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FEEDING EWES IN MID PREGNANCY

In this month’s ruminant nutrition article, Rumenco technical manager David
Thornton discusses the importance of good nutrition for in-lamb ewes at this time
of year and highlights the importance of feeding the placenta during the mid
pregnancy period.

During mild autumns, ewes are usually put to the tup in pretty good body condition.
However, remember that the grass during such seasons often has very high moisture
content and low dry matter.

Imagine a pregnant ewe trying to contend with this sort of material as her only feed. Low
dry matter grass of variable nutritive value is bound to give rise to variation in intakes
depending on how fast she can consume it and how well she digests it – and all of this
with the onset of pregnancy going on in the background and all its associated demands.

No wonder then that when lambing performance is analysed, the worst results are in
years when the ewes have lost most body condition in early and mid-pregnancy. Great
care is generally taken during the tupping period to achieve optimum body condition,
usually by careful grazing management and judicious use of supplementary feeding. But
the early in-lamb ewe is often forgotten until 8-6 weeks before she is expected to lamb.

The relationship observed between loss in weight of the ewe between November and
February in some large hill flocks was recorded by the SAC a few years ago.

(table - download PDF to view)

These observations were made on extensive hill flocks with relatively low weaning
percentages, which could possibly have been improved by controlling loss in body
condition.

In lowland flocks with an average weaning percentage of around 155% you might not
expect such dramatic results as these, but it must be remembered that the difference in
profitability of a ewe producing a single lamb and a ewe producing two lambs is around
£40, so any cost effective method of improving weaning percentage must be worth
consideration.

FEED THE PLACENTA
Rumenco has for a number of years advocated the importance of good nutrition
for ewes during the mid-pregnancy period. Trial work suggests that undernutrition
in this period affects placental development and size, rather than foetal
development and size.

Foetal development appears to be more sensitive to the nutritional plane in early
pregnancy (i.e. up to about day 21 of pregnancy) and again in late pregnancy (i.e. the
final 6 weeks), but is related to the amount of placental tissue present.

Most studies on the affects of nutrition during pregnancy use lamb birthweight as the
main criterion for measurement. This is important as it will determine the lamb’s ability to
survive under poor lambing conditions. However, don’t forget that if a ewe is able to
maintain the body condition gained in the period post weaning to tupping throughout
mid-pregnancy then she is more likely to remain in-lamb (less foetal resorption), requires
lower rates of feeding in late pregnancy and is better able to fight off infectious disease.

Another study carried out in Scotland with hill ewes on the same farm over a three year
period indicated the benefits of supplementation in mid-pregnancy using Rumevite High
Energy + Protein blocks.

(table - download PDF to view)

Partial compensation for poor mid-pregnancy nutrition might occur with higher feeding of
concentrates in late pregnancy, although this is unlikely to happen if the high plane of
nutrition is introduced too late. Very thin ewes in late pregnancy are more likely to
channel nutrients towards restoring their own body condition rather than improving foetal
nutrition. The consequences are usually high feed bills and lambs which are too small at
birth.

The evidence would suggest that if weight loss in mid-pregnancy is more than 10% of
liveweight at tupping time then lamb birthweight is likely to be reduced and survival rate
might be compromised. These effects are likely to be greater in young ewes, older ewes
bearing twins and in harsh outdoor lambing conditions.

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