Effect of Tannins on Feed Intake and Digestibility of Nutrients

Tannins reduce the feed intake by decreasing palatability of the ration because of its astringent effect on oral cavity.  Astringent sensation arise due to binding of tannin with salivary glyco proteins which impart lubricant property to mucin (Glick and Joslyn, 1970). Tannins also lower rumen turnover rate as well as digestibility of nutrients which has greater impact on reducing feed intake than decrease palatability. Digestibility reduction cause filling effect associated with undigested feed stuffs (Waghorn et al., 1994).

Tannins effect the digestibility either by binding the digestive enzymes or by binding feed nutrients. Cellulose and protein degradibility was reduced by gallotannic acid in vitro by mixed culture rumen microbes (Tagari et al., 1965). Feeding of deoiled salssed meal containing about 11% tannins at a level of 20% in total ration of ruminant reduced the digestibility of protein and increased ether extract digestion. Nitrogen retention was reduced and caused negative nitrogen balance (Rai and Shukla, 1977). Singh (1979) also did not find any effect of salseed meal on digestibility of nutrients when used at 30% levels in lactating buffaloes. However, he found that inclusion of treated (0.1 % sodium hydroxide, 3% tannin) and untreated salseed meal (5.75% tannins) at the level of 45% in the concentrate mixture of of lactating buffaloes, reduced drymatter intake and digestibility of dry matter, crude protein, crude fibre, nitrogen free extract than control. Ether extract digestibility was higher in control as well as treated group. Reason in increased ether extract digestibility was not known.

Nitrogen balance was negative in both salseed fed groups. However, treatment of salseed meal with 0.1 % NaOH significantly improved the nitrogen balance. Lohan et al. (1983) reported that inclusion of oak leaves in the ration of bullock at the rate of 0, 14, 19, 25 containing 0, 0.12, 0.18 and 10.68 percent total phenols respectively and 0, 0.06, 0.09 and 4.78 percent condensed tannins did not effect the dry matter intake and digestibility of nutrients except that of ether extract and crude fibre which was decreased significantly with increasing level of oak leaves in the diet. There was also reduction of total bacterial nitrogen, cellulase, urease and proteolytic activity significantly with the increase level.

Feeding of Quercus calliprious leaves with poly ethylene glycol to goats increased the digestible crude protein intake (Silanikove et al.1994; Silanikove et al.1996). In vitro digestibility of dry matter and neutral detergent fibre of Caliandra calothyrsus, Leucaena leucocephala, Leucaena diversifolia and Leucaena pallida by addition of PEG (McSweeney et al.,1999). Feeding of quabracho tannins at the level of 50g per kg basal diet contaning chopped grass hay, grass cubes and whole barley to sheep reduced ruminal ammonia nitrogen, soluble protein, total volatile fatty acids concentration and cellulase and xylanase acitvity. But addition of browse plus (95% PEG and 5% Poly venyl pyrolidone) alleviate the above problems (Salawu et al., 1999). Salem et al.,(2000) also found that inclusion of PEG at different levels in feed block containing acacia foliage increased the dry matter intake, digestible crude protein intake and microbial protein synthesis in sheep. He found that PEG at 18% in the feed block was optimum in increasing nutrient utilization from acacia foliage. However, greater result were obtained with 24% level of PEG.

Palmer and Jones (2001) found increased in in vitro dry matter and nitrogen digestibility by addition of PEG.Tannins protein complexes also bind with NDF,ADF and ADL thereby increase their amount in faeces than intake levels thereby showed a negative digestibility.

• Tanniniferous Feeds for Dairy Animals
• Beneficial Effect of Tannins on Animal Production
• Adverse Effect of Tannins on Animal Health