A major expense of silage production is silage shrink. The losses come with large price tags as the material lost represents some of the highest value nutrients in the feed with energy values similar to corn grain. For example, corn silage shrink of 15 percent represents the effective nutritional dry matter loss of more than 50 kg of corn grain per harvested tonne. That can amount to nearly a quarter of the silage’s dollar value.
The sheer magnitude of the physical and economic losses associated with silage shrink demand that it take a priority in management on farms, especially when profit margins are narrow. Some dry matter loss is unavoidable even with excellent management practices, but typically opportunities to reduce shrink are available. To create a strategy for controlling silage shrink, it is important to appreciate where and why shrink is occurring. All three primary phases of silage storage – fill, fermentation and feedout – result in shrink, so each needs attention.
At harvest, any remaining oxygen in the silage after filling the silo will be consumed via microbial activity, which depletes the silage of valuable feed nutrients. This process also releases water, carbon dioxide and heat into the silage, along with potentially other undesirable microorganisms. Silage fill practices such as harvest moisture, fill rate, packing equipment weight, fill layers, fill slope and other filling factors play an important role in minimising shrinkage at this stage.
During fermentation, sugars are converted into organic acids which reduce the overall pH of the silage thus preserving it. The efficiency at which this conversion takes place is highly variable and largely determined by the specific species and strains of organisms that conduct the process. Homofermentative lactic acid bacteria are best suited to accomplish this task; however, there is typically stiff competition from other wild organisms that can thrive on the nutrients available in the feedstuff. Utilizing a proven silage inoculant is beneficial for enhancing fermentation efficiency.
Application of an effective inoculant to the silage at harvest can ensure that desirable and efficient strains of lactic acid bacteria dominate fermentation in the entire silo. Be aware that silage inoculants, like wild bacteria, also vary widely in efficacy. Different strains even within species of lactobacillus bacteria convert sugars to organic acids within different levels of dry matter loss. Therefore, great care should be taken in evaluating the data behind silage inoculant products to ensure that replicated research supports product claims and ensures minimal shrink.
University and private research indicate that half or more of dry matter losses occur during the feed out uphase when silage is re-exposed to oxygen. The aerobic yeasts and bacteria that remain dormant in the anaerobic and acidic environment of silage storage revive with air exposure, consuming valuable nutrients. The pH also begins to rise with extended oxygen exposure, which invites moulds to grow. Feeds with a tendency to experience excessive microbial activity at feedout are considered aerobically instable.
Aerobic instability results in additional dry matter loss, reduced nutritional value and heating that can reduce silage palatability. Aerobic instability at feedout can be reduced with excellent face management that minimizes air exposure. Maximising density at harvest along with proper harvest moisture will also reduce risk as air becomes less likely to permeate into the feedout face.
Since even the best face management and silage compaction cannot fully relieve risk of aerobic stability – particularly in high moisture corn, corn silage and grass silages – the use of a silage inoculant containing L. buchneri should be considered to slow the dry matter losses and heating at feedout. L. buchneri species are capable of converting lactic acid to acetic acid in storage with minimal energy losses. The acetic acid and associated compounds then act as a natural yeast and mould inhibitor at feedout. Like other lactic acid bacteria, different strains of L. buchneri offer different results in dry matter loss and aerobic stability improvements, so care should be taken in selecting the right product.
Silage dry matter loss will likely remain a challenge for the foreseeable future as some losses are intrinsic to the ensiling process itself. However, implementation of intensive management practices at harvest and feedout along with the use of an effective silage inoculant can significantly reduce the associated costs.