How to tell good from bad silage

It is another time of the year when most farmers are feeding their dairy cows silage and other feeds in the reserve like hay as the dry spell bites.

The analysis shows the intake potential, the value of the feed to the animals, it identifies possible problems or health impacts on the cow and allows the farmer to reflect on possible causes of unsatisfactory quality.

The pH is used to tell the amount of acid in silage. Silage with a pH of 3.5-4.2 indicates excellent fresh acidic/sweet silage, 4.2-4.5 is good acidic, 4.5-5.0 fair less acidic and above 5.0 poor pungent/rancid smelling silage.

Better quality silage has low acetic acid (1-3 per cent), butyric and high in lactic (4-7 per cent) and sugars. Lactic acid is responsible for most of the drop in pH of the silage, which is desirable although very high levels are associated with acidosis-type problems.

On the other hand, high levels of acetic acid and production of butyric acid indicates poorly fermented silage sometimes due to lose packing or very wet silage and this leads to low intake.

Silage of poor quality has slimy soft texture when rubbed from the fibre or leaf and contains moulds. Very dry or even brittle (breaking like biscuit) silage shows the material ensiled had too high dry matter content and there was overheating during storage causing much deterioration.

Leafy and more fibrous silage means low metabolisable energy and crude protein. Metabolisable energy is that energy available to an animal for metabolic processes, growth or reproduction after losses in dung and urine. Stemmy, fibrous silage with seed heads implies the crop was harvested too late.

Presence of moulds mean inadequate compaction or penetration of air during preservation or storage. If you can easily squeeze moisture out of the silage, it implies the ensiled forage had very low dry matter presenting a high risk of poor fermentation and significant losses in terms of quality and quantity.

Black, slightly damp and dark brown colours indicate poor quality silage with extensive heat damage and significant losses in digestibility, usually accompanied by moulds. Heat damage occurs when temperatures are very high especially when the silo is not quickly filled or adequately packed, leaving excess oxygen in the silage.

This allows continuation of plant respiration for extended periods resulting in more heat production than is desired. At these higher temperatures, a chemical reaction occurs between protein and carbohydrate in the forage known as browning reaction, resulting to the dark brown colour and cured tobacco odour.

The aroma desired from silage is mild, pleasantly acidic. Fermented silage has offensive taste and smell that is strong, pungent and very unpleasant with ammonia. Smell of tobacco with burnt sugar flavour denotes the silage overheated during fermentation process.

An alcohol odour is associated with yeast fermentation arising from slow rates of feed outs and air penetration into the silage with high levels of ethanol. Sour vinegar smell shows poor fermentation process dominated by acetic acid producing bacteria and is common in low dry matter and low sugar ensiling material.

Silage of poor quality has low palatability, but the animals might end up eating after allowing some pungent smell to escape or after being mixed with additives such as molasses or fresh forages, but remember animals do not require feeds instead the nutrients in that feed. A farm adviser can also help do the basic silage quality analysis.

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