Profitable Ewe Management |
Farmers
will consider many factors when choosing a joining date. These could include:
·
when the season breaks or dries
off in the district;
·
markets for early prime lambs;
·
fitting in with crop enterprises;
·
the likelihood of supplementary
feeding late lambs.
Early
weaning makes consideration of all these factors easier.
Optimize the ewe’s static and
dynamic body weight
‘Static
body weight’ is body weight measured at any one point in time.
‘Dynamic
body weight’ measures changes in body weight.
If
weaning has been early, ewes will have regained body reserves and achieved high
static body weight before pasture deteriorates in quantity and quality over
summer (winter rainfall area). Ewes
joined at high static weights and at fat score 5, maintaining this fat score
throughout gestation, are likely to experience difficult births and pregnancy
toxaemia.
Body
weight declines later in autumn (winter rainfall area). Any early break in the dry season will see a
dynamic increase in body weight, resulting in a higher lambing
percentage which may go up by 15 %.
An
increase of 1 fat score unit will correspond to an increase in body weight of
7-8 kg, regardless of frame size. One
extra fat score unit in merino ewes at joining results in 12 extra lambs born
per 100 ewes joining.
Producers
wishing to ensure high lambing percentages should try to improve the fat score
of their sheep from 2.5 to 3.5 at joining.
Daylength – Effect on ovulation
Body
weight is not the only factor affecting ovulation. The time of year is also important. Decreasing daylength triggers breeding
activity, that is, the oestrus cycle.
Also, studies with Merino sheep show that higher ovulation rates occur
in autumn. Experiments show that 33 per
cent more Merino lambs were weaned per ewe joined in autumn compared with lambs
weaned per ewe joined in spring.
Body weight at joining
Body
weight of ewes at joining is affected by early weaning and the date of joining.
·
Early weaning gives ewes the
potential to regain body weight but also relies on this date in relation to the
break in the season or drying-off of the season.
·
Ewes joined in December (winter
rainfall area) rely on static body weight to give multiple ovulation coming out
of spring, as daylength is not yet decreasing.
·
Ewes joined in February have a
lower static body weight and lower fat score; they benefit from decreasing
daylength (winter rainfall area).
·
Ewes joined in April benefit from
a dynamic increase in both body weight and fat score as well as from positive
effects from decreasing daylength (winter rainfall area).
Ram harness and twin scanning
The
ram harness is particularly useful for separating ewes into groups to reduce
mismothering and to allow sale of prime lambs at specific weights/ages. This is done by dividing ewes into groups
which will lamb early or late.
Twin
scanning allows ewes bearing single lambs to be managed in harness groups. This reduces the incidence of difficult
births through overfeeding in late pregnancy.
Twin-bearing
ewes should be lambed in groups of 100 or less, comprising ewes lambing at
different times as denoted by raddle marks.
By managing twin-bearing ewes separately, from scanning at 42 days to
lamb marking or weaning, similar growth rates can be achieved for twin lambs as
for single-born lambs. Use of twin
scanning and the ram harness facilitates early weaning and thus the regain of
ewe body condition before the next joining.
Where
scanning for twin-bearing ewes is practised, nutritional management of those
ewes before lambing is made easier by regular fat scoring to ensure adequate
body fat reserves for late pregnancy and lactation. Target fat score during pregnancy should be
3.5. Overfat ewes (4 to 5 score) eat
less in late pregnancy and are likely to suffer pregnancy toxaemia. Reducing the fat score of these ewes to 3.5
between days 90 and 120 will increase their lambs’ birth weights and likely
survival.
Ewes
of fat score 2 or less have insufficient body fat reserves for successful
lactation. It is difficult and
uneconomic to change ewes from 2 to 3.5 score in late pregnancy by means of
supplementation. The desired fat score
of 3.5 for pregnancy should be achieved soon after joining.
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