Weaned lambs 20220316 110209

Weaner lamb performance – SFS newest trial

What is the most robust (resilient, profitable and sustainable) production systems to achieve target performance for weaned lambs (to slaughter or joining) across multiple and variable seasons?  

This is the latest research question for SFS’s newest trial which will compare two systems which staff are busily planning.  

 System 1:  Lambs weaned into a traditional mixed farming system, with challenges at key periods currently addressed by supplementation. 

 System 2:  Lambs weaned into a traditional mixed farming system, improved by an adaptive novel pasture feed source incorporated into the system to replace/reduce the need for supplementary feeding.  

 There has been lots to consider in planning novel feed sources. Below is an outline. But if you have suggestions for a novel feed source for weaner performance, that you have tried or would potentially like to see used then please send them to Lisa E: lmiller@sfs.org.au  

 Key considerations when thinking of using alternative feed sources: 

 Right Plant Right Place 

Many trials had lucerne as the best forage system for finishing livestock, but a key message was that the best summer forage was a product of having the Right Plant in the Right Place. For well drained soils, lucerne was superior, but for poorer drained soils summer active fescue performed best and chicory. 

 Nutrition 

Metabolisable Energy ME and Crude Protein CP are key determinants of lamb performance during pasture-based finishing. However, forage species often have unbalanced proportions of ME and CP, which can lead to below-optimum performance of lambs, particularly in lucerne. High protein feeds of lucerne can be inefficient for growth, in terms of the animal needing to spend more on energy getting rid of excess nitrogen. 

Agricultural Victoria suggested that for lambs the liveweight gains in Hamilton experiments was more due to an increase in ME than protein. Melbourne University researchers suggested that dairy production gains in grazing summer active species over standard species came from the stock being able to selectively graze higher quality feed.  

 Persistence 

To grow some forages over summer, it may be at the expense of persistence and that re-sowing is needed or other management interventions to increase persistence. For example, chicory only survives 2 -3 years (Nie et al, 2022). White clover stolons are likely to die out over summer, but the plant could regenerate from seed and therefore a focus could be on encouraging regeneration from seed, in much the same way as it is in perennial ryegrass. Or growing late flowering sub-clover varieties which may not always be supported by late rainfall to set seed and so would require occasional over-sowing. 

 Quick adjustment onto feed 

Consideration of having stock adjust quickly to the feed would be advantageous for preventing stock from losing body weight, while they adjust to a new feed source. Some producers have reported including millet in with forage Brassicas reduced digestive upsets.  

 Metabolic disorders/toxins 

Stock grazing lucerne may be exposed to red gut but this does not occur with chicory. A limitation with sorghum is its prussic acid, especially if rainfall restricts regrowth as grazing is normally deemed safe when the sorghum has reached 1m in growth when the toxin become  diluted.  

 Preserved spring feed quality 

If it doesn’t rain and there is limited soil moisture, then there is limited growth from summer active species. Another possible less risky approach would be to have standing feed that is already high in quality, at least in December. For example, using late flowering annual clovers or arrowleaf clover. Again, persistence issues could be overcome with use of over-sowing. 

 Standing feed quality could be conserved through hay freezing or spray-topping. This likely extends the feed quality for 4 to 6 weeks or until heavy rain. However, improved digestibility in the spray-topped pasture is achieved at the expense of about 50% of the pasture yield and quality might not be high enough to result in weight gain.  

 Spray-topping has been used successfully in bent grass to keep the plant growing vegetatively when it has higher feed quality. Such a method might be useful in summer active fescue which requires very heavy grazing to stop it from becoming reproductive when feed quality falls.  

 Impact on following crop 

When growing a forage crop, consider how it might impact the following sown crop or pasture. Lucerne might dewater the profile too much and impact on the following crop in drier areas, but this might be an advantage in the HRZ.   

 Other considerations are the removal or addition of nutrients from the preceding crop, how difficult the forage crop is to remove and for Brassicas, if grown repeatedly, its biofumigant qualities are likely to reduce beneficial fungi (mycorrhiza fungi). 

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