Four sheep cannulated in the rumen and proximal duodenum were used in a 4 × 4 cross-over design to investigate the effects of ruminal fatty acid (FA) infusion on duodenal and serum FA profiles. The diets were composed of 85.7% natural grassland hay and 8.6% concentrate supplemented with 5.7% soy oil for diet SO, 5.7% emulsified soy oil for diet ESO, 6.7% calcium salts of soy or palm FA for diets CaSSO and CaSP, respectively. Diets were formulated to be isonitrogenous and isoenergetic; total FA content in dry matter was 6.4–6.6%. Characteristics of ruminal fermentation were not affected by source or physical form of FA. The proportion of stearic acid in the duodenal flow (% of the total C 18 ) was high compared with total diet, e.g., 49.8 vs. 3.5 and 54.3 vs. 9.4% for soy and palm diets, respectively. Ruminal biohydrogenation and unsaturated FA was lower for CaS diets than for SO and ESO diets (48.7 and 60.9 vs. 81.2 and 94.7%, for oleic and linoleic acids, respectively). As a result, trans-vaccenic acid levels in duodenal flow and serum (% or total FA) were lower for the CaS diets than for SO and ESO diets (8.3 vs. 36.0% and 0.9 vs. 7.8%, respectively). Unsaturated FA as CaS were partly protected against ruminal biohydrogenation, and can be effective in increasing intestinal absorption of unsaturated FA.
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Enjalbert et al. (1994) studied this question.