The fate of nitrogen (N) ingested by dairy cows is approximately 34% in milk protein synthesis, 34% eliminated in the urine, 27% in the feces, with only 5% retained to be used in other body processes. These figures show that close to 60% of the nitrogen intake ends up being a source of environmental N load.
Not only is N tied-up in urine and feces but it also results in gaseous N losses through nitrous oxide which is also a greenhouse gas nearly 300-fold more potent than carbon dioxide. Ammonia gas production is also of concern since it is hazardous both for humans and livestock. As a result, improving N partitioning will have an effect in the environmental load associated with livestock production as well as air quality.
What is the effect of adding tannins to the silage on cow’s nitrogen metabolism?
Oak tannins applied to forage before baling it for silage improve protein partitioning in the cow lessening the environmental N load. Research has shown that adding tannins to forages before ensiling can lead to a reduction in ammonia production. Tannins have also been used to protect fermentable protein from rumen degradation which is later digested once it is freed from the tannin complex once it reaches the more acidic pH of the abomasum. This latter effect results in less plasma urea N, less milk urea N, and reduced N excretion in the urine.