few empty ewes, it is not until twinning rates exceed 30% that there is more lambs born as twins than is born as singles and it is known that the average rate of twinning in Merino flocks in Australia is below 30 percent.
With regard to the number of ewes that are pregnant, lambs that are born and lambs that die between birth and marking it is the single-bearing Merino ewes that are, by virtue of their numbers, the most important ewes. The term “twin scanning”, a term that has been in widespread usage for several decades, places the emphasis on the wrong ewes.
A result of this misplaced emphasis is that attention has been drawn away from the single-bearing ewes. Identifying the early and later lambing single-bearing ewes is arguably more important that simply identifying twin-bearing ewes. Where a flock is scanned to identify the early and late lambing single-bearing ewes, the twin lambing ewes will also be identified but the immediate rewards are most likely to come from the correct management of the single-bearing ewes.
Alexander G 1975. Workshop on Perinatal Mortality in Farm Animals, Published Prospect, N.S.W. C.S.I.R.O. Division of Animal Physiology, 1975 Bookmark: http://trove.nla.gov.au/version/22530988.
Fowler DG (2007) Lamb marking performance for ultrasound scanned ewes in Australian sheep flocks. Final Report AHW.131, Meat & Livestock Australia, Sydney. 17 pp. http://www.mla.com.au/General/Search-results-final.