Last month’s article considered principles and techniques for making high quality maize and whole crop silages, including the use of appropriate inoculants. The preference until fairly recently was to rely on homofermentative lactic acid producing bacterial inoculants, due to lactic being a strong acid so aiding rapid fermentation thus lower dry matter losses than untreated silages. Independent trials had also demonstrated improved palatability and more efficient feed utilisation.
However, one drawback when used in large maize or whole crop stacks had been poor aerobic stability, due to growth of yeasts and other moulds on exposure to air, as they require oxygen to metabolise, grow and multiply. University of Delaware researchers demonstrated that aerobic stability was negatively correlated to the number of yeasts present when silos were opened. Milk yields also declined with increasing yeast levels.
This led to the introduction of silage inoculants containing both homofermentative lactic acid producing bacteria, and heterofermentative bacteria (Lactobacillus buchneri) that produce acetic and lactic acids. Acetic acid has antifungal properties, so inhibits the growth of yeasts and moulds, resulting in greater stability of silages once opened, and when mixed with other feeds in partial mixed rations.
A lactic:acetic ratio of more than 3:1 is generally considered desirable in well fermented lactic acid silages. However, this is not appropriate in silages made with L. buchneri due to the higher acetic acid production, so this may be nearer 1:1 at the highest L. buchneri inclusion rates. There have been suggestions that high levels of acetic in silages may depress intakes. USA researchers recorded only moderate increases in the concentration of acetic acid (3.89%) at the highest levels of application of L. buchneri.
Research at the USDA Forage Research Center in Wisconsin and at the University of Delaware research studies have shown that L. buchneri treated corn silage with higher acetic acid levels does not reduce feed intake. Treatment of maize silage at the highest levels with L. buchneri decreased the number of yeasts by 100 fold relative to 10 fold at low application rates. These scientists also reported that inoculation of maize silage with the FDA recommended rate of 400,000 cfu/g L. buchneri was one of the most consistent additives for improving aerobic stability. It is important to note that not all strains of L. buchneri are equally effective, so one needs to check independent trials of efficacy.
As featured in NZ Dairy Farmer