The effects of tannin ingestion on the physiology of boer-goats.
Mbatha, Khanyisile Rebecca.
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This study was conducted to determine the effects of different levels of dietary tannin on the physiology of Boer goats. In particular, dietary intake, digestibility, gastrointestinal tract (GIT) histology and presence of bacteria along the GIT were measured. In addition the ability of goats to detoxify tannins by measuring liver and kidney mass; and urinary glucuronic acid concentration was investigated. Commercialized tannin was used because of wide variation of tannin levels, which can be affected by season, species, and part of the plant. Thirty adult, male goats were fed one of five diet treatments of different tannin levels (0%, 5%, 10%, 15% and 20%) for 6 weeks following which they were kept in metabolic crates for data collection for a further 10 days. Dietary intake of feed decreased significantly as tannin levels increased between the diets. Digestibility of dry matter (DM) tended to decrease with increasing tannin levels. However, digestibility of crude proteins (CP), organic matter, neutral detergent fibre and acid neutral detergent fibre decreased Significantly with increasing tannin levels. Faecal CP increased while urinary CP decreased with increasing tannin levels. There was no tannin present in the faeces. It appears that goats cope with low levels of tannin ingestion. There appears to be a threshold above which greater tannin ingestion has detrimental effects. The linear decreased dietary intake with increased tannin level may indicate that goats limit their intake of tannin below some threshold as a defence strategy. Differences in the histopathology of the oesophagus, reticulum, rumen, abomasum and duodenum were evaluated. Animals on the control diet had more protozoa present in the GIT than the other diets. Number and types of bacteria observed in the reticulum and rumen increased with tannin level in the diet. These may be responsible for tannin-protein complex degradation. Few bacteria were observed in the abomasum. There was a loss of epithelial cells and erosion of microvilli in duodenum with increased tannin levels, which would impair absorption of nutrients. The width of the keratinized GIT epithelial layer increased and villi height decreased as tannin levels increased which could further reduce nutrient absorption. Goats in the present study did not show detoxification abilities because the liver and kidney masses, and urinary glucuronic acid concentration did not increase with increased dietary tannin levels In summary, condensed tannins as large compounds appear to be metabolized and absorbed from the GIT. However, it is not clear if they are detoxified at the epithelial mucosa interface. The main detrimental effect of tannin on goats appears to be the reduction of feed intake and increased faecal CP.