It is important to include fixed (land, interest) and variable (seed, fertiliser, sprays) costs in growing and harvesting pasture or crops to properly evaluate cost benefits of using inoculants when preserving forages.
Effective lactic acid producing inoculants have been demonstrated, in controlled trials, to reduce dry matter losses by 5->10%, under good ensiling conditions. Inoculant costs are recovered with reductions of about 2.5-3% in dry matter (DM) losses with pasture silage valued at 30-35 cents/kg DM, or 3.5-4.3% reductions with maize (or whole crop cereal) silages valued at 20-25 cents/kg DM.
Animal feeding trials have demonstrated improvements in feeding efficiency of inoculant treated silages, even though this is not shown in laboratory predictions of metabolisable energy (ME) or protein. Animal trials in the UK have shown an improvement in ME of about 0.5 MJ/kg DM, and an increase in true protein, i.e. less non-protein nitrogen (NPN). True protein is used more efficiently than NPN. A 0.5 MJ ME/kg DM increase equates to an improvement in feed value of about 1.5 and 1.2 cents/kg DM for the pasture and maize silage examples cited above.
Another type of inoculant containing specific strains of Lactobacillus buchneri has been developed to reduce aerobic spoilage with silages typically subject to heating during feeding out. This can arise with large pit faces relative to silage demand, such that silage is exposed to air for several days before being removed. DM losses can be considerable with heating silages, which is also associated with a loss in feed value. These losses are in addition to ensiling losses. Cost recovery can be achieved with savings of 5-6.5% DM with these types of inoculants.
An oxygen barrier silage sheet has been demonstrated to reduce oxygen infusion by 60 times relative to standard covers, and reduce mould growth and dry matter losses by 50% in the top metre of silage stacks, resulting in average reductions of DM losses of 7% in pits and 4% in bales overall. This equates to a return on investment of about 3:1.
An alternative to preserving as much high quality silage is to purchase supplementary feeds. However, this needs to be financed from cash flow, whereas a significant cost of home grown forages is unavoidable overhead expenses. The most profitable option is to make and use as much home grown forages as efficiently as possible.
As featured in NZ Dairy Farmer