The effect of tannins on the digestive system of free-range ruminants was first observed in browsers such as kudus, which died for no apparent reason. It was after some research concluded that even though there was abundant fodder available, something was limiting the digestions of the fodder. This limiting factor was found to be tannins.
Tannins are phenolic compounds that form strong bonds with proteins, cellulose, starch, and minerals in several plant species which are often consumed by ruminants such as cattle, sheep, goats and also game. The physical and chemical properties of tannins differ from plant species to plant species. The bonds that the tannins form with proteins are often quite unstable and have the ability of breaking and re-assembling. Tannins are found in trees, bushes, shrubs and also some leguminous plants. The tannin content of plants can be increased by several stress factors such as high temperature, limited water supply, poor soil quality but also when the shrub is disturbed by browsing animals.
How do tannins affect the ruminant animal?
Due to these bonds that the tannins form with the proteins, but also with carbohydrates such as starch and fibre in the forages, the microorganisms in the animals’ rumen are not able to digest the protein and the carbohydrates. This causes the digestion to slow down, which in turn slows down the through-flow of digesta out of the rumen which subsequently decreases the voluntary feed intake. The animal thus feels full but starts becoming malnourished and shows a severe loss in condition. Further, the excretion of nitrogen in the faeces is increased. Tannins can also have a negative effect on the palatability of the forages, which in turn can also reduce voluntary feed intake. Concentrations above 10 to 20% could also be toxic to ruminants. Symptoms being kidney failure and elevated serum urea nitrogen.
Some browsing animals have throughout evolution developed mechanisms that allow them to consume plants rich in tannins. Sheep secrete “proline-rich proteins” in their saliva when digesting plants that contain high levels of tannins. These “proline-rich proteins” bind with tannins which might cancel out their negative effect of palatability and digestibility of these plants. Therefore, sheep are not as severely affected by tannins. Cattle, however, do not secrete such proteins. Research has shown that polyethylene glycol (PEG) is able to separate the bonds that tannins form with protein and carbohydrates by binding and inactivating the tannins, thus increasing the digestibility of protein from leafage high in tannins, increasing the nitrogen retention and also increasing the metabolizable energy.
Feedmaster’s Bush Improver Lick is a maintenance lick specially formulated for sheep and cattle which prefer bush and leaves as their source of nutrition. It contains PEG, which increases the animals total protein use. It is also suitable for all antelope species that can use urea. For the farmer that wishes to mix on the farm, this lick is also available as a concentrate (Bush Improver Concentrate).
The staff at Feedmaster will gladly assist you with choosing the right supplement for your circumstances.