Supplementary feeding lambs to increase weight gain is a common practice, however in many cases the protein component of the diet is lacking, resulting in potential weight gain not being achieved.
The two main components of a lamb’s diet are energy and protein. Lambs on feed with a high energy content have the potential to put on weight more rapidly, as shown in the following table. Energy is measured in Megajoules of Metabolisable Energy per kilogram of feed dry matter (MJME/kgDM) which is simply abbreviated to M/D.
For the above weight gains to be achieved, the ratio of energy and protein in the diet must be in balance. Lambs on a high energy diet with insufficient protein will not achieve their potential weight gain. In addition, smaller lambs require a higher protein percentage than larger lambs.
The following table shows the required Crude Protein percentage for varying energy levels and lamb live weight.
When a cereal grain is being fed, it is likely to have an energy level of about 12 M/D, plus a protein level of 11.5% (may vary from 9 to 13%). In this case, lambs require an additional protein source to meet the critical balance.
If lambs are grazing lucerne, they will be sourcing adequate protein from the pasture. If they don’t have access to lucerne, the diet will need a protein supplement in order to maximise their potential weight gain.
The table below shows a summary of average energy and protein levels for some common feed grains.
There are a range of potential protein supplements including grain legumes, lucerne hay and oilseed meals. In southern NSW, the most cost effective and accessible option is most likely lupins.
Lupins contain about 12.5 M/D of energy and 31% Crude Protein making them an ideal additive to cereal grains for lamb finishing. A mixture of 80% barley and 20% lupins will provide a ration which has approximately 12 M/D energy and 15% protein, which is a good general purpose ration for lambs.
Where possible, cracking or rolling the lupins will increase digestibility and hence increase the performance of lambs on this ration.