Grass Silage

Grass Silage

Back in the 1970s, there was a major shift from conserving grass as highly weather-dependent hay to a more flexible system of producing grass silage. In 1980s, big bale silage was introduced. This gave the additional benefits of transportation, flexible storage as well as feeding.

Grass silage is essentially pickled grass. The main goal is to retain as much feed value as possible by encouraging lactic acid bacteria to ferment grass sugar in order to produce lactic acid. 

The lactic acid will help to reduce the pH value and this will prevent the growth of spoilage micro-organisms, thus allowing stable preservation of grass as silage. To achieve this result, it is essential to have sufficient sugar available, the fermentation must occur as fast as possible and the air must be excluded throughout this whole process, also known as anaerobic conditions.

This can be done either in a silage clamp or in big bales. Regardless, both have the same objectives:

  • Remove air completely

  • Rapid fermentation of grass sugars to lactic acid

  • Maintaining anaerobic conditions in the clamp/bale during storage

Storing silage

The silage must be firmly packed in order to minimise the oxygen content to avoid being spoiled. Silage goes through 4 major stages in silo:

  • Pre-sealing - after the first few days after filling a silo, it enables some respiration and some dry matter (DM) loss, but stops

  • Fermentation - occurs over a few weeks, the pH level will drop and there will be more DM loss. However, hemicellulose is broken down and anaerobic respiration stops

  • Infiltration - this would enable some oxygen infiltration, allowing some microbial respiration. The available carbohydrates (CHOs) are lost as heat and gas

  • Emptying - which exposes surface, thus causing additional loses and will increase the rate of loses.

Typical clamp silage DM losses from original crop

By having good ensiling practices and the use of silage additives will help to control the process and minimise these loses. It is suggested that dry matter losses are minimised by ensiling at 25 - 30% DM.

The total dry matter losses during ensiling can vary from as low as 10% to 40% or more when there are high aerobic spoilage losses. This will be a problem as it will increase the cost per tonne of sillage due the the lost of nutritive value, thus, extra supplements are needed to compensate. Assume the average production cost of around USD 80 per tonne of dry matter (without losses) for grass silage. Just by have a 10% DM loss will increase the cost to over USD88 per tonne of dry matter.

Advantages of Grass Silage:

  • Less weather dependent compared to hay

  • High in protein

  • Well established system in place

  • 2 - 3 cuts per year

  • Big bale system offers flexibility

Disadvantages of Grass Silage:

  • Variable fermentation and quality

  • pH can be low

  • Potentially wasteful - loss of dry matter and nutrients

  • Low in dry matter

  • Second and third cuts may not be as cost effective