Ewe Management & Body Weight

Profitable Ewe Management

The success and profitability of a sheep enterprise for either wool or prime lamb production is largely determined by lamb-marketing percentage.  A high body weight or an increasing in body weight at joining can ensure a high weaning percentage (lambs weaned/100 ewes mated).

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.