Digestion and absorption of carotenoids in sheep given fresh red clover

Digestion and absorption of carotenoids were studied in sheep given, twice daily, fresh red clover. Digestive fluxes were measured in six sheep cannulated in the rumen, duodenum and ileum using the double marker technique. Another five sheep were fitted with catheters allowing nutrient net flux measurements across the portal-drained viscera. Carotenoids in the red clover consisted of lutein (136 mu g/g dry matter (DM)), epilutein (40 mu g/g DM), trans-beta-carotene (16 mu g/g DM) and 13-cis-beta-carotene (13 mu g/g DM). Intake was 174, 52, 21 and 17 mg/day, and faecal excretion was 181, 25, 50 and 41 mg/day, for lutein, epilutein, trans- and 13-cis-beta-carotene respectively, indicating net production of beta-carotene in the digestive tract. The difference between duodenum and intake was positive for all carotenoids (30, 4, 43 and 37 g for lutein, epilutein, trans-beta-carotene and 13-cis-beta-carotene, respectively) suggesting net production and/or release of carotenes and xanthophylls by rumen microbes. Apparent digestibility in the small and large intestines was 0(.)18 and -0(.)05 for lutein, 0(.)30 and 0(.)29 for epilutein, 0(.)39 and 0(.)26 for trans-beta-carotene, 0(.)53 and 0(.)21 for 13-cis-beta-carotene. Only lutein and epilutein were recovered in arterial plasma, at a concentration of 14(.)3 and 10(.)8 mu g/l, respectively. Their portal net appearance was not different from 0, suggesting that absorption occurred mainly via the lymphatic system.