The use of tannins as silage additives: effects on silage composition and mobile bag disappearance of dry matter and protein

The effects on silage composition of ensiling perennial ryegrass (PRG) with three commercial tannins (mimosa, myrabolam and quebracho tannins) were assessed (Experiment 1). The effects on silage composition and mobile bag disappearance of DM, nitrogen and true protein of the addition of these tannins or a combination of tannin plus formic acid, formaldehyde alone, formic acid alone, or a combination of formaldehyde and formic acid (Experiment 2) were also studied. In Experiment 1, the PRG was a third cut with a mean oven-dry DM content of 200 g/kg. All silages were prepared on a small laboratory scale (500 g), with the additives added in 20 ml aliquots/kg herbage fresh weight. The tannins were added at the rate of 5 or 50 g/kg herbage DM and in Experiment 1, samples were examined after 7 or 32 days of ensiling. In Experiment 2, a 1st cut PRG with a mean oven-dry DM content of 188 g/kg was used and the samples were taken on days 7, 14 and 49. In Experiment 1, treatment with tannins reduced the soluble nitrogen (SN) and ammonia content of the silages. In Experiment 2, the tannins used also reduced silage SN during ensiling, and were able to reduce degradation of silage nitrogen and true proteins in the rumen. Of the tannins used, quebracho tannin was also able to reduce SN and rumen degradation better than mimosa tannin. However, the tannins were not as good as formaldehyde at protecting silage proteins both during ensiling and in the rumen, neither were they better than formic acid in enhancing silage quality. For both the tannins and formaldehyde, formic acid addition further reduced the SN content as a result of the combined effect of rapid acidification and protein binding.