Reproduction potential and marking rates of the WA sheep flock

Page last updated: Tuesday, 29 September 2020 - 11:56am

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Reproduction rates (foetuses per ewe joined) across the WA flock vary hugely and  depend on seasonal conditions and nutrition.  Marking rates in 2017 across the agricultural region for Merinos was 92%, Merino to meat sire marking rates was 97% and for specialist meat flocks was 107%.

The number of lambs marked (actual lambs present one month after lambing) is a function of reproduction rate (number of foetuses per ewe at day 90 of pregnancy) which sets the potential lambing rate, and the survival of lambs from birth to marking.

The reproduction rate is calculated using results of pregnancy scanning for conception and litter size ie. the number of dry ewes, those with single foetuses and twin/triplet foetuses per ewe mated.

Marking rates give the number of lambs available for slaughter or carryover for breeding stock or for adult production of wool. It is expressed as a percentage (lambs per ewe mated), typically ranging from 50-150%. Some producers report in lambs per hectare (or kilograms of lamb per hectare) as it is a better measure of profitability and efficiency similar to crop yield per hectare.

Typical reproduction rates in WA flocks

Reproduction rates are determined using pregnancy scanning, however, only 17% of producers or 30% of the WA flock is currently scanned for litter size to determine the number of foetuses per ewe. A further 25% of the flock is scanned just to determine pregnancy status (pregnant or not) which doesn’t show the impact of multiple births on the reproduction rate.

Reproduction rate is affected by nutrition and genetics (some strains are more fertile) at mating.  Typically, in Merinos the better the condition of the ewes at mating means less dry ewes and more twinning ewes.

Eighty five per cent of ewes are Merinos and they generally have a lower reproduction rate than prime lamb ewe flocks, however, there is significant variation and many Merino flocks out-perform specialist meat flocks.

In WA average reproduction rates across the state flock are between 1.15 and 1.35 (foetuses per ewe) depending on seasonal conditions and nutrition.  Reproductive rates generally increase in flocks that lamb in winter rather than in autumn, however, seasonal conditions have a bigger impact than breeding season generally (fig 1).

The reproductive rate of ewes by the month of lambing
Figure 1 The reproductive rate of ewes by the month of lambing over four years based on pregnancy scanning data. Source: WA Producer Survey 2018 DPIRD

This translates into a potential marking rate of 115 – 135%. The current marking rate (2018 season) in WA is estimated to be 94%, indicating significant gains can be made in improving lamb survival.

Typical lamb marking rates in WA flocks

Marking rates in 2017 across the agricultural region for Merinos was 92%, Merino to meat sire marking rates was 97% and for specialist meat flocks was 107% (WA Producer Survey DPIRD 2018).

There are usually lower rates in the Medium rainfall zone (woolbelt) than in the Cereal Sheep Zone (wheatbelt), mainly due to higher stocking rates.  The higher stocking rate however, can mean a higher number of lambs per hectare than is indicated by lambs per ewe.

Lambing rates for the WA flock have steadily risen since 2006 (74%) at 1-2% per year. In 2018 however, the poor season in the south and south east parts gave an estimated drop in marking rate in those areas to 89%.

Marking rates based on surveys in WA
Figure 2 Marking rates based on surveys conducted by the Australian Bureau of Statistics, Australian Bureau of Agricultural Research and Resource Economics and Sciences, Meat and Livestock Australia and Australian Wool Innovation
Table 1 The median marking rate for the key mating types in WA based on total number of lambs per total number of ewes

 2017 season

median Merino lamb marking

median crossbred lamb marking

median meat lamb marking

Medium Rain Zone




Cereal Sheep Zone




If the reproductive rate (potential lambs) is 120% and we are achieving 94% marking, it translates to a 26% loss of lambs.  Most lambs that are conceived are lost at birth – due to mis-mothering, starvation, weather conditions and mis-adventure!

Much of this (~70%) is driven by nutrition and management. The condition of the ewe during pregnancy affects the lamb size and vigour at birth and the condition of the ewe at lambing affects her ability to cope with the lambing process and provide mothering including milk.

WA has predominantly a Merino ewe base, either mated to Merino sires or to meat sires (terminal or maternal types). There is genetic variation in both fertility as well as lamb survival of the ewe base.  Ewes mated to meat sires tend to have higher lamb birth weights (directly related to survival at birth) than pure Merino lambs and there is evidence that the sire does have a genetic effect on reproduction from other traits such as vigour and immune response.

Genetic breeding values for Number of Lambs Weaned (NLW) in Merinos can be +25% to less than -30%. This equates to 12% to -15% range in the impact of a sire on changing the number of lambs weaned over a flock. There are negative correlations though with lower fleece weight and shorter wool. This means there are less sires available with both high NLW traits and high fleece value traits.  The heritability of twinning sits at only 10% which makes it only lowly heritable.

Focussing on lifting the reproductive rate (hence the number of twinning ewes) either through genetic selection or nutrition at conception can have little effect if the ewes aren’t managed for a higher reproductive rate.  Twin survival sits between 50 and 75%, based on nutrition, mothering ability and weather conditions at birth. Single lamb survival is generally between 90 and 97%, whatever the external conditions as they are generally bigger (less likely to be affected by hyperthermia) and the ewe is more able to cope with the extra demands of birth and lactation.

Adoption of best practice

The Lifetime Ewe Management program (LTEM) is a nationally accredited small-group training program supported by Australian Wool Innovation (AWI) through producer levies.  It is run by a Victorian Training organisation; Rural Industries Skills Training (RIST) and delivered by WA accredited trainers. In WA the program has been operating since 2010 with initially high participation rates. Approximately 20% of ewes run in WA are being managed by producers who have completed LTEM.

Participants of the Lifetime Ewe Management program increased their whole-farm stocking rates by 14%, increased lamb marking percentages by 11–13% depending on enterprise type, and decreased ewe mortality rates by 43% making it easily the most effective training program run within the sheep industry.

These improvements resulted from a significant change in the perceived importance of managing ewes to condition-score targets to improve profitability and increases in the ability of participants to condition score ewes, assess pasture quantity and quality and feed budget. These changes were consistent regardless of how innovative the participants were at the beginning of the program.

What can we do?

In order to grow the flock or grow turn off without compromising the ewe flock, an increase in marking rates is the only option. This can be done with:

  1. nutritional management of the ewe
  2. improving genetics for reproduction.

An example of the impact of lifting reproductive rates in WA

Analysis by DPIRD 2018.

Increasing the size of the WA flock

To lift the size of the WA flock by approximately 25% from 14.2 million to 18 million head over a period of ten years various combinations of marking rates and turn-off may be possible.

In order for the flock to reach 18 million in ten years a marking rate of 90% would be required every year if the turn-off remained steady at 5 million head and losses are steady at 5% of the opening flock number. If the turn-off lifted to 7 million, a marking rate of 120% would be required for the flock to number 18 million in ten years (Table 2).

Small changes in marking rates have a sizeable impact on the flock size over ten years when turn-off and mortality rates remain constant. As seen in Table 2, at a turn-off of 5 million, a marking rate of 87.7% would cause the flock to decline to 12 million in ten years. By increasing the marking rate by only 1.7% to 89.4%, the flock would increase to 18 million over that time period.

Table 2 Marking rates required to reach particular flock sizes under different levels of turn-off

Flock size (million)

Turn-off (million))

















The impact of turn-off and marking rates

In order to maintain the flock at around 14 million head with a marking rate of 90% total turn-off would be 5.13 million. In order for the flock to grow to 16 million in five years the turn-off would need to be reduced to 4.93 million if the marking rate stayed the same.

Effect of turn-off on flock size under different lamb marking rates
Figure 3 Effect of turn-off on flock size under different lamb marking rate

To maintain the flock at 14.2 million whilst turning off the 5.6 million head identified in previous works as the minimum required to support industry, a marking rate of 98% would be required (Figure 4).

The marking rate required to maintain the flock at 14.2 million at different levels of turn-off
Figure 4 The marking rate required to maintain the flock at 14.2 million at different levels of turn-off

For every increase in turn-off of 0.5 million there must be a marking rate increase of 8% in order to sustain the flock. A 1% gain in marking rates allows for an extra 65 000 head to be turned off while maintaining the flock.

Contact information

Mandy Curnow
+61 (0)8 9892 8422


Mandy Curnow