Silage Advisory Centre

The most important aspect in making high quality silage is the quality of the grass at harvesting.  This in turn is affected by stage of grass growth, but there is a compromise between high quality and high yield.  However with high producing livestock quality should never be compromised for yield. 

Quality and yield alter rapidly during May.  Studies have shown that early May grass had 25% crude protein (CP) and 75% digestibility (D-value) so of high quality, but the yield was only 3 T of DM.  Two weeks later yield had increased to 6 T of DM with a crop quality of 18 % CP, and 68% D-value.  By the end of May the grass only had 12% CP and a D-value of 60%, but with an impressive yield of 8 T of DM.

Further studies compared the milk yields from feeding high and low D-value silages. Two grass silages prepared from similar swards were harvested 3 weeks apart.  At feed-out the early cut silage had an ME of 12.6 (MJ/Kg DM) (75% D-value) and a CP of 19%, compared to an ME of 10.4 (64% D-value) and CP of 13.5% for the later cut.  When fed to dairy cows with 6 kg of concentrates/day the cows fed the early cut silage produced over 2 litres of milk/cow/day than fed the later cut silage. 

This study, and there are many more like it, highlights the importance of harvesting the grass when there are high concentrations of nutrients to optimise animal production.

There are some field based visual assessments that can be made prior to mowing to indicate grass nutritional value.  Young and leafy grass will have a D-value of 70% or greater, the target for high quality grass silage.  Once grass stems begin thickening and lengthening the D-value will drop to 67%.  As the flowering heads begin emerging the D-value will be 64% or lower and finally once seed heads begin setting the D-value will at best be 60%.

So remember high performing livestock require high quality silage which will compromise your forage yield but will enhance your saleable milk and meat product.