Why We Conserve Grass & Key Definitions

In Ireland, winter's cold and dark conditions halt grass growth, but livestock still need feeding. Farmers solve this problem by conserving summer grass to create winter fodder through two main methods: silage and hay making.

Conservation is the process of preserving grass for later use as animal feed. Silage involves pickling grass in acidic, oxygen-free conditions while maintaining high moisture content. Hay preservation works by drying grass until it has very low moisture content.

Some important terms to understand include anaerobic processes $happening without oxygen - crucial for good silage$ and aerobic conditions $requiring oxygen - which spoil silage$. Fermentation occurs when bacteria break down sugars into acid, specifically when anaerobic bacteria convert grass sugars to lactic acid that preserves the grass.

Remember this! Silage is the most common conservation method in Ireland because it's less dependent on good weather than hay making.

The Process of Making Silage

Making silage involves five key steps that transform fresh grass into preserved winter feed. First comes cutting - typically done in late May or early June when sugar content peaks, just before seed heads appear.

Next is wilting, where cut grass remains in the field for up to 48 hours. This allows some water to evaporate, increasing sugar concentration and supporting better fermentation later on.

The harvesting stage uses a forage harvester to collect and chop the grass into small pieces for easier compacting. Then comes the most critical stage - storing and sealing. This can be done through pit silage (packed into concrete clamps and covered with plastic sheeting) or bale silage (compressed into round bales wrapped in multiple layers of plastic film).

You've got two main storage methods:

• Pit silage: Grass is compacted by tractors in a concrete pit, then sealed with plastic and weighted down
• Bale silage: Individual bales are tightly wrapped in plastic film to maintain an airtight seal

Key point: Success depends entirely on excluding oxygen - if air gets in, your silage will spoil!

Fermentation and Hay Making

The magic of silage happens during fermentation. Initially, any remaining oxygen is consumed by plant respiration. Then anaerobic bacteria multiply, converting grass sugars into lactic acid, which lowers the pH to around 4.0. This acidic environment effectively pickles the grass, preventing harmful bacteria and mould growth for months.

Hay making is a more traditional method requiring longer periods of dry, sunny weather. The process begins with cutting grass in June/July when it's more mature. The critical drying stage follows, with grass left in the field for 3-5 days while being turned regularly using a tedder to ensure even drying until it reaches about 85% dry matter content.

Once properly dried, hay is raked into rows for baling into rectangular or round bales. Finally, bales must be properly stored in dry, well-ventilated sheds to prevent mould.

Warning! Never bale damp hay - it can cause bacteria to grow, generate heat, and potentially lead to spontaneous combustion in storage sheds.

Comparing Silage and Hay

Understanding the differences between silage and hay helps you choose the right conservation method for your farm. Silage has lower weather dependence, needing only 1-2 dry days, while hay requires 3-5 consecutive dry, sunny days.

The preservation methods differ fundamentally - silage relies on anaerobic fermentation (pickling) while hay depends on drying (dehydration). This affects their composition, with silage maintaining high moisture content $65-75$ compared to hay's low moisture (around 15% water).

Nutritionally, silage generally offers higher protein and energy content and is more digestible. However, silage requires more expensive machinery like forage harvesters and wrappers. Storage requirements also differ significantly - silage needs airtight conditions (pit or wrapped bales) while hay must be kept in dry sheds.

Exam tip: Learn the comparison table thoroughly as it clearly summarizes the key differences between silage and hay - a likely exam question!

Important Notes and Quick Revision

The quality of your preserved feed depends entirely on the grass quality you start with. For the best results, young leafy grass produces superior silage and hay.

When making silage, ensure you compact pit silage thoroughly to remove all air and regularly check for holes in your plastic coverings. Good silage has a yellowish-green colour with a sweet, slightly acidic smell, while bad silage (where air entered) turns dark brown or black with a horrible odour.

For hay making, timing is everything - only cut when the weather forecast promises several consecutive dry days. Always ensure hay is completely dry before baling to avoid dangerous fire risks in storage.

Remember these key points for revision:

• Silage is WET preservation using anaerobic fermentation to create lactic acid
• Hay is DRY preservation by removing water content to about 15%
• Silage needs airtight conditions while hay must be kept dry
• Silage generally suits high-yielding dairy cows, while hay works well for horses and suckler cows

Quick test: Can you explain why silage fermentation is described as anaerobic and what would happen if oxygen entered the system?