Minimising protein degradation

Challenges of ensilage

Silage management is a key aspect on a working farm. High-performance products from AGRAVIS help with ensilage and create good qualities.

Ensilage aims to maintain feed value and, consequently, the composition of nutrients as far as possible. In the case of grass silage, the objective is also to minimise degradation of raw protein. Animals should thus receive as much protein contained in the origin feed as possible to an optimum quality standard. To achieve this, the entire process must be devised in the best possible way – from the field and ensilaging through to the way silage is removed from storage. Proteolytic conversion or degradation processes take place at all stages in this process. These cause a relatively high loss of pure protein and an increase in easily soluble nitrate compounds (ammonia).

Shape protein degradation

It does not matter if proteolytic conversion and degradation processes are enzymatic or microbial. They will always produce a loss of valuable pure protein and also cause amino acids to convert into ammonia and other undesirable substances, such as amines. It is not possible to prevent a certain degree of protein degradation during ensilage, but it can be minimised if the ensilage process is devised in a suitable way.

Different external factors have an impact on protein degradation. Key influences include the rate of decrease in the pH value, dry matter content or the duration of wilting and temperature development in silages. All these factors can be easily controlled using effective silage management during the different stages of the process – from the field to removal.

Protein degradation starts in the field, during pre-wilting, to be more precise. Proteins are split into peptides and amino acids by plant proteases and aerobic micro-organisms. Such degradation processes can be controlled by devising an efficient wilting method. As a general rule, the faster and more gently you achieve the optimal degree of wilting of 30 to 40 per cent dry matter, the lower the protein losses are. If conditions are less than optimal, you may lose over 10 per cent of pure protein just on the first day of wilting on the field. Some farmers underestimate how quickly grass dries on fields in sunny weather. The target value of 30 per cent dry matter is reached after just three or four hours if hay conditioners and windrows are used, for example, and silage making can then begin.

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Different proteolytic conversions take place during ensilage. These involve enzymes and micro-organisms both at the very beginning of ensilage and during the continued process. The general ensilage conditions determine to what extent these conversions lead to a reduction in the feed value. The quality of the air seal when ensilage starts is not the only decisive factor; the fermentation process itself also plays a role.

Proteases in the plant cells and aerobic micro-organisms are still active when the silage crops are stored away and right from the moment when ensilage starts. Farmers need to create anaerobic conditions quickly in the silo to stop such activity. Nutrient and protein losses are correspondingly high if work is completed too slowly or crops are not compressed sufficiently and not packed, so they are not airtight. Plant cells and micro-organisms will not die until the air enclosed with the plants has been fully used up. The extent of potential protein damage is directly linked to silage management during this time. This phase lasts just a few hours in a well-compacted, hermetically sealed silo. An inadequate air seal – the silage is covered up too late, for example – prolongs the process, causing losses as a result. Another critical issue is the rise in temperature associated with respiratory processes in silage, which consequently increases the risk of a Maillard reaction (see Risk of Maillard reaction).

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If the silage contains butyric acid, Clostridia (butyric acid bacteria) cause incorrect fermentation. A distinction should be made between saccharolytic and proteolytic bacteria within this microbe group. Proteolytic clostridia use proteins and amino acids as a source of nutrients. When amino acids degrade, they produce ammonia, butyric acid and biogenic amines. These metabolites always have a negative effect on animal health. Since the formation of biogenic amines is linked to the ammonia content in silages, levels of more than 8 per cent NH3-N in silage (according to Hoffmann, 2015) will always mean that it contains amines.

Clostridia are hardly ever found on plants. Their natural habitat is soil, which contains many bacteria and spores. They enter the silo in contaminated green fodder. If living conditions in the silage are favourable, they multiply dramatically; this causes undesired butyric acid fermentation. The risk of such incorrect fermentation is particularly high if the sugar content in grass is somewhat low or the weather hasn’t allowed adequate pre-wilting. Dirt and soiling caused by soil and manure increase the risk of incorrect fermentation. Siloferm should be used as an ensilaging agent for moderately difficult silage fodder and RaicoSil Gras for difficult silage fodder to ensure soiling and dirt are eliminated.

Protein degradation also takes place in butyric-acid-free silages. The pure protein content may decrease by up to 30 per cent, depending on the conditions during ensilage. This decrease is primarily caused by enteric bacteria in butyric-acid-free silages. They enter the silage as they form part of the natural micro-flora on the feed. Conditions are favourable for them right at the beginning of ensilage, so they reproduce rapidly. Their living conditions do not worsen until the pH value starts to decrease. Since a pH value of less than 4.5 is regarded as the critical lower limit for bacteria growth, lactic acid fermentation must be controlled in such a way that the pH value quickly falls below this limit. This can be achieved by using the silage additives Siloferm or Proferm. Using these additives increases the existing low number of lactic acid bacteria occurring naturally on the fodder, complemented by highly potent species. This makes it easier for lactic acid bacteria to push ahead in the competition for sugar and they quickly dominate the fermentation process. Unwanted enteric bacteria stand little chance of growing.

The last critical stage for protein degradation is when silage is removed from the silo. If the silage is not sufficiently aerobically stable, yeasts and mould grow and silage becomes warm and mouldy as a result. Effectively ensiled nutrient-rich silages with low acetic acid contents are particularly at risk. Silages with less optimal fermentation processes usually do not cause any problems on removal. The better the quality, the greater the risk for the silage. Reheating also means an increase in temperature and risk of a Maillard reaction. The use of specific silage additives also help in such cases. BioCool,for example, ensures aerobic stability in the silage, thus preserving its protein value.

If sugars, starch and lactic acids are inhaled, this produces an exothermic reaction, thus causing an increase in temperature. A rise in temperature has negative effects on feed value. The extent of these effects depends on how high the rise in temperature is. The risk of what is known as a Maillard reaction also increases, which also has a negative effect on digestibility. A Maillard reaction also decreases the availability of essential amino acids and, consequently, protein potential. The sugar in the silage reacts with free amino acids to form compounds which enzymes can no longer break down. An intense brown colouration of the silage sometimes gives indication of such changes. The critical temperature limit for a Maillard reaction is quickly exceeded if reheating occurs. Temperatures above 50 degrees Celsius are often recorded in silages in such cases. The risk of a Maillard reaction still persists even if most of the residual sugar and lactic acid from yeasts is used as nutrition in such silages.