| This zone is characterised by winter rainfall and hot summers with no effective rainfall. Crops form a substantial part of enterprises and most properties have stubbles available for grazing. Pastures are predominantly a mix of annual grasses, sub clover and medics.Due to a shorter growing season than the medium rainfall zone the constraints of lower feed on offer and total pasture production (2-5t/ha/yr) affect the recommendations for optimum ewe management. These all affect the potential stocking rate and pasture utilisation and therefore affects some of the recommendations for ewe management.
Optimum Ewe Condition Score Profile
Production from ewes and their progeny can be predicted with confidence if the condition of the ewe throughout the season is known. Using these known production levels and matching them with the pasture available for the time of lambing and expected supplementary feeding costs allows an optimum ewe Condition Score (CS) profile to be developed. The profile sets the CS targets for key times during the reproductive cycle. Ewe CS at joining and at lambing are the key points on the profile with condition at lambing being the most important.
Key Points about the May Lambing Profile:
Maintaining condition from joining through to lambing is the most profitable approach to managing ewes for a may lambing in the 300-420mm zone.
The shape of the profile is as important as the actual starting condition score of the ewes, so if ewes are in CS 3.5 pre-joining the most profitable approach is to maintain their condition through to lambing. Similarly if the ewes CS is 2.5 at joining the most profitable approach is to maintain their condition.
Ewe CS for joining is influenced by the condition post-weaning and therefore it is important to monitor changes in ewe condition between weaning and joining.
The break of season is usually close to lambing and paddocks should be deferred until a feed wedge is grown (at least 700 FOO with the optimum 1500 FOO in lactation).
The higher the lambing CS of the ewes, the lower ewe and lamb mortality will be, especially in twinning ewes.
Losing condition (or not regaining condition) in the period before lambing has the biggest impact on lamb survival and progreny production.
- Condition at lambing is a key target as this affects lamb and ewe survival. It is not recommended any breeding ewe is in CS 2 or lower as there are significant mortalities of ewes and lambs particularly twins.
- Ewes in early lactation will tend to lose condition as any available energy is channelled into milk production. Higher pasture FOO gives high lamb growth rates.
- Ewes will regain condition on green feed post peak lactation (~30 days).
Supplementary feeding through Autumn to maintain condition is the most profitable management option.
Maintaining condition, compared to gaining condition, gives the most efficient conversion of feed. It is important then to not allow any loss of condition if it needs to be re-gained prior to lambing using grain. Although feed costs are high, losing condition or having too low a condition by lambing will also decrease the survival of lambs and increase the mortality of ewes during lambing, thereby affecting profit and production.
Cost of missing targets at lambing
Profile 1. Profit is similar to the optimum but requires a lower stocking rate (0.5 DSE).
Profile 2.Optimum due to maintenance feeding in pregnancy and regaining condition on green feed in lactation.
Profile 3. Profit is lower due to the loss of production and lower survival caused by low condition prior to lambing and the cost of grain feeding in early pregnancy.
Profile 4. Ewe and lamb mortality limits profitability through lamb and ewe survival as well as lifetime wool production of the progeny.
Trade-offs of risk for profit
The optimum profile shown in Figure 1. takes into account both profitability and the health of the ewe flock. The other profiles, shown in Figure 2, offer only small differences in profitability but there are some important trade-offs in production to consider if following these profiles.
Ewe mortality generally increases with lower ewe condition by lambing (although there are other factors that influence this, such as weather, age and available feed). Ewe condition in late pregnancy has a large impact on lamb birth weight and therefore lamb survival. Twin lambs are more sensitive to this change in birth weight (& survival) as their birthweight is usually lower than the optimum. Table 1 shows the effect of several profiles on both lamb and ewe survival.
Table 1. Difference in survival of ewes and lambs for late lambing flocks compared to maintaining condition score 3 throughout pregnancy in the Cereal-Sheep Zone.
Following a lower profile (profile 4) to the optimum (profile 2) at lambing means that by lambing the flock average will be CS 2.2 with a significant proportion of the mob below the recommended CS 2 minimum. This leads to severe penalties in ewe and lamb mortality. Profile 4 in Table 1 shows that twin lambs have a predicted decrease in survival of 17% compared to maintaining in CS 3 throughout. This can be compared to the optimum profile which has a decrease in twin lamb survival of 5%.
Following the lower profile has no room for getting it wrong or provides no buffer in poor lambing conditions.
Running Lower Stocking Rates
Producers may choose to run flocks at stocking rates lower than are recommended for maximum profitability. There are many legitimate reasons for doing this, including fitting around changing crop rotations, however, for producers who wish to improve profitability, ewes per hectare are the biggest driver of profitability. By following the lifetimewool ewe profile, you can identify opportunities to lift stocking rate safely during periods where CS targets are being met easily.
In years that ewes' peak condition prior to joining is above the recommended target due to a great season or flock restructuring, it is worthwhile following the same trend of maintaining condition score from joining to lambing for that season rather than trying to drop condition to a lower profile. Continuing to run ewes at this higher flock condition score year in year out will give a slightly lower profitability to running ewes at the optimum profile, as the higher production gains are offset by the higher cost of supplementation.
More details on the economic impacts of managing ewes and the cost of missing targets can be found in the Economics section.
Detailed production impacts can be found in the Ewe Management section or click on the topic below;
Pasture photos, condition scoring and feed budgeting guides for managing ewes to CS profiles can be found in the Tools section
The economic analysis that supports these recommendations is generated using the Eastern Wheatbelt MIDAS model. A full report of the modelling for this region will be posted on this site in October 2007.
For more information on lifetimewool in South Australia contact;
Dr Janelle Hocking Edwards or Katrina Copping
SARDI, Struan Research Centre,
Naracoorte, South Australia