Pregnancy scanning is a very wise move, and scanners are now doing more small flocks, more as a service than a money maker.
After scanning, you know which sheep are carrying multiples (twins and triplets) and will need special care from now on. The demands of the growing foetus are not a great burden on the ewe in the early stages of pregnancy, but in the last three weeks, the lambs really start to grow, drawing heavily on the ewe's body reserves.
Triplets are clearly the biggest drain, and they (and twins too) start to take up space inside the ewe's abdomen, which clearly cannot stretch very far. So this is the reason given for the ewe's drop in appetite in the last weeks before birth. It's also believed to be hormonal.
Whatever the reason, reducing food going in, as well as body reserves being emptied out, is not a good combination for the ewe's general metabolism, and it doesn't take much to upset things. Here are a few things to guard against:
- Too little feed. A sudden cold snap can rapidly cut the feed supply causing added stress, so the ewe has to draw even faster on her body reserves and she ends up with metabolic problems causing pregnancy toxaemia - sometimes called twin-lamb disease as it only happens with multiples. Ewes can die very quickly and require instant injections of glucose.
- Bearings. The pressure inside the ewe from the growing lambs forces the vagina, and worse still the uterus to be pushed out or everted. This is a really nasty prospect to deal with and it needs urgent veterinary attention. The risks of infection are high.
- Getting cast. Ewes with large expanding bellies can often get on their backs and cannot get back on to their feet again. This often happens if they lie and rest in a hollow or start rubbing because of lice. They can very quickly die of bloat as they cannot belch.
It's important not to assume that the scanning percentage (number scanned/100 ewes joined with the ram) will be your lambing percentage (number lambs born.100 ewes joined).
We now know that there can be a 15-20% loss between scanning and birth. In the early days of scanning, we blamed 'scanner error', but not these days when operators are so good at their job. The sheep has an ability to absorb lambs right up to lambing, with the very late ones seen as mummified lambs.
Few farmers count dead lambs at birth as it's too depressing, but they always have an accurate count at docking. So if you compare scanning percentage with docking percentage (number docked/100 ewes joined) you find the figure is frightening and can be as high as 40% - made up of 20% before birth and 20% after (mainly in the first 3 days after birth). It seems to be nature's way of keeping populations under control and ensuring 'survival of the fittest'.
The battle to save lambs
At the Whatawhata Hill Country Research Station, from the 1970s to 1980s, we researched the causes of lamb mortality looking for causes and solutions, and others have repeated this work since - all with the same outcome. We know what lambs die of (starvation/exposure and dystocia or difficult births), but have not really found a practical solution to prevent deaths, other than provide shelter and lambs on flat paddocks.
Starvation/exposure was lumped together as all we saw at post-mortem was that the lamb had never fed. With dystocia you could see extensive bruising on the neck and chest. In our research, we found that this critical birth weight had a wide range. If a lamb was under 3.5kg at birth, then survival chances were low due to starvation/exposure, and similarly above 5.5kg risks were high due to dystocia. But then multiples can die of dystocia if more than one lamb gets stuck in the birth canal.
The frustrating thing is that we never found out how to control birth weight. Feeding is the obvious way, but it's a very hit and miss business. In the past with less fertile sheep, we used to reduce feed intake in the last three weeks of pregnancy, but it's not a wise move with today's highly productive sheep as it may trigger health problems.
It's not economically viable to shepherd lambing ewes intensively, so breeders have been selecting for 'easy-care' traits where ewes with problems are culled. Today's flocks are much more fertile so any losses don't have such an impact on the end result - as long as you can ignore lamb mortality of 40% overall. More lambs born still result in more perinatal (around birth) deaths. It's an awful waste of national sheep resources still waiting for an answer.