4 September 1995 Trends In Silage Quality

Silage quality is very variable.  This is obvious from results of the Analytical Laboratory of the Animal and Veterinary Sciences Group, Lincoln University where large numbers of samples throughout the country are analysed.

A database of results developed at the University over the last few years gives an insight to the quality and viability of silage.  For example:

% Dry Matter - The average dry matter content of silage is 31.5% and 46% for wrapped balage. This is acceptable, but there is a significant 15% of balage material with a dry matter content of above 60%. There are problems of conserving grass this dry.  There is more danger of bacterial and fungal contamination i.e. Listeria if bales are damaged because there is very little, if any protection from fermentation acids present in silage of normal OM.

% Organic Matter - Less than 10% of silage samples have an organic matter value of below 88%.  This demonstrates (a) there is little soil contamination in New Zealand silages and (b) organic matter losses in the stack/bale are low i.e. successful fermentation has been achieved.

pH - Again most samples have a pH which will preserve the stack/bale adequately.  The average for silage is 4.4 and for balage 5.1.  Some of the dryer balages have pH's which are too high, around 6-7. This means the silage making process has not taken place.  Only the wrapping protects the feed.

% Ammonia Nitrogen - This parameter is most important for showing how successful the ensiling process has been.  A high value (above 10%) indicates a secondary fermentation has taken place which decreases quality. The causes are:

•              rain on material before covering

•              poor consolidation (too much air is left in the stack/bale)

•              the covering has been damaged.  (Air or water has entered).

A secondary fermentation will significantly decrease the protein quality and the energy value.

Our results show that generally, silage is well made, most material is ensiled satisfactorily with an average ammonia N value of 8.4% for silage and 6.0% for balage.  A figure of above 10 indicates spoilage; 20% of silages and 10% of balages were above this figure.  In the United Kingdom, up to 2/3 of silages have levels three times higher than this.

% Crude Protein - Protein content in preserved feeds usually reflects the type and maturity of the material used for ensiling.  We have noted an increase in the protein content over the last few seasons. Silage increased from an average of 13.0% in 93/94 to 15.0% in 94/95.  Balages showed the same trend, 12.9% increasing to 14.6%.  One in four silage samples submitted to the laboratory now have a protein value of over 20% which is considered high.

Crude protein is not an accurate measure of protein quality as it contains non nitrogen protein components such as ammonia and nitrate which can be a significant proportion.  Usually protein in silage is highly digestible and does not bypass the rumen.

% Digestibility - Dry matter digestibility values have also risen over the years from 63.8% in 93/94 to 67.9% in 94/95. Balage figures increased from 62.2 to 66.6%. This increase reflects the fact that material submitted for analysis is less mature than previous and contains more leaf and less stem.

Energy (M/D) - The energy value is derived for the digestibility figure, so the same trends are reflected here - silage M/D values have increased from 8.7 to 9.5 and balage from 8.4 to 9.3.  MJME/kgDM. These values are still low compared to the UK, where the average is close to 10.3 MJME/kg DM.

We can safely say that New Zealand farmers who submit samples to our laboratory are 'good' silage makers, but the material they ensile is not of the highest quality.  The techniques are good, the material ensiled is not good.

We believe the main reason for the gradual improvement in energy and protein values of silage is that dairy farmers sending in samples are responding to the drive from the Livestock Improvement Corporation (LIC) to improve the quality of supplementary feed and cutting their silage at a leafier stage. LIC recommend that lactating animals need silage with an M/D over 10 and protein of between 16-20%.

Silage requirements of farmers differ.  High quality silage is not required in all cases.  Older animals and those at maintenance can tolerate lower quality material, but for lactating and young growing animals, silage quality is an important consideration.

Farmers who know the quality of their own silage/balage have an advantage in feed planning, in budgeting of supplementary feeds and in feed purchasing decisions.  The laboratory at Lincoln University is also keen to improve knowledge of supplementary feed quantity by increasing its database with relevant information.

Peter Isherwood

Manager, Analytical Services