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Tannins can be used as chemical feed additive to reduce degradation of protein in the rumen. The tannin-protein complexes (TPCs) are less soluble and less accessible to proteolytic enzymes at the ruminal pH, thereby slowing the rate of ruminal degradation (Broderic,1974). Rai and Shukla (1979 a) noticed nonsignificantly increase in milk production in lactating cows fed on 10 % salseed meal (11% tannic acid) in concentrate mixture, which reduced the feed cost to the extent of Rs. 70.4/tonn as compared to control diet. The inclusion of salseed meal at 10 or 20% in concentrate mixture of lactating cows did not influence body health and rumen fermentation of feed (Rai and Shukla,1979 b). Fibre digesting bacteria are more sensitive to condensed tannin than proteolytic bacteria (Bae et al., 1993; Jones ,1994).
Rodriguez et al. (1999) reported that ensiling of high tannin containing sorghum forage reduced ammonia production during fermentation and tannin concentration decreased gradually with increased duration of fermentation. Barry and Mc Nabb (1999) reported that higher concentration of condensed tannins in Lotus corniculatus and L. pedunculatus reduced the rate and solubilization and degradation of leaf protein in the rumen of grazing sheep and increased doudenal ammonia nitrogen flow. Condensed tannins level of 30 to 40 gm/ Kg DM in L. corinculatus increased the absorption of essential amino acids from small intestine and increased wool growth, milk yield and reproductive rate without affecting voluntary feed intake. But condensed tannin level of 75 to 100 gm/ Kg DM of L. pedunculatus decreased the voluntary feed intake and rumen carbohydrate digestion and had negative effect on growth and wool production. They also reported that feeding of diet containing 5 gm condensed tannin per Kg DM reduced the frothy bloat in cattle and reduced intestinal parasitic infestation in sheep.
Min et al. (1999) reported that ewe grazing on L. corniculatus containing 17 gm total condensed tannin per Kg DM without supplementation of polyethylene glycol (PEG) increased the plasma concentration of branch chain amino acids by 57 percent and essential amino acids by 52 percent resulting in increased production of wool with longer staples and thicker fibre diameter.But PEG treatment reduced the reproductive efficiency and wool growth due to binding of tannins by PEG.
Herves et al. (1999) reported that quabracho tannin at a rate of 15 gm /100 gm of soybean oil meal can be used as a chemical additive to decreased rumen degradation of soybean oil meal in sheep without affecting intestinal digestibility. Similarly, Erlich (1999) found that higher tannin content of sorghum had a positive effect on feed intake during finishing phase of fattening pig but had negative effect on feed conversion effciency and growth during initial period. Bhatt et al.(2000) supplemented compounded feed mixture containing 0,2.5,7.5% tamarind seed husk with a tannin levels of 0,0.2 and 0.74 % in total diet of cross bred dairy cows at mid lactation . They found no effect on intake of DM, NDF and ADF and digestibility of major nutrients except protein which digestibility decreased significantly. There was significant improvement in body weight gain, calculated energy (ME) output as well as milk protein content in animals fed with 7.5% tamarind seed husk in the diet. The N excretion in the faeces was significantly higher where as N excretion in urine was significantly lower in tannin fed animals compared to the control group.
Tannins also reduce bloat and parasitic load in animal the suitable concentration of condensed tannin in Lotus species for prevention of bloat and protection of protein should be 30 to 40 g per kg dry matter (Barry and Manley, 1986). Most of the unconventional feeds contain saponin, lectin, hydrocyanic acid, tannin which make them less utilizable in livestock’s feed formulation because of its deleterious effect on animal. As tannins have antagonist effect against saponin, lectin and hydrocyanic acid so tannin rich feed resources can be mix with other unconventional feed containing the above 3 antimetabolites for animal feed formulation which will not only reduce the feed cost but also reduce the competition between livestock and human for cereals.
