Decision time at weaning

Tim Abbiss discusses knowing when to take your finishing hat off and put your breeding hat on.

For much of the North Island spring has been both late and slow which is leading to a potential headache come weaning time. On the back of good scanning and lamb survival, feed demand is greater than usual combined with slow pasture growth rates. This is being reflected in generally light ewe condition and lamb performance.

With a strong forecast lamb schedule, the temptation is to maximise the weight of every lamb post weaning but is this the right decision?

To achieve consistent performance, capital stock are the number one priority. Therefore, ewe condition needs to be a key driver around weaning decisions in a tight year to influence next year’s production. Understanding the feed requirement of ewes in order to increase their body condition score is fundamental to making decisions about how many lambs need to be sold at weaning and during the following months.

Typically, weaning is completed about 90 days post birth leaving about 115 days for ewes to increase their body condition score (BCS) to the optimum of BCS 3 at mating. Allowing for 90 days to increase ewe weights is more likely to account for management factors (eg. shearing) and weather checks. The difference between BCS 2 to 3 is 8kg and will require the following feeding requirements – assuming that pasture over summer has an energy content of 9.5 megajoules of metabolisable energy (MJME)/kg drymatter (DM).

It is important to allow as much time as possible to increase the BCS of ewes. Allowing 90 days to increase BCS from 2 to 3 requires 89g liveweight gain (LWG)/ day. Shortening the period to achieve this liveweight gain will require over 100g LWG/day. To achieve this, forages above

10 MJME/kg DM are required, which over the summer months are only available in legume dominant pastures, improved forages, or high energy supplements such as grain.

A good option to increase the body condition of light ewes is to mix them undrenched with lambs on high quality pasture for refugia. The importance of driving ewe condition is well documented, but what effect does this have for next year’s lamb crop? Ewe condition pre-tupping maximises ovulation rates in ewes.

If ewe condition is an issue pre-weaning what options are out there? Lambs reach peak growth rates between 20-40 days of lactation and are a fully functional ruminant at 60 days old.

From 60 days until weaning, lamb growth rates are reliant on pasture quality and these growth rates will be maintained if pastures or forages exceed 10.5MJME/kg DM.

Ewes will preferentially graze quality pastures but will maintain weight when pasture quality drops and will be more reliant on pasture quantity.

Early weaning Early weaning is an option particularly post-70 days if ewe condition is light and pasture covers are low creating ewe – lamb competition. Research demonstrates that competition stressed lambs will grow quicker when weaned early compared to equivalent unweaned lambs. This option also creates the ability to control ewe intake early and increase the return/kg of lambs and ewes sold. Typically lambs which are growing at less than 180 – 200g/ day on mum are showing signs of lack of feed allocation and quality due to ewe competition and would be better off weaned.

Split weaning Split weaning can be a valuable tool to reduce feed demand and/or transition different stock classes onto appropriate feed types. Weaning check is important to keep in mind especially with marketable weight lambs. Research shows heavier lambs (30kg plus) have the greatest weaning check.

Therefore, these lambs benefit remaining on mum to maintain their yield until marketed or killed. Lighter lambs have less of a weaning check so would be a better weaning option to reduce feed demand. Some split weaning options include:

• Weaning terminal lambs early.
• Weaning ewe lambs early to reduce demand on the ewe and leave saleable lambs unweaned.
• Weaning light lambs onto alternative forages whilst leaving heavy lambs on mum to maintain yield.
• Weaning 5yr ewes and lambs early.

Marketing

With more lambs on deck but a tough spring, it is important to recalibrate your lamb exit weight and value expectations. The farm system is likely not going to be able to handle finishing the extra 5% of lambs to previous expectations unless alternative quality feed is allocated, especially with more tail end ewes to lift.

Table 2 demonstrates that accepting a greater percentage of lambs sold store does not have an adverse effect on total lamb returns due to the increase in lambing percentage. The benefit of securing next year’s ewe performance by controlling BCS will outweigh the margin of putting more weight on lambs.

As previously stated, the return on increasing the BCS of ewes is 41cents/Kg DM versus the return on increasing the live weight of weaned lambs which is 18 cents/ kg DM. Ultimately, it is a trade-off between increasing the weight and return of this year’s lamb crop or allowing a decreased rate of ewe performance in the year ahead.

A slow season for many has brought its own challenges, but with a strong lamb outlook there is great advantage in maintaining the performance of capital stock and consistency of output.

• Tim Abbiss an agribusiness consultant with BakerAg.